CDK5 regulatory subunit-associated protein 1-like 1 (CDKAL1) is a tail-anchored protein in the endoplasmic reticulum (ER) of insulinoma cells

Lactogenesis factors in the Asian population

The increasing incidence of disrupted lactogenesis in Asian populations underscores the importance of timely identification and efficient intervention. This study acknowledges the influence of ethnicity on genetic variations and aims to investigate the genetic mechanisms that contribute to lactogenesis in individuals of Asian descent. This study examines the possibilities of genetic screening as a means of applying preventive measures, with a particular focus on epigenetic techniques. Additionally, the analysis looks into the underlying mechanisms involved in milk production. This review discusses the intricate mechanisms underlying breast milk production and the potential influence of genetic variables on lactogenesis. Specifically, it explores the association between lactogenesis issues and genetic conditions such as depression, obesity, gestational hypertension, and gestational diabetes. These genetic factors could potentially be found by genetic screening as contributors to disruption in lactogenesis. This study aims to promote future investigation in the subject of genetic testing and its potential association with lactogenesis issues, despite the current scarcity of direct research on this topic. The statement posits that the progress made in genetic testing has the potential to provide novel insights into the timely identification and treatment of disrupted lactogenesis.

Comprehensive sub-mitochondrial protein map of the parasitic protist Trypanosoma brucei defines critical features of organellar biology

We have generated a high-confidence mitochondrial proteome (MitoTag) of the Trypanosoma brucei procyclic stage containing 1,239 proteins. For 337 of these, a mitochondrial localization had not been described before. We use the TrypTag dataset as a foundation and take advantage of the properties of the fluorescent protein tag that causes aberrant but fortuitous accumulation of tagged matrix and inner membrane proteins near the kinetoplast (mitochondrial DNA). Combined with transmembrane domain predictions, this characteristic allowed categorization of 1,053 proteins into mitochondrial sub-compartments, the detection of unique matrix-localized fucose and methionine synthesis, and the identification of new kinetoplast proteins, which showed kinetoplast-linked pyrimidine synthesis. Moreover, disruption of targeting signals by tagging allowed mapping of the mode of protein targeting to these sub-compartments, identifying a set of C-tail anchored outer mitochondrial membrane proteins and mitochondrial carriers likely employing multiple target peptides. This dataset represents a comprehensive, updated mapping of the mitochondrion.

Advances in CRISPR/Cas9

CRISPR/Cas9 technology has become the most examined gene editing technology in recent years due to its simple design, yet low cost, high efficiency, and simple operation, which can also achieve simultaneous editing of multiple loci. It can also be carried out without using plasmids, saving lots of troubles caused by plasmids. CRISPR/Cas9 has shown great potential in the study of genes or genomic functions in microorganisms, plants, animals, and human beings. In this review, we will examine the history, structure, and basic mechanisms of the CRISPR/Cas9 system, describe its great value in precision medicine and sgRNA library screening, and dig its great potential in a new field: DNA information storage.

Involvement of Cdkal1 in the etiology of type 2 diabetes mellitus and microvascular diabetic complications: a review

Diabetes Mellitus, being a polygenic disorder, have a set of risk genes involved in the onset of the insulin resistance, obesity and impaired insulin synthesis. Recent genome wide association studies (GWAS) shows the intimacy of CDK5 regulatory subunit Associated protein 1-Like 1 (Cdkal1) with the pathophysiology of the diabetes mellitus and its complications, although the exact molecular relation is still unknown. In this short review, we have summarized all the diverse biological roles of Cdkal1 in relation to the onset of diabetes mellitus. Variations in the Cdkal1 transcript are responsible for the accumulation of misfolded insulin and thus generating oxidative and ER stress in the pancreatic β-cells, leading to their destruction. Recent studies have shown that Cdkal1 has an intrinsic thiomethyl transferase activity, which is essential for proper posttranslational processing of pre-proinsulin to produce mature insulin. Moreover, Cdkal1 has also been claimed as an endogenous inhibitor of cdk5, which prevents the cdk5-induced interruption in insulin synthesis through PDX1 translocation from nucleus to cytosol. Recent clinical studies have identified the risk single nucleotide polymorphisms (SNPs) of Cdkal1 as one of the root causes for the onset of diabetic complications. To the best of our knowledge, it is the first comprehensive review which elaborates most of the potential Cdkal1-dependent molecular mechanisms studied yet. In this review, we present a compiled and concise summary about all the diverse roles of Cdkal1 in the context of type 2 diabetes mellitus and its associated complications. This review will be helpful to target Cdkal1 as a potential option for the management of type 2 diabetes mellitus in future.

