Mutation in the human SC4MOL gene causes microencephaly...much more.

Mutations in the human SC4MOL gene encoding a methyl sterol oxidase cause psoriasiform dermatitis,  and microcephaly, and developmental delay. Defects in Cholesterol synthesis results in a variety of symptons.This article says that Cholesterol is a key component of cell membrane and lipids rafts and the precursor of asteroids, bali acids, and vitamin D, but some alterations on its synthesis unleash growth delay abnormal morphogenecis and spychomothor disabilities.
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