About familial alpha-lipoprotein deficiency

What is familial alpha-lipoprotein deficiency?

Tangier Disease is an inherited blood disorder involving decreased concentrations of fat compounds in the blood called high-density lipoproteins (sometimes called "good cholesterol"). Large amounts of these compounds may accumulate in certain organs of the body causing tissue discoloration. In later stages, these accumulations may cause organ enlargement and/or blood circulation problems.

What are the symptoms for familial alpha-lipoprotein deficiency?

Most cases of familial LPL deficiency are identified during childhood, usually before the age of 10. In approximately 25 percent of patients, the disorder is identified during the first year of life. Some affected individuals may not be identified until adulthood. For example, some women may not be diagnosed until after becoming pregnant or when they begin taking contraceptive medication.

The severity of familial LPL deficiency varies depending upon the degree of chylomicronemia, which fluctuates depending upon the amount fat in an individual’s diet. The main symptoms are Abdominal pain, pancreatitis, eruptive xanthomas and hepatosplenomegaly.

The most common symptom of familial LPL deficiency is episodic Abdominal pain. The severity of Abdominal pain can vary, ranging from mild to severe and, in some people, can be incapacitating. The pain may be located in the upper, central region (epigastric area) of the abdomen and can radiate to cause back pain. In some people, the pain may be widespread (diffuse) and can potentially resemble acute abdomen (peritonitis). In the past, this has led to unnecessary surgery.

Abdominal pain in individuals with familial LPL deficiency may result from recurrent episodes of inflammation of the pancreas (pancreatitis). The pancreas is a small gland located behind the stomach. The pancreas secretes enzymes that travel to the intestines to aid in digestion and hormones that have specialized roles in the body. The main symptom of pancreatitis is pain, which is sometimes intense, and is most often felt in the upper left side or middle of the abdomen. Pancreatitis can also cause Nausea, sweating, Weakness, Chills, clammy skin, and mild yellowing of the skin or whites of the eyes (jaundice). Some individuals will develop acute, recurrent pancreatitis, which can potentially be lethal.

Chronic pancreatitis can be associated with additional complications including diabetes, hardening of the pancreas due to the accumulation of calcium salts (pancreatic calcification) and stools containing excess amounts of fat causing them to be frothy, foul smelling and to float (steatorrhea). However, these complications are unusual in individuals with familial LPL deficiency. Even in individuals with recurrent episodes of pancreatitis, such complications rarely develop until middle age. Although rare, pancreatitis in LPL deficiency can cause severe, life-threatening complications.

Enlargement of the liver and spleen (hepatosplenomegaly) can also occur, especially in infants and young children. The degree of enlargement varies, often in conjunction with the amount of fat in the diet. Hepatosplenomegaly is caused by the accumulation of a special type of macrophage. Macrophages are white blood cells that ingest foreign or harmful substances. In familial LPL deficiency, macrophages ingest excess triglyceride and transform into foam cells. Foam cells are specialized macrophages that attempt to deal with excess fat in the body and usually contain fatty materials. Foam cells in individuals with familial LPL deficiency abnormally accumulate in the bone marrow, liver and spleen.

Approximately 50 percent of affected individuals develop eruptive cutaneous xanthomas, which are skin lesions make up of certain fats (lipids). Xanthomas may appear as raised, reddish-yellow bumps or nodules on the skin. They often occur on the buttocks, knees and outer arms. Individuals lesions may measure about 1 millimeter in size, but xanthomas often cluster and may grow together (coalesce) to form larger lesions. Eruptive xanthomas are generally not painful or tender, unless they develop on an area of the body where they suffer repeated trauma or abrasion. Xanthomas usually appear within a few days after triglyceride levels in the plasma have begun to increase. They may contain a greasy, yellowish substance and sometimes a milky fluid. Xanthomas will disappear over a period of weeks to months as the amount of triglyceride in the plasma decreases. The persistent presence of xanthomas in individuals with familial LPL deficiency indicates inadequate therapy to lower triglyceride levels.

In the presence of excessive fatty substances in the circulation the small arteries (arterioles) and small veins (venules) in the outer parts of the retina and the back of the eyeball (fundus) may appear pale pink upon examination by an eye specialist (ophthalmologist). This condition may be referred to as “lipemia retinalis”. The change is related to the degree of fatty build up (i.e., large chylomicrons), which causes incoming light to scatter. This discoloration is reversible and does not affect the vision of individuals with familial LPL deficiency.

Additional symptoms have been reported in some individuals with familial LPL deficiency including a variety of reversible neuropsychiatric findings such as depression, memory loss and dementia.

Some individuals with familial LPL deficiency have developed premature atherosclerosis, which is characterized by thickening and obstruction of various blood vessels due to the accumulation of fatty material, potentially causing coronary heart disease or peripheral vascular disease. However, most researchers do not believe that individuals with familial LPL deficiency have an increased risk of developing atherosclerosis.

What are the causes for familial alpha-lipoprotein deficiency?

Familial LPL deficiency is caused by changes (mutations) in the LPL gene. The LPL gene contains instructions for creating (encoding) an enzyme known as lipoprotein lipase. This enzyme is essential for the proper breakdown of certain fats in the body. Fat is obtained through the diet and is absorbed by the intestines. It is transported in the form of triglyceride by large lipoproteins known as chylomicrons. (Triglycerides are fatty molecules that are used by the cells of the body for fuel.) When chylomicrons are released into the bloodstream, a protein within chylomicrons called apolipoprotein C2 is activated. This protein is recognized by the enzyme lipoprotein lipase, ultimately resulting in the breakdown of triglyceride. When lipoprotein lipase is inadequate or impaired, chylomicrons accumulate in the plasma, which, in turn, causes abnormal amounts of triglyceride to accumulate in the plasma as well. The accumulation of excess.

