Cap disease is a rare congenital skeletal muscle disorder characterized by the presence of cap-like structures which are well demarcated and peripherally located under the sarcolemma and show abnormal accumulation of sarcomeric proteins.1,2 Clinical features are early onset of hypotonia and nonprogressive or slowly progressive muscle weakness. Respiratory problems are common. Five dominant mutations have been reported in association with cap disease, all in the β-tropomyosin (βTm) gene ( TPM2 ).3-5 We report a mutation in the αTmslow (γTm) gene ( TPM3 ) in a patient with cap disease, supporting the concept that cap disease is genetically heterogeneous and closely related to nemaline myopathy.4 ### Case report. This 38-year-old woman was first described in 2002 (patient K.D.).2 There was no family history of neuromuscular disorder. She was born at term after an uncomplicated pregnancy, labor, and delivery. She had somewhat delayed motor milestones and at age 5 years mild motor difficulties were noted. She could not keep up with her peers and could not run. At age 18 years, a muscle biopsy was performed and the diagnosis of congenital myopathy (cap disease) was established (figure). Nemaline rods were not identified. EMG showed a myopathic pattern. She was admitted to hospital with pneumonia when she was 21 years old …