MTTP

The MTTP gene provides instructions for making a protein called microsomal triglyceride transfer protein. The microsomal triglyceride transfer protein helps produce beta-lipoproteins, which are molecules that consist of proteins combined with cholesterol and particular types of fats called phospholipids and triglycerides. These beta-lipoproteins contain the protein apolipoprotein B, which is critical for the creation of molecules called chylomicrons. Chylomicrons are formed when dietary fats and cholesterol are absorbed from the intestines. Chylomicrons are also necessary for the absorption of certain fat-soluble vitamins, especially vitamins E, A, and sometimes K.

Other beta-lipoproteins containing apolipoprotein B, particularly low-density lipoproteins (LDL) and very low-density lipoproteins (VLDL), are created by microsomal triglyceride transfer protein in the liver. These lipoproteins transport fats, cholesterol, and fat-soluble vitamins throughout the body in the bloodstream. Sufficient levels of fats, cholesterol, and vitamins are necessary for normal growth, development, and maintenance of the body's cells and tissues, particularly nerve cells and tissues in the eye.

abetalipoproteinemia - caused by mutations in the MTTP gene

More than 30 mutations that cause abetalipoproteinemia have been identified in the MTTP gene. One particular mutation is more common in people of Ashkenazi (eastern and central European) Jewish descent; this mutation replaces the protein building block (amino acid) glycine with a stop signal at position 865 (written as Gly865X or G865X). As a result of this amino acid change, an abnormally small, nonfunctional version of the protein is made. Similarly, many other mutations that cause abetalipoproteinemia produce abnormally short microsomal triglyceride transfer proteins. A shortened protein is unable to produce beta-lipoproteins, resulting in a severe deficiency of chylomicrons, low-density lipoproteins, and very low-density lipoproteins. The absence of these lipoproteins prevents dietary fats and fat-soluble vitamins from being absorbed and carried to the rest of the body, leading to the nutritional and neurological problems seen in people with abetalipoproteinemia.