Chylomicron retention disease; Anderson´s disease - SAR1B gene
Chylomicron retention disease, also known as Anderson's disease, is a hereditary process that affects the normal absorption of fats, cholesterol and certain vitamins from food. The characteristics of the disease mainly affect the gastrointestinal system and the nervous system.
Signs and symptoms related to this process usually begin in childhood or early childhood and include slow growth and weight gain, chronic diarrhea and steatorrhea, hypocholesterolemia, hepatic stenosis and enlarged liver. Other features develop later in childhood and often affect the function of the nervous system. In addition, affected people may develop hyporeflexia and a reduced ability to perceive vibrations. Rarely, affected people have heart abnormalities or amyotrophy.
This process is due to mutations in the SAR1B (secretion associated Ras related GTPase 1B) gene, located on the long arm of chromosome 5 (5q31.1), which encodes a protein that is needed for the transport of chylomicrons. During digestion, chylomicrons form inside the enterocytes that line the small intestine and absorb nutrients. Chylomicrons are needed to absorb fat-soluble vitamins and transport fats and cholesterol from the small intestine into the bloodstream. In other tissues, such as the heart and other muscles, the SAR1B protein is probably involved in the transport of calcium inside the cells.
In other tissues, such as the heart and other muscles, the SAR1B protein is probably involved in the transport of calcium inside the cells.
More than 20 mutations in the SAR1B gene have been described in individuals with chylomicron retention disease. Most of the identified mutations change a single amino acid in the SAR1B protein. Other mutations result in the synthesis of an abnormally small version of the protein that cannot function properly. All the mutations described inhibit the ability of the SAR1B protein to transport immature chylomicrons of the endoplasmic reticulum to the Golgi apparatus. As a consequence, mature chylomicrons are not released into the bloodstream. The deteriorated transport of chylomicrons causes malabsorption of dietary fats and fat-soluble vitamins, which leads to nutritional and developmental problems.
This disease is inherited with an autosomal recessive pattern, which means that both copies of the gene in each cell must have the mutations for the alteration to be expressed. The parents of an individual with an autosomal recessive disease have a copy of the mutated gene, but usually do not show signs and symptoms of the disease.
Tests performed in IVAMI: in IVAMI we perform the detection of mutations associated with chylomicron retention disease, by complete PCR amplification of the exons of the SAR1B gene, and their subsequent sequencing.
Recommended samples: blood drawn with EDTA for separation of blood leukocytes, or card impregnated with dried blood sample (IVAMI can mail the card to deposit the blood sample).