HLA alleles and type 1 diabetes mellitus in low disease incidence populations of Southern Europe: a comparison of Greeks and Albanians.

Type 1 diabetes mellitus (DM1) is caused by environmental factors acting on genetically susceptible individuals. HLA-DQA1 and -DQB1 are major genetic determinants of the disease. Greece and Albania represent the low DM1 incidence countries of South-Eastern Europe. The HLA-DQA1 and -DQB1 associations with DM1 were investigated in these two groups, as reference for comparisons to the high-risk populations of Northern Europe. One hundred and thirty Greeks and 64 Albanians with DM1 were studied; 1,842 Greeks and 186 Albanians were analysed as controls. The samples were typed for six HLA-DQB1 alleles, using time-resolved fluorometry to detect the hybridisation of lanthanide labelled oligonucleotides with PCR products. Individuals positive for DQB1*0201 were selectively typed for three DQA1 alleles. In both populations DQB1*0201 increased the risk for DM1 while DQB1*0301 was protective. DQB1*0302 was associated with lower risk than *0201, while *0602 and *0603 were protective in Greeks but not in Albanians. It was also shown that DQA1 has a modifying effect, altering the risk conferred by the susceptible DQB1*0201. The low incidence of DM1 in these two countries correlates with the high frequency of the protective allele DQB1*0301 and the low impact of the susceptible DQB1*0302.