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What causes it?
Familial Hypobetalipoproteinaemia is caused by a problem in the APOB gene. This gene provides the instructions to make two proteins called apolipoprotein B-48 and apolipoprotein B-100, which transport and absorb fats and cholesterol through the blood. This process is needed to move fats around the body to provide you with energy.
If you have a problem in the APOB gene, your apolipoprotein B-48 and/or apolipoprotein B-100 protein will be abnormally short. Therefore, you will be unable to absorb and transport fats and cholesterol properly which causes them to build up to dangerously high levels in your body, particularly in your liver.
How common is it?
Familial Hypobetalipoproteinaemia is believed to affect around 1 in every 1,000 to 3,000 people.
It is difficult to accurately measure the prevalence of this disorder because some people have a mild form of the disorder which does not have any symptoms, and so they may not get a diagnosis.
What are the signs and symptoms?
There are two forms of Familial Hypobetalipoproteinaemia. The signs and symptoms are dependent on which form you have. They are known as early onset (or homozygous) Familial Hypobetalipoproteinaemia and benign Familial Hypobetalipoproteinaemia.
Early onset Familial Hypobetalipoproteinaemia is a much rarer, more severe form of the disorder. It usually starts in early childhood and causes:
- Growth delays (failure to thrive)
- Diarrhoea with steatorrhea (abnormal amounts of fat in faeces)
- Severe swelling (hepatic steatosis)
- Eye dysfunction
- Enlargement of the liver, or liver disease
If left untreated, symptoms will progress and become more severe as you reach adulthood. They can include:
- Damage to the retinas in your eyes (retinal degeneration)
- Loss of full control of bodily movements (ataxia)
- Issues with your nervous system (neurological symptoms)
Life expectancy for early onset Familial Hypobetalipoproteinaemia depends upon the severity of the symptoms, however the disorder usually results in a limited life span. It is important to follow the advice of your medical team in order to increase your quality of life.
Benign Familial Hypobetalipoproteinaemia is a less severe form of the disorder and is typically asymptomatic, however you may develop fatty liver. Some cases have been known to have similar symptoms to the early onset form of the disorder, however these cases are extremely rare.
Typically, the life expectancy of somebody with benign Familial Hypobetalipoproteinaemia is very good, with many documented cases of people living beyond the age of 85.
How is it diagnosed?
Familial Hypobetalipoproteinaemia is diagnosed using a specialised blood test and sometimes a stool sample. Your medical team may also want to test your parents, if possible, to help confirm the diagnosis.
You may also be given a neurological examination to test your nervous system, a scan on your liver (hepatic ultrasound), and an eye examination. This will help to determine the severity of your symptoms.
If a member of your family, such as a parent, child, or sibling, has been diagnosed with Familial Hypobetalipoproteinaemia, you may also have the disorder. Consult your medical team to find out whether you may benefit from having diagnostic tests.
Can it be treated?
There is currently no cure for Familial Hypobetalipoproteinaemia, but there are treatments available to improve symptoms. These treatments mostly consist of following a specialised diet that is low in fat, and taking supplements such as vitamin E. For people with early onset Familial Hypobetalipoproteinaemia, high doses of vitamin E are required early on in order to reduce the severity of the disorder.
Changes to your diet should always be made following the advice of a specialist dietitian to ensure that your body is getting all the nutrients it needs to function properly.
For people with a severe form of the disorder, treatment may include a number of different supplements and other interventions specific to your needs in order to reduce the symptoms. It is important that treatment is started early in life to increase its effectiveness.
Do my family need to be tested?
Familial Hypobetalipoproteinaemia is inherited from either parent in an autosomal co-dominant inheritance pattern. This means that only one parent has to be affected to pass on the disorder through their genes.
All genes come in pairs. You inherit two different versions of the APOB gene from your parents. If one or both of your parents has a faulty gene, then you will inherit Familial Hypobetalipoproteinaemia.
The APOB gene is co-dominant, which means that faulty and working genes will exist and work together equally, rather than one dominating over the other. Therefore, if you inherit one faulty gene and one working gene, you will have a mild or moderate form of the disorder because the two genes balance each other out. This is the reason why some people with Familial Hypobetalipoproteinaemia are asymptomatic. People with abnormalities in both genes will present with a more severe form of the disorder.
If you think somebody in your immediate family, such as your parents, siblings, or children, may have Familial Hypobetalipoproteinaemia, contact your medical team who may refer you for genetic testing.