SAR1B

The SAR1B gene provides instructions for making a protein found in enterocytes, which are cells that line the intestine and absorb nutrients. Within enterocytes, the SAR1B protein aids in the transport of molecules called chylomicrons. As food is digested after a meal, chylomicrons are formed to carry fat and cholesterol from the intestine into the bloodstream. Chylomicrons are also necessary for the absorption of certain fat-soluble vitamins, such as vitamin E and vitamin D.

Chylomicrons are made up mostly of various types of fats (lipids); they also contain some proteins, mainly a protein called apolipoprotein B-48 that is produced only in the intestine. Because chylomicrons are made up of lipids and proteins, they are known as lipoproteins. Chylomicrons are released from enterocytes into the bloodstream so the body can use the lipids and fat-soluble vitamins they carry. Sufficient levels of fats, cholesterol, and vitamins are necessary for normal growth and development.

chylomicron retention disease - caused by mutations in the SAR1B gene

More than 10 mutations in the SAR1B gene have been found to cause chylomicron retention disease. Most of these mutations change one protein building block (amino acid) in the SAR1B protein. Other mutations lead to the production of an abnormally small version of the protein that cannot function properly. Mutations disrupt the SAR1B protein's ability to transport chylomicrons within cells, which prevents chylomicron release into the bloodstream. This retention of chylomicrons prevents dietary fats and fat-soluble vitamins from being used by the body, leading to the nutritional and developmental problems seen in people with chylomicron retention disease.