Understanding of the molecular basis of BTHS was advanced when it was determined that the protein encoded by the TAZ gene [7,8] is a monolysocardiolipin (MLCL) transacylase that transfers unsaturated fatty acyl chains from phosphatidyl or phosphoethanolamine to MLCL to produce mature cardiolipin (CL). The gene discussed is TAFAZZIN; the disease is Barth syndrome.