Graphical abstract

Silencing of the tRNA Modification Enzyme Cdkal1 Effects Functional Insulin Synthesis in NIT-1 Cells: tRNALys3 Lacking ms2- (ms2t6A37) is Unable to Establish Sufficient Anticodon:Codon Interactions to Decode the Wobble Codon AAG

Human Genome Wide Association Studies found a significant risk of Type 2 Diabetes Mellitus (T2DM) in single nucleotide polymorphisms in the cdkal1 gene. The cdkal1 gene is remote from the insulin gene and with the surprising function of a specific tRNA modification. Population studies and case control studies acquired evidences of the connection between Cdkal1 protein and insulin production over the years. To obtain biochemical proofs directly linking potential SNPs to their roles in insulin production and availability is challenging, but the development of Cdkal1 knock out mice and knock out cell lines made it possible to extend our knowledge towards therapeutic field of diabetic research. Supporting the evidences, here we show that knock down of the cdkal1 gene using small interfering and short hairpin RNA in the NIT-1 cell line, a β-cell line inducible for insulin resulted in reduced levels of cdkal1 and mature insulin mRNAs, increased the level of precursor insulin mRNA, decreased Cdkal1 and insulin proteins, and diminished modification of tRNA^Lys3 from t⁶A₃₇ to ms²t⁶A₃₇, the specified function of Cdkal1. tRNA^Lys3 lacking ms²- is incapable of establishing sufficient hydrogen bonding energy and hydrophobic stabilization to decode the wobble codon AAG.

tRNA Biology in the Pathogenesis of Diabetes: Role of Genetic and Environmental Factors

The global rise in type 2 diabetes results from a combination of genetic predisposition with environmental assaults that negatively affect insulin action in peripheral tissues and impair pancreatic β-cell function and survival. Nongenetic heritability of metabolic traits may be an important contributor to the diabetes epidemic. Transfer RNAs (tRNAs) are noncoding RNA molecules that play a crucial role in protein synthesis. tRNAs also have noncanonical functions through which they control a variety of biological processes. Genetic and environmental effects on tRNAs have emerged as novel contributors to the pathogenesis of diabetes. Indeed, altered tRNA aminoacylation, modification, and fragmentation are associated with β-cell failure, obesity, and insulin resistance. Moreover, diet-induced tRNA fragments have been linked with intergenerational inheritance of metabolic traits. Here, we provide a comprehensive review of how perturbations in tRNA biology play a role in the pathogenesis of monogenic and type 2 diabetes.

S-adenosylmethionine tRNA modification: unexpected/unsuspected implications of former/new players

S-adenosylmethionine supplies methyl groups to many acceptors, including lipids, proteins, RNA, DNA, and a wide range of small molecules. It acts as the precursor in the biosynthesis of metal ion chelating compounds, such as nicotianamine and phytosiderophores, of the polyamines spermidine and spermine and of some plant hormones. Finally, it is the source of catalytic 5′-deoxyadenosyl radicals.

Radical S-adenosylmethionine (SAM) enzymes (RS) represent one of the most abundant groups (more than 100,000) of enzymes, exerting a plethora of biological functions, some of which are still unknown.

In this work, we will focus on two RS: CDK5RAP1 and CDKAL1, both of which are involved in tRNA modifications that result in important tRNA folding and stability and in maintaining high translational fidelity. Based on this crucial role, their impairment can be important in the development of different human diseases.

