Ala45Thr polymorphism of the NEUROD1 gene and diabetes susceptibility: a meta-analysis

Neuronal Differentiation 1 gene Ala45Thr polymorphism and type 2 diabetes mellitus: A meta-analysis of 7,940 subjects

BACKGROUND AND AIMS

Previous studies have shown that there was a possible relationship between human Neuronal Differentiation 1 (NEUROD1) gene Ala45Thr polymorphism and type 2 diabetes mellitus (T2DM) susceptibility. Nevertheless, no public opinion has been formed because of the conflicting results in the past studies. In order to illuminate the potential association of human NEUROD1 gene Ala45Thr polymorphism and T2DM, the present meta-analysis was conducted.

METHODS AND RESULTS

In the current meta-analysis, 7940 subjects from 14 individual studies were included. The fixed or random effects models were used to evaluate the pooled odds ratios (ORs) and their corresponding 95% confidence intervals (CIs). The current meta-analysis found a significant association between NEUROD1 gene Ala45Thr polymorphism and T2DM under allelic (OR: 1.21, 95% CI: 1.04-1.41, P = 0.01), dominant (OR: 0.819, 95% CI: 0.734-0.913, P = 3.31 × 10^-4), heterozygous (OR:1.199, 95% CI: 1.068-1.346, P = 0.002), and additive (OR: 1.33, 95% CI: 1.09-1.62, P = 0.004) genetic models.

CONCLUSIONS

NEUROD1 gene Ala45Thr polymorphism was significantly related to T2DM, especially in the Asian population. More particularly, the Thr45 allele carriers of the NEUROD1 gene may be more susceptible to T2DM.

Diabetes and Genetics: A Relationship Between Genetic Risk Alleles, Clinical Phenotypes and Therapeutic Approaches

Unveiling human genome through successful completion of Human Genome Project and International HapMap Projects with the advent of state of art technologies has shed light on diseases associated genetic determinants. Identification of mutational landscapes such as copy number variation, single nucleotide polymorphisms or variants in different genes and loci have revealed not only genetic risk factors responsible for diseases but also region(s) playing protective roles. Diabetes is a global health concern with two major types - type 1 diabetes (T1D) and type 2 diabetes (T2D). Great progress in understanding the underlying genetic predisposition to T1D and T2D have been made by candidate gene studies, genetic linkage studies, genome wide association studies with substantial number of samples. Genetic information has importance in predicting clinical outcomes. In this review, we focus on recent advancement regarding candidate gene(s) associated with these two traits along with their clinical parameters as well as therapeutic approaches perceived. Understanding genetic architecture of these disease traits relating clinical phenotypes would certainly facilitate population stratification in diagnosing and treating T1D/T2D considering the doses and toxicity of specific drugs.

Identification of nucleotide polymorphism within the NeuroD1 candidate gene and its association with type 1 diabetes susceptibility in Iranian people by polymerase chain reaction-restriction fragment length polymorphism

Objectives Diabetes is a serious disease, and the number of affected individuals with diabetes is considerably high. The aim of this study is the identification of NeuroD1 Ala45Thr polymorphism and its association with type 1 diabetes susceptibility in Iranian people. Methods Clinical and biochemical characteristics for 146 people (76 diabetics and 70 nondiabetics) were measured, such as fasting blood sugar, triacylglycerol, total cholesterol, age, and weight in each individual. Polymerase chain reaction-restriction fragment length polymorphism technique (MwoI restriction-enzyme) was used for genotyping of the NeuroD1 Ala45Thr polymorphism. Results In this study, the frequency of the A allele in diabetic patients in comparison with the healthy control group had a significantly higher percentage (p < 0.01), whereas diabetic patients had the AA genotype, approximately four times more than the healthy control group (p < 0.01). In addition, we observed that fasting blood sugar had a higher concentration in the AA genotype than in AG + GG genotypes (p < 0.01). Conclusions The A allele may be a risk factor for the expansion of type 1 diabetes in the Iranian population. However, the NeuroD1 Ala45Thr polymorphism and its role in type 1 diabetes in different populations are controversial.

