A missense variant in SLC39A8 is associated with severe idiopathic scoliosis

Reduced Mn uptake of pleiotropic ZIP8 SNP is caused by its loss of Mn-responsive accumulation on the cell-surface

Zrt/Irt-like protein 8 (ZIP8), which is a Zn transporter, plays a pivotal role as a Mn transporter. Recent studies have shown that a ZIP8 SNP (rs13107325 C→T, A391T) is associated with multiple diseases, likely by causing systemic Mn deficiency. However, the underlying molecular mechanisms remain unclear. We attempted to address this issue in cell-based experiments using Madin-Darby canine kidney cells stably expressing ZIP8 WT or the A391T SNP mutant under the control of the Tet-regulatable promoter. We showed that the A391T mutant lost the property of Mn-responsive accumulation on the cell surface, which was observed in WT ZIP8. We also showed that the loss of Mn-responsive accumulation of A391T mutant was associated with its reduced Mn uptake, compared with WT ZIP8, in the Mn uptake assay using the radioisotope 54Mn. Our results potentially explain how the ZIP8 A391T substitution is associated with disease pathogenesis caused by Mn deficiency.

Aberrant N-glycosylation is a therapeutic target in carriers of a common and highly pleiotropic mutation in the manganese transporter ZIP8

The treatment of defective glycosylation in clinical practice has been limited to patients with rare and severe phenotypes associated with congenital disorders of glycosylation (CDG). Carried by approximately 5% of the human population, the discovery of the highly pleiotropic, missense mutation in a manganese transporter ZIP8 has exposed under-appreciated roles for Mn homeostasis and aberrant Mn-dependent glycosyltransferases activity leading to defective N-glycosylation in complex human diseases. Here, we test the hypothesis that aberrant N-glycosylation contributes to disease pathogenesis of ZIP8 A391T-associated Crohn's disease. Analysis of N-glycan branching in intestinal biopsies demonstrates perturbation in active Crohn's disease and a genotype-dependent effect characterized by increased truncated N-glycans. A mouse model of ZIP8 391-Thr recapitulates the intestinal glycophenotype of patients carrying mutations in ZIP8. Borrowing from therapeutic strategies employed in the treatment of patients with CDGs, oral monosaccharide therapy with N-acetylglucosamine ameliorates the epithelial N-glycan defect, bile acid dyshomeostasis, intestinal permeability, and susceptibility to chemical-induced colitis in a mouse model of ZIP8 391-Thr. Together, these data support ZIP8 391-Thr alters N-glycosylation to contribute to disease pathogenesis, challenging the clinical paradigm that CDGs are limited to patients with rare diseases. Critically, the defect in glycosylation can be targeted with monosaccharide supplementation, providing an opportunity for genotype-driven, personalized medicine.

Rare variant association analyses reveal the significant contribution of carbohydrate metabolic disturbance in severe adolescent idiopathic scoliosis

BACKGROUND

Adolescent idiopathic scoliosis (AIS), the predominant genetic-influenced scoliosis, results in spinal deformities without vertebral malformations. However, the molecular aetiology of AIS remains unclear.

METHODS

Using genome/exome sequencing, we studied 368 patients with severe AIS (Cobb angle >40°) and 3794 controls from a Han Chinese cohort. We performed gene-based and pathway-based weighted rare variant association tests to assess the mutational burden of genes and established biological pathways. Differential expression analysis of muscle tissues from 14 patients with AIS and 15 controls was served for validation.

RESULTS

SLC16A8, a lactate transporter linked to retinal glucose metabolism, was identified as a novel severe AIS-associated gene (p=3.08E-06, false discovery rate=0.009). Most AIS cases with deleterious SLC16A8 variants demonstrated early onset high myopia preceding scoliosis. Pathway-based burden test also revealed a significant enrichment in multiple carbohydrate metabolism pathways, especially galactose metabolism. Patients with deleterious variants in these genes demonstrated a significantly larger spinal curve. Genes related to catabolic processes and nutrient response showed divergent expression between AIS cases and controls, reinforcing our genomic findings.

CONCLUSION

This study uncovers the pivotal role of genetic variants in carbohydrate metabolism in the development of AIS, unveiling new insights into its aetiology and potential treatment.

The manganese transporter SLC39A8 links alkaline ceramidase 1 to inflammatory bowel disease

The metal ion transporter SLC39A8 is associated with physiological traits and diseases, including blood manganese (Mn) levels and inflammatory bowel diseases (IBD). The mechanisms by which SLC39A8 controls Mn homeostasis and epithelial integrity remain elusive. Here, we generate Slc39a8 intestinal epithelial cell-specific-knockout (Slc39a8-IEC KO) mice, which display markedly decreased Mn levels in blood and most organs. Radiotracer studies reveal impaired intestinal absorption of dietary Mn in Slc39a8-IEC KO mice. SLC39A8 is localized to the apical membrane and mediates 54Mn uptake in intestinal organoid monolayer cultures. Unbiased transcriptomic analysis identifies alkaline ceramidase 1 (ACER1), a key enzyme in sphingolipid metabolism, as a potential therapeutic target for SLC39A8-associated IBDs. Importantly, treatment with an ACER1 inhibitor attenuates colitis in Slc39a8-IEC KO mice by remedying barrier dysfunction. Our results highlight the essential roles of SLC39A8 in intestinal Mn absorption and epithelial integrity and offer a therapeutic target for IBD associated with impaired Mn homeostasis.

Association between genetic polymorphisms and risk of adolescent idiopathic scoliosis in case-control studies: a systematic review

BACKGROUND

Adolescent idiopathic scoliosis (AIS) is a structural lateral spinal curvature of ≥10° with rotation. Approximately 2%-3% of children across populations are affected with AIS, and this condition is responsible for ~$3 billion in costs within the USA. Although AIS is believed to have a strong genetic contribution, clinical translation of identified genetic variants has stalled.

METHODS

The databases MEDLINE (via PubMed), Embase, Google Scholar and Ovid MEDLINE were searched and limited to articles in English. Title and abstract, full-text and data extraction screening was conducted through Covidence, followed by data transfer to a custom REDCap database. Studies containing variant-level data using genome-wide methodology as well as validation studies of genome-wide methods were considered. Quality assessment was conducted using Q-Genie.

RESULTS

33 studies were included, including 9 genome-wide association studies, 4 whole exome sequencing and 20 validation studies. Combined, these studies included data from >35,000 cases and >67,000 controls, not including validation cohorts. Additionally, results from six meta-analyses containing novel cohorts were also reported. All included study cohorts were from populations of primarily East Asian or Caucasian descent. Quality assessment found that overall study quality was high and control group selection was moderate. The highest number of reported associations were in single nucleotide polymorphisms (SNPs) in or near LBX1, LBX1-AS1, GPR126/ADGRG6 or BNC2.

CONCLUSION

AIS risk may be influenced by specific SNPs, particularly those in/near LBX1 and GPR126. Translatability of study findings is unknown due to an underrepresentation of most ethnic groups as well as few identified genome-wide studies. Further studies may benefit from increased cohort diversity and thorough evaluation of control cohort groups.

Impaired glycine neurotransmission causes adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is the most common form of spinal deformity, affecting millions of adolescents worldwide, but it lacks a defined theory of etiopathogenesis. Because of this, treatment of AIS is limited to bracing and/or invasive surgery after onset. Preonset diagnosis or preventive treatment remains unavailable. Here, we performed a genetic analysis of a large multicenter AIS cohort and identified disease-causing and predisposing variants of SLC6A9 in multigeneration families, trios, and sporadic patients. Variants of SLC6A9, which encodes glycine transporter 1 (GLYT1), reduced glycine-uptake activity in cells, leading to increased extracellular glycine levels and aberrant glycinergic neurotransmission. Slc6a9 mutant zebrafish exhibited discoordination of spinal neural activities and pronounced lateral spinal curvature, a phenotype resembling human patients. The penetrance and severity of curvature were sensitive to the dosage of functional glyt1. Administration of a glycine receptor antagonist or a clinically used glycine neutralizer (sodium benzoate) partially rescued the phenotype. Our results indicate a neuropathic origin for "idiopathic" scoliosis, involving the dysfunction of synaptic neurotransmission and central pattern generators (CPGs), potentially a common cause of AIS. Our work further suggests avenues for early diagnosis and intervention of AIS in preadolescents.

BMP6 participates in the pathogenesis of adolescent idiopathic scoliosis by regulating osteopenia

Adolescent idiopathic scoliosis (AIS) is a complex disease characterized by three-dimensional structural deformities of the spine. Its pathogenesis is associated with osteopenia. Bone-marrow-derived mesenchymal stem cells (BMSCs) play an important role in bone metabolism. We detected 1919 differentially expressed mRNAs and 744 differentially expressed lncRNAs in BMSCs from seven patients with AIS and five patients without AIS via high-throughput sequencing. Multiple analyses identified bone morphogenetic protein-6 (BMP6) as a hub gene that regulates the abnormal osteogenic differentiation of BMSCs in AIS. BMP6 expression was found to be decreased in AIS and its knockdown in human BMSCs significantly altered the degree of osteogenic differentiation. Additionally, CAP1-217 has been shown to be a potential upstream regulatory molecule of BMP6. We showed that CAP1-217 knockdown downregulated the expression of BMP6 and the osteogenic differentiation of BMSCs. Simultaneously, knockout of BMP6 in zebrafish embryos significantly increased the deformity rate. The findings of this study suggest that BMP6 is a key gene that regulates the abnormal osteogenic differentiation of BMSCs in AIS via the CAP1-217/BMP6/RUNX2 axis.

