Hypocomplementaemic and normocomplementaemic multiple sclerosis. Genetic determinism and association with specific HLA determinants (B18 and B7).

Seventy-five patients with multiple sclerosis (MS) were treated for complement components C3, after factor B, C4, and tested for HLA-A and B-determinants. Levels of IgG, IgA, IgD, IgE and titres of measles antibodies were also determined. Correlations between these immunological values and HLA determinants could be obtained in siblings, parents and/or children of the patients in 13 families. B18 frequency is strongly associated with the hypocomplementaemic group (x2 = 8.9). An association of B18 with the population of cases with low B levels is also found (x2 = 8.02). Familial data showed that low C3 and/or low B levels are associated with the HLA haplotyes, especially with those containing B18. A "complement abnormality susceptibility gene", linked to the HLA genes, is postulated. Infections are significantly more frequent in families of hypocomplementaemic MS, the existence of a genetic immunodeficiency affecting the synthesis of the complement components, linked to the HLA determinants. In 1 case studied in this article, a heterozygous C2 deficiency linked to HLA-A10, B18 was found and might confirm this hypothesis.