[HLA and familial multiple sclerosis].

Some data suggest an environmental perhaps a viral factor but also of a genetic factor in the etiology of multiple sclerosis. Among the latter is the notably increased risk for a twin when the other twin has the disease, a risk further increased if they are monozygotic. There is also a greater than chance frequency of common HLA haplotypes in 2 affected siblings. The frequency of familial forms of multiple sclerosis is estimated at approximately 6 p. 100. We have studied 14 families of which 12 included 2 members with multiple sclerosis and 2 with 3 affected members. Parental relation between patients was parent to child (7 cases), brother to sister (5 cases), sister to sister including two pairs of twins (4 cases) and cousin to cousin on the mother's side (2 cases). When compared with non-familial multiple sclerosis there were no particular features in clinical disorders or course: 4 forms were progressive, the others evolving by episodes. In 26 patients in whom HLA antigens were determined, the DR2 antigen was present 19 times, the B7 antigen 9 times and the A3 antigen 7 times. In the 8 pairs of siblings with multiple sclerosis, 2 were HLA-identical and 5 semi-identical. One pair had no common haplotype. Grouping of HLA in 22 healthy members allowed 8 genealogic trees to be established. If a gene for susceptibility to multiple sclerosis exists, it is of low penetration, of dominant transmission and of limited frequency. It probably lies close to the region D of chromosome 6, because of the disequilibrium of crossed linking with A3, B7 and DR2 antigens.