Abetalipoproteinemia

Abetalipoproteinemia is a rare inherited disorder caused by defective microsomal triglyceride transfer protein, preventing formation of apolipoprotein B-containing lipoproteins. Fat malabsorption and deficiencies of fat-soluble vitamins can lead to progressive neurologic and retinal damage.

Microsomal triglyceride transfer protein: A protein that transfers lipids to apolipoprotein B during assembly of lipoproteins. Mutations in its gene disrupt the lipid-loading step that abetalipoproteinemia requires.
Fat malabsorption: Impaired digestion or absorption of dietary fats in the intestine. It causes steatorrhea, poor growth, and loss of fat-soluble vitamins in the disorder.
Familial hypobetalipoproteinemia: An inherited condition, usually caused by APOB variants, that lowers blood apoB and LDL cholesterol. It can resemble abetalipoproteinemia but often has milder symptoms and detectable apoB-containing particles.
Steatorrhea: Excess fat in stool, often producing bulky, pale, foul-smelling bowel movements. It is a direct consequence of unabsorbed dietary fat in abetalipoproteinemia.
Autosomal recessive inheritance: Inheritance in which disease usually occurs when a person receives a pathogenic gene variant from each parent. Abetalipoproteinemia usually requires pathogenic variants in both copies of MTTP.
MTTP: The gene encoding microsomal triglyceride transfer protein. Disease-causing variants in MTTP are the usual genetic cause of abetalipoproteinemia.
Acanthocytosis: The presence of red blood cells with irregular, thorn-like projections. Acanthocytes on a blood smear are a classic clue to abetalipoproteinemia.
Chylomicron retention disease: An inherited disorder in which enterocytes cannot efficiently secrete chylomicrons because of SAR1B variants. It also causes childhood fat malabsorption, but its defect is distinct from MTTP-related disease.
Spinocerebellar ataxia: A group of disorders involving progressive impairment of coordination from cerebellar or related pathway damage. Vitamin E-related nervous-system injury can produce an ataxic pattern in affected people.
Lipoprotein: A particle made of lipids and proteins that transports water-insoluble fats through blood and lymph. The disorder is defined by failure to assemble a major family of these transport particles.

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MalabsorptionBroader topic: Impaired lipid transport causes fat malabsorption and deficiencies of fat-soluble vitamins.