Four genetically different types have been described so far: an autosomal dominant form caused by mutations in the DNM2 gene [2]; an autosomal dominant or recessive form related to mutations in the BIN1 gene [3], [4]; an autosomal dominant or recessive form caused by mutations in the RYR1 gene [5]; and an X-linked myotubular myopathy (XLMTM) due to mutations in the MTM1 gene [6]. The gene discussed is MTM1; the disease is X-linked myotubular myopathy.