AN INFLAMMATORY, FAMILIAL, INCLUSION-BODY MYOSITIS WITH AUTOIMMUNE FEATURES AND A PHENOTYPE IDENTICAL TO SPORADIC INCLUSION-BODY MYOSITIS -STUDIES IN 3 FAMILIES

We describe the occurrence of an inflammatory inclusion body myositis in siblings of a single generation in three separate families. The dis ease in this total of seven patients was characterized by selective an d early involvement of forearm and finger flexors, confirmed by MRI, a nd weakness of the quadriceps, triceps and foot extensors. Muscle biop sies in at least two members from each family showed endomysial inflam mation red-rimmed vacuoles, intracellular amyloid deposition and 15-18 -nm tubulofilaments within the vacuolated muscle fibres. Immunocytoche mistry on serial muscle biopsy sections demonstrated an abundance of C D8+ cells invading non-necrotic, MHC-I-expressing muscle fibres. Immun ogenetic studies showed the presence of the DR3 allele (DRB10301/0302 ) in all seven patients. The combination of the clinical, histological , immunopathological and immunogenetic features indicate that these pa tients have a disease identical to sporadic inclusion body myositis (s -IBM). We conclude that the classic inflammatory s-IBM can also occur in families (familial inclusion body myositis), in a pattern analogous to the familial occurrence of other autoimmune neurological diseases such as myasthenia gravis and multiple sclerosis. These observations s trengthen the view that s-IBM behaves like other autoimmune diseases a nd has disease susceptibility linked to the DR3 allele.