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Chylomicron syndrome is an inherited disorder resulting in the accumulation of chylomicrons as well as triglycerides. Chylomicron syndrome is an extremely rare disorder, with an occurrence of about 1 out of every 1,000,000 people worldwide. Chylomicron syndrome has alternative names including, chylomicronemia, familial lipoprotein lipase deficiency and Apolipoprotein CII deficiency.
In the following essay I will give an introduction to the disease and outline the symptoms experienced by people with chylomicron syndrome. I will discuss the biochemistry of the disease, how it occurs in the body and talk about the two different forms of the disorder. In a discussion I will then outline the diagnosis and treatments and also discuss the importance of research in the area, and associated risks.
Chylomicron syndrome is mostly caused by a defective gene that is passed down through generations of families. This inherited condition causes a disruption in the normal breakdown of fats in the body. The inheritance of the mutated gene is in an autosomal recessive pattern. "This means that both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each contain one copy of the mutated gene", but may not necessarily show signs or symptoms of the condition.. The syndrome affects males and females equally. Chylomicron syndrome mostly occurs in childhood. It can occur before the age of one, but in most cases, symptoms develop before the age of ten. Although rare, in some cases, symptoms present for the first time in women during pregnancy. There are a variety of symptoms of this syndrome. The severity of symptoms reflects the degree of chylomicronemia. Symptoms include; Abdominal pain, loss of appetite, nausea, pain in the muscles and bones, bloating and gas, bulky of fatty stools, chronic diarrhoea, failure to thrive during infancy, muscle wasting and weight loss, swollen liver or spleen, and yellowing of the skin and eyes. In most cases only a small number of these symptoms are present. The two main indicators that lead to the diagnosis of chylomicron syndrome are eruptive xanthomas and multiple bouts of pancreatitis, along with high levels of triglycerides in the blood. Xanthomas are small deposits of fats on the surface of the skin. They occur in up to 50% of individuals with this syndrome. These fatty droplets on the skin usually appear over the trunk, buttocks, knees and the anterior surface of the lower arms.
In the body there are five different classifications of lipoproteins. Chylomicrons are one of the five groups of lipoproteins that allow the fats and cholesterol to move around within the bloodstream. Chlyomicrons consist of proteins, cholesterol, phospholipids and its main component, triglycerides which makes up roughly 85-92% of the chylomicron. Chylomicrons are formed in the vili, in the lining or the mucosa of the intestine. They are then secreted into the blood system at the thoracic duct, from where they transport lipids to other locations of the body, including the liver, adipose, cardiac and skeletal muscle tissue. "At these target tissues the triglycerides are hydrolyzed by lipoprotein lipase on the surface of the cells and the released fatty acids are taken up either for metabolism to generate energy or for storage". Chylomicrons are also important for the absorption of vitamin E and D.
Chylomicron syndrome is a disorder of the rate of clearance of chylomicrons from the blood. Two forms of this syndrome occur.
Lipoprotein lipase deficiency.
Apolipoprotein C-II deficiency.
Lipoprotein lipase is an enzyme involved in transporting fats and breaking down lipoproteins. A mutation in the gene for this enzyme can mean that there is a very low level of lipoprotein lipase or that it is absent from the body, effectively preventing the enzyme from breaking down lipoproteins. Without lipoprotein lipase, an individual's body cannot break down fats from digested food. Due to the lipoproteins not being broken down, fat substances from the digested food build up in the blood. "Due to a deficiency of lipoprotein lipase, clearance of chylomicrons from the blood is impaired, causing an increased concentration of triglycerides in the plasma". "As a result of this, the fatty substances build up in the blood, leading to the signs and symptoms of familial lipoprotein lipase deficiency".
"Apolipoprotein C-II (Apo C-II) is a protein component of chylomicrons and is the physiological activator of lipoprotein lipase". Lipoprotein lipase only functions correctly in the presence of Apo-CII. A deficiency of this enzyme causes Chylomicron syndrome due to the lack of lipoprotein lipase, which in turn causes the build-up of chylomicrons in the blood.
As previously stated, chylomicron syndrome is a very rare disease, which only affects about 1 per million people. Diagnosis of the syndrome usually consists of blood tests. "Blood tests will be done to check cholesterol and triglyceride levels. Chylomicronemia is present if triglyceride levels exceed 1000mg/dl. A special blood test maybe done after a patient is given blood thinners through a vein. This test looks for lipoprotein lipase activity in the blood. Genetic testing may also occur, including one for apolipoprotein CII deficiency."
Treatment for chylomicron syndrome is a very low fat diet. No more than 20grams of fat should be consumed per day. This treatment aims to control blood triglyceride levels, and prevent the symptoms from returning. When left untreated, the excess chyomicrons may lead to bouts of pancreatitis. This disease can also be corrected by a blood plasma diffusion.
Research into the side effects of chylomicron syndrome is a very important are. Numerous studies have been carried out worldwide on the risk of an individual developing atherosclerosis if they have chylomicronemia. In one particular study, it was found that "premature atherosclerosis can occur in patients with familial chylomicronemia as a result of mutations in the lipoprotein lipase gene. In all the four patients of this study, peripheral or coronary atherosclerosis was observed before the age of 55." However, during the research of websites and journals I carried out, it seemed in most cases that chylomicron syndrome caused no increased risk for atherosclerosis. To conclude, chylomicron syndrome although a very dangerous disease, can be very managble if treated, and by sticking to a fat free diet. Research is still taking place on the incresed risk of athersclerosis associated with this syndrome.