Chylomicron Retention Disease

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Chylomicron retention disease is caused by a change in the SARB1 gene. The gene provides instructions for a protein called Sarb1. The body uses this protein to transport molecules called chylomicrons. Chylomicrons are made in the cells which line the intestine (enterocytes) and are secreted (released) to absorb certain vitamins and to transport cholesterol and fat from the small intestine into the bloodstream.

In this disorder, the chylomicrons cannot be released into the blood. This causes problems with the body’s ability to soak up (absorb) fat, cholesterol, and fat-soluble vitamins from the diet and this leads to the signs and symptoms of this disorder

Currently, around 55 cases of this disorder have been reported worldwide. There have been no reports of an increased risk existing between males and females or between different ethnic groups.

Symptoms generally begin during infancy with the following:

• Failure to grow or gain weight at the expected rates
• Vomiting
• Diarrhoea
• Swollen abdomen

The inability to absorb fat, cholesterol, and fat-soluble vitamins means that fats are excreted into the stools (poo). This can make them foul smelling, greasy, foamy, and sometimes difficult to flush away (steatorrhoea).

Other symptoms may include:

• Low levels of cholesterol in the blood (hypocholesterolemia)
• An accumulation of fat in the liver which may also cause an enlarged liver

From later in childhood, children may develop the following:

• A decreased reflex response (your muscles are less responsive to stimulation – diagnosed by tapping certain muscles with a reflex hammer)
• Damage to the sensory nerves (symptoms include pain, sensitivity, numbness, tingling, and/or burning sensations)
• Bone abnormalities caused by vitamin D deficiency
• Wasting away of the muscles (rare)
• Heart problems (rare)
• Mild symptoms affecting the sight

Symptoms and severity may vary between individuals.

The diagnosis is based on a history of chronic diarrhoea with fat malabsorption and an abnormal lipid/fat profile which can be identified through blood tests. Diagnosis can be delayed due to the rarity and the similarity of symptoms to other diseases and other metabolic conditions.

An upper endoscopy may be performed to aid diagnosis. This involves passing a thin tube with a small camera on the end, down your throat into your stomach. This may result in some mild discomfort; you will be offered a sedative to help you relax.

Vitamin E and creatine kinase levels can be determined though a routine blood test.

Genotyping can be undertaken to check for the genetic defect present within this metabolic condition.

Treatment for this condition should be aimed at avoiding the potential complications associated with this disorder. Chylomicron retention disease is generally managed through dietary intervention with the help of a specialist dietitian. Nutrition and growth will be monitored regularly by your metabolic team. A low-fat diet may be prescribed to you with the addition of essential fatty acids and supplements (such as vitamin E and fat-soluble vitamins) to make sure your body receives the vitamins you would usually obtain from a normal level of fat in the diet.

Regular follow-ups and examinations are required to monitor the condition and check for any development of new symptoms to ensure they can be identified and managed early. Many of the individual symptoms are caused by specific vitamin deficiencies so treatment may be adjusted to reflect any changes in your condition.

Long term prognosis is good with early diagnosis and appropriate lifelong vitamin supplementation and follow-up.

Chylomicron retention 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.

References are available on request. Please contact us by phoning 0845 241 2173 or emailing contact@metabolicsupportuk.org [Resource Library No: CLL009