,21,22 MtSSB (SSBP1, encoded by SSBP1) is an indispensable component of the mtDNA replication machinery and, as demonstrated previously, defects in SSBP1 may lead to an isolated or syndromic phenotype characterized by optic atrophy and retinal dystrophy.1 The gene discussed is SSBP1; the disease is optic atrophy.