P.074 Clinical features of a family with distal myopathy and rimmed vacuoles due to a digenic interaction

Abstract

Background: The interaction between mutations in two or more genes is increasingly recognised as an important contributor to the phenotypic variability in genetic disorders. Co-occurrence of variants in SQSTM1 and TIA1 is reported as a cause of myopathy in 3 prior cases, but limited clinical data were presented. We present detailed clinical features of a family with two siblings having a distal myopathy with rimmed vacuoles (DMRV), and genetic variants in SQSTM1 and TIA1. Methods: Clinicopathologic study of a family with DMRV to describe clinical features, laboratory and neurophysiology studies, neuroimaging, and genetic sequencing. Results: Two siblings with variants in SQSTM1 and TIA1 developed myopathy in their early 60’s, with early involvement of ankle dorsiflexors and finger extensors. A decade after onset, patients remain ambulatory and have not developed cardiac or respiratory complications. MRI of the legs showed selective involvement of adductor magnus, vastus lateralis, and in lower legs the anterior compartment and medial gastrocnemius. Muscle pathology demonstrated rimmed vacuoles, disrupted myofibrillar architecture, and mislocalised TDP43. Two unaffected family members had one genetic variant but not both. Conclusions: We describe a fourth family with co-occurrence of TIA1 and SQSTM1 genetic variants and describe their detailed phenotype. Future study should address the mechanism of the interaction between these two variants.