We describe an unique patient presenting with severe leukodystrophy compatible with Pelizaeus-Merzbacher disease and peripheral neuropathy consistent with Charcot-Marie-Tooth disease type 1 in addition to Waardenburg-Hirschsprung syndrome. A novel mutation was identified in her SOX10 gene, which encodes a transcription factor preferentially expressed in the late embryonic glial cell lineage and in mature myelin-forming cells of both the central nervous system and peripheral nervous system, as well as in the early neural crest cells. Heterozygous SOX10 loss-of-function mutations have been reported in patients with Waardenburg-Hirschsprung syndrome and its murine model, Dominant megacolon. However, neither Waardenburg-Hirschsprung syndrome patients nor Dominant megacolon mice have dysmyelinating features, suggesting the question of how SOX10 acts in the glial lineage in vivo. The novel mutation described herein does not disrupt the coding region but extends the peptide and hence is likely to act as a dominant-negative allele. Our findings indicate that dysfunction of SOX10 may lead to deficiency of myelination in the central nervous system and peripheral nervous system as well as hypopigmentation and enteric aganglionosis.