Abetalipoproteinemia

Abetalipoproteinemia (ABL), also known as Bassen-Kornzweig syndrome, is a rare inherited metabolic disorder characterized by the inability to properly absorb dietary fats, fat-soluble vitamins, and cholesterol from the intestine. It is caused by mutations in the MTTP gene, which encodes microsomal triglyceride transfer protein, essential for the assembly and secretion of apolipoprotein B-containing lipoproteins (chylomicrons in the intestine and VLDL in the liver). As a result, affected individuals have extremely low or absent levels of low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), and chylomicrons in the blood. The disease typically presents in infancy with failure to thrive, steatorrhea (fatty, foul-smelling stools), and abdominal distension due to fat malabsorption. Over time, deficiency of fat-soluble vitamins (A, D, E, and K) leads to progressive multi-system complications. Vitamin E deficiency is particularly damaging, causing progressive spinocerebellar degeneration (ataxia), peripheral neuropathy, and retinitis pigmentosa that can lead to blindness. A hallmark hematologic finding is acanthocytosis — the presence of abnormally shaped red blood cells with thorny projections — which can contribute to mild hemolytic anemia. Coagulopathy may occur due to vitamin K deficiency. Early diagnosis and treatment are critical to preventing irreversible neurological and ophthalmological damage. The cornerstone of management includes a low-fat diet supplemented with medium-chain triglycerides (which are absorbed directly into the portal circulation without requiring chylomicron formation) and high-dose supplementation of fat-soluble vitamins, particularly vitamin E (often at doses of 100–300 IU/kg/day) and vitamin A. With early and consistent treatment, many of the severe neurological and retinal complications can be significantly delayed or prevented, though lifelong monitoring and supplementation are required.

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