A rare autosomal recessive familial disorder of cholesterol metabolism, characterized by extremely low HDL-cholesterol, reduced total cholesterol, and increased triglyceride levels in serum. Clinical features include the onset before age 20 years of HEPATOMEGALY; SPLENOMEGALY; the deposition of cholesterol in each TONSIL (creating a yellow-orange appearance); and RETINITIS PIGMENTOSA. A sensorimotor or distal sensory POLYNEUROPATHY occurs in approximately 50% of affected individuals. The condition is associated with decreased synthesis and increased catabolism of APOLIPOPROTEIN A-I and APOLIPOPROTEIN A-II, and a defect in cellular signaling and mobilization of lipids. (From Nat Genet 1998 Sep;20(1):96-8; Adams et al., Principles of Neurology, 6th ed, pp1347-8; Menkes, Textbook of Child Neurology, 5th ed, p118)