Contributor: Gordon K Klintworth
Niemann-Pick disease type IC (adult Niemann-Pick disease) is a variant of Niemann-Pick disease type I that only becomes clinically apparent in adulthood. The metabolic defect  is a deficiency of the lysosomal enzyme sphingomyelinase, but low levels of sphingomyelinase activity are present. Both splenomegaly or hepatomegaly develop, but they are not marked. The disorder results in an opaque perimacular region with minimum optic nerve pallor and only the fibroblasts of the conjunctiva accumulate multivesicular inclusions.