In the zebrafish, we observed mtmr5 expression restricted to the CNS from 1 to 3 dpf, and the onset of microcephaly phenotype in >10 dpf mtmr5-KO zebrafish larvae, supporting the expanded CNS phenotype in CMT4B3 patients, and a novel role of MTMR5 in CNS development. The gene discussed is SBF1; the disease is microcephaly.