Abetalipoproteinemia is a genetic disorder that interferes with the intestines’ ability to absorb fats, cholesterol, and fat-soluble vitamins. Due to their lipid and vitamin deficiencies, people with this condition develop progressive symptoms that affect many important functions, predominantly vision, blood low, and the nervous and gastrointestinal systems. With early diagnosis and treatment, physicians can combat abetalipoproteinemia’s progression and improve prognosis.
Abetalipoproteinemia is the result of mutations in the MTTP gene, which provides instructions for making MTP proteins that help create beta-lipoproteins that transport cholesterol, fats, and fat-soluble vitamins from the intestine and through the bloodstream for various tissues to absorb. The mutations render the body unable to create MTP proteins, without which the body cannot transport the nutrients; deficiencies develop, leading to health problems.
Doctors Bassen and Kornzweig first reported abetalipoproteinemia in 1950, giving it the name Bassen-Kornzweig syndrome. Over the years, several other specialists began to discover more information about individuals with the condition and how it functioned. In 1960, H. B. Salt discovered the absence of serum beta-lipoprotein in a patient, and the condition gained the name abetalipoproteinemia. Eventually, further research and discovery revealed the genetic cause.
Most people receive an abetalipoproteinemia diagnosis as children because symptoms typically appear in the first few months after birth. These early signs usually include bulky stools with foul odors, vomiting, diarrhea, and abdominal swelling. Without treatment, infants with abetalipoproteinemia fail to gain weight or grow at a healthy pace -- symptoms doctors classify as "failure to thrive." Because children who have the condition have poor fat absorption, they also cannot absorb fat-soluble vitamins, which leads to vitamin deficiencies. Individuals with abetalipoproteinemia also have no apoB-containing lipoproteins in their blood, meaning they have low levels of triglycerides, phospholipids, and cholesterol. Without these, the body can’t properly transport lipids and fat-soluble vitamins through the bloodstream.
As a person with abetalipoproteinemia ages, their symptoms progress and cause other issues. For example, many people develop an inability to coordinate voluntary movements, called ataxia. Other neurological symptoms include poor tendon reflexes, tremors, muscle weakness, and trouble speaking. Blood abnormalities, fibrosis, and cirrhosis of the liver are also common. Some people with abetalipoproteinemia also have skeletal disorders such as lordosis, high arches, or clubfoot. Experts believe these disorders are due to muscle imbalances resulting from a lack of important fats and vitamins.
Among the fat-soluble vitamin deficiencies abetalipoproteinemia causes, low vitamin A and E are the most common. Some experts suspect that lacking these vitamins leads to retinitis pigmentosa, a degenerative condition that affects the retina, causing night blindness, tunnel vision, and loss of color and peripheral vision. Without treatment, it can lead to blindness. Vitamin K deficiency, also a possible result of abetalipoproteinemia, may lead to blood abnormalities that can reduce blood clotting or cause anemia.
Abetalipoproteinemia has an autosomal recessive inheritance pattern, meaning both copies of the gene in each cell have mutations. For this condition, both parents must have MTTP gene mutations and pass them on to their child. Many people with these mutations have no signs or symptoms, so they may not even be aware of the impending effects.
Estimations suggest abetalipoproteinemia affects fewer than one in one million people. From the available research, experts believe the condition affects men and women equally and lacks any significant ethnic bias. However, it is more common in cultures that practice consanguineous marriages or marrying a person with the same ancestor, because this increases the likelihood a child will receive two mutated MTTP genes.
Abetalipoproteinemia can be quite difficult to diagnose, requiring thorough clinical evaluation and many tests to confirm. Common tests include measuring lipid and beta-lipoprotein levels and determining the shape of red blood cells to discover blood abnormalities. Blood tests can detect these factors, while also measuring fat-soluble vitamin levels. Some people require a complete neurological assessment and eye examinations to find symptoms of abetalipoproteinemia. Some molecular genetic testing may detect MTTP gene mutations.
Because abetalipoproteinemia is a rare condition, it is difficult for experts to create an accurate and effective treatment plan and a patient often requires a team of specialists to develop the most effective path to recovery. Most treatments focus on minimizing and preventing the progression of specific symptoms. Many people respond well to dietary therapy that consists of low-fat foods. High doses of fat-soluble vitamins ensure the body absorbs some of them. Treating abetalipoproteinemia requires constant measurements and tests to verify fat, lipid, and vitamin levels.
In recent years, some experts have studied gene therapy as a treatment for abetalipoproteinemia. The process would require introducing a normal MTTP gene into the body of a person with the condition. Ideally, the healthy gene will then produce the MTP protein, so the body can create beta-lipoproteins. Gene therapy could prevent the development and progression of abetalipoproteinemia. Currently, many factors prevent gene therapy from being a viable alternative treatment, but this may change as research continues.
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