DNM1L (dynamin 1-like), another GTPase, is required for fission of mitochondria.137 To date, only a single DNM1L has been identified in an infant presenting with both defective mitochondrial and peroxisomal fission.138 The patient presented in the first days of life with severe microcephaly, abnormal brain development, optic atrophy with hyperplasia and lactic acidemia.138. The gene discussed is DNM1L; the disease is optic atrophy.