Contribution of a single DQ beta chain residue to multiple sclerosis in French Canadians

Putative disease susceptibility and resistance HLA class II alleles were studied in 78 French Canadian multiple sclerosis (MS) patients and 79 controls by using sequence-specific oligonucleotide probes to analyze in vitro amplified DNA (PCR-SSOP) typing). In this relatively homogeneous ethnic group, MS was positively associated with DRB5*0101, DQB1*0602, and DQA1*0102 and negatively associated with DQB1*0301. The strongest disease association was with DQB1*0602. Complete DQB1 typing of these individuals, plus RFLP DQ beta typing of an additional five patients showed that 98% of patients compared with 73% of controls carry DQB1 alleles encoding leucine at residue 26. In contrast, 16% of patients compared with 38% of controls carry DQB1 alleles encoding tyrosine at the same residue, and 22% of patients versus 44% of controls carry DQB1 alleles encoding glycine at residue 26. The positive disease correlation was confirmed with SSO probes designed to hybridize to codons for amino acids 22-27 of DQB1*0602, 0603, 0604, 0302, 0303 or to codons for amino acids 25-31 of DQB1*0201; all of these alleles encode Leu 26. These findings suggest that DQ beta chain polymorphisms at a single residue contribute to the development of MS in the French Canadian population.