Patterns of item nonresponse behaviour to survey questionnaires are systematic and associated with genetic loci

Response to survey questionnaires is vital for social and behavioural research, and most analyses assume full and accurate response by participants. However, nonresponse is common and impedes proper interpretation and generalizability of results. We examined item nonresponse behaviour across 109 questionnaire items in the UK Biobank (N = 360,628). Phenotypic factor scores for two participant-selected nonresponse answers, 'Prefer not to answer' (PNA) and 'I don't know' (IDK), each predicted participant nonresponse in follow-up surveys (incremental pseudo-R2 = 0.056), even when controlling for education and self-reported health (incremental pseudo-R2 = 0.046). After performing genome-wide association studies of our factors, PNA and IDK were highly genetically correlated with one another (rg = 0.73 (s.e. = 0.03)) and with education (rg,PNA = -0.51 (s.e. = 0.03); rg,IDK = -0.38 (s.e. = 0.02)), health (rg,PNA = 0.51 (s.e. = 0.03); rg,IDK = 0.49 (s.e. = 0.02)) and income (rg,PNA = -0.57 (s.e. = 0.04); rg,IDK = -0.46 (s.e. = 0.02)), with additional unique genetic associations observed for both PNA and IDK (P < 5 × 10-8). We discuss how these associations may bias studies of traits correlated with item nonresponse and demonstrate how this bias may substantially affect genome-wide association studies. While the UK Biobank data are deidentified, we further protected participant privacy by avoiding exploring non-response behaviour to single questions, assuring that no information can be used to associate results with any particular respondents.

Diverse monogenic subforms of human spermatogenic failure

Non-obstructive azoospermia (NOA) is the most severe form of male infertility and typically incurable. Defining the genetic basis of NOA has proven challenging, and the most advanced classification of NOA subforms is not based on genetics, but simple description of testis histology. In this study, we exome-sequenced over 1000 clinically diagnosed NOA cases and identified a plausible recessive Mendelian cause in 20%. We find further support for 21 genes in a 2-stage burden test with 2072 cases and 11,587 fertile controls. The disrupted genes are primarily on the autosomes, enriched for undescribed human "knockouts", and, for the most part, have yet to be linked to a Mendelian trait. Integration with single-cell RNA sequencing data shows that azoospermia genes can be grouped into molecular subforms with synchronized expression patterns, and analogs of these subforms exist in mice. This analysis framework identifies groups of genes with known roles in spermatogenesis but also reveals unrecognized subforms, such as a set of genes expressed across mitotic divisions of differentiating spermatogonia. Our findings highlight NOA as an understudied Mendelian disorder and provide a conceptual structure for organizing the complex genetics of male infertility, which may provide a rational basis for disease classification.

Single-gene knockout-coupled omics analysis identifies C9orf85 and CXorf38 as two uncharacterized human proteins associated with ZIP8 malfunction

Human transmembrane protein metal cation symporter ZIP8 (SLC39A8) is a member of the solute carrier gene family responsible for intracellular transportation of essential micronutrients, including manganese, selenium, and zinc. Previously, we established a ZIP8-knockout (KO) human cell model using the CRISPR/Cas9 system and explored how the expression of ZIP8 could possibly contribute to a wide range of human diseases. To further assess the biophysiological role of ZIP8, in the current study, we employed isobaric tags for relative and absolute quantitation (iTRAQ) and detected the changes of the proteome in ZIP8-KO cells (proteomic data are available via ProteomeXchange with identifier PXD036680). A total of 286 differentially expressed proteins (206 downregulated and 80 upregulated proteins) were detected in the ZIP8-KO cell model, and subsequent bioinformatics analyses (GO, KEGG, KOG, and PPI) were performed on these proteins. Interestingly, four "uncharacterized" proteins (proteins with unknown biological function) were identified in the differentially expressed proteins: C1orf198, C9orf85, C17orf75, and CXorf38-all of which were under-expressed in the ZIP8-KO cells. Notably, C9orf85 and CXorf38 were amongst the top-10 most downregulated proteins, and their expressions could be selectively induced by essential micronutrients. Furthermore, clinical-based bioinformatic analysis indicated that positive correlations between the gene expressions of ZIP8 and C9orf85 or CXorf38 were observed in multiple cancer types. Overall, this study reveals the proteomic landscape of cells with impaired ZIP8 and uncovers the potential relationships between essential micronutrients and uncharacterized proteins C9orf85 and CXorf38. The differentially expressed proteins identified in ZIP8-KO cells could be the potential targets for diagnosing and/or treating human ZIP8-associated diseases, including but not limited to malnutrition, viral infection, and cancers.

Zebrafish: an important model for understanding scoliosis

Scoliosis is a common spinal deformity that considerably affects the physical and psychological health of patients. Studies have shown that genetic factors play an important role in scoliosis. However, its etiopathogenesis remain unclear, partially because of the genetic heterogeneity of scoliosis and the lack of appropriate model systems. Recently, the development of efficient gene editing methods and high-throughput sequencing technology has made it possible to explore the underlying pathological mechanisms of scoliosis. Owing to their susceptibility for developing scoliosis and high genetic homology with human, zebrafish are increasingly being used as a model for scoliosis in developmental biology, genetics, and clinical medicine. Here, we summarize the recent advances in scoliosis research on zebrafish and discuss the prospects of using zebrafish as a scoliosis model.

The schizophrenia-associated missense variant rs13107325 regulates dendritic spine density

The missense variant rs13107325 (C/T, p.Ala391Thr) in SLC39A8 consistently showed robust association with schizophrenia in recent genome-wide association studies (GWASs), suggesting the potential pathogenicity of this non-synonymous risk variant. Nevertheless, how this missense variant confers schizophrenia risk remains unknown. Here we constructed a knock-in mouse model (by introducing a threonine at the 393th amino acid of mouse SLC39A8 (SLC39A8-p.393T), which corresponds to rs13107325 (p.Ala391Thr) of human SLC39A8) to explore the potential roles and biological effects of this missense variant in schizophrenia pathogenesis. We assessed multiple phenotypes and traits (associated with rs13107325) of the knock-in mice, including body and brain weight, concentrations of metal ions (including cadmium, zinc, manganese, and iron) transported by SLC39A8, blood lipids, proliferation and migration of neural stem cells (NSCs), cortical development, behaviors and cognition, transcriptome, dendritic spine density, and synaptic transmission. Many of the tested phenotypes did not show differences in SLC39A8-p.393T knock-in and wild-type mice. However, we found that zinc concentration in brain and blood of SLC39A8-p.393T knock-in mice was dysregulated compared with wild-types, validating the functionality of rs13107325. Further analysis indicated that cortical dendritic spine density of the SLC39A8-p.393T knock-in mice was significantly decreased compared with wild-types, indicating the important role of SLC39A8-p.393T in dendritic spine morphogenesis. These results indicated that SLC39A8-p.393T knock-in resulted in decreased dendritic spine density, thus mimicking the dendritic spine pathology observed in schizophrenia. Our study indicates that rs13107325 might confer schizophrenia risk by regulating zinc concentration and dendritic spine density, a featured characteristic that was frequently reported to be decreased in schizophrenia.

Adolescent idiopathic scoliosis : a review of aetiological theories of a multifactorial disease

Adolescent idiopathic scoliosis (AIS), defined by an age at presentation of 11 to 18 years, has a prevalence of 0.47% and accounts for approximately 90% of all cases of idiopathic scoliosis. Despite decades of research, the exact aetiology of AIS remains unknown. It is becoming evident that it is the result of a complex interplay of genetic, internal, and environmental factors. It has been hypothesized that genetic variants act as the initial trigger that allow epigenetic factors to propagate AIS, which could also explain the wide phenotypic variation in the presentation of the disorder. A better understanding of the underlying aetiological mechanisms could help to establish the diagnosis earlier and allow a more accurate prediction of deformity progression. This, in turn, would prompt imaging and therapeutic intervention at the appropriate time, thereby achieving the best clinical outcome for this group of patients. Cite this article: Bone Joint J 2022;104-B(8):915-921.

