Lack of association of the insulin gene region with type 1 (insulin-dependent) diabetes mellitus in Japanese subjects

Association of insulin gene VNTR INS -23/Hph1 A>T (rs689) polymorphism with type 1 diabetes mellitus in Egyptian children

Background

Type1 diabetes mellitus (T1DM) has a multi-factorial pathogenesis; the interplay between genetic susceptibility and environmental factors is thought to provide the fundamental element for the disease. Apart from HLA, more than 50 genetic variants are associated with T1DM. INS -23/Hph1 A>T (rs689) is one of the effective loci with inconsistent reports in the literature. Accordingly, this study was designed to define the frequencies of INS -23/Hph1 A>T polymorphism and its association with T1DM in Egyptian diabetic children and their non-diabetic family members as compared to healthy controls.

Methods

Using polymerase chain reaction-restriction fragment length polymorphism methodology, analysis of insulin gene VNTR polymorphism was performed for 496 samples (91 patients, 179 parents, 130 siblings, and 96 controls); parents and siblings were apparently healthy.

Results

INS genotypes and allele frequencies were comparable between patients, non-diabetic siblings, and parents (p = 0.97 and 0.77, respectively). However, the TT/AT genotype and T allele were over-presented in the three family groups compared to controls (p = 0.0015 and 0.0029, respectively).

Comparing patients to controls, the T allele is considered a risk factor for the development of TIDM (OR 2.56, 95% CI 1.42–4.62, p = 0.0017).

INS -23/Hph1 A>T polymorphism showed concordance between patients and their mothers (Kappa = 0.446, p = 0.000) but not with their fathers (Kappa = 0.031, p = 0.765).

Conclusions

INS -23/Hph1 A>T gene polymorphism was shown to be a risk factor for the development of TIDM. This is in agreement with some and in disagreement with other reports. Studies of risk susceptibility factors have to be carried out locally in each community; results cannot be extrapolated from one ethnic group to another.

A case of novel de novo paired box gene 6 (PAX6) mutation with early-onset diabetes mellitus and aniridia

BACKGROUND

Paired box gene 6 (PAX6) is a transcription factor involved in eye development. Mutations of PAX6 cause congenital eye anomalies, such as aniridia. PAX6 is also involved in the development of the endocrine pancreas, and reported to be a genetic factor common to aniridia and glucose intolerance, although the latter is usually mild. Here, we describe a case of PAX6 mutation with early-onset diabetes mellitus.

CASE REPORT

A 27-year-old woman was referred to our clinic. She was diagnosed having diabetes at the age of 15 with negative glutamic acid decarboxylase (GAD) antibody. Insulin treatment was started at age 24. Because she had aniridia, PAX6 gene mutation was investigated and a heterozygous 2-bp deletion (c.402del2) was identified. Her parents did not have aniridia and PAX6 mutations. Heterozygous PAX6 mutation may cause glucose intolerance. However, cases of early-onset diabetes mellitus have not been reported. Her parents did not have diabetes, but their insulinogenic indices were low (0.25 and 0.3, respectively). We thought her early-onset diabetes was partly as a result of PAX6 mutation and partly because of an unknown insulin secretory defect inherited from her parents. We could not find any mutations in HNF-1alpha, -1beta, -4alpha, IPF-1, ISL-1, BEAT2/NeuroD1, PAX4, and amylin genes.

CONCLUSIONS

We report a case of PAX6 gene mutation with early-onset diabetes mellitus and aniridia. Low insulin secretory capacity in her parents suggested that her insulin secretory defect is as a result of not only PAX6 mutation but other genetic factors inherited from her parents.

