HLA-DQA1 and DQB1 gene polymorphisms in type I diabetic patients from central Italy and their use for risk prediction

Clinical worthlessness of genetic prediction of common forms of diabetes mellitus and related chronic complications: A position statement of the Italian Society of Diabetology

AIM

We are currently facing several attempts aimed at marketing genetic data for predicting multifactorial diseases, among which diabetes mellitus is one of the more prevalent. The present document primarily aims at providing to practicing physicians a summary of available data regarding the role of genetic information in predicting diabetes and its chronic complications.

DATA SYNTHESIS

Firstly, general information about characteristics and performance of risk prediction tools will be presented in order to help clinicians to get acquainted with basic methodological information related to the subject at issue. Then, as far as type 1 diabetes is concerned, available data indicate that genetic information and counseling may be useful only in families with many affected individuals. However, since no disease prevention is possible, the utility of predicting this form of diabetes is at question. In the case of type 2 diabetes, available data really question the utility of adding genetic information on top of well performing, easy available and inexpensive non-genetic markers. Finally, the possibility of using the few available genetic data on diabetic complications for improving our ability to predict them will also be presented and discussed. For cardiovascular complication, the addition of genetic information to models based on clinical features does not translate in a substantial improvement in risk discrimination. For all other diabetic complications genetic information are currently very poor and cannot, therefore, be used for improving risk stratification.

CONCLUSIONS

In all, nowadays the use of genetic testing for predicting diabetes and its chronic complications is definitively of little value in clinical practice.

Antibodies to glutamic acid decarboxylase in Syrian and Jordanian type I diabetes patients and their siblings

BACKGROUND

Attempts to identify the earliest events in the autoimmune process in type I diabetes mellitus suggests the glutamic acid decarboxylase (GAD) is one of the first and most important autoantigens. We conducted this study to determine the prevalence of antibodies to glutamic acid decarboxylase (anti-GAD) in both Syrian and Jordanian children with Type I diabetes and their siblings.

PATIENTS AND METHODS

sera were obtained from 85 Syrian patients with type I diabetes (mean age 13.6 + 5.9 years), from 45 of their siblings (mean age 11 + 6.1 years), from 78 randomly selected Syrian control subjects (mean age 9.9 + 43 years), and from 95 Jordanian patients with type I diabetes (mean age 13.9 + 65 years), from 78 of their siblings (mean age 12.3 + 7.1 years), and from 100 randomly selected Jordanian control subjects (mean age 7.8 + 4.5 years). Sera were analyzed from anti-GAD using the enzyme linked immunosorbent assay (ELISA) technique.

RESULTS

Prevalence of anti-GAD was 34.1% (29/85) in Syrian type I diabetes patients, 20% (9/45) in their siblings, 1.3% (1/78) in Syrian control subjects, 49.5% (47/95) in Jordanian type I diabetes patients, 23% (18/78) in their siblings, and 2% (2/100) in Jordanian control subjects. Differences between the Syrian and Jordanian type I diabetes groups and their siblings and controls were statistically significant. In patients with less than two years of diabetes duration, the frequency was 88.8% (16/18) for both groups. There was no correlation between sex and anti-GAD levels in their Syrian and Jordanian type I diabetes patients and their siblings. The positivity of anti-GAD tended to be more frequent at the age range of 5 to 8 years in siblings. Anti-GAD titers >90 ng/ml were found in 58.8% of type I diabetes patients and in 38% of siblings who were anti-GAD positive.

CONCLUSION

Syria and Jordan have prevalence rates of anti-GAD among type I diabetes patients and their siblings that are among the highest reported in the world. Therefore, anti-GAD may be valuable as an early predictive marker for type I diabetes.

Relative and absolute HLA-DQA1-DQB1 linked risk for developing type I diabetes before 40 years of age in the Belgian population: implications for future prevention studies