Irp2 regulates insulin production through iron-mediated Cdkal1-catalyzed tRNA modification

Regulation of cellular iron homeostasis is crucial as both iron excess and deficiency cause hematological and neurodegenerative diseases. Here we show that mice lacking iron-regulatory protein 2 (Irp2), a regulator of cellular iron homeostasis, develop diabetes. Irp2 post-transcriptionally regulates the iron-uptake protein transferrin receptor 1 (TfR1) and the iron-storage protein ferritin, and dysregulation of these proteins due to Irp2 loss causes functional iron deficiency in β cells. This impairs Fe-S cluster biosynthesis, reducing the function of Cdkal1, an Fe-S cluster enzyme that catalyzes methylthiolation of t⁶A37 in tRNA^Lys_UUU to ms²t⁶A37. As a consequence, lysine codons in proinsulin are misread and proinsulin processing is impaired, reducing insulin content and secretion. Iron normalizes ms²t⁶A37 and proinsulin lysine incorporation, restoring insulin content and secretion in Irp2^-/- β cells. These studies reveal a previously unidentified link between insulin processing and cellular iron deficiency that may have relevance to type 2 diabetes in humans.

Human stem cell models: lessons for pancreatic development and disease

A comprehensive understanding of mechanisms that underlie the development and function of human cells requires human cell models. For the pancreatic lineage, protocols have been developed to differentiate human pluripotent stem cells (hPSCs) into pancreatic endocrine and exocrine cells through intermediates resembling in vivo development. In recent years, this differentiation system has been employed to decipher mechanisms of pancreatic development, congenital defects of the pancreas, as well as genetic forms of diabetes and exocrine diseases. In this review, we summarize recent insights gained from studies of pancreatic hPSC models. We discuss how genome-scale analyses of the differentiation system have helped elucidate roles of chromatin state, transcription factors, and noncoding RNAs in pancreatic development and how the analysis of cells with disease-relevant mutations has provided insight into the molecular underpinnings of genetically determined diseases of the pancreas.

Validation of Identified Susceptible Gene Variants for New-Onset Diabetes in Renal Transplant Recipients

Genome-wide association studies (GWAS) and candidate gene approaches have identified single nucleotide polymorphisms (SNPs) associated with new-onset diabetes after renal transplantation (NODAT). We evaluated associations between NODAT and SNPs identified in previous studies. We genotyped 1102 renal transplant recipients from the Korean Organ Transplantation Registry (KOTRY) database; 13 SNPs were assessed for associations with NODAT (occurring in 254 patients; 23.0%), within one year after transplantation. The frequency of the T allele at KCNQ1 rs2237892 was significantly lower in patients with NODAT compared to control patients (0.30 vs. 0.39; p = 8.5 × 10^-5). The T allele at rs2237892 was significantly associated with decreased risk of NODAT after adjusting for multiple variables, compared to the C allele (OR 0.63, 95% CI 0.51-0.79; p = 5.5 × 10^-5). Dominant inheritance modeling showed that CT/TT genotypes were associated with a lower risk for development of NODAT (OR 0.56, 95% CI 0.42-0.76; p = 2.0 × 10^-4) compared to the CC genotype. No other SNPs were associated with NODAT. Our study validated the protective effect of T allele at KCNQ1 rs2237892 on the development of NODAT in a large cohort of renal transplant recipients. Our findings on susceptibility variants might be a useful tool to predict NODAT development after renal transplantation.

The tRNA Epitranscriptome and Diabetes: Emergence of tRNA Hypomodifications as a Cause of Pancreatic β-Cell Failure

tRNAs are crucial noncoding RNA molecules that serve as amino acid carriers during protein synthesis. The transcription of tRNA genes is a highly regulated process. The tRNA pool is tissue and cell specific, it varies during development, and it is modulated by the environment. tRNAs are highly posttranscriptionally modified by specific tRNA-modifying enzymes. The tRNA modification signature of a cell determines the tRNA epitranscriptome. Perturbations in the tRNA epitranscriptome, as a consequence of mutations in tRNAs and tRNA-modifying enzymes or environmental exposure, have been associated with human disease, including diabetes. tRNA fragmentation induced by impaired tRNA modifications or dietary factors has been linked to pancreatic β-cell demise and paternal inheritance of metabolic traits. Herein, we review recent findings that associate tRNA epitranscriptome perturbations with diabetes.

