Functional validation of novel compound heterozygous variants in B3GAT3 resulting in severe osteopenia and fractures: expanding the disease phenotype

Discovery of Novel 2-Oxoacetamide Derivatives as B3GAT3 Inhibitors for the Treatment of Hepatocellular Carcinoma

Beta-1,3-glucuronosyltransferase (B3GAT3), overexpressed in hepatocellular carcinoma (HCC) and negatively correlated to prognosis, is a promising target for cancer therapy. Currently, no studies have reported small molecule inhibitors of B3GAT3. In this study, we designed and synthesized a series of small-molecule inhibitors of B3GAT3 through virtual screening and structure optimization. The lead compound TMLB-C16 exhibited potent B3GAT3 inhibitory activity (KD = 3.962 μM) by effectively suppressing proliferation and migration, and inducing cell cycle arrest and apoptosis in MHCC-97H (IC50= 6.53 ± 0.18 μM) and HCCLM3 (IC50= 6.22 ± 0.23 μM) cells. Furthermore, compound TMLB-C16 demonstrated favorable pharmacokinetic properties with a relatively high bioavailability of 68.37%. It significantly inhibited tumor growth in both MHCC-97H and HCCLM3 xenograft tumor models without causing obvious toxicity. These results indicate that compound TMLB-C16 is an effective small molecule inhibitor of B3GAT3, providing a basis for the future development of B3GAT3-targeted drugs.

Metabolic Cardiomyopathies and Cardiac Defects in Inherited Disorders of Carbohydrate Metabolism: A Systematic Review

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

The Landscape of Using Glycosyltransferase Gene Signatures for Overall Survival Prediction in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a heterogeneous disease that occurs in the setting of chronic liver diseases. The role of glycosyltransferase (GT) genes has recently been the focus of research associated with tumor development. However, the prognostic value of GT genes in HCC remains unclear. Therefore, this study aimed to identify GT genes related to HCC prognosis through bioinformatics analysis. We firstly constructed a prognostic signature based on four GT genes using univariate and least absolute shrinkage and selection operator (LASSO) Cox regression analyses in The Cancer Genome Atlas (TCGA) dataset. Next, the risk score of each patient was calculated, and HCC patients were divided into high- and low-risk groups. Kaplan–Meier analysis showed that the survival rate of high-risk patients was significantly lower than that of low-risk patients. Receiver operating characteristic (ROC) curves assessed that risk scores calculated with a four-gene signature could predict 3- and 5-year overall survival (OS) of HCC patients, revealing the prognostic ability of this gene signature. Moreover, univariate and multivariate Cox regression analyses demonstrated that the risk score was an independent prognostic factor of HCC. Finally, functional analysis revealed that immune-related pathways were enriched and the immune status was different between the two risk groups in HCC. In summary, the novel GT gene signature could be used for prognostic prediction of HCC. Thus, targeting the GT genes may serve as an alternative treatment strategy for HCC.

Understanding Musculoskeletal Disorders Through Next-Generation Sequencing

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An insight into musculoskeletal disorders through advancements in next-generation sequencing (NGS) promises to maximize benefits and improve outcomes through improved genetic diagnosis.

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The primary use of whole exome sequencing (WES) for musculoskeletal disorders is to identify functionally relevant variants.

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The current evidence has shown the superiority of NGS over conventional genotyping for identifying novel and rare genetic variants in patients with musculoskeletal disorders, due to its high throughput and low cost.

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Genes identified in patients with scoliosis, osteoporosis, osteoarthritis, and osteogenesis imperfecta using NGS technologies are listed for further reference.

Severe phenotypes of B3GAT3-related disorder caused by two heterozygous variants: a case report and literature review

Background

Linkeropathies refers to a series of extremely rare hereditary connective tissue diseases affected by various glycosyltransferases in the biosynthesis of proteoglycans. We report for the first time two heterozygous variants of B3GAT3 in a Chinese infant, in whom Marfan syndrome was suspected at birth.

Case presentation

A 2-month-old boy from a non-consanguineous Chinese family without a family history presented severe phenotypes of joint dislocation, obvious flexion contractures of the elbow, arachnodactyly with slightly adducted thumbs, cranial dysplasia, foot abnormalities and aortic root dilation; Marfan syndrome was suspected at birth. Our patient was the youngest, at the age of 2 months, to experience aortic root dilation. Two B3GAT3 variants, NM_012200.2, c.752T>C, p.V251A and c.47C>A, p.S16*, with heterozygosity were identified in the patient by whole-exome sequencing; the variants were inherited from his parents. During close follow-up, significant changes in the cranial profile and obvious external hydrocephalus were present at the age of 7 months, which differs from previously reported cases.

