What else is it called?
- A-alphalipoprotein Neuropathy
- Alpha High-Density Lipoprotein Deficiency Disease
- Cholesterol thesaurismosis
- Familial High-Density Lipoprotein Deficiency Disease
- Familial Hypoalphalipoproteinemia
- HDL Lipoprotein Deficiency Disease
- Lipoprotein Deficiency Disease, HDL, Familial
- Tangier Disease Neuropathy
- Tangier Hereditary Neuropathy
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What causes it?
Mutations in the ABCA1 gene causes Tangier disease. 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 colour. A build-up 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.
How common is it?
Tangier disease is a rare disorder with approximately 100 cases identified worldwide. More cases are likely undiagnosed. Due these low numbers it is difficult to state whether this condition is more common with males or females or with specific populations.
What are the signs and symptoms?
Symptoms for this condition progressively build up over time, whilst they may no be present in childhood, they are likely to present as your child reaches infancy. Biochemical levels of high levels of fat molecules may be present in your child’s body from birth. Other symptoms may include:
- Mild hypertriglyceridemia
- Enlarged, orange-coloured tonsils
Affected individuals often develop atherosclerosis due to the high levels of fat building up with the tissue. Other features of this condition may include an enlarged spleen, type 2 diabetes and an enlarged liver.
How is it diagnosed?
Additional signs and symptoms of Tangier disease include a slightly elevated amount of fat in the blood; therefore, a blood test may be carried out to diagnose this condition.
Diagnosis of Tangier disease is also achieved through clinical evaluation and can be confirmed through genetic testing involving the sequencing of the ABCA1 gene. HDL-C deficiency and an extremely low apolipoprotein A1 (ApoA1) level are typical diagnostic criteria. This method will be discussed further with you and your child if it is thought that they may have this condition.
Can it be treated?
To our knowledge there is no specific treatment for Tangier disease. Drugs known to increase high density lipoprotein levels in unaffected people, such as estrogens, nicotinic acid, statins, or phenytoin, have shown not to work in people with Tangier disease.
To reduce the risk for heart and blood vessel disease, people with this condition should maintain a low fat (especially saturated fat) diet and overall healthy lifestyle. Individuals with Tangier disease may benefit from referral to specialized lipid centres for advanced management. Consultation with a multidisciplinary team may be required.
Do my family need to be tested?
Tangier disease can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier.
If both parents are carriers, their child has a one in four (25%) chance of inheriting the disorder, and a one in two chance (50%) of being a carrier. This is the same for each child the parents have.
If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.
Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inheritedTangier disease. They can also tell you about genetic testing for the rest of your family. They can provide advice and support if you go on to have children of your own.
If you have previously had a child with Tangier disease and go on to have further children, their New-born Screening test should be carried out within 24-48 hours of birth.