Abetalipoproteinemia

Definition & Etymology

Abetalipoproteinemia is a rare, autosomal recessive inherited disorder of lipoprotein metabolism characterized by the virtual absence of apolipoprotein B (apoB) containing lipoproteins in the plasma. This defect leads to an inability to form and secrete chylomicrons and very-low-density lipoproteins (VLDL) from enterocytes and hepatocytes, respectively. (From Greek a-, “without”; beta-lipoprotein; and haima, “blood,” signifying the absence of beta-lipoproteins in the blood).

Clinical Significance

The clinical significance of abetalipoproteinemia stems from the severe malabsorption of dietary fats and fat-soluble vitamins (A, D, E, and K). This malabsorption manifests in infancy with steatorrhea, diarrhea, and failure to thrive. The most debilitating consequences arise from severe, progressive vitamin E deficiency, which causes neurological dysfunction, including spinocerebellar ataxia, peripheral neuropathy, and muscle weakness. Vitamin A deficiency leads to atypical retinitis pigmentosa and potential night blindness. Hematologically, the condition is characterized by acanthocytosis (also known as “spur cells”), which are spiculated red blood cells resulting from abnormal lipid composition of the cell membrane. Diagnosis is confirmed by the absence of apoB, VLDL, and LDL in plasma, with extremely low levels of cholesterol and triglycerides.

Related Conditions

Abetalipoproteinemia, also known as Bassen-Kornzweig syndrome, is caused by mutations in the microsomal triglyceride transfer protein (MTTP) gene. This gene is crucial for assembling apoB-containing lipoproteins. The primary differential diagnosis is familial hypobetalipoproteinemia (FHBL), a related but typically less severe disorder where some apoB is produced. Conditions associated with its long-term complications include progressive spinocerebellar degeneration, myopathy, and pigmentary retinopathy. Management focuses on a low-fat diet supplemented with very high doses of fat-soluble vitamins, particularly vitamin E, to mitigate neurological damage.

Key Takeaways

• It is a rare genetic disorder caused by MTTP gene mutations, preventing the synthesis of apolipoprotein B.
• The core pathophysiology is the inability to form chylomicrons and VLDL, leading to severe fat malabsorption and profound deficiency of fat-soluble vitamins, especially vitamin E.
• Hallmark clinical features include steatorrhea in infancy, progressive neurological deficits (ataxia, neuropathy), retinitis pigmentosa, and acanthocytosis on a blood smear.

Note: This content is for informational purposes only and does not substitute for professional medical advice. Always consult your doctor for diagnosis and treatment.