The tRNA-associated dysregulation in diabetes mellitus

Diabetes mellitus (DM) is a complex endocrine and metabolic disorder for human health and well-being. Deregulated glucose and lipid metabolism are the primary underlying manifestations associated with this disease. Transfer RNAs (tRNAs) are considered to mainly participate in protein translation and may contribute to complex human pathologies. Although the molecular mechanisms remain, for the most part, unknown, accumulating evidence indicates that tRNAs play a vital role in the pathogenesis of DM. This paper reviews different aspects of tRNA-associated dysregulation in DM, such as tRNA mutations, tRNA modifications, tRNA aminoacylation and tRNA derivatives, aiming at a better understanding of the pathogenesis of DM and providing new ideas for the personalized treatment of this metabolism-associated disease.

tRNA modifications and islet function

Efficient and accurate protein translation is essential to producing insulin in pancreatic β-cells. Transfer RNA (tRNA) is known as the key component of the protein translational machinery. Interestingly, tRNA contains a wide variety of chemical modifications, which are posttranscriptionally catalysed by tRNA modifying enzymes. Recent advances in genome-sequencing technology have unveiled a number of genetic variations that are associated with the development of type 2 diabetes (T2D). Some of these mutations are located in the genes of tRNA modifying enzymes. Using cellular and animal models, it has been showed that dysregulation of tRNA modification impairs protein translation in pancreatic β-cells and leads to aberrant insulin production. In this review, we discuss the recent findings in the molecular functions of tRNA modifications and their involvement in the development of T2D.

An Isogenic Human ESC Platform for Functional Evaluation of Genome-wide-Association-Study-Identified Diabetes Genes and Drug Discovery

Genome-wide association studies (GWASs) have increased our knowledge of loci associated with a range of human diseases. However, applying such findings to elucidate pathophysiology and promote drug discovery remains challenging. Here, we created isogenic human ESCs (hESCs) with mutations in GWAS-identified susceptibility genes for type 2 diabetes. In pancreatic beta-like cells differentiated from these lines, we found that mutations in CDKAL1, KCNQ1, and KCNJ11 led to impaired glucose secretion in vitro and in vivo, coinciding with defective glucose homeostasis. CDKAL1 mutant insulin+ cells were also hypersensitive to glucolipotoxicity. A high-content chemical screen identified a candidate drug that rescued CDKAL1-specific defects in vitro and in vivo by inhibiting the FOS/JUN pathway. Our approach of a proof-of-principle platform, which uses isogenic hESCs for functional evaluation of GWAS-identified loci and identification of a drug candidate that rescues gene-specific defects, paves the way for precision therapy of metabolic diseases.

Tail-anchored Protein Insertion in Mammals: FUNCTION AND RECIPROCAL INTERACTIONS OF THE TWO SUBUNITS OF THE TRC40 RECEPTOR

The GET (guided entry of tail-anchored proteins)/TRC (transmembrane recognition complex) pathway for tail-anchored protein targeting to the endoplasmic reticulum (ER) has been characterized in detail in yeast and is thought to function similarly in mammals, where the orthologue of the central ATPase, Get3, is known as TRC40 or Asna1. Get3/TRC40 function requires an ER receptor, which in yeast consists of the Get1/Get2 heterotetramer and in mammals of the WRB protein (tryptophan-rich basic protein), homologous to yeast Get1, in combination with CAML (calcium-modulating cyclophilin ligand), which is not homologous to Get2. To better characterize the mammalian receptor, we investigated the role of endogenous WRB and CAML in tail-anchored protein insertion as well as their association, concentration, and stoichiometry in rat liver microsomes and cultured cells. Functional proteoliposomes, reconstituted from a microsomal detergent extract, lost their activity when made with an extract depleted of TRC40-associated proteins or of CAML itself, whereas in vitro synthesized CAML and WRB together were sufficient to confer insertion competence to liposomes. CAML was found to be in ∼5-fold excess over WRB, and alteration of this ratio did not inhibit insertion. Depletion of each subunit affected the levels of the other one; in the case of CAML silencing, this effect was attributable to destabilization of the WRB transcript and not of WRB protein itself. These results reveal unanticipated complexity in the mutual regulation of the TRC40 receptor subunits and raise the question as to the role of the excess CAML in the mammalian ER.

