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Abetalipoproteinemia

What is Abetalipoproteinemia?

Abetalipoproteinemia is a rare disease that lowers the body’s ability to absorb fats from food in the intestine and mobilize it in the liver. The disease is caused by a lack of functional protein known as microsomal triglyceride transfer protein (MTTP) which forms beta-liposomes in the liver. Beta-liposomes are a biomolecule that attach to and transfer other lipid molecules, such as dietary fats, lipids, and cholesterol, to places in the body such as the liver and intestine. People with abetalipoproteinemia have low levels of cholesterol and lipoproteins in their bloodstream. Less beta-liposome production leads to less fats being transported in the bloodstream, reducing the biomolecules known as lipids in the body which are essential for different bodily developments and functions. Abetalipoproteinemia affects growth and development of the neurological system, functioning of the gastrointestinal tract, eyesight, and blood flow. 

The term abetalipoproteinemia can be broken down to better understand the disorder. The disorder itself affects the body’s production of liposomes known as apo-beta (a-beta or apo-B) lipoproteins, and “emia” is a suffix that signifies a blood condition (such as anemia). This rare disease was first described in 1950 by Bassen and Kornzweig, giving rise to the disease’s synonym Bassen-Kornzweig syndrome.

 

 

Synonyms

  • Bassen-Kornzweig Syndrome
  • Low density lipoprotein deficiency
  • Microsomal triglyceride transfer protein deficiency
  • Familial hypobetalipoproteinemia due to secretion defect 1

Abetalipoproteinemia is a rare disease that lowers the body’s ability to absorb fats from food in the intestine and mobilize it in the liver. The disease is caused by a lack of functional protein known as microsomal triglyceride transfer protein (MTTP) which forms beta-liposomes in the liver. Beta-liposomes are a biomolecule that attach to and transfer other lipid molecules, such as dietary fats, lipids, and cholesterol, to places in the body such as the liver and intestine. People with abetalipoproteinemia have low levels of cholesterol and lipoproteins in their bloodstream. Less beta-liposome production leads to less fats being transported in the bloodstream, reducing the biomolecules known as lipids in the body which are essential for different bodily developments and functions. Abetalipoproteinemia affects growth and development of the neurological system, functioning of the gastrointestinal tract, eyesight, and blood flow. 

The term abetalipoproteinemia can be broken down to better understand the disorder. The disorder itself affects the body’s production of liposomes known as apo-beta (a-beta or apo-B) lipoproteins, and “emia” is a suffix that signifies a blood condition (such as anemia). This rare disease was first described in 1950 by Bassen and Kornzweig, giving rise to the disease’s synonym Bassen-Kornzweig syndrome.

 

Acknowledgement of Abetalipoproteinemia has not been added yet.

Abetalipoproteinemia is a rare disease that is estimated to affect less than 1 in 1 million people in the worldwide population. It can affect people born genetically male and female with equal likelihood. One mutation type of the MTTP gene that causes abetalipoproteinemia is more common in people of Ashkenazi Jewish descent. This is a replacement of a glycine in the protein (one of 20 amino acid types that can make up the protein structure) at position 865 with a stop codon. This means that the gene is not adequately read to the end, leading to an abnormally small and nonfunctional version of the MTTP protein.

 

Name Abbreviation
ABL
ABL
ABL
Bassen-Kornzweig Syndrome BKS
Low density lipoprotein deficiency
Microsomal triglyceride transfer protein deficiency MTP deficiency
Familial hypobetalipoproteinemia due to secretion defect 1 FHBL-SD1

The rare disease abetalipoproteinemia is caused by a genetic mutation in the MTTP gene which encodes a protein called microsomal triglyceride transfer protein. There are more than 33 known mutations to this gene that can cause abetalipoproteinemia. This disease can be passed down from parents to their offspring in an autosomal recessive genetic inheritance pattern, meaning that both parents must have a copy of the mutated gene to pass to their offspring (see RareShare Guide on Genetic Inheritance for more information https://rareshare.org/articles/guide ). 

The MTTP gene encodes the genetic information for the body to produce the microsomal triglyceride transfer protein (MTTP) which is responsible for assembling and secreting apoB-lipoproteins in the liver and intestines. They do this by attaching lipids onto apoB proteins to form the very large apolipoprotein biomolecule. Lipoproteins are a combination of two types of biomolecules: lipids and proteins. They act as transporters for lipid, or hydrophobic, molecules that don’t dissolve easily in water or the aqueous environments of the body. Thus, they are necessary to transport fats and fat-soluble vitamins, and without them these nutrients don’t reach locations in the body that need them to function properly. When the MTTP protein isn’t formed properly or isn’t readily available, it reduces the body’s liver and intestines’ ability to absorb and transport fat molecules and fat-soluble vitamins. 

 

The lack of apo-B lipoproteins caused by this rare disease causes a lack of essential vitamins and nutrients in the body, such as triglycerides, cholesterol, phospholipids, ceramides, vitamins A, E, and K, and reduced apo-A1 liposomes. Deficient lipids in the bloodstream lower the body’s phospholipids that form cell membranes, causing abnormally shaped red blood cells (acanthocytosis) which can lead to anemia. MTTP protein is also expressed in the heart, and abetalipoproteinemia could lead to a build-up of fats in the heart and cause heart problems.