A Baseline for Skeletal Investigations in Medaka (Oryzias latipes): The Effects of Rearing Density on the Postcranial Phenotype

Oryzias latipes is increasingly used as a model in biomedical skeletal research. The standard approach is to generate genetic variants with particular skeletal phenotypes which resemble skeletal diseases in humans. The proper diagnosis of skeletal variation is key for this type of research. However, even laboratory rearing conditions can alter skeletal phenotypes. The subject of this study is the link between skeletal phenotypes and rearing conditions. Thus, wildtype medaka were reared from hatching to an early juvenile stage at low (LD: 5 individuals/L), medium (MD: 15 individuals/L), and high (HD: 45 individuals/L) densities. The objectives of the study are: (I) provide a comprehensive overview of the postcranial skeletal elements in medaka; (II) evaluate the effects of rearing density on specific meristic counts and on the variability in type and incidence of skeletal anomalies; (III) define the best laboratory settings to obtain a skeletal reference for a sound evaluation of future experimental conditions; (IV) contribute to elucidating the structural and cellular changes related to the onset of skeletal anomalies. The results from this study reveal that rearing densities greater than 5 medaka/L reduce the animals' growth. This reduction is related to decreased mineralization of dermal (fin rays) and perichondral (fin supporting elements) bone. Furthermore, high density increases anomalies affecting the caudal fin endoskeleton and dermal rays, and the preural vertebral centra. A series of static observations on Alizarin red S whole mount-stained preural fusions provide insights into the etiology of centra fusion. The fusion of preural centra involves the ectopic formation of bony bridges over the intact intervertebral ligament. An apparent consequence is the degradation of the intervertebral ligaments and the remodeling and reshaping of the fused vertebral centra into a biconoid-shaped centrum. From this study it can be concluded that it is paramount to take into account the rearing conditions, natural variability, skeletal phenotypic plasticity, and the genetic background along with species-specific peculiarities when screening for skeletal phenotypes of mutant or wildtype medaka.

Divalent Metal Uptake and the Role of ZIP8 in Host Defense Against Pathogens

Manganese (Mn) and Zinc (Zn) are essential micronutrients whose concentration and location within cells are tightly regulated at the onset of infection. Two families of Zn transporters (ZIPs and ZnTs) are largely responsible for regulation of cytosolic Zn levels and to a certain extent, Mn levels, although much less is known regarding Mn. The capacity of pathogens to persevere also depends on access to micronutrients, yet a fundamental gap in knowledge remains regarding the importance of metal exchange at the host interface, often referred to as nutritional immunity. ZIP8, one of 14 ZIPs, is a pivotal importer of both Zn and Mn, yet much remains to be known. Dietary Zn deficiency is common and commonly occurring polymorphic variants of ZIP8 that decrease cellular metal uptake (Zn and Mn), are associated with increased susceptibility to infection. Strikingly, ZIP8 is the only Zn transporter that is highly induced following bacterial exposure in key immune cells involved with host defense against leading pathogens. We postulate that mobilization of Zn and Mn into key cells orchestrates the innate immune response through regulation of fundamental defense mechanisms that include phagocytosis, signal transduction, and production of soluble host defense factors including cytokines and chemokines. New evidence also suggests that host metal uptake may have long-term consequences by influencing the adaptive immune response. Given that activation of ZIP8 expression by pathogens has been shown to influence parenchymal, myeloid, and lymphoid cells, the impact applies to all mucosal surfaces and tissue compartments that are vulnerable to infection. We also predict that perturbations in metal homeostasis, either genetic- or dietary-induced, has the potential to impact bacterial communities in the host thereby adversely impacting microbiome composition. This review will focus on Zn and Mn transport via ZIP8, and how this vital metal transporter serves as a "go to" conductor of metal uptake that bolsters host defense against pathogens. We will also leverage past studies to underscore areas for future research to better understand the Zn-, Mn- and ZIP8-dependent host response to infection to foster new micronutrient-based intervention strategies to improve our ability to prevent or treat commonly occurring infectious disease.

The Allelic Variant A391T of Metal Ion Transporter ZIP8 (SLC39A8) Leads to Hypotension and Enhanced Insulin Resistance

The metal ion transporter ZIP8 (SLC39A8) mediates cellular uptake of vital divalent metal ions. Genome-wide association studies (GWAS) showed that the single-nucleotide polymorphism (SNP) variant A391T (rs13107325) is associated with numerous human traits, including reduced arterial blood pressure, increased body mass index and hyperlipidemia. We analyzed in vitro the transport properties of mutant ZIP8 A391T and investigated in vivo in mice the physiological effects of this polymorphism. In vitro, the intrinsic transport properties of mutant ZIP8 were similar to those of wild type ZIP8, but cellular uptake of zinc, cadmium and iron was attenuated due to reduced ZIP8 plasma membrane expression. We then generated the ZIP8 A393T mice (ZIP8KI) that carry the corresponding polymorphism and characterized their phenotype. We observed lower protein expression in lung and kidney membrane extracts in ZIP8KI mice. The ZIP8KI mice exhibited striking changes in metal ion composition of the tissues, including cobalt, palladium, mercury and platinum. In agreement with GWAS, ZIP8KI mice showed reduced arterial blood pressure. Body weight and plasma lipid composition remained unchanged, although these features were reported to be increased in GWAS. ZIP8KI mice also exhibited remarkable insulin resistance and were protected from elevated blood glucose when challenged by dietary sucrose supplementation. We showed that increased hepatic insulin receptor expression and decreased ZnT8 (slc30a8) metal ion transporter mRNA expression are associated with this phenotypic change. In conclusion, our data reveal that ZIP8 plays an important role in blood pressure regulation and glucose homeostasis.

Predictive value of single-nucleotide polymorphisms in curve progression of adolescent idiopathic scoliosis

PURPOSE

Genetic diagnosis is a promising approach because several single-nucleotide polymorphisms (SNPs) associated with adolescent idiopathic scoliosis (AIS) progression have been reported. We review the predictive value of SNPs in curve progression of adolescent idiopathic scoliosis.

METHODS

We reviewed DNA-based prognostic testing to predict curve progression. Then, the multiple polymorphisms in loci related to AIS progression were also reviewed, and we elucidated the predictive value of SNPs from four functional perspectives, including endocrine metabolism, neuromuscular system, cartilage and extracellular matrix, enzymes, and cytokines.

RESULTS

The ScoliScores were less successful predictors than expected, and the weak power of predictive SNPs might account for its failure. Susceptibility loci in ESR1, ESR2, GPER, and IGF1, which related to endocrine metabolism, have been reported to predict AIS progression. Neuromuscular imbalance might be a potential mechanism of scoliosis, and SNPs in LBX1, NTF3, and SOCS3 have been reported to predict the curve progression of AIS. Susceptibility loci in SOX9, MATN1, AJAP1, MMP9, and TIMP2, which are related to cartilage and extracellular matrix, are also potentially related to AIS progression. Enzymes and cytokines play essential roles in regulating bone metabolism and embryonic development. SNPs in BNC2, SLC39A8, TGFB1, IL-6, IL-17RC, and CHD7 were suggested as predictive loci for AIS curve progression.

CONCLUSIONS

Many promising SNPs have been identified to predict the curve progression of AIS. However, conflicting results from replication studies and different ethnic groups hamper their reliability. Convincing SNPs from multiethnic populations and functional verification are needed.

Current and Future Approaches to Classify VUSs in LGMD-Related Genes

Next-generation sequencing (NGS) has revealed large numbers of genetic variants in LGMD-related genes, with most of them classified as variants of uncertain significance (VUSs). VUSs are genetic changes with unknown pathological impact and present a major challenge in genetic test interpretation and disease diagnosis. Understanding the phenotypic consequences of VUSs can provide clinical guidance regarding LGMD risk and therapy. In this review, we provide a brief overview of the subtypes of LGMD, disease diagnosis, current classification systems for investigating VUSs, and a potential deep mutational scanning approach to classify VUSs in LGMD-related genes.

The axonemal dynein heavy chain 10 gene is essential for monocilia motility and spine alignment in zebrafish

Adolescent idiopathic scoliosis (AIS) is a common pediatric musculoskeletal disorder worldwide, characterized by atypical spine curvatures in otherwise healthy children. Human genetic studies have identified candidate genes associated with AIS, however, only a few of these have been shown to recapitulate adult-viable scoliosis in animal models. Using an F0 CRISPR screening approach in zebrafish, we demonstrate that disruption of the dynein axonemal heavy chain 10 (dnah10) gene results in recessive adult-viable scoliosis in zebrafish. Using a stably segregating dnah10 mutant zebrafish, we showed that the ependymal monocilia lining the hindbrain and spinal canal displayed reduced beat frequency, which was correlated with the disassembly of the Reissner fiber and the onset of body curvatures. Taken together, these results suggest that monocilia function in larval zebrafish contributes to the polymerization of the Reissner fiber and straightening of the body axis.

Manganese transport in mammals by zinc transporter family proteins, ZNT and ZIP

Manganese (Mn) is an essential trace element required for various biological processes. However, excess Mn causes serious side effects in humans, including parkinsonism. Thus, elucidation of Mn homeostasis at the systemic, cellular, and molecular levels is important. Many metal transporters and channels can be involved in the transport and homeostasis of Mn, and an increasing body of evidence shows that several zinc (Zn) transporters belonging to the ZIP and ZNT families, specifically, ZNT10, ZIP8, and ZIP14, play pivotal roles in Mn metabolism. Mutations in the genes encoding these transporter proteins are associated with congenital disorders related to dysregulated Mn homeostasis in humans. Moreover, single nucleotide polymorphisms of ZIP8 are associated with multiple clinical phenotypes. In this review, we discuss the recent literature on the structural and biochemical features of ZNT10, ZIP8, and ZIP14, including transport mechanisms, regulation of expression, and pathophysiological functions. Because a disturbance in Mn homeostasis is closely associated with a variety of phenotypes and risk of human diseases, these transporters constitute a significant target for drug development. An understanding of the roles of these key transporters in Mn metabolism should provide new insights into pharmacological applications of their inhibitors and enhancers in human diseases.

