What else is it called?
- Bassen-Kornzweig syndrome
- Low-density lipoprotein deficiency
- Microsomal triglyceride transfer protein deficiency
- MTP deficiency
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What causes it?
This disorder is caused by a problem in the MTTP gene. This gene provides instructions for the development of a protein which is required to create beta-lipoproteins. The process is needed because the beta-lipoproteins absorb the fat from your diet and transport it around your body to be used as energy.
If you have a problem in the MTTP gene, you will not produce enough beta-lipoproteins. Therefore, you cannot fully absorb fats, cholesterol, and fat-soluble vitamins (such as vitamin E), or transport them around your body and this causes nutritional deficiencies.
Deficiencies can stop you from getting all of the energy you need from your diet. A lack of energy in your body is dangerous because it can stop your body developing at the normal rate and lead to significant neurological issues.
How common is it?
Familial Abetalipoproteinaemia is very rare, with reports suggesting that less than 1 in one million people are affected by the disorder.
Reports seem to suggest that the disorder does not appear to affect any particular ethnicity or race more prominently than others, and males and females are both likely to be affected. However, it is more likely to occur in populations that have a high rate of consanguineous marriage.
What are the signs and symptoms?
Symptoms usually appear in the first few months of life. The first noticeable signs are:
- An inability to gain weight and grow as expected (failure to thrive)
- Diarrhoea and steatorrhea (fatty, foul-smelling stools)
- Abnormal, star-shaped red blood cells (acanthocytosis)
People with Familial Abetalipoproteinaemia typically present with a range of neurological problems beginning in childhood. These include:
- Slower than average intellectual development
- Damaged nerves in extremities such as hands and feet (peripheral neuropathy) which may cause a feeling of “pins and needles”
- Poor muscle coordination and struggling to voluntarily move your muscles (ataxia)
- Tremors during purposeful movements, often getting worse as you reach your target (intention tremors)
Another area of the body where you may experience significant problems is the eye. Symptoms may include:
- Decreased night and colour vision
- Eye disease (retinitis pigmentosa) typically beginning in adolescence
- Gradual deterioration of your ability to see, often leading to total blindness in your 40s
These symptoms tend to get worse as time goes on because they happen as a result of a deficiency in nutrients that your body cannot absorb. Treatment will typically focus on ensuring that your body has the nutrients it requires to work properly.
To reduce the likelihood of your symptoms getting worse, you need to follow the management plans that your medical team give you. If treatment is not undertaken, or the disorder is undiagnosed, it is likely that the symptoms will progressively grow worse and this can lead to death. However, when diagnosed and treated early, the prognosis for people with Familial Abetalipoproteinaemia is typically improved. Because of this, life expectancy for this disorder is varied and tends to be dependent on the stage at which it is diagnosed.
How is it diagnosed?
Diagnosis of Familial Abetalipoproteinaemia involves specialised blood tests and a stool sample. Medical professionals will take into account your symptoms and any family history of the disorder. A genetic test may also be carried out.
It is likely that your medical team will conduct tests such as a neurological assessment, an eye examination, an endoscopy, and a liver (hepatic) ultrasound in order to learn more about your symptoms. This will also help to identify the correct course of treatment for you.
If your parent, sibling, or child has diagnosed with Familial Abetalipoproteinaemia, it may be possible that you are also affected.
Can it be treated?
Treatment for Familial Abetalipoproteinaemia helps to stop any symptoms from getting progressively worse and supports you to manage your symptoms. There is currently no cure for Familial Abetalipoproteinaemia. However, if the treatment is started early, the risk of developing life-threatening symptoms reduces significantly.
Your medical team will develop a treatment programme to suit your needs. This will depend upon the symptoms that you present with, but it is likely that you will have a dietician who will help you to follow a low-fat, high carbohydrate diet. You may also be offered vitamin supplements and other medication to support your diet.
It is important that you carefully follow any plan offered by your dietician and discuss any changes to your diet with your medical team before you undertake them. This is to avoid worsening the symptoms of your disorder.
Other specialists that may be involved in your care include neurologists, liver specialists (hepatologists), eye specialists (ophthalmologists), specialists in the study of fats (lipidologists), gastroenterologists, nutritionists, among other healthcare professionals. You may require regular check-ups to ensure that your treatment is working effectively, and to monitor for any changes to your condition.
Do my family need to be tested?
Familial Abetalipoproteinaemia is inherited from both parents in an autosomal recessive inheritance pattern. This means that both parents are carriers of the disorder through their genes.
All genes come in pairs. Carriers of Familial Abetalipoproteinaemia have one working MTTP gene and one faulty gene. Children inherit one gene from each parent to make their pair. Whether you have Familial Abetalipoproteinaemia depends on the genes you inherit:
- There is a 50% chance that the child will inherit one faulty and one working gene, which means they will also be a carrier.
- There is a 25% chance that the child will inherit two working genes and not inherit or carry the faulty gene.
- There is a 25% chance that the child will inherit two faulty genes, which means they will have Familial Abetalipoproteinaemia.
If you think you, or somebody in your family, may have Familial Abetalipoproteinaemia, or that you may be a carrier, contact your medical team who may refer you for genetic testing.