Wednesday, November 1, 2017

Introduction To Abetalipoprotienemia



This rare autosomal recessive disorder of lipoprotein metabolism is associated with severe fat malabsorption from birth.

Clinical Features:

Children fail to thrive during the 1st year of life, and their stools are pale, foul smelling, and bulky. The abdomen is distended, and deep tendon reflexes are absent as a result of peripheral neuropathy, which is secondary to vitamin E deficiency. Intellectual development tends to be slow. After 10 yr of age, intestinal symptoms are less severe, ataxia develops, and there is a loss of position and vibration sensation with the onset of intention tremors. These last symptoms reflect involvement of the posterior columns, cerebellum, and basal ganglia. In adolescence, atypical retinitis pigmentosa develops.

Diagnosis:

Diagnosis rests on finding acanthocytes in the peripheral blood and extremely low plasma levels of cholesterol (<50 mg/dL); triglycerides are very low (<20 mg/dL). Chylomicrons and very low density lipoproteins are not detectable, and the low-density lipoprotein (LDL) fraction is virtually absent from the circulation; marked triglyceride accumulation in villus enterocytes occurs in the fasting duodenal mucosa. Steatorrhea occurs in younger patients, but other processes of assimilation are intact. Rickets may be an unusual initial manifestation of abetalipoproteinemia and hypobetalipoproteinemia. Rickets is caused by steatorrhea-induced calcium losses. Patients have mutations of the microsomal triglyceride transfer protein (MTP) gene, resulting in absence of MTP function in the small bowel. This protein is required for normal assembly and secretion of very low density lipoproteins and chylomicrons.

Treatment:

Specific treatment is not available. Large supplements of the fat-soluble vitamins A, D, E, and K should be given. Vitamin E (100–200 mg/kg/24 hr) and vitamin A (10,000–25,000 IU/day) may arrest the neurologic and retinal degeneration. Limiting long-chain fat intake can alleviate intestinal symptoms; medium-chain triglycerides can be used to supplement the fat intake.

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