Mixed connective tissue disease in siblings.

Mixed connective tissue disease (MCTD) was diagnosed in a brother and sister, and 18 additional family members spanning three generations were studied to detect evidence of autoimmune disease. Symptoms or signs of MCTD without complete expression of the disease were found in 8 relatives of the original cases. Antibodies to ribonucleoprotein and high-titer antinuclear antibodies were found only in the affected siblings. Tests for rheumatoid factor were positive in 9 of 17 relatives of the patients; the titers ranged from 1:160 to 1:2560. The brother and sister with MCTD had an identical HLA genotype--11,12/2,12. The same genotype was inherited by 3 of their siblings, who had impressive rheumatic complaints. This report emphasizes the association between inflammatory connective tissue disease and a specific HLA type within a single kindred.