Conclusion

We diagnosed a patient with congenital heart defects at an early age with a B3GAT3-related disorder instead of Marfan syndrome and expanded the spectrum of B3GAT3-related disorders. We also provide a literature review of reported B3GAT3 cases; for at least one of the variants, this is the first report of genotype–phenotype correlations in individuals with cardiovascular defects being related to the acceptor substrate-binding subdomain of B3GAT3.

Congenital Disorders of Deficiency in Glycosaminoglycan Biosynthesis

Glycosaminoglycans (GAGs) including chondroitin sulfate, dermatan sulfate, and heparan sulfate are covalently attached to specific core proteins to form proteoglycans, which are distributed at the cell surface as well as in the extracellular matrix. Proteoglycans and GAGs have been demonstrated to exhibit a variety of physiological functions such as construction of the extracellular matrix, tissue development, and cell signaling through interactions with extracellular matrix components, morphogens, cytokines, and growth factors. Not only connective tissue disorders including skeletal dysplasia, chondrodysplasia, multiple exostoses, and Ehlers-Danlos syndrome, but also heart and kidney defects, immune deficiencies, and neurological abnormalities have been shown to be caused by defects in GAGs as well as core proteins of proteoglycans. These findings indicate that GAGs and proteoglycans are essential for human development in major organs. The glycobiological aspects of congenital disorders caused by defects in GAG-biosynthetic enzymes including specific glysocyltransferases, epimerases, and sulfotransferases, in addition to core proteins of proteoglycans will be comprehensively discussed based on the literature to date.

B3GAT3-related linkeropathy and an in-frame homozygous deletion in an adult patient

BACKGROUND

Proteoglycans (PGs) are complex macromolecules consisting of a core protein and glycosaminoglycan (GAG) side chains. PGs are important for the constitution and functioning of the connective tissue. The normal composition of the GAG side chains defines the nature of the PGs and a wide range of biological events. Deficiencies of specific enzymes involved in the linkage of GAGs to the core protein to form functional PGs, lead to a heterogeneous disease group called Linkeropathies. This is a group of multisystem conditions characterized by different phenotypes that include skeletal dysplasia and various extra-skeletal features: developmental delay/intellectual disability, ophthalmological abnormalities including blue sclerae, facial characteristics, cardiac defects, abdominal wall defects (hernias), cutis laxa, hypermobility and hypotonia. The conditions show variable severity and often overlapping phenotypes. The enzyme β-1,3-glucuronyltransferase 3, encoded by B3GAT3, is involved in the linkage process to form functional PGs. Biallelic pathogenic variants in B3GAT3 hence lead to Linkeropathy due to loss of function or decreased activity of this enzyme.

PATIENT PRESENTATION

We describe a 22-year-old female patient, born of consanguineous parents. The disease history includes congenital severe joint malalignment of elbows, hips, knees and feet, hypermobility, severe kyphoscoliosis, osteoporosis with multiple fractures in childhood, congenital diaphragmatic hernia, minor dental anomalies, digital malformations, and characteristic facial features. Whole exome sequencing was performed, and homozygosity for a novel in-frame deletion in B3GAT3, (c.61_63delCTC (p.(Leu21del))) was detected. Both unaffected parents (double second cousins) were shown to be heterozygous carriers.

CONCLUSION

This is the first report to describe homozygosity for this specific in-frame deletion in B3GAT3 (p.(Leu21del)). We present a young adult phenotype and a summary of previous reported patients with other biallelic B3GAT3-variants for comparison. Previously described patients of B3GAT3-deficiency were, however, all children with phenotypes ranging from prenatal manifestation and early lethality to less severe. We suggest that this novel homozygous in-frame deletion in B3GAT3 may be the cause of a recessive form of Linkeropathy.

