Mutations in the mitochondrial pyrroline-5-carboxylate reductase 1 protein result in extensive fragmentation of the mitochondrial network, which is the genetic basis of autosomal recessive cutis laxa type IIB (ARCL2B), a progeroid skin syndrome characterized by wrinkled and sagging skin102. The gene discussed is PYCR1; the disease is autosomal recessive cutis laxa type 2B.