The Ala45Thr polymorphism of BETA2/NeuroD1 gene and susceptibility to type 1 diabetes mellitus in caucasians

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.

Monogenic Diabetes: What It Teaches Us on the Common Forms of Type 1 and Type 2 Diabetes

To date, more than 30 genes have been linked to monogenic diabetes. Candidate gene and genome-wide association studies have identified > 50 susceptibility loci for common type 1 diabetes (T1D) and approximately 100 susceptibility loci for type 2 diabetes (T2D). About 1-5% of all cases of diabetes result from single-gene mutations and are called monogenic diabetes. Here, we review the pathophysiological basis of the role of monogenic diabetes genes that have also been found to be associated with common T1D and/or T2D. Variants of approximately one-third of monogenic diabetes genes are associated with T2D, but not T1D. Two of the T2D-associated monogenic diabetes genes-potassium inward-rectifying channel, subfamily J, member 11 (KCNJ11), which controls glucose-stimulated insulin secretion in the β-cell; and peroxisome proliferator-activated receptor γ (PPARG), which impacts multiple tissue targets in relation to inflammation and insulin sensitivity-have been developed as major antidiabetic drug targets. Another monogenic diabetes gene, the preproinsulin gene (INS), is unique in that INS mutations can cause hyperinsulinemia, hyperproinsulinemia, neonatal diabetes mellitus, one type of maturity-onset diabetes of the young (MODY10), and autoantibody-negative T1D. Dominant heterozygous INS mutations are the second most common cause of permanent neonatal diabetes. Moreover, INS gene variants are strongly associated with common T1D (type 1a), but inconsistently with T2D. Variants of the monogenic diabetes gene Gli-similar 3 (GLIS3) are associated with both T1D and T2D. GLIS3 is a key transcription factor in insulin production and β-cell differentiation during embryonic development, which perturbation forms the basis of monogenic diabetes as well as its association with T1D. GLIS3 is also required for compensatory β-cell proliferation in adults; impairment of this function predisposes to T2D. Thus, monogenic forms of diabetes are invaluable "human models" that have contributed to our understanding of the pathophysiological basis of common T1D and T2D.

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.

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

A meta-analysis assessed whether the Ala45Thr polymorphism of the neurogenic differentiation 1 (NEUROD1) gene is associated with increased risk of diabetes mellitus type 1 (T1D) or type 2 (T2D). Fourteen case-control studies were analyzed, including genotype data on 3,057 patients with diabetes (T1D n=1,213, T2D n=1,844) and 2,446 controls. Overall and race-specific summary odds ratios (ORs) were obtained with fixed and random effects models. The Thr allele did not significantly increase the overall risk for T1D (OR 1.27 [0.94-1.71], P=0.12) or T2D (OR 1.07 [0.90-1.28], P=0.46). The Thr allele conferred increased susceptibility in subjects of Asian racial descent to T1D (OR 1.88 [1.10-3.21], P=0.020), but not to T2D (OR 1.08 [0.74-1.56], P=0.70). There was no association in subjects of European descent (OR 0.97 [0.76-1.23], P=0.80 for T1D; OR 1.03 [0.88-1.21], P=0.68 for T2D). Larger studies seemed to show more conservative estimates for the association with T1D (P=0.083). The Ala45Thr polymorphism of the NEUROD1 gene has no effect on susceptibility to T2D. It may however be a risk factor for susceptibility to T1D, in particular for subjects of Asian descent, although bias cannot be totally excluded.