 

Symptoms of abetalipoproteinemia mostly affect the neurological system, gastrointestinal tract, function of the retinas and eyesight, and red blood cells and blood flow. Loss of fats in the bloodstream causes loss of functions such as neurological deterioration, weakness of the muscles and difficulty walking, abnormally shaped red blood cells (acanthocytosis) resulting in anemia or low blood flow, degeneration of the retina and loss of vision. These symptoms often develop in infants and early childhood development with specific symptoms giving rise to a diagnosis:

Infantile Form

Infants with abetalipoproteinemia will often experience gastrointestinal problems due to poor digestion:

  • Pale, bulky, foul-smelling stools (steatorrhea)

  • Diarrhea

  • Vomiting

  • Swollen abdomen

  • Lack of weight gain or growing to the expected milestones

Juvenile Form

Between the ages of 2-20 years, children and young adults with abetalipoproteinemia may develop neurological degeneration characterized by loss of ability to coordinate voluntary movements and/or loss of deep tendon reflexes such as the kneecap. Some may have difficulty speaking at this time. Eyesight degeneration in the form of retinitis pigmentosa - where the retina breaks down and causes vision loss - often develops around age 10 due to vitamin deficiency. Most children with abetalipoproteinemia will have normal intellectual capabilities, but may develop at a slower rate and/or experience disability. Other signs of neurological degeneration include tremors, motor tics, and muscle weakness.

Due to a lack of lipids to form phospholipids, the cell membranes of different cell types may be weakened in people with abetalipoproteinemia. This often affects the shape and function of red blood cells, causing acanthocytosis and resulting in less blood circulation and symptoms such as tiredness, weakness, lightheadedness, dizziness, irritability, palpitations, headaches, and pale complexion.

Less common symptoms of abetalipoproteinemia includes skeletal abnormalities such as backward or sideways curvatures of the spine, arched foot or clubfoot, difficulty walking, involuntary eye movements, droopy eyelids or crossed eyes, unequal size of pupils, and development of fatty liver which can cause liver damage if left untreated. 

 

A diagnosis of abetalipoproteinemia depends on a genetic analysis to determine a mutation of the MTTP gene. This is often done in tandem with testing levels of lipoproteins available in the body, observing the form of red blood cells, and performing an eye exam.

  • Measure lipids available in the body: blood tests for triglycerides, cholesterol, and apoB-containing lipoprotein content such as fasting lipid profile or stool study

  • Study morphology of red blood cells: complete blood count and blood smear to show acanthocytes (abnormally shaped red blood cells)

  • Ophthalmological exam: eye exam to observe the retinas for signs of deterioration

  • Hepatic scan or ultrasonogram to assess health of the liver and prevent the development of fatty liver disease

  • Magnetic resonance imaging (MRI) of spinocerebellar region to assess development of the spine despite muscle weakness

There is no cure for abetalipoproteinemia, yet there are treatments prescribed to treat specific symptoms that people with this rare disease may be experiencing. It is important that people diagnosed with abetalipoproteinemia receive routine medical examinations, especially for neurological and optical deterioration, to prevent worsening of any symptoms. Some treatment options include:

  • Dietary supplements – adding vitamins and reducing dietary fats generally relieve gastrointestinal symptoms, but medium chain fatty acids should be supplemented for long chain fatty acids so that the body can adequately transport shorter lipid molecules

Most people diagnosed with abetalipoproteinemia early in their lifetime are able to receive vitamin and lipid dietary treatment, and avoid fatty foods in general, which reduces their symptoms and lowers the likelihood of neurological, gastrointestinal, optical, and anemia complications. However, it is important to receive regular examinations by doctors to monitor symptoms to prevent damage to the liver and other organ systems. In particular, individuals with abetalipoproteinemia should use caution when taking fat-soluble drugs as they may have trouble delivering them to the area of the body that needs them.

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Last updated 7 Sep 2019, 03:32 AM

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Abetalipoproteinemia - the search for a cure

Abeta Research Study at UPenn Created by jtabita
Last updated 15 Jan 2013, 04:16 PM

Posted by jtabita
15 Jan 2013, 04:16 PM

Hello Everyone, My name is Jenn and I am a research coordinator working with Dr. Daniel Rader at the University of Pennsylvania (UPenn) in Philadelphia, PA. I hope that you may be interested in assisting us with our research study to better understand Abetalipoproteinemia. The purpose of this study is to verify if cells called "induced pluripotent stem (iPS) cells" that are created using a technology have characteristics similar to the cells collected from the body. We are also studying how changes in certain genes affect how these cells work and behave. The iPS technology allows researchers to take cells from blood samples and to make different cells which can be grown in the laboratory, stored and studied in the future. We will use the cells collected to create a type of cell known as a pluripotent cell. This type of cell can then be used to create different types of tissue, including liver cells that are difficult to obtain otherwise. The information obtained in this study will be used to better understand how changes in genes lead to disorders like Abetalipoproteinemia and will aid in the discovery and development of better therapeutic options for patients. The study involves a single blood draw. If you do not live close to Philadelphia or if it is not easy for you to travel to UPenn, I will mail you a package containing instructions and all the necessary materials to have the blood drawn at your doctor's office or a laboratory of your choice. If you are able to travel, the visit can be conducted in the Clinical and Translational Research Center at the Hospital of the University of Pennsylvania. Thank you so much for taking the time to read this post. Please feel free to contact me if you are interested in participating, would like more information or have any questions. Take care, Jennifer Tabita-Martinez Research Coordinator Senior University of Pennsylvania (P) 215-615-3421 jtabita@mail.med.upenn.edu

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