HLA family studies and multiple sclerosis: A common gene, dominantly expressed.

All available Australian families with more than one member suffering multiple sclerosis (MS) were HLA typed. As with all other individual published studies, convincing evidence for linkage between the HLA system and disease was not obtained. An analysis of 100 published affected sib-pairs and 17 cousin-pairs, however, established the existence of an HLA-linked disease susceptibility gene for MS, which is likely to be dominantly expressed. Dominance was also supported by the finding of only three HLA-DR2 (Dw2) homozygous individuals out of 60 unrelated patients which enabled rejection of a recessive gene hypothesis (p less than 0.02). Analysis of the sib-pair data strongly suggested that this MS gene is not rare in the normal population and may be as common as DR2.