Niemann-Pick Disease is defined by the accumulation of which lipid?

Niemann-Pick Disease is characterized by the accumulation of sphingomyelin within lysosomes due to a deficiency of the enzyme sphingomyelinase. This condition leads to the progressive damage of various tissues, most notably the liver, spleen, and brain. The buildup of sphingomyelin is a direct consequence of the inability to break it down effectively, resulting in the pathological features associated with the disease.

In this metabolic disorder, the abnormal storage of sphingomyelin manifests in a variety of clinical symptoms, including hepatosplenomegaly, neurological deficits, and lymphadenopathy. The specific enzyme deficiency and lipid accumulation create a distinctive biochemical and clinical profile that helps in diagnosing Niemann-Pick Disease.

The other lipids mentioned in the options play roles in different lysosomal storage disorders. For instance, galactocerebrosides are associated with Krabbe disease, sulfatides with metachromatic leukodystrophy, and ceramide trihexosides with Fabry disease. Each of these conditions is tied to different enzyme deficiencies and lipid accumulations, which is why only sphingomyelin accurately describes the pathology of Niemann-Pick Disease.