Abetalipoproteinemia: An Inherited Condition of Very Low Cholesterol Levels

Abetalipoproteinemia, also known as Bassen-Kornzweig Syndrome, is an inherited condition that causes dangerously low cholesterol levels. It is characterized by a mutation in the gene for a protein called microsomal triglyceride transfer protein. This protein is very important in the formation of lipids like very low-density lipoproteins (VLDL) and chylomicrons.

Without this protein, your body cannot make the lipoproteins needed to help digest and transport cholesterol and lipids to other areas of the body. Although low cholesterol levels are good for your heart, your body does need some fat and cholesterol for many biological processes. If your body cannot get the lipids it needs, many health complications can arise.

What Are the Symptoms of Abetalipoproteinemia

Abetalipoproteinemia usually appears in infancy. It is an inherited condition that is autosomal recessive, meaning that both parents must have this gene mutation in order to for their child to have this condition.

Babies with this condition may have a variety of gastrointestinal problems because of the difficulty they have in digesting and absorbing fats. These symptoms would include:

• Bloating
• Diarrhea
• Vomiting
• Presence of fatty, pale-colored, foul smelling stools

Besides gastrointestinal symptoms, the infant will display other symptoms of not having a lot of lipids in the blood. The presence of cholesterol and other lipids in the body are vital especially to babies, since it is needed for the development and growth. Other symptoms include:

• Vitamin deficiency – especially of the fat-soluble vitamins A, K, and E. Lipids are important in transporting these vitamins to other areas of the body. If lipids are not present in the blood, these vitamins cannot travel to where they are needed.
• Problems with blood clotting – may be due to the low amounts of vitamin K in the blood. Red blood cells may also appear abnormal.
• Neurological problems – may be due to the low amounts of lipids or fat-soluble vitamins circulating in the blood. These problems include tremors, weakness, difficulty walking, and mental retardation.
• Sensory disorders – could be due to low amounts of lipids or fat-soluble vitamins in the blood. These difficulties improve problems with eyesight and touch sensation.

Because fats consumed by the infant cannot be absorbed, you will also find that amount of lipids circulating though the infant’s blood is minimal.

How is Abetalipoproteinemia Diagnosed?

A lipid panel will be performed to examine the levels of cholesterol and other fats circulating in the blood. This cholesterol test would reveal the following findings:

• Undetectable LDL (low density lipoprotein) levels
• Triglyceride levels less than 20 mg/dL
• Total cholesterol levels less than 40 mg/dL

These levels are extremely low, and apolipoprotein B, which is the protein attached to LDL cholesterol, will be absent in the blood. A biopsy of the intestine may also be taken, which will confirm the absence of the essential protein, microsomal triglyceride transfer protein. A blood smear may also be helpful in confirming the abnormal red blood cells, which is also known as acanthocytosis. These factors, coupled with some of the symptoms that the infant is experiencing, will help to confirm a diagnosis of abetalipoproteinemia.

How is Abetalipoproteinemia Treated?

Vitamin supplementation, especially vitamin E, is extremely important. Vitamin E supplements, with doses ranging between 100 and 300 mg/kg once a day are usually administered. A dietician should be consulted and a special diet for fat supplementation should be implemented. Other fat-soluble vitamins are also usually administered.

_Sources:

Fauci AS, ed. Harrison's Principles of Internal Medicine. 14th ed. New York, NY: McGraw-Hill; 1998.

The Merck Manual of Diagnosis of Therapy, 18th edition. 2006.