Extensive and Progressing Congenital Dermal Melanocytosis Leading to Diagnosis of GM1 Gangliosidosis.

Congenital dermal melanocytosis (CDM) is a birthmark composed of macular blue-grey hyperpigmentation commonly observed in the lumbosacral region of infants. Generally resolving by childhood, it is traditionally considered a benign condition, but it may be a sign of underlying lysosomal storage disease. We report a case of biopsy-confirmed CDM in a 2-month-old girl of Brazilian descent later diagnosed with infantile GM1 gangliosidosis.