Chondrodysplasias With Multiple Dislocations Caused by Defects in Glycosaminoglycan Synthesis

Chondrodysplasias with multiple dislocations form a group of severe disorders characterized by joint laxity and multiple dislocations, severe short stature of pre- and post-natal onset, hand anomalies, and/or vertebral anomalies. The majority of chondrodysplasias with multiple dislocations have been associated with mutations in genes encoding glycosyltransferases, sulfotransferases, and transporters implicated in the synthesis or sulfation of glycosaminoglycans, long and unbranched polysaccharides composed of repeated disaccharide bond to protein core of proteoglycan. Glycosaminoglycan biosynthesis is a tightly regulated process that occurs mainly in the Golgi and that requires the coordinated action of numerous enzymes and transporters as well as an adequate Golgi environment. Any disturbances of this chain of reactions will lead to the incapacity of a cell to construct correct glycanic chains. This review focuses on genetic and glycobiological studies of chondrodysplasias with multiple dislocations associated with glycosaminoglycan biosynthesis defects and related animal models. Strong comprehension of the molecular mechanisms leading to those disorders, mostly through extensive phenotypic analyses of in vitro and/or in vivo models, is essential for the development of novel biomarkers for clinical screenings and innovative therapeutics for these diseases.

b3galt6 Knock-Out Zebrafish Recapitulate β3GalT6-Deficiency Disorders in Human and Reveal a Trisaccharide Proteoglycan Linkage Region

Proteoglycans are structurally and functionally diverse biomacromolecules found abundantly on cell membranes and in the extracellular matrix. They consist of a core protein linked to glycosaminoglycan chains via a tetrasaccharide linkage region. Here, we show that CRISPR/Cas9-mediated b3galt6 knock-out zebrafish, lacking galactosyltransferase II, which adds the third sugar in the linkage region, largely recapitulate the phenotypic abnormalities seen in human β3GalT6-deficiency disorders. These comprise craniofacial dysmorphism, generalized skeletal dysplasia, skin involvement and indications for muscle hypotonia. In-depth TEM analysis revealed disturbed collagen fibril organization as the most consistent ultrastructural characteristic throughout different affected tissues. Strikingly, despite a strong reduction in glycosaminoglycan content, as demonstrated by anion-exchange HPLC, subsequent LC-MS/MS analysis revealed a small amount of proteoglycans containing a unique linkage region consisting of only three sugars. This implies that formation of glycosaminoglycans with an immature linkage region is possible in a pathogenic context. Our study, therefore unveils a novel rescue mechanism for proteoglycan production in the absence of galactosyltransferase II, hereby opening new avenues for therapeutic intervention.

CSGALNACT1-congenital disorder of glycosylation: A mild skeletal dysplasia with advanced bone age

Congenital disorders of glycosylation (CDGs) comprise a large number of inherited metabolic defects that affect the biosynthesis and attachment of glycans. CDGs manifest as a broad spectrum of disease, most often including neurodevelopmental and skeletal abnormalities and skin laxity. Two patients with biallelic CSGALNACT1 variants and a mild skeletal dysplasia have been described previously. We investigated two unrelated patients presenting with short stature with advanced bone age, facial dysmorphism, and mild language delay, in whom trio-exome sequencing identified novel biallelic CSGALNACT1 variants: compound heterozygosity for c.1294G>T (p.Asp432Tyr) and the deletion of exon 4 that includes the start codon in one patient, and homozygosity for c.791A>G (p.Asn264Ser) in the other patient. CSGALNACT1 encodes CSGalNAcT-1, a key enzyme in the biosynthesis of sulfated glycosaminoglycans chondroitin and dermatan sulfate. Biochemical studies demonstrated significantly reduced CSGalNAcT-1 activity of the novel missense variants, as reported previously for the p.Pro384Arg variant. Altered levels of chondroitin, dermatan, and heparan sulfate moieties were observed in patients' fibroblasts compared to controls. Our data indicate that biallelic loss-of-function mutations in CSGALNACT1 disturb glycosaminoglycan synthesis and cause a mild skeletal dysplasia with advanced bone age, CSGALNACT1-CDG.

Pseudodiastrophic dysplasia expands the known phenotypic spectrum of defects in proteoglycan biosynthesis

Background

Pseudodiastrophic dysplasia (PDD) is a severe skeletal dysplasia associated with prenatal manifestation and early lethality. Clinically, PDD is classified as a ‘dysplasia with multiple joint dislocations’; however, the molecular aetiology of the disorder is currently unknown.

Methods

Whole exome sequencing (WES) was performed on three patients from two unrelated families, clinically diagnosed with PDD, in order to identify the underlying genetic cause. The functional effects of the identified variants were characterised using primary cells and human cell-based overexpression assays.