HLA-DQ genotyping remains the cornerstone of genetic risk stratification in type I diabetes prediction and prevention studies. We developed a genetic screening strategy for predisposition to type I diabetes in the Belgian population based upon HLA-DQA1-DQB1 typing and taking into account the age at clinical onset. A group of 1866 autoantibody-positive type I patients below age 40 years recruited by the Belgian Diabetes Registry and a group of 750 control subjects were DQA1-DQB1 genotyped. In the total study population 16 different DQA1-DQB1 haplotypes were revealed, allowing the stratification of 81 genotypes in ten different genotype groups. Apart from the highest risk DQA1*-DQB1* genotype 0301-0302/0501-0201 (odds ratio 21; absolute risk 6%), three other genotype groups conferred a highly significant disease risk (p < 10(-6)). Altogether, these susceptibility genotypes were carried by 9% of the control subjects versus 60% of the patients diagnosed before age 40 years and up to 70% of those under age 5 years. All other genotypes were protective, neutral, infrequent or associated with a moderate protection or susceptibility. A strong, although not absolute protection was conferred by DQB1*0602-positive haplotypes (odds ratio = 0.03). This study in a large cohort of autoantibody-positive patients shows that a DQA1-DQB1-based genotyping strategy allows the identification of a subgroup representing less than 10% of the Belgian population but harbouring the majority of future type I patients arising in childhood or early adulthood. Future prediction and prevention studies should take into account the age dependency of this HLA-DQ associated risk.

The distribution of HLA class II susceptible/protective haplotypes could partially explain the low incidence of type 1 diabetes in continental Italy (Lazio region)

HLA class II is the primary susceptibility gene to type 1 diabetes and the analysis of HLA class II association could help to clarify the relative weight of genetic contribution to the incidence of the disease. Here we present an extensive typing for HLA class II alleles and their haplotypes in a homogenous population of type 1 diabetic patients (n=134) and controls (n=128) and in simplex (n=100) and multiplex families (n=50) from continental Italy (Lazio region). Among the various haplotypes tested, the DRB1*0301-DQA1*0501-DQB1*0201 was the most frequent found in type 1 diabetic patients and was transmitted in 82% of affected siblings, whereas DRB1*0402-DQA1*0301-DQB1*0302 appeared to have the highest odds ratio (10.4), this haplotype was transmitted in 96.3% of affected siblings, followed by DRB1*0405-DQA1*0301-DQB1*0302, DRB1*0405-DQA1*0301-DQB1*0201, DRB1*0401-DQA1*0301-DQB1*0302 and DRB1*0404-DQA1*0301-DQB1*0302. The following haplotypes showed a significant decreased transmission to diabetic siblings: DRB1*0701-DQA1*0201-DQB1*0303, DR2-DQA1*01-DQB1*0602, DR5-DQA1*0501-DQB1*0301. We suggest that the HLA DR/DQ haplotype/genotype frequencies observed could in part explain the low incidence of type 1 diabetes registered in Lazio region (8.1/100.000/year), for a number of reasons: i) the low frequency, in the general control population, of the most susceptible haplotypes and genotype for type 1 diabetes DRB1*0301-DQA1*0501-DQB1*0201 (14%), and DR4-DQA1*0301-DQB1*0302 (9%) and DRB1*0301-DQA1*0501-DQB1*0201/DR4-DQA1*0301-DQB1*0302 (0.8%) compared to other countries characterised by high incidence rate of the disease, Sardinia and Finland, respectively; ii) a significant lower ratio, in the control population, between the susceptible DRB1*0301-DQA1*0501-DQB1*0201 and the neutral DRB1*0701-DQA1*0501-DQB1*0201 haplotypes compared to the Sardinian population; iii) the high frequency of protection haplotypes/genotypes as the DR5-DQA1*0501-DQB1*0301, and DR5-DQA1*0501-DQB1*0301/DR5-DQA1*0501-DQB1*0301 very common in the control population of Lazio region and the DRB1*1401-DQA1*0101-DQB1*0503 haplotype.

Autoantibody negative new onset type 1 diabetic patients lacking high risk HLA alleles in a caucasian population: are these type 1b diabetes cases?

BACKGROUND

In Caucasians, a small number of Type 1 diabetic patients do not show evidence of humoral islet autoimmunity at disease onset, at least with common screening procedures. In African- and Hispanic-American diabetic children at time of diagnosis, many show no evidence of autoimmunity but have an atypical clinical form of the disease. According to the recent American Diabetes Association classification, this subgroup of autoantibody negative patients is referred to as Type 1b diabetic subjects. In the present study, a homogeneous Caucasian Type 1 diabetic clinic-based cohort has been evaluated at diagnosis using a large panel of diabetes-related antibodies and then characterized for various genetic features in order to identify newly diagnosed Type 1 diabetics who are potentially autoantibody negative, i.e. possibly referrable to as idiopathic Type 1b diabetes.

