The ratio of absorbed cholesterol:glucose is elevated in Npc1a^57A first instar larvae relative to wild type.

Mutant larvae show an accumulation of sterol-rich trafficking organelles in the midgut epithelium.

Most homozygotes die as first instar larvae, but some survive to the second larval instar. The mutant larvae live for prolonged periods of time (up to 10 days) in their final larval stage, and appear to die due to a failure to moult into the next larval instar. The long-lived larvae gradually become swollen due to the accumulation of fluid.

48% of homozygotes survive past the second instar stage when the larvae are fed dietary 20-hydroxyecdysone.

Homozygotes fed standard food supplemented with 200ng/ml cholesterol show a dramatic improvement in survival, with some animals surviving as far as the adult stage. These cholesterol-fed animals appear generally normal in morphology, although they often arrest as wandering third instar larvae and fail to form a puparium. The cholesterol-fed animals that do survive to adulthood appear to be behaviourally normal, but show a substantial reduction in life span compared to controls and are male sterile. Heterozygous adults which have been fed on a high cholesterol diet mated to heterozygous adults fed on a standard diet give rise to homozygous offspring which survive to later stages of development than the offspring of heterozygotes fed on a standard diet.