Frequency analysis of HLA-DQA1 and HLA-DQB1 gene alleles and susceptibility to type 1 diabetes mellitus in Russian patients

Full genotyping of a highly polymorphic human gene trait by time-resolved fluorescence resonance energy transfer

The ability of detecting the subtle variations occurring, among different individuals, within specific DNA sequences encompassed in highly polymorphic genes discloses new applications in genomics and diagnostics. DQB1 is a gene of the HLA-II DQ locus of the Human Leukocyte Antigens (HLA) system. The polymorphisms of the trait of the DQB1 gene including codons 52-57 modulate the susceptibility to a number of severe pathologies. Moreover, the donor-receiver tissue compatibility in bone marrow transplantations is routinely assessed through crossed genotyping of DQB and DQA. For the above reasons, the development of rapid, reliable and cost-effective typing technologies of DQB1 in general, and more specifically of the codons 52-57, is a relevant although challenging task. Quantitative assessment of the fluorescence resonance energy transfer (FRET) efficiency between chromophores labelling the opposite ends of gene-specific oligonucleotide probes has proven to be a powerful tool to type DNA polymorphisms with single-nucleotide resolution. The FRET efficiency can be most conveniently quantified by applying a time-resolved fluorescence analysis methodology, i.e. time-correlated single-photon counting, which allows working on very diluted template specimens and in the presence of fluorescent contaminants. Here we present a full in-vitro characterization of the fluorescence responses of two probes when hybridized to oligonucleotide mixtures mimicking all the possible genotypes of the codons 52-57 trait of DQB1 (8 homozygous and 28 heterozygous). We show that each genotype can be effectively tagged by the combination of the fluorescence decay constants extrapolated from the data obtained with such probes.

The carriage of the type 1 diabetes-associated R262W variant of human LNK correlates with increased proliferation of peripheral blood monocytes in diabetic patients

OBJECTIVE

Lymphocyte adaptor protein (LNK) plays a pivotal role as a suppressor of T-cell receptor-mediated immune signaling and negative regulator of lymphopoiesis and early hematopoiesis. Recently, association between the R262W (c.784T>C) variant of the SH2B3 gene (rs3184504) encoding human LNK and type 1 diabetes (T1D) was found in several populations. In this study, we aimed to check whether this marker is associated with T1D in a Russian population.

METHODS

Using a Taqman allele discrimination assay, we genotyped 1062 unrelated Russian individuals with diabetes at childhood and adolescence onset and 1020 healthy controls. T-cell proliferation assay based on the measurement of incorporation of bromo-2'-deoxyuridine incorporation into newly synthesized DNA was used to evaluate whether carriage of SH2B3 784T>C correlates with T-cell proliferation in patients' peripheral mononuclear blood cells (PMBCs) stimulated with anti-CD28 and anti-CD3 antibodies.

RESULTS

The allele 784C of SH2B3 was related to a higher risk of T1D (odds ratio of 1.52, p = 1.2 × 10(-12)). A correlation between the carriage of the predisposing C/C variant of LNK and increased proliferation of T lymphocytes was shown in PMBCs of both diabetic [C/C vs. C/T vs.T/T = optical density at 450 nm (OD(450)) 6.3 ± 0.8 vs. 4.4 ± 0.7 vs. 2.7 ± 0.5, p = 0.0007] and non-diabetic (C/C vs. C/T vs.T/T = OD(450) 2.9 ± 0.6 vs. 2.2 ± 0.4 vs. 1.7 ± 0.4, p = 0.022) patients.

CONCLUSIONS

The SH2B3 784T>C variant could contribute to the pathogenesis of T1D through impaired immune response that promotes activation and expansion of self-reactive lymphocytes in susceptible individuals.

Distribution of insulin-dependent diabetes mellitus (IDDM)-related HLA alleles correlates with the difference in IDDM incidence in four populations of the Eastern Baltic region

The high incidence of insulin-dependent diabetes mellitus (IDDM) in Finland contrasts strikingly with the low rates in the neighbouring populations of countries in the Eastern Baltic region: Estonia, Latvia and Russia. To evaluate the possible contribution of genetic factors to these differences, the frequencies of HLA-DQB1 alleles and relevant DQB1-DQA1 or DQB1-DRB1 haplotypes associated with IDDM risk or protection were analysed among IDDM patients and control subjects from these four populations. An increased frequency of HLA-DQB1*0302, DQB1*02-DQA1*05 and DQB1*0302-DRB1*0401 was observed in subjects with IDDM in all studied populations, whereas the prevalence of DQB1*0301 and DQB1*0602 and/or *0603 was decreased among patients. The degree of IDDM risk associated with HLA alleles analysed here did not differ significantly between the populations. Comparisons of the distribution of IDDM-related HLA alleles and haplotypes in the background populations revealed its consonance with IDDM incidence. The combined frequency of high risk genotypes was significantly higher among Finns than in other populations studied. Our data support the hypothesis that variance in the dispersion of HLA alleles is the genetic basis of variation of IDDM incidence observed in the Eastern Baltic region.

Ethical concerns in the research and treatment of complex disease

Research on and treatment of complex diseases raise familiar ethical issues concerning informed consent, privacy, confidentially, insurability, employability and social stigma. Consideration of the family as the unit of study, or point of medical intervention, presents some additional twists to these common ethical concerns. In addition, complex diseases present particular ethical challenges because different social and political incentives accompany placing emphasis on either the genetic or the environmental components of the diseases (e.g. in allocating research funds or ascribing responsibility for illness).