METHODS

Newly diagnosed Type 1 diabetic patients of Italian origin (n=141, mean age 12.0+/-7.6 years) were tested for anti-islet cell, anti-insulin, anti-65 kDa isoform of glutamic acid decarboxylase and anti-amino acid residues 256-979 of the tyrosine-phosphatase IA-2 molecule autoantibodies (Step 1). Only those patients found to be autoantibody negative were tested for anti-disialo-ganglioside GD3, anti-thyroid peroxidase, anti-thyroglobulin, anti-21-OH hydroxylase, anti-gastric parietal cell and anti-transglutaminase antibodies (Step 2). Sera negative for the presence of these six autoantibodies as well were characterized in terms of HLA DRB1, DQB1 and CTLA-4.

RESULTS

Six out of 141 subjects (3.5%) were autoantibody negative in the first step of the study and five out of six in the second. These five autoantibody negative patients underwent genetic analysis. Three of them had at least one Type 1 diabetes-related high risk HLA haplotype (3/141, 2.1%) while the remaining two cases showed neutral (DR5-DQB1*0301/DR5-DQB1*0301) or strongly protective (DR2-DQB1*0602/DR2-DQB1*0602) HLA genotypes, respectively (2/141, 1. 4%).

CONCLUSIONS

Clinically defined Type 1 diabetic patients with no sign of autoimmunity do exist in a Caucasian population. These patients (2 out of 141) that cannot be classified as Type 1a diabetic patients lack clinical characteristics of Type 1b diabetes and have to be reconsidered for a more appropriate ADA classification. These data suggest the need of further large population-based studies to understand if Type 1b diabetes really occurs in a Caucasian population. The patient with a strongly protective HLA genotype is particularly interesting considering that among Caucasians only a few sporadic cases with Type 1 diabetes and DQB1*0602, have been reported, none of whom was homozygous at DQB1 locus.

Complex interaction between HLA DR and DQ in conferring risk for childhood type 1 diabetes

Type 1 (insulin-dependent) diabetes mellitus is associated with HLA DR and DQ factors, but the primary risk alleles are difficult to identify because recombination events are rare in the DQ-DR region. The risk of HLA genotypes for type 1 diabetes was therefore studied in more than 420 incident new onset, population-based type 1 diabetes children and 340 age, sex and geographically matched controls from Sweden. A stepwise approach was used to analyse risk by relative and absolute risks, stratification analysis and the predispositional allele test. The strongest relative and absolute risks were observed for DQB1*02-DQA1*0501/DQB1*0302-DQA1*0301 heterozygotes (AR 1/46, P < 0.001) or the simultaneous presence of both DRB1*03 and DQB1*0302 (AR 1/52, P < 0.001). Stratification analysis showed that DQB1*0302 was more frequent among DRB1*04 patients than DRB1*04 controls (P < 0.001), while DRB1*03 was more frequent among both DQA1*0501 (P < 0.001) and DQB1*02 (P < 0.001) patients than respective controls. The predispositional allele test indicated that DRB1*03 (P < 0.001) would be the predominant risk factor on the DRB1*03-DQA1*0501-DQB1*02 haplotype. In contrast, although DQB1*0302 (P < 0.001) would be the predominant risk factor on the DRB1*04-DQA1*0301-DQB1*0302 haplotype, the predispositional allele test also showed that DRB1*0401, but no other DRB1*04 subtype, had an additive risk to that of DQB1*0302 (P < 0.002). It is concluded that the association between type 1 diabetes and HLA is due to a complex interaction between DR and DQ since (1) DRB1*03 was more strongly associated with the disease than DQA1*0501-DQB1*02 and (2) DRB1*0401 had an additive effect to DQB1*0302. The data from this population-based investigation suggest an independent role of DR in the risk of developing type 1 diabetes, perhaps by providing diseases-promoting transcomplementation molecules.