Functional significance and physiological regulation of essential trace metals in fish

Trace metals such as iron, copper, zinc and manganese play essential roles in various biological processes in fish, including development, energy metabolism and immune response. At embryonic stages, fish obtain essential metals primarily from the yolk, whereas in later life stages (i.e. juvenile and adult), the gastrointestine and the gill are the major sites for the acquisition of trace metals. On a molecular level, the absorption of metals is thought to occur at least in part via specific metal ion transporters, including the divalent metal transporter-1 (DMT1), copper transporter-1 (CTR1), and Zrt- and Irt-like proteins (ZIP). A variety of other proteins are also involved in maintaining cellular and systemic metal homeostasis. Interestingly, the expression and function of these metal transport- and metabolism-related proteins can be influenced by a range of trace metals and major ions. Increasing evidence also demonstrates an interplay between the gastrointestine and the gill for the regulation of trace metal absorption. Therefore, there is a complex network of regulatory and compensatory mechanisms involved in maintaining trace metal balance. Yet, an array of factors is known to influence metal metabolism in fish, such as hormonal status and environmental changes. In this Review, we summarize the physiological significance of iron, copper, zinc and manganese, and discuss the current state of knowledge on the mechanisms underlying transepithelial metal ion transport, metal-metal interactions, and cellular and systemic handling of these metals in fish. Finally, we identify knowledge gaps in the regulation of metal homeostasis and discuss potential future research directions.

C Deletion at the re74650330 Locus of the SLC39A8 Gene (rs74650330) Increases the Risk of Coronary Artery Disease in Individuals with Low-Density Lipoprotein Cholesterol Levels

Background: Genetic variants of the SLC39A8 gene are associated with several cardiovascular disease risk factors, including body mass index, systolic blood pressure (SBP), diastolic blood pressure (DBP), N-terminal pro-B-type natriuretic peptide (NT-proBNP) and high-density lipoprotein cholesterol (HDL-C) levels. The present study aimed to investigate the association between the SLC39A8 SNPs rs13107325 and rs74650330 and CAD in the Han population in Jiangsu (China). Methods: Genotyping of these SNPs was performed in 258 patients with CAD and 170 healthy controls using the base-quenched probe technique. The association between the alleles of the rs74650330 locus and blood lipid and glucose profiles was investigated. Receiver operating characteristic (ROC) curve analysis was used to quantify the optimal thresholds for lipid and FBG levels and the risk factors for CAD were estimated by logistic regression analysis. Results: The rs13107325 polymorphism was not found in the 428 Chinese individuals enrolled in the current study. For rs74650330, individuals harboring the C allele had significantly higher HDL levels than those without this allele in the control group (p = 0.039), while the opposite was true for low-density lipoprotein cholesterol (LDL-C) levels (p = 0.046). Further analysis indicated that when LDL-C levels were lower than 2.365 mmol/L, subjects with C/del and del/del had a 7.293-fold increased risk of CAD compared with that of controls without the mutation (odds ratio: 7.293; 95% confidence interval: 0.953-55.79). Conclusions: The susceptibility of SLC39A8 polymorphisms to CAD were studied and revealed a possible role for the deletion variant of rs74650330 in increasing the risk of CAD among the Chinese Han population.

The Impact of ZIP8 Disease-Associated Variants G38R, C113S, G204C, and S335T on Selenium and Cadmium Accumulations: The First Characterization

The metal cation symporter ZIP8 (SLC39A8) is a transmembrane protein that imports the essential micronutrients iron, manganese, and zinc, as well as heavy toxic metal cadmium (Cd). It has been recently suggested that selenium (Se), another essential micronutrient that has long been known for its role in human health and cancer risk, may also be transported by the ZIP8 protein. Several mutations in the ZIP8 gene are associated with the aberrant ion homeostasis of cells and can lead to human diseases. However, the intricate relationships between ZIP8 mutations, cellular Se homeostasis, and human diseases (including cancers and illnesses associated with Cd exposure) have not been explored. To further verify if ZIP8 is involved in cellular Se transportation, we first knockout (KO) the endogenous expression of ZIP8 in the HeLa cells using the CRISPR/Cas9 system. The elimination of ZIP8 expression was examined by PCR, DNA sequencing, immunoblot, and immunofluorescence analyses. Inductively coupled plasma mass spectrometry indicated that reduced uptake of Se, along with other micronutrients and Cd, was observed in the ZIP8-KO cells. In contrast, when ZIP8 was overexpressed, increased Se uptake could be detected in the ZIP8-overexpressing cells. Additionally, we found that ZIP8 with disease-associated single-point mutations G38R, G204C, and S335T, but not C113S, showed reduced Se transport ability. We then evaluated the potential of Se on Cd cytotoxicity prevention and therapy of cancers. Results indicated that Se could suppress Cd-induced cytotoxicity via decreasing the intracellular Cd transported by ZIP8, and Se exhibited excellent anticancer activity against not all but only selected cancer cell lines, under restricted experimental conditions. Moreover, clinical-based bioinformatic analyses revealed that up-regulated ZIP8 gene expression was common across multiple cancer types, and selenoproteins that were significantly co-expressed with ZIP8 in these cancers had been identified. Taken together, this study concludes that ZIP8 is an important protein in modulating cellular Se levels and provides insights into the roles of ZIP8 and Se in disease prevention and therapy.

A genome-wide association study for shoulder impingement and rotator cuff disease

BACKGROUND

The purpose of the study was to identify genetic variants associated with rotator cuff disease by performing a genome-wide association study (GWAS) for shoulder impingement using the UK Biobank (UKB) cohort and then combining the GWAS data with a prior GWAS for rotator cuff tears. The loci identified by the GWAS and meta-analysis were examined for changes in expression following rotator cuff tearing using RNA sequencing.

METHODS

A GWAS was performed using data from UKB with 3864 cases of shoulder impingement. The summary statistics from shoulder impingement and a prior study on rotator cuff tears were combined in a meta-analysis. Also, the previous association of 2 single-nucleotide polymorphisms (SNPs) with shoulder impingement from a published GWAS using the UKB was tested. Rotator cuff tendon biopsies were obtained from 24 patients with full-thickness rotator cuff tears who underwent arthroscopic rotator cuff repair (cases) and 9 patients who underwent open reduction internal fixation for a proximal humeral fracture (controls). Total RNA was extracted and differential gene expression was measured by RNA sequencing for genes with variants associated with rotator cuff tearing.

RESULTS

The shoulder impingement GWAS identified 4 new loci: LOC100506457, LSP1P3, LOC100506207, and MIS18BP1/LINC00871. Combining data with a prior GWAS for rotator cuff tears in a meta-analysis resulted in the identification of an additional 7 loci: SLC39A8/UBE2D3, C5orf63, ASTN2, STK24, FRMPD4, ACOT9/SAT1, and LINC00890/ALG13. Many of the identified loci have known biologic functions or prior associations with diseases, suggesting possible biologic pathways leading to rotator cuff disease. RNA sequencing experiments show that expression of STK24 increases whereas expression of SAT1 and UBE2D3 decreases following rotator cuff tearing. Two SNPs previously reported to show an association with shoulder impingement from a prior UKB GWAS were not validated in our study.

CONCLUSION

This is the first GWAS for shoulder impingement in which new data from UKB enabled the identification of 4 loci showing a genetic association. A meta-analysis with a prior GWAS for rotator cuff tearing identified an additional 7 loci. The known biologic roles of many of the 11 loci suggest plausible biologic mechanisms underlying the etiology of rotator cuff disease. The risk alleles from each of the genetic loci can be used to assess the risk for rotator cuff disease in individual patients, enabling preventative or restorative actions via personalized medicine.

The role of endocrine hormones in the pathogenesis of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a common spinal deformity characterized by changes in the three-dimensional structure of the spine. It usually initiates during puberty, the peak period of human growth when the secretion of numerous hormones is changing, and it is more common in females than in males. Accumulating evidence shows that the abnormal levels of many hormones including estrogen, melatonin, growth hormone, leptin, adiponectin and ghrelin, may be related to the occurrence and development of AIS. The purpose of this review is to provide a summary and critique of the research published on each hormone over the past 20 years, and to highlight areas for future study. It is hoped that the presentation will help provide a better understanding of the role of endocrine hormones in the pathogenesis of AIS.

Relationship Between Electromyographic Frequency of the Erector Spinae and Location, Direction, and Number of Spinal Curvatures in Children with Scoliotic Changes

INTRODUCTION

The aim of the study was to assess the relationship between erector spinae electromyographic frequency (SEMG) and the location, direction and number of spinal curvatures in children with scoliotic changes.

METHODS

Analysis comprised 103 (42,21%) children with scoliosis and 141 (57.79%) with scoliotic posture. Body posture and the spine were examined using the Diers formetric III 4D optoelectronic method. Electromyographic analysis was performed using a 14-channel Noraxon TeleMyo DTS apparatus.