A HuGE Review and Meta-Analyses of Genetic Associations in New Onset Diabetes after Kidney Transplantation

PURPOSE

New onset diabetes after transplantation (NODAT) is a serious complication following solid organ transplantation. There is a genetic contribution to NODAT and we have conducted comprehensive meta-analysis of available genetic data in kidney transplant populations.

METHODS

Relevant articles investigating the association between genetic markers and NODAT were identified by searching PubMed, Web of Science and Google Scholar. SNPs described in a minimum of three studies were included for analysis using a random effects model. The association between identified variants and NODAT was calculated at the per-study level to generate overall significance values and effect sizes.

RESULTS

Searching the literature returned 4,147 citations. Within the 36 eligible articles identified, 18 genetic variants from 12 genes were considered for analysis. Of these, three were significantly associated with NODAT by meta-analysis at the 5% level of significance; CDKAL1 rs10946398 p = 0.006 OR = 1.43, 95% CI = 1.11-1.85 (n = 696 individuals), KCNQ1 rs2237892 p = 0.007 OR = 1.43, 95% CI = 1.10-1.86 (n = 1,270 individuals), and TCF7L2 rs7903146 p = 0.01 OR = 1.41, 95% CI = 1.07-1.85 (n = 2,967 individuals).

CONCLUSION

Evaluating cumulative evidence for SNPs associated with NODAT in kidney transplant recipients has revealed three SNPs associated with NODAT. An adequately powered, dense genome-wide association study will provide more information using a carefully defined NODAT phenotype.

Genome-wide meta-analysis identifies five new susceptibility loci for cutaneous malignant melanoma

Thirteen common susceptibility loci have been reproducibly associated with cutaneous malignant melanoma (CMM). We report the results of an international 2-stage meta-analysis of CMM genome-wide association studies (GWAS). This meta-analysis combines 11 GWAS (5 previously unpublished) and a further three stage 2 data sets, totaling 15,990 CMM cases and 26,409 controls. Five loci not previously associated with CMM risk reached genome-wide significance (P < 5 × 10(-8)), as did 2 previously reported but unreplicated loci and all 13 established loci. Newly associated SNPs fall within putative melanocyte regulatory elements, and bioinformatic and expression quantitative trait locus (eQTL) data highlight candidate genes in the associated regions, including one involved in telomere biology.

Proteomics analysis of rough endoplasmic reticulum in pancreatic beta cells

Pancreatic beta cells have well-developed ER to accommodate for the massive production and secretion of insulin. ER homeostasis is vital for normal beta cell function. Perturbation of ER homeostasis contributes to beta cell dysfunction in both type 1 and type 2 diabetes. To systematically identify the molecular machinery responsible for proinsulin biogenesis and maintenance of beta cell ER homeostasis, a widely used mouse pancreatic beta cell line, MIN6 cell was used to purify rough ER. Two different purification schemes were utilized. In each experiment, the ER pellets were solubilized and analyzed by 1D SDS-PAGE coupled with HPLC-MS/MS. A total of 1467 proteins were identified in three experiments with ≥95% confidence, among which 1117 proteins were found in at least two separate experiments and 737 proteins found in all three experiments. GO analysis revealed a comprehensive profile of known and novel players responsible for proinsulin biogenesis and ER homeostasis. Further bioinformatics analysis also identified potential beta cell specific ER proteins as well as ER proteins present in the risk genetic loci of type 2 diabetes. This dataset defines a molecular environment in the ER for proinsulin synthesis, folding and export and laid a solid foundation for further characterizations of altered ER homeostasis under diabetes-causing conditions. All MS data have been deposited in the ProteomeXchange with identifier PXD001081 (http://proteomecentral.proteomexchange.org/dataset/PXD001081).

