Molecular genotyping for the major histocompatibility complex (MHC) class II loci, HLA-DRB1, -DQB1 and -DQA1, in 100 patients with relapsing/remitting multiple sclerosis (MS) demonstrated an association with the HLA-DR2, DQw6-associated alleles DRB1*1501, DQB1*0602 and DQA1*0102, thereby extending this finding among MS patients in several countries to an Australian population. Analysis by the relative predispositional effect (RPE) method provided no evidence for a second susceptibility allele at either DQA1 or DQB1. However, our data and that of others suggest a negative association with DQA1*0101. Associations were found with DQB1 alleles sharing sequence homology with DQB1*0602, with DQB1 alleles encoding leucine at residue 26 (Leu 26), with DQA1 alleles encoding glutamine at residue 34 (Gln 34) and with Leu 26 plus Gln 34 alleles, but each was shown by two-loci linkage analysis to be secondary to the DRB1*1501, DQB1*0602, DQA1*0102 association. The recently reported negative association with DQA1 alleles encoding phenylalanine at amino acid 25, leucine at amino acid 69 and arginine at amino acid 52 was not found in this study, although there was a trend towards reduced phenylalanine at amino acid 25. The determination at a molecular level of an explanation for the world-wide association with these alleles remains elusive despite major advances in MHC typing.

PCR-RFLP typing methods for DQA1 and DQB1 in conjunction with the analysis of heteroduplex and homoduplex patterns have allowed a simple method for typing all of the major DQA1 and DQB1 alleles. This method has advantages over PCR amplification with sequence-specific primers (PCR-SSP), PCR hybridization with sequence-specific oligonucleotide probes (PCR-SSO) and other PCR-RFLP strategies for typing DQ alleles. The analysis of heteroduplex and homoduplex patterns can be used in conjunction with other PCR typing systems such as PCR-SSP as a confirmatory step with little additional work. In addition, a PCR-RFLP strategy was designed for resolving the DQB1*0602 and DQB1*0603 alleles, which involved the use of a primer containing a base mutation, creating a new restriction site which distinguished the two alleles. These techniques have enabled resolution of the major homozygous and heterozygous combinations of these DQA1 and DQB1 alleles. The PCR-RFLP technique does not require the large number of oligonucleotides that are necessary for both the PCR-SSP and PCR-SSO techniques and is thus both time and cost effective for infrequent or small numbers of samples.