Results

WES resulted in the identification of biallelic variants in the established skeletal dysplasia genes, B3GAT3 (family 1) and CANT1 (family 2). Mutations in these genes have previously been reported to cause ‘multiple joint dislocations, short stature, and craniofacial dysmorphism with or without congenital heart defects’ (‘JDSCD’; B3GAT3) and Desbuquois dysplasia 1 (CANT1), disorders in the same nosological group as PDD. Follow-up of the B3GAT3 variants demonstrated significantly reduced B3GAT3/GlcAT-I expression. Downstream in vitro functional analysis revealed abolished biosynthesis of glycosaminoglycan side chains on proteoglycans. Functional evaluation of the CANT1 variant showed impaired nucleotidase activity, which results in inhibition of glycosaminoglycan synthesis through accumulation of uridine diphosphate.

Conclusion

For the families described in this study, the PDD phenotype was caused by mutations in the known skeletal dysplasia genes B3GAT3 and CANT1, demonstrating the advantage of genomic analyses in delineating the molecular diagnosis of skeletal dysplasias. This finding expands the phenotypic spectrum of B3GAT3-related and CANT1-related skeletal dysplasias to include PDD and highlights the significant phenotypic overlap of conditions within the proteoglycan biosynthesis pathway.

[Hereditary Skeletal and Skin Disorders Caused by Defects in the Biosynthesis of Chondroitin/Dermatan Sulfate, and Molecular Mechanisms of Pulmonary Metastasis]

The roles of chondroitin sulfate (CS) and dermatan sulfate (DS) have been demonstrated in various biological events such as the construction of the extracellular matrix, tissue development, and cell signaling through interactions with extracellular matrix components, morphogens, and growth factors. Human genetic diseases, including skeletal abnormalities, connective tissue diseases, and heart defects, were reported to be caused by mutations in the genes encoding glycosyltransferases, epimerases, and sulfotransferases that are responsible for the biosynthesis of CS and DS. Glycobiological approaches revealed that mutations in CS- and DS-biosynthetic enzymes led to reductions in their enzymatic activities and in the levels of CS and DS. Furthermore, CS at the surface of tumor cells plays a key role in pulmonary metastasis. A receptor for advanced glycation end-products (RAGE) was predominantly expressed in the lung, and was identified as a functional receptor for CS chains. CS and anti-RAGE antibodies inhibited the pulmonary metastasis of not only Lewis lung carcinoma but also B16 melanoma cells. Hence, RAGE and CS are potential targets of drug discovery for pulmonary metastasis and a number of other pathological conditions involving RAGE in the pathogenetic mechanism. This review provides an overview of glycobiological studies on characterized genetic disorders caused by the impaired biosynthesis of CS, as well as DS, and on the pulmonary metastasis of Lewis lung carcinoma cells involving CS and RAGE.

Further Defining the Phenotypic Spectrum of B3GAT3 Mutations and Literature Review on Linkeropathy Syndromes

The term linkeropathies (LKs) refers to a group of rare heritable connective tissue disorders, characterized by a variable degree of short stature, skeletal dysplasia, joint laxity, cutaneous anomalies, dysmorphism, heart malformation, and developmental delay. The LK genes encode for enzymes that add glycosaminoglycan chains onto proteoglycans via a common tetrasaccharide linker region. Biallelic variants in XYLT1 and XYLT2, encoding xylosyltransferases, are associated with Desbuquois dysplasia type 2 and spondylo-ocular syndrome, respectively. Defects in B4GALT7 and B3GALT6, encoding galactosyltransferases, lead to spondylodysplastic Ehlers-Danlos syndrome (spEDS). Mutations in B3GAT3, encoding a glucuronyltransferase, were described in 25 patients from 12 families with variable phenotypes resembling Larsen, Antley-Bixler, Shprintzen-Goldberg, and Geroderma osteodysplastica syndromes. Herein, we report on a 13-year-old girl with a clinical presentation suggestive of spEDS, according to the 2017 EDS nosology, in whom compound heterozygosity for two B3GAT3 likely pathogenic variants was identified. We review the spectrum of B3GAT3-related disorders and provide a comparison of all LK patients reported up to now, highlighting that LKs are a phenotypic continuum bridging EDS and skeletal disorders, hence offering future nosologic perspectives.

