Wikipedia's article on type-1 diabetes (T1D) is a good starting point.
Classically, the highest risk factor for type-1 diabetes is associated with HLA genotypes DR3/4 and DQ8. SNPs rs2040410 and rs7454108 encode the corresponding alleles, and a genoset (Gs121) evaluates Promethease users to assess whether they are DR3/4 or DQ8 carriers.
Genes likely to affect susceptibility include the following. [PMID 19430480]
Many other SNPs may contribute to the likelihood and severity of type-1 diabetes, including:
- Twelve SNPs published in 2007 from a large, multi-lab consortium's effort [PMID 17554300]:
- rs7574865 is associated with type-1 diabetes in addition to multiple autoimmune disorders such as rheumatoid arthritis and lupus
- rs3087243 is the best studied SNP in the negative regulator CTLA4 linked to Type-1 diabetes in some populations. [PMID 15629882]
- A particular mutation raises risk 80%
- rs3772534 has been reported to increase the risk of T1D (type 1 diabetes) in a Danish population studied, but in a larger English study, this did not replicate [PMID 17209142]
Islet transplantation seems to be emerging as an effective treatment 
Type 1 Diabetes
DeCode reports that the following SNPs also contribute to susceptibility to T1D: