Anderson’s disease is also known as chylomicron retention disease which is a rare hereditary disease. It is an autosomal recessive disease characterized by low plasma lipid and low lipid-soluble vitamins (such as vitamin E and vitamin D). After the digestion of food, lipids, and lipid soluble vitamins are absorbed in the human body with the help of chylomicrons. A lack of chylomicron can interrupt the transport of molecules from intestine to the bloodstream resulting in malabsorption. Subjects with these disorders show different clinical manifestations which were initially described by Anderson and colleagues, hence it was called as “Anderson’s disease”. Genotyping has revealed that Anderson’s and chylomicron retention disease are in fact the same disease.
What is The Major Cause of Anderson’s Disease?
Anderson’ disease and chylomicron retention disease is the same disease which has been proved genotypically. The disease is caused by the mutation in the gene SAR1B (formerly SARA2), which encodes the SAR1B protein. Mutation results in the defect in chylomicron secretion, a transport protein. A lack of transport of dietary lipids from the intestine to the bloodstream causes malabsorption, which is the main characteristic of the disorder. Malabsorption syndrome with steatorrhea and growth retardation is usually seen in chylomicron retention disease.
Structure of Chylomicrons
Chylomicrons are the transport lipids that primarily involved in carrying of dietary lipids such as triglyceride-rich lipoproteins which are secreted generally from the enterocytes. It is produced in the endoplasmic reticulum of the absorptive cells (enterocytes) of the small intestine. These large lipoproteins range from 700 to 6000 Å size which contains a single molecule of apolipoprotein (apo) B-48. It is a sole molecule, essential for chylomicron structure organization. Apo B-100 is different which is found within very-low-density lipoproteins (VLDL) secreted by the liver and in low-density lipoprotein (LDL), a catabolic product of VLDL.
Impact of The Disorder
It is rarely diagnosed in infants presenting with failure to thrive and chronic diarrhea. Malabsorption syndrome with steatorrhea and growth retardation is usually seen in chylomicron retention disease. Steatorrhea is the excretion of abnormal quantities of fat with the feces owing to reduced absorption of fat by the intestine. If not treated, it can cause subsequent neurological impairment. Neurological signs, although variable, consisting most frequently of a loss of reflexes. There is little acanthocytosis (red blood cells appear like thorny), hypocholesterolemia, hypotriglyceridemia, lipid malabsorption, diarrhea, retinitis pigmentosa, and spinocerebellar degeneration are negative of chylomicron retention disease.
Chylomicron retention disease is usually caused by gene mutations, particularly in the SAR1B gene. The SAR1B gene has instruction for Sar1b protein, which is involved in chylomicron transport from the endoplasmic reticulum to the Golgi apparatus. In fact, Sar1-GTP forms a coating protein complex with two heterodimers Sec23/24 and Sec 13/31, which initiates budding and captures cargo to eject vesicles from the endoplasmic reticulum to the Golgi apparatus.
SAR1B gene mutations impair the release of chylomicrons into the bloodstream. A lack of chylomicrons in the blood 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.
Why Is It Referred To As Autosomal Recessive Pattern?
Chylomicron retention disease is a good example for inherited autosomal recessive pattern. The parents of an individual with an autosomal recessive condition typically do not show any signs or symptoms of the condition. To have an autosomal recessive disorder, entities must inherit two mutated genes, one from each parent. These conditions are commonly passed on by two carriers. Their health is not often pretentious, but they have one mutated gene (recessive gene) and one normal gene (dominant gene) for the condition. With each pregnancy, two carriers have a 25 percent chance of having an unaffected child with two normal genes, a 50 percent chance of having an unaffected child who is also a carrier and a 25 percent chance of having an affected child with two recessive genes.