HLA-DQ screening for risk assessment of insulin dependent diabetes in northern Italy

Genetic markers may be used to improve the prediction of insulin-dependent diabetes mellitus (type 1) in individuals with islet autoantibodies. In order to develop a risk assessment strategy for the Lombardy region of northern Italy based on genetic and immunological markers, we analyzed HLA DQA1 and DQB1 alleles in 60 type 1 probands and their first-degree relatives and 65 unrelated control subjects from the same area using polymerase chain reaction (PCR) and oligonucleotide probes. The major risk haplotypes were DQA1 *0501-DQB1*0201 (39.1% of diabetic vs. 8.9% of non-diabetic haplotypes) and DQA1 *0301-DQB1*0302(20% of diabetic vs 7.1% of non-diabetic haplotypes). Stratified analysis showed DQA1*0102-DQB1*0502 also to be associated with type 1 susceptibility when found together with DQA1*0501-DQB1*0201 or DQA1*0301-DQB1*0302. One type 1 patient had the type 1-protective DQA1*0102-DQB1*0602 haplotype. Overall, 88% of patients and 20% of unrelated control subjects had either DQA1*0501-DQB1*0201 or DQA1*0301-DQB1*0302 in the absence of DQA1*0102-DQB1*0602. These data suggest that typing for markers identifying these three haplotypes in the Lombardy population will achieve a sensitivity of almost 90% and exclude 80% of children from subsequent islet autoantibody testing.

Double blind trial of nicotinamide in recent-onset IDDM (the IMDIAB III study)

Nicotinamide has been recently introduced, in addition to intensive insulin therapy for patients with recent-onset insulin-dependent diabetes mellitus (IDDM) to protect beta cells from end-stage destruction. However, available data are conflicting. A double blind trial in 56 newly-diagnosed IDDM patients receiving nicotinamide for 12 months at a dose of 25 mg/kg body weight or placebo was designed in order to determine whether this treatment could improve the integrated parameters of metabolic control (insulin dose, glycated haemoglobin and C-peptide secretion) in the year after diagnosis. In addition to nicotinamide or placebo, patients received three to four insulin injections daily to optimize blood glucose levels. Patients treated with nicotinamide or placebo received similar doses of insulin during follow-up and 1 year after diagnosis with comparable glycated haemoglobin levels 6.7 +/- 1.8% nicotinamide vs 7.1 +/- 0.6% placebo). Basal and glucagon stimulated C-peptide secretion detectable at diagnosis were similarly preserved in the course of 12 months follow-up both in nicotinamide and placebo treated patients. No adverse effects were observed in patients receiving nicotinamide. When age at diagnosis was taken into account, nicotinamide treated older patients ( > 15 years of age) showed significantly higher stimulated C-peptide secretion than placebo treated patients (p < 0.02). These results suggest that nicotinamide can preserve and improve stimulated beta-cell function only in patients diagnosed after puberty.(ABSTRACT TRUNCATED AT 250 WORDS)

Additive susceptibility to insulin-dependent diabetes conferred by HLA-DQB1 and insulin genes

Several genomic polymorphisms at the insulin (INS) gene and its flanking regions were analyzed in 197 unrelated Caucasian patients affected by insulin-dependent diabetes (IDDM) and 159 ethnically matched, normal controls ascertained from the South-Eastern United States. We found that the frequency of homozygotes for the common variant at the insulin gene was significantly increased in the diabetic population (RR = 2.0, p < 0.005). However, the polymorphisms in the 5' and 3' regions flanking the INS were not significantly associated with IDDM. These results suggest that the IDDM susceptibility locus on chromosome 11p is located within the region extending from the 5' VNTR to the 3' end of the INS gene. We determined the HLA-DQB1 genotypes by denaturing gradient gel electrophoresis (DGGE) and/or sequence-specific primers (SSP) techniques to assess the possible interactions between INS and HLA. DQB1*0302 had the strongest predisposing effect on IDDM susceptibility (RR = 9.3) and DQB1*0602 the strongest protective effect (RR = 0.02). However, a significant predisposing effect of DQB1*0201 could be demonstrated only after removal of the effects of DQB1*0302 and DQB1*0602. Analyses of the genotypes revealed that all genotypes containing 0602 were protective and that the heterozygous genotype 0201/0302 and homozygous genotype 0302/0302 confer the highest risk (RR = 20.9 and 12.9 respectively). However, heterozygous genotypes 0302/X (X excludes 0201, 0302 and 0602) have a significantly lower predisposing risk. Similarly, there is heterogeneity in risk between predisposing 0201/0201 homozygous individuals and protective 0201/X individuals. When subjects were stratified by HLA genotypes, the relative risks conferred by INS did not vary, thus suggesting that the susceptibility effects conferred by HLA and INS are additive rather than interactive.