Transcriptomic Analysis of mRNAs in Human Monocytic Cells Expressing the HIV-1 Nef Protein and Their Exosomes

The Nef protein of human immunodeficiency virus (HIV) promotes viral replication and progression to AIDS. Besides its well-studied effects on intracellular signaling, Nef also functions through its secretion in exosomes, which are nanovesicles containing proteins, microRNAs, and mRNAs and are important for intercellular communication. Nef expression enhances exosome secretion and these exosomes can enter uninfected CD4 T cells leading to apoptotic death. We have recently reported the first miRNome analysis of exosomes secreted from Nef-expressing U937monocytic cells. Here we show genome-wide transcriptome analysis of Nef-expressing U937 cells and their exosomes. We identified four key mRNAs preferentially retained in Nef-expressing cells; these code for MECP2, HMOX1, AARSD1, and ATF2 and are important for chromatin modification and gene expression. Interestingly, their target miRNAs are exported out in exosomes. We also identified three key mRNAs selectively secreted in exosomes from Nef-expressing U937 cells and their corresponding miRNAs being preferentially retained in cells. These are AATK, SLC27A1, and CDKAL and are important in apoptosis and fatty acid transport. Thus, our study identifies selectively expressed mRNAs in Nef-expressing U937 cells and their exosomes and supports a new mode on intercellular regulation by the HIV-1 Nef protein.

Association of variants in CDKN2A/2B and CDKAL1 genes with gestational insulin sensitivity and disposition in pregnant Han Chinese women

Aims/Introduction

Variants in cell cycle regulation genes, CDKAL1 and CDKN2A/2B, have been suggested to be associated with type 2 diabetes, and also play a role in insulin procession in non-diabetic European individuals. Rs7754580 in CDKAL1 and rs7020996 in CDKN2A/2B were found to be associated with gestational diabetes in Chinese individuals. In order to understand the metabolism mechanism of greatly upregulated maternal insulin signaling during pregnancy and the pathogenesis of gestational diabetes, we investigated the impact of rs7754580 and rs7020996 on gestational insulin regulation and procession.

Materials and Methods

We recruited 1,146 unrelated, non-diabetic, pregnant Han Chinese women (age 28.5 ± 4.1 years, body mass index 21.4 ± 2.6 kg/m²), and gave them oral glucose tolerance tests. The indices of insulin sensitivity, insulin disposition, insulin release and proinsulin to insulin conversion were calculated. Rs7754580 in the CDKAL1 gene and rs7020996 in the CDKN2A/2B gene were genotyped. Under an additive model, we analyzed the associations between the variants and gestational insulin indices using logistic regression.

Results

By adjusting for maternal age, body mass index and the related interactions, CDKAL1 rs7754580 risk allele C was detected to be associated with increased insulin sensitivity (P = 0.011), decreased insulin disposition (P = 0.0002) and 2-h proinsulin conversion (P = 0.017). CDKN2A/2B rs7020996 risk allele T was found to be related to decreased insulin sensitivity (P = 0.002) and increased insulin disposition (P = 0.0001).

Conclusions

The study showed that cell cycle regulating genes might have a distinctive effect on gestational insulin sensitivity, β-cell function and proinsulin conversion in pregnant Han Chinese women.

Joint identification of genetic variants for physical activity in Korean population

There has been limited research on genome-wide association with physical activity (PA). This study ascertained genetic associations between PA and 344,893 single nucleotide polymorphism (SNP) markers in 8842 Korean samples. PA data were obtained from a validated questionnaire that included information on PA intensity and duration. Metabolic equivalent of tasks were calculated to estimate the total daily PA level for each individual. In addition to single- and multiple-SNP association tests, a pathway enrichment analysis was performed to identify the biological significance of SNP markers. Although no significant SNP was found at genome-wide significance level via single-SNP association tests, 59 genetic variants mapped to 76 genes were identified via a multiple SNP approach using a bootstrap selection stability measure. Pathway analysis for these 59 variants showed that maturity onset diabetes of the young (MODY) was enriched. Joint identification of SNPs could enable the identification of multiple SNPs with good predictive power for PA and a pathway enriched for PA.