Familial LPL deficiency is inherited in an autosomal recessive pattern. Recessive genetic disorders occur when an individual inherits a non-working gene from each parent. If an individual receives one working gene and one non-working gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the non-working gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier, like the parents, is 50% with each pregnancy. The chance for a child to receive working genes from both parents is 25%. The risk is the same for males and females.

Individuals who inherit one mutated gene and one normal gene (heterozygotes) do not develop familial LPL deficiency. However, these individuals may have a slightly increased risk of developing mixed dyslipidemia with low HDL cholesterol levels. Heterozygotes may also be more susceptible to developing atherosclerosis than non-carriers, especially if they gain weight or remain on a high fat diet.

What are the treatments for familial alpha-lipoprotein deficiency?

A proportion of LPL deficient individuals can be successfully treated by dietary restriction of fats, but many are still plagued by recurrent abdominal pain and episodes of acute pancreatitis. The goal of restricting fat intake is to reduce chylomicronemia and hypertriglyceridemia enough to prevent symptoms. Many individuals learn on their own to avoid foods containing fat. However, many physicians recommend reducing fat intake significantly to no more than 20 g/day or 15 percent of total energy intake in order to prevent symptoms.

Drugs that lower lipid levels in the body are not effective in reducing fat levels in individuals with familial LPL deficiency. Alcohol and drugs that increase triglyceride levels should be avoided. Such drugs include oral contraceptives, diuretics, beta-adrenergic blocking agents, isotretinoin and Zoloft®.

Medium chain fatty acids can be used for cooking because they are absorbed directly by the portal vein of the liver. Many individuals have been successfully treated with a diet rich in medium chain fatty acids. Fish oil supplements are not effective for individuals with familial LPL deficiency and are contraindicated.

An enlarged liver or spleen will usually shrink to normal size within one week of reducing triglyceride levels. Eruptive xanthomas usually clear up within several weeks to months. If xanthomas persist or recur despite treatment, it indicates inadequate therapeutic efforts.

Pancreatitis is treated following standard guidelines.

Genetic counseling is recommended for affected individuals and their families.

Gene Therapy

In 2012, the European Commission approved the marketing authorization of alipogene tiparvovec gene therapy (Glybera®) developed UniQure for the treatment of individuals with familial LPL deficiency. Glybera was the first approved gene therapy in the Western world but was never approved in the US. In 2017, Glybera was taken off the market by UniQure due to low demand from the patient community.

What are the risk factors for familial alpha-lipoprotein deficiency?

Familial alpha-lipoprotein deficiency, also known as familial hypo alpha-lipoproteinemia, is a heterogeneous group of genetic disorders.

  • Lipids are one of the essential biomolecules that play active roles in various physiological activities and are made of cholesterol and protein. The protein is called a lipoprotein.
  • In patients with alpha-lipoprotein deficiency, the serum levels of high-density lipoprotein fall below normal and reduce the metabolism and excretion of cholesterol.
  • Consequently, cholesterol levels increase in the blood and lead to cardiovascular diseases such as atherosclerosis.

Risk factors

  • Family history: The involvement of the responsible genes is complex as they exist in different combinations. In addition, the genotypes could be homozygous, heterozygous, or combined heterozygous. Most genes are inherited in an autosomal recessive manner. However, the risk is high as the homozygous genotype induces mild conditions.
  • Obesity: A person can develop obesity due to other genetic disorders as well. It adds to the risks of hypo alpha-lipoproteinemia.
  • Low physical activities: Low body movements or exercises raise blood cholesterol, which otherwise would have burned calories.
  • Diets containing high fats: Foods containing high levels of fats and oils increase the risk of cardiovascular complications.

Steakhouse syndrome,Dysphagia,Barret's esophagus,Hiatal hernia
Difficulty during swallowing,Bolus obstruction,Chest pain,Heartburn

Is there a cure/medications for familial alpha-lipoprotein deficiency?

Familial alpha-lipoprotein deficiency is a condition of low levels of high-density lipoprotein in serum. Alpha-lipoprotein-cholesterol, referred to as good cholesterol, is involved in the transfer of low-density lipids from tissues of different organs to the liver for its metabolism and excretion. Thus, the deficiency leads to several pathophysiologies.

The disorders include Tangier syndrome, LCAT deficiency, Fish Eye disease, A1 variants syndrome, and Vergani disease. The individual disorder is defined by different states of the combination of genes involved, the concentration of triglyceride, and low-density lipids in the blood.

The treatment options are:

  • Statins: Statins are lipid-lowering medications. Atorvastatin, Fluvastatin, and pravastatin are the most common used
  • Niacin and gemfibrozil: Niacin and gemfibrozil are very effective hyperlipoproteinemic agents, with the result of 15 – 30 percent increase in serum high-density lipoprotein concentration. These are best effective in patients with no other lipid abnormalities.
  • Apolipoprotein A1 infusion: IV infusion of apolipoprotein is promising for raising high-density lipoprotein in the future. The side effects of liver abnormalities are still being addressed.
  • Surgery: Surgical intervention with coronary bypass or Percutaneous Coronary Intervention (PCI) with a stent is necessary for patients with myocardial infarction.
  • Regular exercises
  • Low-fat diet
  • Cessation of alcohol and smoking
  • Stress-relived state of mind

Steakhouse syndrome,Dysphagia,Barret's esophagus,Hiatal hernia
Difficulty during swallowing,Bolus obstruction,Chest pain,Heartburn

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