CTLA4 gene polymorphism contributes to the mode of onset of diabetes with antiglutamic acid decarboxylase antibody in Japanese patients: genetic analysis of diabetic patients with antiglutamic acid decarboxylase antibody

AIM

The mode of onset is occasionally similar in Type 1 and Type 2 diabetes mellitus, and some patients with Type 2 diabetes are positive for antiglutamic acid decarboxylase antibody (GAD Ab). We investigated the contribution of Type 1 diabetes susceptibility genes to the progression of the insulin-deficient state and mode of onset of Type 2 diabetes in GAD Ab-positive (GAD-Ab+) patients. We examined the variable number of tandem repeats in the promoter region of the insulin gene (INS-VNTR, insulin-dependent diabetes mellitus (IDDM) 2) and cytotoxic T lymphocyte antigen 4 (CTLA4, IDDM12) as representative of Type 1 diabetes susceptibility genes.

METHODS

Patients with Type 2 diabetes who were GAD-Ab+ (n = 51) were selected for this study. In INS-VNTR, the class I allele was classified according to length (1S, 25-38 repeat units; 1M, 39-41 repeat units; 1L, 42-44 repeat units) and the exact class I allele length was analysed by specific polymerase chain reaction (PCR) amplifications. Analyses of classes II and III were performed by Southern blot. CTLA4 gene polymorphism (exon 1 position 49, G/A) was analysed by PCR-restriction fragment length polymorphism.

RESULTS

The distribution of INS-VNTR was no different between Type 1 diabetes and Type 2 diabetes with GAD Ab. The allele frequencies of CTLA4 gene polymorphism G and A in Type 2 diabetes/GAD-Ab+ were significantly different from those of Type 1 diabetes/GAD-Ab+ (G: 53%, A: 47% vs. G: 84%, A: 16%; P < 0.0001).

CONCLUSIONS

Our data showed that GAD-Ab+ Japanese patients presenting with Type 2 diabetes have shifted A allele while patients with abrupt onset have shifted G allele of CTLA4 gene polymorphism. Our results suggest that immunological function and polymorphism of the CTLA4 gene may contribute to the pathogenesis and progression of Type 1 diabetes.

Prevention of type 1 diabetes from laboratory to public health

Despite recent progress in immunology and genetics, the causes of type 1 diabetes remain unknown. Prevention of autoimmune diseases through immunomodulation or gene therapy has not yet been successful in humans. In contrast, some autoimmune diseases such as celiac disease, rheumatic fever, and congenital rubella induced diabetes can be avoided through modification of environmental factors. Candidate environmental causes of type 1 diabetes are now being characterized in cohort studies and clinical trials. An alternative approach to prevention of type 1 diabetes may include a "vaccination" in early childhood to induce tolerance to critical autoantigen(s). This paper reviews the status of current diabetes prevention trials in humans and selected new interventions that are being tested in animal models. We estimate the cost of public health implementation of selected screening and intervention scenarios. The ethical, logistic, and funding issues underlying these scenarios are discussed.

The insulin gene region and susceptibility to insulin-dependent diabetes mellitus in four races; new insights from Afro-Caribbean race-specific haplotypes

The IDDM2 component of the genetic susceptibility to insulin-dependent diabetes mellitus (IDDM) has been mapped to chromosome 11p15.5. The exact identity of IDDM2 remains uncertain. It has been suggested that IDDM2 maps within the 5' VNTR (variable number tandem repeat) polymorphism upstream of the insulin gene (INS). This has not been confirmed and a contribution from other INS gene region polymorphisms cannot be excluded. We present INS region genotype data from four racial groups: the Japanese, Hong Kong Chinese, North Indian Asians and Afro-Caribbeans (two groups; one born and resident in the UK, one in Jamaica). These races have not been previously studied with the range of INS region polymorphisms included here. No INS polymorphism was associated with IDDM across all races. These data from this study thus do not identify any INS polymorphism as IDDM2. The Afro-Caribbean race showed a very different distribution of INS genotypes from the other races and novel race-specific INS haplotypes were identified. Analysis of these excluded a contribution to susceptibility to IDDM from the- 23HphI INS polymorphism. An Afro-Caribbean INS haplotype which differed only at the VNTR from the very protective INS haplotype (VPH) identified in white Caucasians was detected. Population analysis of this haplotype will allow direct assessment of the role of the VNTR in susceptibility to IDDM. In conclusion, the diverse Afro-Caribbean TH/INS/IGF2 haplotypes identified in this study will be valuable in mapping IDDM2 more precisely.