Different types of secondary information in the genetic code

Whole-genome and functional analyses suggest a wealth of secondary or auxiliary genetic information (AGI) within the redundancy component of the genetic code. Although there are multiple aspects of biased codon use, we focus on two types of auxiliary information: codon-specific translational pauses that can be used by particular proteins toward their unique folding and biased codon patterns shared by groups of functionally related mRNAs with coordinate regulation. AGI is important to genetics in general and to human disease; here, we consider influences of its three major components, biased codon use itself, variations in the tRNAome, and anticodon modifications that distinguish synonymous decoding. AGI is plastic and can be used by different species to different extents, with tissue-specificity and in stress responses. Because AGI is species-specific, it is important to consider codon-sensitive experiments when using heterologous systems; for this we focus on the tRNA anticodon loop modification enzyme, CDKAL1, and its link to type 2 diabetes. Newly uncovered tRNAome variability among humans suggests roles in penetrance and as a genetic modifier and disease modifier. Development of experimental and bioinformatics methods are needed to uncover additional means of auxiliary genetic information.

CDKAL1-related single nucleotide polymorphisms are associated with insulin resistance in a cross-sectional cohort of Greek children

Five novel loci recently found to be associated with body mass in two GWAS of East Asian populations were evaluated in two cohorts of Swedish and Greek children and adolescents. These loci are located within, or in the proximity of: CDKAL1, PCSK1, GP2, PAX6 and KLF9. No association with body mass has previously been reported for these loci in GWAS performed on European populations. The single nucleotide polymorphisms (SNPs) with the strongest association at each loci in the East Asian GWAS were genotyped in two cohorts, one obesity case control cohort of Swedish children and adolescents consisting of 496 cases and 520 controls and one cross-sectional cohort of 2293 nine-to-thirteen year old Greek children and adolescents. SNPs were surveyed for association with body mass and other phenotypic traits commonly associated with obesity, including adipose tissue distribution, insulin resistance and daily caloric intake. No association with body mass was found in either cohort. However, among the Greek children, association with insulin resistance could be observed for the two CDKAL1-related SNPs: rs9356744 (β = 0.018, p = 0.014) and rs2206734 (β = 0.024, p = 0.001). CDKAL1-related variants have previously been associated with type 2 diabetes and insulin response. This study reports association of CDKAL1-related SNPs with insulin resistance, a clinical marker related to type 2 diabetes in a cross-sectional cohort of Greek children and adolescents of European descent.

Whole genome SNP genotyping and exome sequencing reveal novel genetic variants and putative causative genes in congenital hyperinsulinism

Congenital hyperinsulinism of infancy (CHI) is a rare disorder characterized by severe hypoglycemia due to inappropriate insulin secretion. The genetic causes of CHI have been found in genes regulating insulin secretion from pancreatic β-cells; recessive inactivating mutations in the ABCC8 and KCNJ11 genes represent the most common events. Despite the advances in understanding the molecular pathogenesis of CHI, specific genetic determinants in about 50 % of the CHI patients remain unknown, suggesting additional locus heterogeneity. In order to search for novel loci contributing to the pathogenesis of CHI, we combined a family-based association study, using the transmission disequilibrium test on 17 CHI patients lacking mutations in ABCC8/KCNJ11, with a whole-exome sequencing analysis performed on 10 probands. This strategy allowed the identification of the potential causative mutations in genes implicated in the regulation of insulin secretion such as transmembrane proteins (CACNA1A, KCNH6, KCNJ10, NOTCH2, RYR3, SCN8A, TRPV3, TRPC5), cytosolic (ACACB, CAMK2D, CDKAL1, GNAS, NOS2, PDE4C, PIK3R3) and mitochondrial enzymes (PC, SLC24A6), and in four genes (CSMD1, SLC37A3, SULF1, TLL1) suggested by TDT family-based association study. Moreover, the exome-sequencing approach resulted to be an efficient diagnostic tool for CHI, allowing the identification of mutations in three causative CHI genes (ABCC8, GLUD1, and HNF1A) in four out of 10 patients. Overall, the present study should be considered as a starting point to design further investigations: our results might indeed contribute to meta-analysis studies, aimed at the identification/confirmation of novel causative or modifier genes.