RESULTS

In girls, the highest mean SEMG frequency of the erector spinae, calculated from 16 measurements, occurred in the case of scoliotic posture (Mean = 73.69 Hz), while in boys, the greatest values were noted for scoliosis (Mean = 79.75 Hz). There was a significant correlation between erector spinae SEMG frequency and curvature location, both in the scoliosis group (p = 0.003) and in the group with scoliotic posture (p = 0.04). There was also a significant correlation between SEMG frequency of the erector spinae and direction of the curvature, both in the scoliosis (p = 0.01) and scoliotic posture groups (p = 0.04), as well as between the erector spinae SEMG frequency and the number of spinal curvatures (scoliosis group: p = 0.03; scoliotic posture group: p = 0.03).

CONCLUSION

The study is of applicative value and fills the gap in research on erector spinae SEMG frequency of in low-grade scoliosis among small children. Our research can also be used in research on the etiology and progression scoliosis. Visible disturbances in the erector spinae SEMG frequency (activity and tension) contribute to the development of curvature and testify to the fact that these changes are the primary cause of idiopathic scoliosis. Scoliosis is merely a symptom, an external expression of CNS dysfunction that is not fully recognised. It is also visible on the SEMG record of postural muscles. Our objective is to contribute to creating a future model record for SEMG of the postural muscles, characteristic for children with scoliosis. Then, based on electromyographic examination, it will be possible to identify initial symptoms of scoliosis and start preventive rehabilitation before irreversible bone changes occur.

Lower androgen levels promote abnormal cartilage development in female patients with adolescent idiopathic scoliosis

Background

Adolescent idiopathic scoliosis (AIS) is a disease characterized by changes in the three-dimensional structure of the spine. Studies have shown that the development of AIS might be associated with genetic, biomechanics, endocrine factors and abnormal bone or cartilage development.

Methods

Blood samples collected from 301 female patients (161 females with AIS and 140 females without AIS) were used for genotyping. Forty-eight serum samples from 161 females with AIS and 40 serum samples from 140 females without AIS were subjected to enzyme-linked immunosorbent assays (ELISAs). We also evaluated 32 facet joints (18 females with AIS and 14 females without AIS from the 301 female patients) using immunohistochemistry, Western blotting, and isolation of human primary chondrocytes, among other methods. We treated the AIS primary chondrocytes with dihydrotestosterone (DHT) to verify the relationship among androgen, the androgen receptor (AR), and its downstream pathway proteins.

Results

The serum androgen level in the AIS group was significantly decreased (1.94±0.09 vs. 2.284±0.103) compared with that in the non-AIS (control) group. The single nucleotide polymorphism genotyping results showed that the mutation rates of rs6259 between the AIS and control groups were significantly different (G/G genotype: 48.4% vs. 42.1%, G/A genotype: 40.4% vs. 35.7%, P<0.05). The levels of interleukin (IL)-6 and metalloproteinase (MMP)-13 were increased in the cartilage of AIS patients, and these patients also exhibited decreased AR levels. The cell experiment results showed that androgen reduced the degree of abnormal cartilage development in female AIS patients through the AR/IL-6/signal transducer and activator of transcription 3 (STAT3) signaling pathway.

Conclusions

Our study provides a new perspective on the pathogenesis of AIS and indicates that decreased androgen levels in female AIS patients play a potential role in the development of AIS via the AR/IL-6/STAT3 signaling pathway.

Plasticity of the skeleton and skeletal deformities in zebrafish (Danio rerio) linked to rearing density

The teleost zebrafish (Danio rerio), an established model for human skeletal diseases, is reared under controlled conditions with defined parameters for temperature and photoperiod. Studies aimed at defining the proper rearing density have been performed with regard to behavioural and physiological stress response, sex ratio and reproduction. Studies concerning the effect of rearing density on the skeletal phenotype are lacking. This study analyses the response of the skeleton to different rearing densities and describes the skeletal deformities. Wild-type zebrafish were reared up to 30 dpf (days post-fertilization) in a common environment. From 30 to 90 dpf, animals were reared at three different densities: high density (HD), 32 fish l^-1 ; medium density (MD), 8 fish l^-1 and low density (LD), 2 fish l^-1 . Animals at 30 and 90 dpf were collected and whole-mount stained with Alizarin red S to visualize mineralized tissues. The entire skeleton was analysed for meristic counts and 172 types of deformities. The results showed that the rearing density significantly influenced the specimens' average standard length, which decreased with the increase in the rearing density. Differences in meristic counts among the three groups were not observed. Rearing density-independent malformations affected the ribs, neural arches and the spines of the abdominal region, as well as vertebrae of the caudal complex. The HD group showed the highest number of deformities per specimen, the highest number of observed types of deformities and, together with the MD group, the highest frequency of specimens affected by severe deformities. In particular, the HD group showed deformities affecting arches, spines and vertebral centra in the caudal region of the vertebral column. This study provides evidence of an effect of the rearing density on the development of different skeletal phenotypes.

Brain Magnetic Resonance Imaging Phenome-Wide Association Study With Metal Transporter Gene SLC39A8

The SLC39A8 gene encodes a divalent metal transporter, ZIP8. SLC39A8 is associated with pleiotropic effects across multiple tissues, including the brain. We determine the different brain magnetic resonance imaging (MRI) phenotypes associated with SLC39A8. We used a phenome-wide association study approach followed by joint and conditional association analysis. Using the summary statistics datasets from a brain MRI genome-wide association study on adult United Kingdom (UK) Biobank participants, we systematically selected all brain MRI phenotypes associated with single-nucleotide polymorphisms (SNPs) within 500 kb of the SLC39A8 genetic locus. For all significant brain MRI phenotypes, we used GCTA-COJO to determine the number of independent association signals and identify index SNPs for each brain MRI phenotype. Linkage equilibrium for brain phenotypes with multiple independent signals was confirmed by LDpair. We identified 24 brain MRI phenotypes that vary due to MRI type and brain region and contain a SNP associated with the SLC39A8 locus. Missense ZIP8 polymorphism rs13107325 was associated with 22 brain MRI phenotypes. Rare ZIP8 variants present in a published UK Biobank dataset are associated with 6 brain MRI phenotypes also linked to rs13107325. Among the 24 datasets, an additional 4 association signals were identified by GCTA-COJO and confirmed to be in linkage equilibrium with rs13107325 using LDpair. These additional association signals represent new probable causative SNPs in addition to rs13107325. This study provides leads into how genetic variation in SLC39A8, a trace mineral transport gene, is linked to brain structure differences and may affect brain development and nervous system function.

Novel Mutations in UTS2R are Associated with Adolescent Idiopathic Scoliosis in the Chinese Population

STUDY DESIGN

A case-control study.

OBJECTIVES

To investigate the association of urotensin II (UTS2) signals with the susceptibility of adolescent idiopathic scoliosis (AIS) in the Chinese Han population.

SUMMARY OF BACKGROUND DATA

Dysregulated UTS2 signals induced by impaired cerebrospinal fluid flow have been implicated in the development of idiopathic scoliosis through studies on zebrafish. Furthermore, mutations in urotensin II receptor (UTS2R) were reported to cause severe scoliosis in zebrafish. In spite of the evidence presented in animal models, there is still a lack of knowledge concerning the role of UTS2 signaling related genes in AIS.

METHODS

In the discovery stage, exons of UTS2, UTS2R, and UTS2D were sequenced for 200 AIS patients and 200 healthy controls. Newly identified mutations were further genotyped in another independent cohort of 1000 AIS patients and 1000 controls by allelic-specific multiple ligase detection reactions. Gene expression analysis was performed in 36 AIS patients and 36 age-matched congenital scoliosis patients. The Chi-square test was used to compare the genotyping data between the groups. Gene expression analysis was compared with the Student t test.

RESULTS

Association between two novel mutations (rs11654140, c.51T > C; rs568196624, c.1146C > G) and the development of AIS was identified. Allele C of rs11654140 and allele G of rs568196624 were significantly associated with the risk of AIS (1.5% vs. 0.5%, odds ratio = 3.02, P = 0.01 for rs11654140; 1.41% vs. 0.58%, odds ratio = 2.29, P = 0.04 for rs568196624). The mRNA expression of UTS2R in the AIS group was significantly higher as compared with that in the control group (0.059 ± 0.015 vs. 0.035 ± 0.013, P < 0.01).

CONCLUSIONS

Rare mutations in UTS2R were significantly associated with AIS. Expression of UTS2R was significantly increased in AIS patients. The role of UTS2 signaling in the development of AIS is worthy of further investigation.Level of Evidence: N/A.

Zinc transporters and their functional integration in mammalian cells

Zinc is a ubiquitous biological metal in all living organisms. The spatiotemporal zinc dynamics in cells provide crucial cellular signaling opportunities, but also challenges for intracellular zinc homeostasis with broad disease implications. Zinc transporters play a central role in regulating cellular zinc balance and subcellular zinc distributions. The discoveries of two complementary families of mammalian zinc transporters (ZnTs and ZIPs) in the mid-1990s spurred much speculation on their metal selectivity and cellular functions. After two decades of research, we have arrived at a biochemical description of zinc transport. However, in vitro functions are fundamentally different from those in living cells, where mammalian zinc transporters are directed to specific subcellular locations, engaged in dedicated macromolecular machineries, and connected with diverse cellular processes. Hence, the molecular functions of individual zinc transporters are reshaped and deeply integrated in cells to promote the utilization of zinc chemistry to perform enzymatic reactions, tune cellular responsiveness to pathophysiologic signals, and safeguard cellular homeostasis. At present, the underlying mechanisms driving the functional integration of mammalian zinc transporters are largely unknown. This knowledge gap has motivated a shift of the research focus from in vitro studies of purified zinc transporters to in cell studies of mammalian zinc transporters in the context of their subcellular locations and protein interactions. In this review, we will outline how knowledge of zinc transporters has been accumulated from in-test-tube to in-cell studies, highlighting new insights and paradigm shifts in our understanding of the molecular and cellular basis of mammalian zinc transporter functions.

