A new lipid storage myopathy observed in individuals with the Ruvalcaba-Myhre-Smith syndrome.

Four patients with the Ruvalcaba-Myhre-Smith syndrome (primary macrocephaly with associated anomalies including pigmented macules on the penis in affected males, hamartomatous intestinal polyps, and lipomas) had evidence of delayed psychomotor development and/or hypotonia in childhood. Electromyography in 3 patients showed evidence of a myopathic process. Muscle biopsy in all four demonstrated a lipid storage myopathy with increased numbers of neutral lipid droplets--predominatly in type 1 fibers. The type 2 fibers were consistently smaller than expected. Electron microscopy was unremarkable except for evidence of lipid accumulation. Muscle carnitine and carnitine palmityl transferase levels were normal in one patient. This appears to be a previously unreported type of lipid storage myopathy characteristic of the Ruvalcaba-Myhre-Smith syndrome, a probable autosomal dominant trait.