Geographical differences within Finland in the frequency of HLA-DQ genotypes associated with Type 1 diabetes susceptibility

Geographical variations in the HLA-DQ genotypes associated with risk for ty pe 1 diabetes were evaluated in Finland. Samples of 280 diabetic children d iagnosed in Turku (south-west of the country) and 405 in Oulu (north of the country) were studied as well as a series of 14 096 and 10 016 newborns co llected from the same hospitals. There were no major differences in the ris k or protection conferred by various HLA-DQB1 genotypes between south-weste rn and northern parts of the country when genotypes of children with type 1 diabetes from these two centres were compared with those of newborns, repr esenting the background populations. However, the distribution of various g enotypes was different, both in diabetic children and in newborns, when com pared between the two regions (P < 0.0001, chi(2) test). These differences reflected the allele frequencies in newborn cohorts in which HLA-DQB1*02 an d DQB1*0301 were found more often in Turku and DQB1*0302 more often in Oulu (P < 0.0001 for all differences). Similar types of differences were detect ed when children who were diagnosed as having diabetes during the national 'Childhood Diabetes in Finland' (DiMe) study between the years 1986-1989 we re compared according to their residence. The observed differences in genot ype and allele frequencies demonstrate the heterogeneity for HLA alleles ev en in a population that is generally regarded as highly homogeneous. These differences also affect the sensitivity and efficiency of the screening pro gramme used for identifying infants with genetic susceptibility to IDDM in the ongoing Finnish Diabetes Prediction and Prevention Study.