Congenital fiber type disproportion (CFTD) is a relatively rare subtype of congenital myopathy characterized by hypotonia and generalized muscle weakness. Pathologic diagnosis of CFTD is based on the presence of type 1 fiber hypotrophy of at least 12% in the absence of other notable pathological findings, in addition to a clinical presentation typical of congenital myopathies. CFTD is a genetically heterogenous condition with X-linked, autosomal dominant, and autosomal recessive inheritance patterns. Mutations of the ACTA1 and SEPN1 genes have been identified in a small percentage of CFTD cases, and recently mutations in the TPM3 gene were also found to cause CFTD.
