“…24 Twelve single peroxisomal enzyme disorders and a peroxisomal-microsomal disorder that appear secondary to a defect in a microsomal enzyme have also been identified, including a defect in 7-dehydrocholesterol-␦-7-reductase for Smith-LemliOpitz syndrome (SLOS), a defect in phytanoyl-coenzyme A hydroxylase (PAHX gene) for some cases of Refsum disease (RD), a defect in catalase for acatalasemia, a defect in the ATP-binding cassette transporter adrenoleukodystrophy protein for X-linked adrenoleukodystrophy, and a probable defect in microsomal 3-hydroysteroid-⌬8,⌬7-isomerase (⌬8,⌬7-sterol-isomerase) [patients with increased levels of 8-dehydrocholesterol and cholest-8(9)-en-3-ol] for some cases of XCDP2 and CHILD syndrome. 14,16,22,23 The phenotypic expression of the known PEX disorders and enzymatic defects appear to vary with the nature of the mutation. 22 In general, milder phenotypes are associated with mutations that do not abolish function completely or are associated with mosaicism.…”