Insulin gene region contributes to genetic susceptibility to, but may not to low incidence of, insulin-dependent diabetes mellitus in Japanese

In the Caucasian population, it has been demonstrated that the insulin gene (INS) region contains the insulin-dependent diabetes mellitus locus (IDDM2). In the Japanese population, however, there has been no report demonstrating the contribution of IDDM2 to the pathogenesis of IDDM. We conducted an association study of IDDM in a large number of Japanese subjects with multiple polymorphisms in INS region. We found a significant association of the INS region with IDDM. Alleles positively associated with IDDM in INS region were the same as those positively-associated with IDDM in Caucasian population, although positively-associated alleles are very common (allele frequencies > 0.9) in the Japanese general population. These data suggest that IDDM2 is involved in the genetic susceptibility to IDDM in Japanese. The high frequencies of disease-associated alleles in the general population suggest that IDDM2 locus is not responsible for the low incidence of IDDM in Japanese.

Association of polymorphism in the interferon gamma gene with IDDM

Cytokines may play important roles in the pathogenesis of insulin-dependent diabetes mellitus (IDDM). We analysed a dinucleotide repeat polymorphism within the first intron of the interferon gamma (IFN-gamma) gene in Japanese diabetic patients (175 IDDM and 145 non-insulin-dependent diabetes mellitus) and 267 control subjects. A significant difference was observed in the global allele distribution of the polymorphism between the IDDM and control groups (p = 0.039). The difference from the control group was more evident in the patients whose insulin therapy started within 1 year from onset (p = 0.006) or in the young-onset (< 10 years) patients (p = 0.0006). The alleles "3" and "6" were increased in the IDDM patients, and a significant increase in the frequency of the "3/6" genotype was observed in the IDDM patient group (9.1%, RR 2.9, p = 0.010), in the patients with initial insulin therapy less than 1 year from onset (10.6%, RR 3.4, p = 0.004), or in the young-onset patients (16.7%, RR 5.7, p = 0.0003) in comparison to the control subjects (3.4%). There was a tendency towards frequent occurrence of clinical characteristics which reflect young or abrupt onset of diabetes or both, and depletion of insulin secretion capacity in the patients with "3/6" or "6/6" in comparison to the patients with other genotypes. These results suggest that the IFN-gamma gene region may contribute to the pathogenesis of IDDM and could be a genetic marker for IDDM.

Genetic markers for insulin-dependent diabetes mellitus in Japanese

Although the HLA class II genes are clearly associated with insulin-dependent diabetes mellitus (IDDM) in all ethnic groups, considerable variation in the associated haplotypes is observed among the ethnic groups. In Japanese, DRB1*0405-DQA1*0301-DQB1*0401, DRB1*0901-DQA1*0301-DQB1*0303 and DRB1*0802-DQA1*0301-DQB1*0302 are the major susceptibility haplotypes to IDDM, while DRB1*1501-DQA1*0102-DQB1*0602 and DRB1*1502-DQA1*0103-DQB1*0601 are the major resistance haplotypes. The hypothesis that alleles encoding amino acids other than aspartic acid at the DQB1 position 57 contribute to IDDM susceptibility is not applicable to the Japanese, mainly because the first and second susceptibility haplotypes listed above have aspartic acid at DQB1 position 57. In the 5' insulin gene polymorphism, the shorter insertion (class 1 allele) is predominant, and is not associated with diabetes in Japanese. Subdivision of the class 1 alleles also failed to show an association with IDDM in Japanese. The insulin gene region appeared to be of less value as a genetic marker for IDDM in Japanese. Little is known about other genetic markers.