The Susceptibility and Potential Functions of the LBX1 Gene in Adolescent Idiopathic Scoliosis

Genome-wide association studies have identified many susceptibility genes for adolescent idiopathic scoliosis (AIS). However, most of the results are hard to be replicated in multi-ethnic populations. LBX1 is the most promising candidate gene in the etiology of AIS. We aimed to appraise the literature for the association of LBX1 gene polymorphisms with susceptibility and curve progression in AIS. We also reviewed the function of the LBX1 gene in muscle progenitor cell migration and neuronal determination processes. Three susceptibility loci (rs11190870, rs625039, and rs11598564) near the LBX1 gene, as well as another susceptibility locus (rs678741), related to LBX1 regulation, have been successfully verified to have robust associations with AIS in multi-ethnic populations. The LBX1 gene plays an essential role in regulating the migration and proliferation of muscle precursor cells, and it is known to play a role in neuronal determination processes, especially for the fate of somatosensory relay neurons. The LBX1 gene is the most promising candidate gene in AIS susceptibility due to its position and possible functions in muscle progenitor cell migration and neuronal determination processes. The causality between susceptibility loci related to the LBX1 gene and the pathogenesis of AIS deserves to be explored with further integrated genome-wide and epigenome-wide association studies.

A missense variant in SLC39A8 confers risk for Crohn's disease by disrupting manganese homeostasis and intestinal barrier integrity

SLC39A8 A391T exhibits remarkable pleiotropic effects on multiple conditions, including cardiovascular diseases, Parkinson’s disease, and Crohn’s disease. However, how this single coding variant impacts such a wide range of pathologies has not been investigated. We generated Slc39a8 A391T knockin mice and show that they exhibit severe Mn deficiency in the colon, and impaired intestinal barrier integrity due to glycoprotein barrier structure defects, leading to indolent inflammation that can prime further inflammation driven by epithelial injury. Thus, we highlight the importance of Mn in gut homeostasis, and mechanistically unravel how A391T impacts intestinal barrier integrity.

Common genetic variants interact with environmental factors to impact risk of heritable diseases. A notable example of this is a single-nucleotide variant in the Solute Carrier Family 39 Member 8 (SLC39A8)geneencoding the missense variant A391T, which is associated with a variety of traits ranging from Parkinson’s disease and neuropsychiatric disease to cardiovascular and metabolic diseases and Crohn’s disease. The remarkable extent of pleiotropy exhibited by SLC39A8 A391T raises key questions regarding how a single coding variant can contribute to this diversity of clinical outcomes and what is the mechanistic basis for this pleiotropy. Here, we generate a murine model for the Slc39a8 A391T allele and demonstrate that these mice exhibit Mn deficiency in the colon associated with impaired intestinal barrier function and epithelial glycocalyx disruption. Consequently, Slc39a8 A391T mice exhibit increased sensitivity to epithelial injury and pathological inflammation in the colon. Taken together, our results link a genetic variant with a dietary trace element to shed light on a tissue-specific mechanism of disease risk based on impaired intestinal barrier integrity.

N-glycome analysis detects dysglycosylation missed by conventional methods in SLC39A8 deficiency

Congenital disorders of glycosylation (CDG) are a growing group of inborn metabolic disorders with multiorgan presentation. SLC39A8-CDG is a severe subtype caused by biallelic mutations in the manganese transporter SLC39A8, reducing levels of this essential cofactor for many enzymes including glycosyltransferases. The current diagnostic standard for disorders of N-glycosylation is the analysis of serum transferrin. Exome and Sanger sequencing were performed in two patients with severe neurodevelopmental phenotypes suggestive of CDG. Transferrin glycosylation was analyzed by high-performance liquid chromatography (HPLC) and isoelectric focusing in addition to comprehensive N-glycome analysis using matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry (MS). Atomic absorption spectroscopy was used to quantify whole blood manganese levels. Both patients presented with a severe, multisystem disorder, and a complex neurological phenotype. Magnetic resonance imaging (MRI) revealed a Leigh-like syndrome with bilateral T2 hyperintensities of the basal ganglia. In patient 1, exome sequencing identified the previously undescribed homozygous variant c.608T>C [p.F203S] in SLC39A8. Patient 2 was found to be homozygous for c.112G>C [p.G38R]. Both individuals showed a reduction of whole blood manganese, though transferrin glycosylation was normal. N-glycome using MALDI-TOF MS identified an increase of the asialo-agalactosylated precursor N-glycan A2G1S1 and a decrease in bisected structures. In addition, analysis of heterozygous CDG-allele carriers identified similar but less severe glycosylation changes. Despite its reliance as a clinical gold standard, analysis of transferrin glycosylation cannot be categorically used to rule out SLC39A8-CDG. These results emphasize that SLC39A8-CDG presents as a spectrum of dysregulated glycosylation, and MS is an important tool for identifying deficiencies not detected by conventional methods.

Pleiotropic ZIP8 A391T implicates abnormal manganese homeostasis in complex human disease

ZIP8 is a metal transporter with a role in manganese (Mn) homeostasis. A common genetic variant in ZIP8 (rs13107325; A391T) ranks in the top 10 of pleiotropic SNPs identified in GWAS; A391T has associations with an increased risk of schizophrenia, obesity, Crohn’s disease, and reduced blood Mn. Here, we used CRISPR/Cas9-mediated knockin (KI) to generate a mouse model of ZIP8 A391T (Zip8 393T-KI mice). Recapitulating the SNP association with blood Mn, blood Mn was reduced in Zip8 393T-KI mice. There was restricted abnormal tissue Mn homeostasis, with decreases in liver and kidney Mn and a reciprocal increase in biliary Mn, providing in vivo evidence of hypomorphic Zip8 function. Upon challenge in a chemically induced colitis model, male Zip8 393T-KI mice exhibited enhanced disease susceptibility. ZIP8 391-Thr associated with reduced triantennary plasma N-glycan species in a population-based cohort to define a genotype-specific glycophenotype hypothesized to be linked to Mn-dependent glycosyltransferase activity. This glycophenotype was maintained in a cohort of patients with Crohn’s disease. These data and the pleiotropic disease associations with ZIP8 391-Thr suggest underappreciated roles of Mn homeostasis in complex human disease.

Abnormal manganese homeostasis is implicated by a GWAS disease-associated SNP, rs13107325 (ZIP8 A391T), studied in a knockin mouse model and human N-glycome analyses.

The schizophrenia risk locus in SLC39A8 alters brain metal transport and plasma glycosylation

A common missense variant in SLC39A8 is convincingly associated with schizophrenia and several additional phenotypes. Homozygous loss-of-function mutations in SLC39A8 result in undetectable serum manganese (Mn) and a Congenital Disorder of Glycosylation (CDG) due to the exquisite sensitivity of glycosyltransferases to Mn concentration. Here, we identified several Mn-related changes in human carriers of the common SLC39A8 missense allele. Analysis of structural brain MRI scans showed a dose-dependent change in the ratio of T2w to T1w signal in several regions. Comprehensive trace element analysis confirmed a specific reduction of only serum Mn, and plasma protein N-glycome profiling revealed reduced complexity and branching. N-glycome profiling from two individuals with SLC39A8-CDG showed similar but more severe alterations in branching that improved with Mn supplementation, suggesting that the common variant exists on a spectrum of hypofunction with potential for reversibility. Characterizing the functional impact of this variant will enhance our understanding of schizophrenia pathogenesis and identify novel therapeutic targets and biomarkers.

Genome-wide and Mendelian randomisation studies of liver MRI yield insights into the pathogenesis of steatohepatitis

BACKGROUND & AIMS

MRI-based corrected T1 (cT1) is a non-invasive method to grade the severity of steatohepatitis and liver fibrosis. We aimed to identify genetic variants influencing liver cT1 and use genetics to understand mechanisms underlying liver fibroinflammatory disease and its link with other metabolic traits and diseases.

METHODS

First, we performed a genome-wide association study (GWAS) in 14,440 Europeans, with liver cT1 measures, from the UK Biobank. Second, we explored the effects of the cT1 variants on liver blood tests, and a range of metabolic traits and diseases. Third, we used Mendelian randomisation to test the causal effects of 24 predominantly metabolic traits on liver cT1 measures.

RESULTS

We identified 6 independent genetic variants associated with liver cT1 that reached the GWAS significance threshold (p <5×10-8). Four of the variants (rs759359281 in SLC30A10, rs13107325 in SLC39A8, rs58542926 in TM6SF2, rs738409 in PNPLA3) were also associated with elevated aminotransferases and had variable effects on liver fat and other metabolic traits. Insulin resistance, type 2 diabetes, non-alcoholic fatty liver and body mass index were causally associated with elevated cT1, whilst favourable adiposity (instrumented by variants associated with higher adiposity but lower risk of cardiometabolic disease and lower liver fat) was found to be protective.

