A simple nonradioactive method of DNA typing for subsets of HLA-DR4: prevalence data on HLA-DR4 subsets in three diabetic population groups.

The molecular basis of eight DR4 subtypes resides in several nucleotide substitutions in the third hypervariable region of the DR beta 1 chain. The typing of DR4 subsets using the mixed lymphocyte culture (MLC) assay or allele-specific oligonucleotide hybridization is expensive, cumbersome, and requires the use of radioisotopes. We have therefore developed a rapid and safe procedure for subtyping DR4-alleles that involves selective amplification of the second exon of the DR4-DRBI gene followed by unambiguous subtype discrimination after digestion with five allele-specific endonucleases [polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP)] and visualization of the polymorphic fragments with silver or ethidium bromide staining. Validity of this subtyping procedure was initially examined by the use of cell lines of known subtypes. Three groups of DR4 patients with insulin-dependent diabetes mellitus (IDDM) from Chinese, Tunisian, and Caucasian populations were subtyped and the prevalence of subtype associations with IDDM was compared.