The clinical and mutational spectrum of B3GAT3 linkeropathy: two case reports and literature review

Background

Proteoglycans are large and structurally complex macromolecules which can be found in abundancy in the extracellular matrix and on the surface of all animal cells. Mutations in the genes encoding the enzymes responsible for the formation of the tetrasaccharide linker region between the proteoglycan core protein and the glycosaminoglycan side chains lead to a spectrum of severe and overlapping autosomal recessive connective tissue disorders, collectively coined the ‘glycosaminoglycan linkeropathies’.

Results

We report the clinical findings of two novel patients with a complex linkeropathy due to biallelic mutations in B3GAT3, the gene that encodes glucuronosyltransferase I, which catalyzes the addition of the ultimate saccharide to the linker region. We identified a previously reported c.667G > A missense mutation and an unreported homozygous c.416C > T missense mutation. We also performed a genotype and phenotype-oriented literature overview of all hitherto reported patients harbouring B3GAT3 mutations. A total of 23 patients from 10 families harbouring bi-allelic mutations and one patient with a heterozygeous splice-site mutation in B3GAT3 have been reported. They all display a complex phenotype characterized by consistent presence of skeletal dysplasia (including short stature, kyphosis, scoliosis and deformity of the long bones), facial dysmorphology, and spatulate distal phalanges. More variably present are cardiac defects, joint hypermobility, joint dislocations/contractures and fractures. Seven different B3GAT3 mutations have been reported, and although the number of patients is still limited, some phenotype-genotype correlations start to emerge. The more severe phenotypes seem to have mutations located in the substrate acceptor subdomain of the catalytic domain of the glucuronosyltransferase I protein while more mildly affected phenotypes seem to have mutations in the NTP-sugar donor substrate binding subdomain.

Conclusions

Loss-of-function mutations in B3GAT3 are associated with a complex connective tissue phenotype characterized by disproportionate short stature, skeletal dysplasia, facial dysmorphism, spatulate distal phalanges and -to a lesser extent- joint contractures, joint hypermobility with dislocations, cardiac defects and bone fragility. Based on the limited number of reported patients, some genotype-phenotype correlations start to emerge.

High Expression B3GAT3 Is Related with Poor Prognosis of Liver Cancer

Liver cancer is one of the most malignant tumors with poor prognosis. Finding molecular markers that can predict prognosis is very important for the treatment of liver cancer. The present research is trying to find a new biomarker for human liver cancer. The analysis of abnormal expression genes and prognosis value on liver cancer by Gene Expression Profiling Interactive Analysis (GEPIA) database, the Pathology Atlas of the Human Protein Atlas (HPA), and Kaplan Meier-plotter (KM plotter), proved that B3GAT3 might be one of the important candidates. Furthermore, we investigated the specific role of B3GAT3 on liver cancer through the transfection of B3GAT3 siRNA in HepG2 cells. The proliferation was detected using CCK8, and migration and invasion were determined using Transwell assay. Our results proved that knockdown of B3GAT3 inhibited the proliferation, migration, and invasion. Moreover, B3GAT3 knockdown inhibited the expression of EMT related proteins, N-cad, Snail, and Twist, while promoting the expression of E-cad, suggesting that B3GAT3 knockdown reversed the EMT process of liver cancer cells. In conclusion, overexpressed B3GAT3 promotes the process of tumor EMT, which is an independent prognostic marker to predict the prognosis of liver cancer and might be a potential new target for liver cancer therapy.

Novel Splicing Mutation in B3GAT3 Associated with Short Stature, GH Deficiency, Hypoglycaemia, Developmental Delay, and Multiple Congenital Anomalies

B3GAT3, encoding β-1,3-glucuronyltransferase 3, has an important role in proteoglycan biosynthesis. Homozygous B3GAT3 mutations have been associated with short stature, skeletal deformities, and congenital heart defects. We describe for the first time a novel heterozygous splice site mutation in B3GAT3 contributing to severe short stature, growth hormone (GH) deficiency, recurrent ketotic hypoglycaemia, facial dysmorphism, and congenital heart defects. A female infant, born at 34 weeks' gestation to nonconsanguineous Caucasian parents with a birth weight of 1.9 kg, was noted to have cloacal abnormality, ventricular septal defect, pulmonary stenosis, and congenital sensorineural deafness. At 4 years of age, she was diagnosed with GH deficiency due to her short stature (height < 2.5 SD). MRI of the pituitary gland revealed a small anterior pituitary. She has multiple dysmorphic features: anteverted nares, small upturned nose, hypertelorism, slight frontal bossing, short proximal bones, hypermobile joints, and downslanting palpebral fissures. Whole exome sequencing (WES) was performed on the genomic DNA from the patient and biological mother. A heterozygous mutation in B3GAT3 (c.888+262T>G) in the invariant “GT” splice donor site was identified. This variant is considered to be pathogenic as it decreases the splicing efficiency in the mRNA.

