Abetalipoproteinemia (also known as Bassen-Kornzweig syndrome) is a rare autosomal recessive inherited disorder affecting the lipid metabolism and is characterized by a severely decreased levels of apolipoprotein B. Growth retardation can already occur in infancy due to a malabsorption syndrome. Due to the decreased absorption of fat-soluble vitamins (especially vitamin E and A), patients will later present with ataxia, a loss of deep tendon reflexes, retinal pigmentation disorders, and acanthocytosis. In addition to a decrease in total cholesterol to less than 50 mg/dl and a decrease in Apo B-containing lipoproteins, only low levels of immunoreactive Apo B are found in the serum.
The molecular genetic cause of the disease are pathogenic variants in the gene encoding Microsomal Triglyceride Transfer Protein (MTTP). MTTP is a multifunctional heterodimeric protein involved in the assembly and secretion of Apo B-containing lipoproteins (mainly LDL and VLDL) in the liver. Loss of function of MTTP leads to increased degradation of Apo B in the liver. Since the synthesis and secretion of Apo B-containing chylomicrons in the intestine is also impaired, malabsorption of fat-soluble vitamins occurs. Early dietary measures and supplementation with vitamins A and E can prevent the progression of neurological symptoms and retinopathy.
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