<unk>  is a group of severe inherited metabolic disorders, in which sphingomyelin accumulates in lysosomes in cells (the lysosomes normally degrade material that comes from out of cells). These disorders involve the dysfunctional metabolism of sphingolipids, which are fats found in cell membranes (so it is a kind of sphingolipidosis, which is included in the larger family of lysosomal storage diseases).
Niemann–Pick disease
Wilson's disease
Wilson–Mikity syndrome
Haemochromatosis type 3
Mowat–Wilson syndrome
Hemochromatosis type 4
Gaucher's disease
Maroteaux–Lamy syndrome