A homozygous missense mutation in NEUROD1 is associated with nonsyndromic autosomal recessive retinitis pigmentosa

PURPOSE

Mutations in the same gene can lead to different clinical phenotypes. In this study, we aim to identify novel genotype-phenotype correlations and novel disease genes by analyzing an unsolved autosomal recessive retinitis pigmentosa (ARRP) Han Chinese family.

METHODS

Whole exome sequencing was performed for one proband from the consanguineous ARRP family. Stringent variants filtering and prioritizations were applied to identify the causative mutation.

RESULTS

A homozygous missense variant, c.724G>A; p.V242I, in NEUROD1 was identified as the most likely cause of disease. This allele perfectly segregates in the family and affects an amino acid, which is highly conserved among mammals. A previous study showed that a homozygous null allele in NEUROD1 causes severe syndromic disease with neonatal diabetes, systematic neurological abnormalities, and early-onset retinal dystrophy. Consistent with these results, our patients who are homozygous for a less severe missense allele presented only late-onset retinal degeneration without any syndromic symptoms.

CONCLUSIONS

We identified a potential novel genotype-phenotype correlation between NEUROD1 and nonsyndromic ARRP. Our study supports the idea that NEUROD1 is important for maintenance of the retina function and partial loss-of-function mutation in NEUROD1 is likely a rare cause of nonsyndromic ARRP.

Genes involved in type 1 diabetes: an update

Type 1 Diabetes (T1D) is a chronic multifactorial disease with a strong genetic component, which, through interactions with specific environmental factors, triggers disease onset. T1D typically manifests in early to mid childhood through the autoimmune destruction of pancreatic β cells resulting in a lack of insulin production. Historically, prior to genome-wide association studies (GWAS), six loci in the genome were fully established to be associated with T1D. With the advent of high-throughput single nucleotide polymorphism (SNP) genotyping array technologies, enabling investigators to perform high-density GWAS, many additional T1D susceptibility genes have been discovered. Indeed, recent meta-analyses of multiple datasets from independent investigators have brought the tally of well-validated T1D disease genes to almost 60. In this mini-review, we address recent advances in the genetics of T1D and provide an update on the latest susceptibility loci added to the list of genes involved in the pathogenesis of T1D.

Evaluation of variant A45T in NEUROD1/BETA2 for its association with type 2 diabetes mellitus

Heterozygous loss-of-function mutations in NEUROD1 have been identified as a very rare cause of maturity-onset diabetes of the young and neonatal diabetes. Previous studies showed that a common A45T variant located in NEUROD1 was inconsistently associated with type 2 diabetes mellitus (T2DM) in different ethnic populations. This study aimed to evaluate the contribution of variant A45T in the genetic pathogenesis of T2DM. A case-control study in a Chinese Han population was conducted, which included 3,554 (1,155 males/2,399 females) patients with T2DM and 4,181 (1,798 males/2,383 females) control subjects from 13 different regions of China. The A45T variant was genotyped by the Illumina GoldenGate platform. A meta-analysis was used to estimate the effects of variant A45T in populations from different ethnic backgrounds. No association in Chinese Han subjects was confirmed in our case control study. A relationship between variant A45T and postprandial glucose was observed in the control group (β = 0.05, p = 0.002). Meta-analyses did not find an association of this polymorphism with T2DM in Chinese, Japanese, and East Asian descent, but did for European descent Caucasians (odds ratio = 1.15, 95 %CI 1.03-1.28, p = 0.01). Our study suggests the variant A45T does not play a major role in the development of T2DM in East Asian descent, and the role in European descent Caucasian needs to be confirmed.

[Genetic and humoral autoimmunity markers of type 1 diabetes: from theory to practice]

Type 1 A diabetes mellitus (T1AD) results from the autoimmune destruction of the insulin producing pancreatic beta-cells. The largest contribution to genetic susceptibility comes from several genes located in the major histocompatibility complex on chromosome 6p21.3 (IDDM1 locus), accounting for at least 40% of the family aggregation of this disease. The highest-risk human leukocyte antigen HLA genotype for T1AD is DR3-DQA1*0501-DQB1*0201/DR4-DQA1*0301-DQB1*0302, whereas -DR15-DQA1*0102-DQB1*0602 haplotype is associated with dominant protection. Three other T1D loci associated with predisposition are the Variable Number for Tandem Repeats (VNTR) near the insulin gene (IDDM2), which accounts to 10% of genetic susceptibility, the Cytotoxic T-Lymphocyte-associated Antigen (CTLA-4)(IDDM 12) and the Protein Tyrosine Phosphatasis Nonreceptor-type 22 (PTPN22). Many other gene suspected to predispose to autoimmunity have been investigated. T1AD is frequently associated with autoimmune thyroid disease, celiac disase, Addison s disease and many other autoimmune diseases, characterized by organ-specific autoantibodies and related to the same genetic background. Using these autoantibodies, organ specific autoimmunity may be detected before the development of clinical disease preventing significant morbidity.

