Phenotypic Divergence in Siblings with the Same Genotype: Diffuse Dermal Melanocytosis in Infantile-Onset Galactosialidosis

This report highlights diffuse dermal melanocytosis as a possible novel cutaneous marker of GS, potentially aiding early recognition. It also illustrates intrafamilial phenotypic variability despite identical genotypes. Our findings underscore the importance of dermatologic clues in the diagnostic workup of lysosomal storage disorders and advocate for family-based genetic screening to identify asymptomatic or mildly affected individuals.