Expanding the clinical and mutational spectrum of B4GALT7-spondylodysplastic Ehlers-Danlos syndrome

Background

Spondylodysplastic EDS (spEDS) is a rare connective tissue disorder that groups the phenotypes caused by biallelic B4GALT7, B3GALT6, and SLC39A13 mutations. In the 2017 EDS nosology, minimal criteria (general and gene-specific) for a clinical suspicion of spEDS have been proposed, but molecular analysis is required to reach a definite diagnosis. The majority of spEDS patients presented with short stature, skin hyperextensibility, facial dysmorphisms, peculiar radiological findings, muscle hypotonia and joint laxity and/or its complications. To date only 7 patients with β4GALT7-deficiency (spEDS-B4GALT7) have been described and their clinical data suggested that, in addition to short stature and muscle hypotonia, radioulnar synostosis, hypermetropia, and delayed cognitive development might be a hallmark of this specific type of spEDS. Additional 22 patients affected with an overlapping phenotype, i.e., Larsen of Reunion Island syndrome, all carrying a homozygous B4GALT7 mutation, are also recognized.

Results

Herein, we report on a 30-year-old Moroccan woman who fitted the minimal criteria to suspect spEDS, but lacked radioulnar synostosis and intellectual disability and presented with neurosensorial hearing loss and limb edema of lymphatic origin. Sanger sequencing of B4GALT7 was performed since the evaluation of the spEDS gene-specific minor criteria suggested this specific subtype. Mutational screening revealed the homozygous c.829G>T, p.Glu277* pathogenetic variant leading to aberrant splicing.

Conclusions

Our findings expand both the clinical and mutational spectrum of this ultrarare connective tissue disorder. The comparison of the patient’s features with those of the other spEDS and Larsen of Reunion Island syndrome patients reported up to now offers future perspectives for spEDS nosology and clinical research in this field.

Cardiac complications of congenital disorders of glycosylation (CDG): a systematic review of the literature

Congenital disorders of glycosylation (CDG) are inborn errors of metabolism due to protein and lipid hypoglycosylation. This rapidly growing family of genetic diseases comprises 103 CDG types, with a broad phenotypic diversity ranging from mild to severe poly-organ -system dysfunction. This literature review summarizes cardiac involvement, reported in 20% of CDG. CDG with cardiac involvement were divided according to the associated type of glycosylation: N-glycosylation, O-glycosylation, dolichol synthesis, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, COG complex, V-ATPase complex, and other glycosylation pathways. The aim of this review was to document and interpret the incidence of heart disease in CDG patients. Heart disorders were grouped into cardiomyopathies, structural defects, and arrhythmogenic disorders. This work may contribute to improved early management of cardiac complications in CDG.

B3GAT3-related disorder with craniosynostosis and bone fragility due to a unique mutation

PurposeBased on prenatal suspicion of the combination of radioulnar or radiohumeral synostosis and a peculiar shape of the skull suggestive of craniosynostosis, we report on six patients from four unrelated consanguineous families in whom Antley-Bixler syndrome was suspected during the prenatal period without mutation in genes known to be associated with the syndrome.MethodsMolecular diagnosis involved whole-exome and gene-panel sequencing.

RESULTS

All sequenced patients showed a unique homozygous mutation of c.667G>A, p.Gly223Ser (NM_012200) in the beta-1,3-glucuronyltransferase 3 (B3GAT3) gene known to be involved in linkeropathy syndrome. Linkeropathies correspond to a recently identified group of heterogeneous genetic syndromes along a spectrum of skeletal and connective tissue disorders. These patients featured mainly craniosynostosis, midface hypoplasia, bilateral radioulnar synostosis, multiple neonatal fractures, dislocated joints, joint contracture, long fingers, foot deformity, and cardiovascular abnormalities. All died before 1 year of age.ConclusionWe identified a novel B3GAT3-related disorder with craniosynostosis and bone fragility, due to a unique homozygous mutation in B3GAT3. This syndrome should be considered in the prenatal period in light of the severe outcome and as an alternative diagnosis to Antley-Bixler or Shprintzen-Goldberg syndrome.