Congenital myopathy with nemaline rods and cap structures caused by a mutation in the β-tropomyosin gene (TPM2)

Objective: To describe the clinical, morphologic, and genetic findings in a family in which one woman had nemaline myopathy, whereas her daughter showed features of cap disease. Patients: A 66-year-old woman and her 35-year-old daughter had congenital, slowly progressive muscle weakness. They had weakness in both proximal and distal muscles and facial diplegia with bilateral ptosis, a long narrow face, a high arched palate, and micrognathia. Results: Muscle biopsy specimens in the mother at age 57 years had shown nemaline myopathy, whereas a biopsy specimen at age 32 years had demonstrated no rods. Muscle biopsy specimens in the daughter at age 26 years had shown features of cap disease and no apparent nemaline rods. A missense mutation, Glu41Lys, in the beta-tropomyosin gene TPM2 was identified in both patients but was absent in their healthy relatives. Conclusions: The results indicate that mutations in TPM2 may cause nemaline myopathy as well as cap disease with a dominant mode of inheritance. These disorders may thus be phenotypic variants of the same genetic defect.