What is the connection among the following three medical conditions: N
iemann-Pick type C disease (a cause of mental retardation and early de
ath), systemic lipidosis (in which an obscure side effect of numerous
drugs transforms lysosomes into lamellar bodies), and holoprosencephal
y (a catastrophe in embryonic development)? Recent evidence suggests t
hat the pathogenesis in each case involves impaired sensing of cellula
r cholesterol.