Tangier's Disease
| Tangier disease | |
|---|---|
| Classification and external resources | |
| Specialty | endocrinology |
| ICD-10 | E78.6 |
| ICD-9-CM | 272.5 |
| OMIM | 205400 |
| DiseasesDB | 12901 |
| MeSH | D013631 |
Tangier disease (also known as Familial alpha-lipoprotein deficiency) or Hypoalphalipoproteinemia is a rare inherited disorder characterized by a severe reduction in the amount of high density lipoprotein (HDL), often referred to as "good cholesterol," in the bloodstream.
Individuals that are homozygotes for Tangier's disease develop various cholesterol ester depositions. These are especially visible in the tonsils, as they may appear yellow/orange. The cholesterol esters may also be found in lymph nodes, bone marrow, the liver and spleen.
Due to the cholesterol ester depositions the tonsils may be enlarged. Hepatosplenomegaly (enlarged liver and spleen) is common.
Neuropathy and cardiovascular disease are the most devastating developments caused by Tangier's disease.
Mutations to chromosome 9q31 lead to a defective ABCA1 transporter. These mutations prevent the ABCA1 protein from effectively transporting cholesterol and phospholipids out of cells for pickup by ApoA1 in the bloodstream. This inability to transport cholesterol out of cells leads to a deficiency of high-density lipoproteins in the circulation, which is a risk factor for coronary artery disease. Additionally, the buildup of cholesterol in cells can be toxic, causing cell death or impaired function. These combined factors lead to the signs and symptoms of Tangier disease.
This condition is inherited in an autosomal recessive pattern, meaning that for the phenotype to appear, two copies of the gene must be present in the genotype. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.
High-density lipoproteins are created when a protein in the bloodstream, Apolipoprotein A1 (apoA1), combines with cholesterol and phospholipids. The cholesterol and phospholipids used to form HDL originate from inside cells but are transported out of the cell into the blood via the ABCA1 transporter. People with Tangier disease have defective ABCA1 transporters resulting in a greatly reduced ability to transport cholesterol out of their cells, which leads to an accumulation of cholesterol and phospholipids in many body tissues, which can cause them to increase in size. Reduced blood levels of high-density lipoproteins is sometimes described as hypoalphalipoproteinemia.
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