Phospholipid and Sphingolipid Metabolism

A 3-year-old girl from Tamil Nadu presents with progressive neurological deterioration over 6 months. Parents report developmental regression, loss of previously acquired milestones, and recurrent seizures. On examination, she has hepatosplenomegaly, cherry-red spot on the macula, and a positive Babinski sign bilaterally. Serum acid sphingomyelinase activity is markedly reduced. Which of the following metabolic pathways is primarily disrupted in this patient?

A 2-year-old boy from Kerala is brought to the pediatric clinic with a history of progressive irritability, feeding difficulties, and developmental delay over the past 8 months. On examination, he has generalized hypotonia, brisk deep tendon reflexes, and a positive Babinski sign. Ophthalmologic examination reveals a cherry-red spot. MRI brain shows white matter changes. Enzyme assay shows deficiency of galactocerebrosidase. Which of the following best describes the primary biochemical defect in this patient?

Niemann–Pick disease type C is characterized by impaired intracellular cholesterol trafficking. Which sphingolipid accumulates as a secondary consequence in this lysosomal storage disorder?

Which enzyme catalyzes the first committed step in sphingolipid synthesis, condensing palmitoyl-CoA with serine?