Newly identified loci highlight beta cell dysfunction as a key cause of type 2 diabetes: where are the insulin resistance genes?

Although type 2 diabetes has been traditionally understood as a metabolic disorder initiated by insulin resistance, it has recently become apparent that an impairment in insulin secretion contributes to its manifestation and may play a prominent role in its early pathophysiology. The genetic dissection of Mendelian and, more recently, polygenic types of diabetes confirms the notion that primary defects in insulin synthesis, processing and/or secretion often give rise to the common form of this disorder. This concept, first advanced with the discovery and physiological characterisation of various genetic subtypes of MODY, has been extended to other forms of monogenic diabetes (e.g. neonatal diabetes). It has also led to the identification of common risk variants via candidate gene approaches (e.g. the E23K polymorphism in KCNJ11 or common variants in the MODY genes), and it has been validated by the description of the robust physiological effects conferred by polymorphisms in the TCF7L2 gene. More recently, the completion and integration of genome-wide association scans for this disease has uncovered a number of heretofore unsuspected variants, several of which also affect insulin secretion. This review provides an up-to-date account of genetic loci that influence risk of common type 2 diabetes via impairment of beta cell function, outlines their presumed mechanisms of action, and places them in the context of gene-gene and/or gene-environment interactions. Finally, a strategy for the analogous discovery of insulin resistance genes is proposed.

Insights on pathogenesis of type 2 diabetes from MODY genetics

Maturity-onset diabetes of the young (MODY) is a type of non-insulin-dependent diabetes mellitus caused by rare autosomal-dominant mutations. MODY genes play key biochemical roles in the pancreatic beta cell; therefore, common variants of MODY genes are excellent candidate genes for type 2 diabetes. We review recent studies that suggest that common MODY gene variation contributes modestly to the heritability of type 2 diabetes.

Evaluation of common variants in the six known maturity-onset diabetes of the young (MODY) genes for association with type 2 diabetes

An important question in human genetics is the extent to which genes causing monogenic forms of disease harbor common variants that may contribute to the more typical form of that disease. We aimed to comprehensively evaluate the extent to which common variation in the six known maturity-onset diabetes of the young (MODY) genes, which cause a monogenic form of type 2 diabetes, is associated with type 2 diabetes. Specifically, we determined patterns of common sequence variation in the genes encoding Gck, Ipf1, Tcf2, and NeuroD1 (MODY2 and MODY4-MODY6, respectively), selected a comprehensive set of 107 tag single nucleotide polymorphisms (SNPs) that captured common variation, and genotyped each in 4,206 patients and control subjects from Sweden, Finland, and Canada (including family-based studies and unrelated case-control subjects). All SNPs with a nominal P value <0.1 for association to type 2 diabetes in this initial screen were then genotyped in an additional 4,470 subjects from North America and Poland. Of 30 nominally significant SNPs from the initial sample, 8 achieved consistent results in the replication sample. We found the strongest effect at rs757210 in intron 2 of TCF2, with corrected P values <0.01 for an odds ratio (OR) of 1.13. This association was observed again in an independent sample of 5,891 unrelated case and control subjects and 500 families from the U.K., for an overall OR of 1.12 and a P value <10(-6) in >15,000 samples. We combined these results with our previous studies on HNF4alpha and TCF1 and explicitly tested for gene-gene interactions among these variants and with several known type 2 diabetes susceptibility loci, and we found no genetic interactions between these six genes. We conclude that although rare variants in these six genes explain most cases of MODY, common variants in these same genes contribute very modestly, if at all, to the common form of type 2 diabetes.

