Description, Causes and Risk Factors:
High-density lipoprotein deficiency; a heritable disorder of lipid metabolism characterized by almost complete absence from plasma of high density lipoproteins, and by storage of cholesterol esters in foam cells, tonsillar enlargement, an orange or yellow-gray color of the pharyngeal and rectal mucosa, hepatosplenomegaly, lymph node enlargement, corneal opacity, and peripheral neuropathy; autosomal recessive inheritance.
Tangier disease is an inherited disorder characterized by significantly reduced levels of high-density lipoprotein (HDL) in the blood. HDL transports cholesterol and certain fats called phospholipids from the body's tissues to the liver, where they are removed from the blood. HDL is often referred to as "good cholesterol" because high levels of this substance reduce the chances of developing heart and blood vessel (cardiovascular) disease. Because people with Tangier disease have very low levels of HDL, they have a moderately increased risk of cardiovascular disease.
Tangier disease is caused by mutations in the 'ATP-Binding Cassette transporter A1' (ABCA1) gene, which encodes the membrane transporter ABCA1. Mutations to chromosome 9q31 lead to a defective ABCA1 transporter. This gene provides instructions for making a protein that releases cholesterol and phospholipids from cells. These substances are used to make HDL, which transports them to the liver.
Mutations in the ABCA1 gene prevent the release of cholesterol and phospholipids from cells. As a result, these substances accumulate within cells, causing certain body tissues to enlarge and the tonsils to acquire a yellowish-orange color. A buildup of cholesterol can be toxic to cells, leading to impaired cell function or cell death. In addition, the inability to transport cholesterol and phospholipids out of cells results in very low HDL levels, which increases the risk of cardiovascular disease.
This condition is inherited in an autosomal recessive pattern. 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.
Documentation shows that as of 1988, 27 cases of Tangier disease had been reported and in 1992 the reported cases were still fewer than 50 persons Worldwide. The majority of the cases tend to localize in one single area of the U.S., Tangier island, Virginia.
Enlarged tonsils, an orange or yellow-gray color.
Type II diabetes.
A lipid panel will be performed to examine the levels of cholesterol circulating in the blood. A cholesterol test would typically reveal the following findings:
HDL cholesterol between 5 and 30 mg/dL in heterozygous individuals.
Low total cholesterol levels (ranging between 38 and 112 mg/dL).
Normal or elevated triglycerides (ranging between 116 and 332 mg/dL).
HDL cholesterol < 5 mg/dL in homozygous individuals.
Levels of apolipoprotein A may also be low to nonexistent. Based upon an abnormal lipid panel, as well as the symptoms experienced by the individual, a diagnosis of Tangier disease will be made.
To date there is no specific treatment for Tangier disease. Old and recently designed drugs, known to increase HDL levels, have been shown to be ineffective in Tangier patients. The possible and more realistic therapeutic strategy should be designed to obtain a selective increase of mature HDL concentration to restore cholesterol efflux. Recently designed drugs like the cholesteryl ester transfer protein (CETP) inhibitors dalcetrapib and anacetrapib and reconstituted forms of HDL could be considered until the development of Gene therapy.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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