The HLA-DQ molecule is an important determinant of the risk of type 1 diabetes. The level of expression of predisposing and protective DQ variants may contribute to their influence on disease risk. Chapter 2 shows that the alleles encoding these variants differ in their expression at the mRNA level; DQA1 *0301 and DQB1 *06 were overexpressed compared with other alleles, while DQB1 *02 transcripts were less abundant. These differences correlate with differences in the promoter activity of the alleles, reported in Chapter 3. There was no simple relationship between the level of I expression of an allele and its influence on disease risk. Chapter 4 describes the first study to report the prevalence of latent autoimmune diabetes in adults (LADA), a subtype of diabetes, in the UK-resident South Asian , population. This disease is uncommon in the Punjabi population of Birmingham, but islet autoimmunity is associated with a similar clinical and HLA genetic profile to that seen in other ethnic groups.