Genomics of Type 1 Diabetes Mellitus and Its Late Complications

In ethnic Russians, MHC (HLA) was shown to be the major locus determining the predisposition to type 1 diabetes mellitus (T1DM). To map the regions linked to T1DM, families with concordant or discordant sib pairs were selected from the Russian population of Moscow. With these families, linkage to T1DM was demonstrated for the CTLA4 gene (IDDM12, 2q32.1–q33), which codes for a T-cell surface antigen, and the PDCD2 gene (IDDM8, 6q25–q27), which is homologous to the mouse programmed cell death activator gene. Using polymorphic microsatellites, we could also observe the linkage to T1DM of regions 3q21–q25 (IDDM9) and 10p12.2 (IDDM10). Complex analysis of linkage and association of the polymorphic markers from region 11p13 in the vicinity of the catalase gene (CAT) based on the case/control groups and two groups of families allowed us to reveal a new T1DM locus; the linkage to this locus was not reported earlier for other populations. Diabetic polyneuropathy (DPN) proved to be associated with polymorphic markers Ala(–9)Val of the SOD2 gene, Arg213Gly of the SOD3 gene, and T(–262)C of the CAT gene, and with a polymorphic microsatellite located in the promoter region of the NOS2 gene. It has been supposed that one of the main risk factors of DPN development in patients with type 1 diabetes is oxidative stress arising in hyperglycemia because of increased production of superoxide radicals in mitochondria and insufficient activity of antioxidative enzymes. Diabetic nephropathy (DN) showed no association with the antioxidative enzyme genes. However, the association was observed for the insertion/deletion (I/D) polymorphism of ACE and the ecNOS34a/4b polymorphism of NOS3, two genes involved in controlling vascular tonus, as well as for the I/D polymorphism of APOB and the 2/3/4 polymorphism of APOE, two genes involved in lipid transport. In addition, polymorphic microsatellites of chromosome 3q21–q25 proved to be closely associated with DN. The tightest association was established for D3S1550, carriers of allele 12 or genotype 12/14 having high risk of DN (OR = 4.85 and 6.25, respectively). Region 3q21–q25 perhaps contains a major gene determining DN development, while the other DN-associated genes mostly influence the progression of DN.