Cholesterol and Steroid Hormone Metabolism in Abetalipoproteinemia
Phenotypic abetalipoproteinemia (ABL) may occur on the basis of two genotypically distinct disorders in which affected patients are homozygotes. The classic form of ABL is inherited as an autosomal recessive trait and obligate heterozygote parents have normal concentrations of plasma cholesterol. In contrast, homozygous hypoabetalipoprotein- emia (HHBL) is transmitted by an autosomal dominant mode of inheritance and heterozygotes have reduced levels of total and LDL cholesterol. The biochemical and clinical features of ABL and HHBL are similar and both disorders are characterised by a total absence of all apoprotein B containing lipoproteins from plasma hypocholesterolemia (plasma cholesterol 25–30 mg/dl), acanthocytes and fat malabsorption with steatorrhea. These features are present from birth whereas in untreated patients the development of progressive neurological symptoms and pigmentary retinal degeneration develop insidiously and first become clinically evident in childhood. The present report aims to briefly review three areas: 1) What is the basis for the acquired neurological changes in ABL? 2) Does an absence of plasma LDL result in increased rates of cellular cholesterol synthesis (such as occurs in vitro when cultured cells are grown in LDL depleted media)? and 3) Is steroid hormone production impaired in patients with phenotypic ABL?
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