[Insulin-dependent diabetes mellitus in Santiago, Chile: the role of immunogenetic and environmental factors].

The role of HLA class II alleles in the genetic susceptibility to develop insulin-dependent diabetes mellitus (IDDM) was examined by means of PCR and oligospecific probes in 63 IDDM children and 74 controls subjects. In diabetic patients we found a significant increase in the alleles frequency DR3, DR4, DQB10302 and DQA10301 compared to the control group, where the most prevalent alleles were DR2, DR14 (DRB11402), DQA10101 and DQA10201. All the risk genotypes in the diabetic group were similar than in other caucasian groups: DR3/DR4-DQB10201/0302-DQA10301/0501 and DR4/DR4-DQB10302/0302-DQA10301/0301. The homozygote character no asp57 conferred an absolute risk (AR) of 3.87 and the marker Arg52 an AR of 5.78/100.000 bab year. The homozygosis for both markers (no Asp57 + Arg52) had an AR of 7.56/100.000 bab year. Regarding environmental factors associated with IDDM, our population under study showed a low prevalence of infectious agents (mainly mumps and rubella, specifically associated with IDDM) and a high prevalence of effective breast-feeding (over 3 months). These factors could be exercising a protector role in the development of IDDM. The factors that appear to be important in the low incidence of IDDM in Santiago de Chile are: the low prevalence of infectious agents related to IDDM, the high percentage of breast-feeding children in the population, the reduced frequency of susceptible molecules as DR3, DQB10201 (compared to other caucasian groups) and the presence of protective genotypes related to DR13 and DR14 observed in the non diabetic children.