CONCLUSION

The association between 2 metal ion transporters and cT1 indicates an important new mechanism in steatohepatitis. Future studies are needed to determine whether interventions targeting the identified transporters might prevent liver disease in at-risk individuals.

LAY SUMMARY

We estimated levels of liver inflammation and scarring based on magnetic resonance imaging of 14,440 UK Biobank participants. We performed a genetic study and identified variations in 6 genes associated with levels of liver inflammation and scarring. Participants with variations in 4 of these genes also had higher levels of markers of liver cell injury in blood samples, further validating their role in liver health. Two identified genes are involved in the transport of metal ions in our body. Further investigation of these variations may lead to better detection, assessment, and/or treatment of liver inflammation and scarring.

Role of zinc transporter ZIP12 in susceptibility-weighted brain magnetic resonance imaging (MRI) phenotypes and mitochondrial function

Brain zinc dysregulation is linked to many neurological disorders. However, the mechanisms regulating brain zinc homeostasis are poorly understood. We performed secondary analyses of brain MRI GWAS and exome sequencing data from adults in the UK Biobank. Coding ZIP12 polymorphisms in zinc transporter ZIP12 (SLC39A12) were associated with altered brain susceptibility weighted MRI (swMRI). Conditional and joint association analyses revealed independent GWAS signals in linkage disequilibrium with 2 missense ZIP12 polymorphisms, rs10764176 and rs72778328, with reduced zinc transport activity. ZIP12 rare coding variants predicted to be deleterious were associated with similar impacts on brain swMRI. In Neuro-2a cells, ZIP12 deficiency by short hairpin RNA (shRNA) depletion or CRISPR/Cas9 genome editing resulted in impaired mitochondrial function, increased superoxide presence, and detectable protein carbonylation. Inhibition of Complexes I and IV of the electron transport chain reduced neurite outgrowth in ZIP12 deficient cells. Transcriptional coactivator PGC-1α, mitochondrial superoxide dismutase (SOD2), and chemical antioxidants α-tocopherol, MitoTEMPO, and MitoQ restored neurite extension impaired by ZIP12 deficiency. Mutant forms of α-synuclein and tau linked to familial Parkinson's disease and frontotemporal dementia, respectively, reduced neurite outgrowth in cells deficient in ZIP12. Zinc and ZIP12 may confer resilience against neurological diseases or premature aging of the brain.

Analysis of genetically independent phenotypes identifies shared genetic factors associated with chronic musculoskeletal pain conditions

Chronic musculoskeletal pain affects all aspects of human life. However, mechanisms of its genetic control remain poorly understood. Genetic studies of pain are complicated by the high complexity and heterogeneity of pain phenotypes. Here, we apply principal component analysis to reduce phenotype heterogeneity of chronic musculoskeletal pain at four locations: the back, neck/shoulder, hip, and knee. Using matrices of genetic covariances, we constructed four genetically independent phenotypes (GIPs) with the leading GIP (GIP1) explaining 78.4% of the genetic variance of the analyzed conditions, and GIP2–4 explain progressively less. We identified and replicated five GIP1-associated loci and one GIP2-associated locus and prioritized the most likely causal genes. For GIP1, we showed enrichment with multiple nervous system-related terms and genetic correlations with anthropometric, sociodemographic, psychiatric/personality traits and osteoarthritis. We suggest that GIP1 represents a biopsychological component of chronic musculoskeletal pain, related to physiological and psychological aspects and reflecting pain perception and processing.

Yakov Tsepilov, Maxim Freidin et al. find that chronic musculoskeletal pain conditions at four distinct anatomical sites share a common genetic background. The authors constructed genetically independent phenotypes (GIP) from principal components analysis of the different pain phenotypes and used the GIPs to perform genome-wide association studies to identify underlying genetic factors.

The cartilage matrisome in adolescent idiopathic scoliosis

The human spinal column is a dynamic, segmented, bony, and cartilaginous structure that protects the neurologic system and simultaneously provides balance and flexibility. Children with developmental disorders that affect the patterning or shape of the spine can be at risk of neurologic and other physiologic dysfunctions. The most common developmental disorder of the spine is scoliosis, a lateral deformity in the shape of the spinal column. Scoliosis may be part of the clinical spectrum that is observed in many developmental disorders, but typically presents as an isolated symptom in otherwise healthy adolescent children. Adolescent idiopathic scoliosis (AIS) has defied understanding in part due to its genetic complexity. Breakthroughs have come from recent genome-wide association studies (GWAS) and next generation sequencing (NGS) of human AIS cohorts, as well as investigations of animal models. These studies have identified genetic associations with determinants of cartilage biogenesis and development of the intervertebral disc (IVD). Current evidence suggests that a fraction of AIS cases may arise from variation in factors involved in the structural integrity and homeostasis of the cartilaginous extracellular matrix (ECM). Here, we review the development of the spine and spinal cartilages, the composition of the cartilage ECM, the so-called "matrisome" and its functions, and the players involved in the genetic architecture of AIS. We also propose a molecular model by which the cartilage matrisome of the IVD contributes to AIS susceptibility.

A Novel Coding Variant in SLC39A8 Is Associated With Adolescent Idiopathic Scoliosis in Chinese Han Population

STUDY DESIGN

A genetic case-control association study.

OBJECTIVE

The aim of this study was to investigate the association of SLC39A8 with the susceptibility of adolescent idiopathic scoliosis (AIS) in Chinese Han population.

SUMMARY OF BACKGROUND DATA

A recent exome-wide association study identified a missense variant rs13107325 in SLC39A8 that was associated with AIS. However, there was a lack of study validating the association of this novel mutation with AIS in other populations.

METHODS

The variant rs13107325 was genotyped in 965 AIS patients and 976 healthy controls by allelic specific multiple ligase detection reactions. Variants located in the coding region of SLC39A8 were identified by exon sequencing for 192 AIS patients and 192 controls. Paraspinal muscles from 36 AIS patients and 36 age-matched congenital scoliosis patients were collected for the gene expression analysis. Comparison between the cases and controls was performed with the χ test for genotyping data or with Student t test for gene expression analysis.

RESULTS

For the missense variant rs13107325, there was no case of mutation detected in the patients or the controls. All the subjects had homozygous genotype CC. Exon sequencing revealed that a coding variant rs11097773 of SLC39A8 had a significantly different distribution of minor allele frequency between patients and controls (7.81% vs. 14.8%, P = 0.002). The mRNA expression of SLC39A8 in the patients was remarkably lower than that in the controls (0.0015 ± 0.00026 vs. 0.0021 ± 0.00033, P < 0.001).

CONCLUSION

The association of previously reported novel mutation (rs13107325 in SLC39A8) with AIS was not replicated in the Chinese population. Interestingly, a novel coding variant rs11097773 of SLC39A8 is found significantly associated with AIS. Moreover, the expression of SLC39A8 was obviously decreased in AIS patients. Further study is warranted to clarify the functional role of rs11097773 in the development of AIS.

LEVEL OF EVIDENCE

3.

Notochord vacuoles absorb compressive bone growth during zebrafish spine formation

The vertebral column or spine assembles around the notochord rod which contains a core made of large vacuolated cells. Each vacuolated cell possesses a single fluid-filled vacuole, and loss or fragmentation of these vacuoles in zebrafish leads to spine kinking. Here, we identified a mutation in the kinase gene dstyk that causes fragmentation of notochord vacuoles and a severe congenital scoliosis-like phenotype in zebrafish. Live imaging revealed that Dstyk regulates fusion of membranes with the vacuole. We find that localized disruption of notochord vacuoles causes vertebral malformation and curving of the spine axis at those sites. Accordingly, in dstyk mutants the spine curves increasingly over time as vertebral bone formation compresses the notochord asymmetrically, causing vertebral malformations and kinking of the axis. Together, our data show that notochord vacuoles function as a hydrostatic scaffold that guides symmetrical growth of vertebrae and spine formation.

Zebrafish: A Resourceful Vertebrate Model to Investigate Skeletal Disorders

Animal models are essential tools for addressing fundamental scientific questions about skeletal diseases and for the development of new therapeutic approaches. Traditionally, mice have been the most common model organism in biomedical research, but their use is hampered by several limitations including complex generation, demanding investigation of early developmental stages, regulatory restrictions on breeding, and high maintenance cost. The zebrafish has been used as an efficient alternative vertebrate model for the study of human skeletal diseases, thanks to its easy genetic manipulation, high fecundity, external fertilization, transparency of rapidly developing embryos, and low maintenance cost. Furthermore, zebrafish share similar skeletal cells and ossification types with mammals. In the last decades, the use of both forward and new reverse genetics techniques has resulted in the generation of many mutant lines carrying skeletal phenotypes associated with human diseases. In addition, transgenic lines expressing fluorescent proteins under bone cell- or pathway- specific promoters enable in vivo imaging of differentiation and signaling at the cellular level. Despite the small size of the zebrafish, many traditional techniques for skeletal phenotyping, such as x-ray and microCT imaging and histological approaches, can be applied using the appropriate equipment and custom protocols. The ability of adult zebrafish to remodel skeletal tissues can be exploited as a unique tool to investigate bone formation and repair. Finally, the permeability of embryos to chemicals dissolved in water, together with the availability of large numbers of small-sized animals makes zebrafish a perfect model for high-throughput bone anabolic drug screening. This review aims to discuss the techniques that make zebrafish a powerful model to investigate the molecular and physiological basis of skeletal disorders.

