Abetalipoproteinemia, or Bassen-Kornzweig syndrome, is a rare autosomal recessive disorder that interferes with the normal absorption of fat and fat-soluble vitamins from food. It is not to be confused with dysbetalipoproteinemia.
The signs and symptoms of abetalipoproteinemia appear in the first few months of life. They can include failure to gain weight and grow at the expected rate (failure to thrive); diarrhea; abnormal star-shaped red blood cells (acanthocytosis); and fatty, foul-smelling stools (steatorrhea). The stool may contain large chunks of fat and or blood. Other features of this disorder may develop later in childhood and often impair the function of the nervous system. They can include poor muscle coordination, difficulty with balance and movement (ataxia), and progressive degeneration of the light-sensitive layer (retina) at the back of the eye that can progress to near-blindness. Adults in their thirties or forties may have increasing difficulty with balance and walking. Many of the signs and symptoms of abetalipoproteinemia result from a severe vitamin deficiency, especially vitamin E deficiency, which typically results in eye problems with degeneration of the spinocerebellar and dorsal columns tracts.
Often symptoms will arise that indicate the body is not absorbing or making the lipoproteins that it needs. These symptoms usually appear en masse, meaning that they happen all together, all the time. These symptoms come as follows:
There is an absence of apolipoprotein B. On intestinal biopsy, vacuoles containing lipids are seen in enterocytes. Since there is no or little assimilation of chylomicrons, their levels in plasma remains low. This disorder may also result in fat accumulation in the liver (hepatic steatosis). Because the epithelial cells of the bowel lack the ability to place fats into chylomicrons, lipids accumulate at the surface of the cell, crowding the functions that are necessary for proper absorption.
Mutations in the microsomal triglyceride transfer protein (MTTP) gene has been associated with this condition. . (Apolipoprotein B deficiency, a related condition, is associated with deficiencies of apolipoprotein B.)
The MTTP gene provides instructions for making a protein called microsomal triglyceride transfer protein, which is essential for creating beta-lipoproteins. These lipoproteins are both necessary for the absorption of fats, cholesterol, and fat-soluble vitamins from the diet and necessary for the efficient transport of these substances in the bloodstream. Most of the mutations in this gene lead to the production of an abnormally short microsomal triglyceride transfer protein, which prevents the normal creation of beta-lipoproteins in the body. MTTP-associated mutations are inherited in an autosomal recessive pattern, which means both copies of the gene must be faulty to produce the disease.
Treatment normally consists of rigorous dieting, involving mass amounts of vitamin E. Vitamin E helps the body restore and produce lipoproteins, which people with abetalipoprotenimia usually lack. Vitamin E also helps keep skin and eyes healthy, which studies show that many males whom are affected will have vision problems later on in life. Dyspraxia and muscle weakness is usually combated with psysiotherapy, or occupational therapy. Dietary restriction of triglycerides has also been useful.