Common variants in maturity-onset diabetes of the young genes contribute to risk of type 2 diabetes in Finns

Prior reports have suggested that variants in the genes for maturity-onset diabetes of the young (MODY) may confer susceptibility to type 2 diabetes, but results have been conflicting and coverage of the MODY genes has been incomplete. To complement our previous studies of HNF4A, we examined the other five known MODY genes for association with type 2 diabetes in Finnish individuals. For each of the five genes, we selected 1) nonredundant single nucleotide polymorphisms (SNPs) (r(2)< 0.8 with other SNPs) from the HapMap database or another linkage disequilibrium map, 2) SNPs with previously reported type 2 diabetes association, and 3) nonsynonymous coding SNPs. We tested 128 SNPs for association with type 2 diabetes in 786 index cases from type 2 diabetic families and 619 normal glucose-tolerant control subjects. We followed up 35 of the most significant SNPs by genotyping them on another 384 case subjects and 366 control subjects from Finland. We also supplemented our previous HNF4A results by genotyping 12 SNPs on additional Finnish samples. After correcting for testing multiple correlated SNPs within a gene, we find evidence of type 2 diabetes association with SNPs in five of the six known MODY genes: GCK, HNF1A, HNF1B, NEUROD1, and HNF4A. Our data suggest that common variants in several MODY genes play a modest role in type 2 diabetes susceptibility.

Ala45Thr variation in neuroD1 gene is associated with early-onset type 2 diabetes with or without diabetic pedigree in Chinese

OBJECTIVE

Based on onset-age stratified analysis may be useful to determine the association of NeuroD1-Ala45Thr variation with susceptibility to genetic heterogeneous type 2 diabetes mellitus (T2DM), we investigated the Ala45Thr variation in unrelated early-onset and late-onset T2DM with or without diabetic pedigree and unrelated non-diabetic control subjects in Chinese.

METHODS

175 early-onset and 194 late-onset type 2 diabetic patients were further divided into two subgroups according to with or without diabetic pedigree respectively. This NeuroD1-Ala45Thr variation were screened by PCR-direct sequencing in above 369 type 2 diabetic patients and 87 unrelated non-diabetic control subjects. We then compared the distribution of the Ala45Thr variation among the groups, searching for the predictive trends.

RESULTS

Frequencies of the variant (AA + GA genotype) in early-onset T2DM are obviously elevated, especially among diabetic pedigree subjects when compared to non-diabetic controls (p= 0.003) and late-onset T2DM subjects (p = 0.014). However, no significant differences were observed between late-onset T2DM with or without diabetic pedigree and non-diabetic control subjects.

CONCLUSIONS

Our results suggest that 1) the NeuroD1-Ala45Thr variation may itself have an important role in susceptibility to or be in disequilibrium with early-onset T2DM in Chinese; 2) the Ala45Thr may affect the onset pattern of T2DM, i.e., early-onset but not late-onset T2DM in Chinese; and 3) onset-age stratified analysis may be useful to determine the association of NeuroD1-Ala45Thr variation with susceptibility to genetic heterogeneous T2DM in Chinese.

The Ala45Thr polymorphism of NEUROD1 is associated with type 1 diabetes in Brazilian women

BACKGROUND

NEUROD1 encodes a transcription factor expressed in the endocrine pancreas, and involved in beta-cell development, function and mechanisms of apoptosis. In this study, we investigated the association of a frequent polymorphism in exon 2 of NEUROD1 (G > A; Ala45Thr) with Type 1 diabetes in Brazilian subjects.

METHODS

A population/association study comprising 246 unrelated Type 1 diabetic and 275 nondiabetic white Brazilian subjects. The Ala45Thr variant was genotyped by a PCR-RFLP method.

RESULTS

The frequency of the Thr allele was significantly higher in patients with Type 1 diabetes than in controls (42.3% vs 35.3%, P=0.02). Stratification by gender showed that homozygosity for the Thr allele was associated with Type 1 diabetes in women with odds ratio of 3.66 (95% C.I. 1.43-10.11, P=0.009) as compared to homozygosity for the Ala allele. This effect was not observed in men.

CONCLUSIONS

We found a gender-specific association of the Ala45Thr variant of NEUROD1 with Type 1 diabetes in Brazilian women. Our results suggest that gender as well as ethnicity might modulate the association of NEUROD1 with Type 1 diabetes.