X-linked disorder caused bay mutations in TAZ, encoding tafazzin. Characterised by 3-methylglutaconic aciduria associated with DCM, skeletal myopathy (mainly proximal), impaired growth and (cyclic) neutropenia. Other cardiac features are endocardial fibroelastosis, left ventricular non-compaction and HCM. The gene discussed is TAFAZZIN; the disease is Skeletal myopathy.