The spectrum of familial inclusion body myopathies in 13 families and a description of a quadriceps-sparing phenotype in non-Iranian Jews

Abstract

The frequency, patterns of inheritance and clinical phenotypes of inherited myopathies with histologic features of rimmed vacuoles, tubulofilamentous inclusions and absence of inflammation (familial and hereditary inclusion body myopathy [f-IBM]) are poorly defined. Quadriceps sparing is a characteristic of f-IBM seen in the Iranian Jewish population. Among 101 patients with the feature of a red-rimmed vacuolar myopathy, characterized as inclusion body myopathy, seen during the last 4 years, we identified 13 families with f-IBM (12.8% frequency when one member per family was considered). Five families had an autosomal dominant and eight had an autosomal recessive form of inheritance. Among the latter group, five patients with early-onset disease (two Caucasian Americans, an Asian Indian, and two unrelated Iranian Jews) had the distinct feature of quadriceps sparing, which was confirmed by MRI of the thighs. Their disease began with weakness and strophy of the foot extensors, forearm flexors, and first dorsal interossei muscles and progressed to the forearm flexors, girdle, and axial muscles, but spared the quadriceps. Serum CK was normal. Muscle biopsies showed rimmed vacuoles, small fibers in groups, amyloid deposition (in one patient), tubulofilaments, and no inflammation. Immunocytochemistry did not reveal abnormalities of various membrane or cytoskeletal proteins. Major histocompatibility complex (MHC) class I antigen was expressed only in a few degenerating fibers invaded by macrophages. T-cell infiltrates were not present. We conclude that in a large referral population, dominant and recessive hereditary and familial forms of IBM are not rare. Quadriceps-sparing myopathy appears to be a clinically distinct, autosomal recessive, nonimmune, distal vacuolar myopathy that is not limited to Iranian-Jewish ethnic groups.