Nemaline myopathy type 6: clinical and myopathological features.

Nemaline myopathy (NEM) is one of the most common congenital myopathies. A unique subtype, NEM6, maps to chromosome 15q21-q23 in two pedigrees, but the causative gene has not been determined. We conducted clinical examination and myopathological studies in a new NEM family. Genotyping and gene screening were accomplished by searching known and 18 new candidate genes. The disease started in childhood by affecting proximal and distal muscles and causing slowness of movements. Muscle biopsies showed numerous nemaline rods and core-like formations. Suggestive linkage to chromosome 15q22-q23 was established. Genes known to be mutated in NEM or core-rod myopathy were screened and excluded. No pathogenic mutations were identified in other candidate genes. The disease in this Spanish family was classified as NEM6. It is phenotypically similar and probably allelic to the two previously reported NEM6 pedigrees. Further studies of these families will lead to the identification of the NEM6 gene.