Molecular genetics of systemic sclerosis.
Much recent work has focused on associations of progressive systemic sclerosis with genetic factors, particularly those of the major histocompatibility complex. Increased frequencies of a variety of major histocompatibility complex genes have been inconsistent and variable from center to center. Progressive systemic sclerosis, however, is a clinically and serologically heterogeneous disease, with autoantibody subsets that occur in differing frequencies in different ethnic groups, and previous variability in the major histocompatibility complex associations may reflect ethnic differences between the groups studied. Recent data suggest that progressive systemic sclerosis is a composite disease of HLA class II-associated autoantibody responses. Moreover, amino acid residues at specific positions in HLA class II molecules have been implicated in promoting these responses, especially in HLA-DQ beta outermost domains. The role of other genetic factors is less well defined and needs further study.