The solute carriers ZIP8 and ZIP14 regulate manganese accumulation in brain microvascular endothelial cells and control brain manganese levels

Manganese supports numerous neuronal functions but in excess is neurotoxic. Consequently, regulation of manganese flux at the blood-brain barrier (BBB) is critical to brain homeostasis. However, the molecular pathways supporting the transcellular trafficking of divalent manganese ions within the microvascular capillary endothelial cells (BMVECs) that constitute the BBB have not been examined. In this study, we have determined that ZIP8 and ZIP14 (Zrt- and Irt-like proteins 8 and 14) support Mn²⁺ uptake by BMVECs and that neither DMT1 nor an endocytosis-dependent pathway play any significant role in Mn²⁺ uptake. Specifically, siRNA-mediated knockdown of ZIP8 and ZIP14 coincided with a decrease in manganese uptake, and kinetic analyses revealed that manganese uptake depends on pH and bicarbonate and is up-regulated by lipopolysaccharide, all biochemical markers of ZIP8 or ZIP14 activity. Mn²⁺ uptake also was associated with cell-surface membrane presentation of ZIP8 and ZIP14, as indicated by membrane protein biotinylation. Importantly, surface ZIP8 and ZIP14 biotinylation and Mn²⁺-uptake experiments together revealed that these transporters support manganese uptake at both the apical, blood and basal, brain sides of BMVECs. This indicated that in the BMVECs of the BBB, these two transporters support a bidirectional Mn²⁺ flux. We conclude that BMVECs play a critical role in controlling manganese homeostasis in the brain.

SLC39A8 gene encoding a metal ion transporter: discovery and bench to bedside

SLC39A8 is an evolutionarily highly conserved gene that encodes the ZIP8 metal cation transporter in all vertebrates. SLC39A8 is ubiquitously expressed, including pluripotent embryonic stem cells; SLC39A8 expression occurs in every cell type examined. Uptake of ZIP8-mediated Mn2+, Zn2+, Fe2+, Se4+, and Co2+ represents endogenous functions-moving these cations into the cell. By way of mouse genetic differences, the phenotype of "subcutaneous cadmium-induced testicular necrosis" was assigned to the Cdm locus in the 1970s. This led to identification of the mouse Slc39a8 gene, its most closely related Slc39a14 gene, and creation of Slc39a8-overexpressing, Slc39a8(neo/neo) knockdown, and cell type-specific conditional knockout mouse lines; the Slc39a8(-/-) global knockout mouse is early-embryolethal. Slc39a8(neo/neo) hypomorphs die between gestational day 16.5 and postnatal day 1-exhibiting severe anemia, dysregulated hematopoiesis, hypoplastic spleen, dysorganogenesis, stunted growth, and hypomorphic limbs. Not surprisingly, genome-wide association studies subsequently revealed human SLC39A8-deficiency variants exhibiting striking pleiotropy-defects correlated with clinical disorders in virtually every organ, tissue, and cell-type: numerous developmental and congenital disorders, the immune system, cardiovascular system, kidney, lung, liver, coagulation system, central nervous system, musculoskeletal system, eye, and gastrointestinal tract. Traits with which SLC39A8-deficiency variants are currently associated include Mn2+-deficient hypoglycosylation; numerous birth defects; Leigh syndrome-like mitochondrial redox deficiency; decreased serum high-density lipoprotein-cholesterol levels; increased body mass index; greater risk of coronary artery disease, hypotension, cardiovascular death, allergy, ischemic stroke, schizophrenia, Parkinson disease, inflammatory bowel disease, Crohn disease, myopia, and adolescent idiopathic scoliosis; systemic lupus erythematosus with primary Sjögren syndrome; decreased height; and inadvertent participation in the inflammatory progression of osteoarthritis.

Genetic Variants of ABO and SOX6 are Associated With Adolescent Idiopathic Scoliosis in Chinese Han Population

STUDY DESIGN

A genetic association study.

OBJECTIVE

The aim of this study was to determine whether variants of ABO, SOX6, and CDH13 are associated with the susceptibility of AIS in Chinese Han population.

SUMMARY OF BACKGROUND DATA

A recent large-scale genome-wide association study reported three novel loci in CDH13, ABO, and SOX6 genes associated with adolescent idiopathic scoliosis (AIS) in Japanese population. However, the association of these three genes with AIS in other populations remains obscure.

METHODS

The SNPs rs4513093, rs687621, and rs1455114 were genotyped in 1208 female patients and 2498 healthy controls. Samples for the expression analysis in paraspinal muscles were collected from 49 AIS and 33 congenital scoliosis (CS) patients during surgical interventions. Chi-square analysis was used to assess the difference regarding genotype and allele frequency between cases and controls. Tissue expressions of ABO, CDH13, and SOX6 were compared between AIS and CS patients by the Student t test.

RESULTS

SNPs rs4513093 of CDH13 and rs687621 of ABO were found to be significantly associated with AIS with an odds ratio of 0.8691 and 1.203, respectively. There was no significant association of rs1455114 with AIS. Moreover, AIS patients were found to have significantly increased expression of ABO. As for expression of CDH13 and SOX6, no remarkable difference was found between the two groups.

CONCLUSION

The association of CDH13 and ABO variants with AIS was successfully replicated in the Chinese Han population. More studies are warranted to explore the functional role of ABO in the development of AIS.

LEVEL OF EVIDENCE

N/A.

Genome-wide association study identifies 14 previously unreported susceptibility loci for adolescent idiopathic scoliosis in Japanese

Adolescent idiopathic scoliosis (AIS) is the most common pediatric spinal deformity. Several AIS susceptibility loci have been identified; however, they could explain only a small proportion of AIS heritability. To identify additional AIS susceptibility loci, we conduct a meta-analysis of the three genome-wide association studies consisting of 79,211 Japanese individuals. We identify 20 loci significantly associated with AIS, including 14 previously not reported loci. These loci explain 4.6% of the phenotypic variance of AIS. We find 21 cis-expression quantitative trait loci-associated genes in seven of the fourteen loci. By a female meta-analysis, we identify additional three significant loci. We also find significant genetic correlations of AIS with body mass index and uric acid. The cell-type specificity analyses show the significant heritability enrichment for AIS in multiple cell-type groups, suggesting the heterogeneity of etiology and pathogenesis of AIS. Our findings provide insights into etiology and pathogenesis of AIS.

Adolescent idiopathic scoliosis (AIS) is a common pediatric disease leading to spinal deformities. Here, the authors report GWAS followed by genome-wide meta-analysis in up to 79,211 Japanese individuals, identifying 20 genetic loci for AIS, 14 of which were previously unreported, and perform in vitro validation for rs1978060.

Ghrelin up-regulates cartilage-specific genes via the ERK/STAT3 pathway in chondrocytes of patients with adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a severe spinal deformity that often occurs during puberty. The occurrence of AIS is suggested to be related to abnormal development of cartilage. Our previous study found increased serum ghrelin levels in AIS patients that may linked to the development of AIS. However, whether ghrelin affects cartilage in AIS patients is unclear. We used quantitative real-time PCR (qRT-PCR) and immunohistochemistry to detect the expression of cartilage-specific genes and the ghrelin receptor, growth hormone secretagogue receptor (GHSR). The mRNA and protein levels of collagen II (COLII), SOX9, AGGRECAN (ACAN) and GHSR were higher in AIS patients than in controls. In addition, the protein levels of GHSR downstream signaling pathway members p-STAT3 (Ser727), and p-ERK1/2 were increased. Furthermore, we treated chondrocytes from AIS patients with 100 nM ghrelin, the cell proliferation assay and Western blotting showed that ghrelin promotes chondrocyte proliferation and enhances COLII, SOX9, ACAN, p-ERK1/2 and p-STAT3 expression, respectively. Interestingly, all these observed alterations were abolished by ghrelin + [D-Lys3]-GHRP-6 (a ghrelin receptor inhibitor) treatment. And after U0126 (an inhibitor of ERK1/2 phosphorylation) treatment, ERK1/2 and STAT3 (Ser727) phosphorylation was simultaneously suppressed indicating that ERK1/2 is an upstream pathway protein of STAT3 (Ser727). In conclusion, ghrelin plays an important role in upregulating cartilage-specific genes on AIS primary chondrocytes by activating ERK/STAT3 signaling pathway.

Zebrafish and medaka as models for biomedical research of bone diseases

The identification of disease-causing mutations has in recent years progressed immensely due to whole genome sequencing approaches using patient material. The task accordingly is shifting from gene identification to functional analysis of putative disease-causing genes, preferably in an in vivo setting which also allows testing of drug candidates or biotherapeutics in whole animal disease models. In this review, we highlight the advances made in the field of bone diseases using small laboratory fish, focusing on zebrafish and medaka. We particularly highlight those human conditions where teleost models are available.