Symptoms And Causes Of Abetalipoproteinemia

September 6, 2023

Abetalipoproteinemia is a very rare genetic disorder that was first identified in 1950. It is estimated to affect only one hundred individuals worldwide. Also known as Bassen-Kornzweig syndrome, the condition impairs the body's ability to digest fats and some kinds of vitamins. If left untreated, abetalipoproteinemia can lead to vitamin deficiencies that may produce serious complications. Generally, abetalipoproteinemia affects the eyes, blood, nervous system, and gastrointestinal tract. Patients with this ailment may experience wide-ranging symptoms such as coordination problems, slurred speech, protrusion of the abdomen, and poor balance and dexterity. Vision problems are also common, and infants with the disorder may have delayed growth patterns. To diagnose this disorder, doctors perform specialized blood tests to measure the levels of certain lipids, and patients may also need to have neurological and eye examinations. An ultrasound of the liver and an endoscopy can assist with diagnosis. Current treatment methods emphasize dietary modifications, including the adoption of a diet low in long-chain saturated fatty acids. Patients typically need to take high doses of vitamins K, E, and A for effective symptom management. Potential gene therapies for the treatment of abetalipoproteinemia are currently being studied.

The major causes and symptoms of abetalipoproteinemia are outlined below.

Genetic Mutation

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Abetalipoproteinemia occurs due to a genetic mutation in an autosomal recessive fashion. To be diagnosed with the condition, an individual must inherit two copies of the mutated gene, one from each of their parents. Scientists have determined problems with the MTTP gene are a cause of Bassen-Kornzweig syndrome. This gene holds instructions for the encoding of a protein called the microsomal triglyceride transfer protein (MTP). Without the MTP protein, apoB-containing lipoproteins cannot be properly manufactured and released within the liver and intestines. This results in low levels of MTP and triggers the problems with fat and vitamin absorption that take place with abetalipoproteinemia. Recent studies have shown the MTTP gene is responsible for transporting lipids away from the heart, and low levels of MTP associated with abetalipoproteinemia may cause a buildup of fat within the heart, resulting in reduced function of this organ.

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Retinitis Pigmentosa

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Retinitis pigmentosa is an eye condition that is typical among patients with abetalipoproteinemia, and it can be triggered by deficiencies in vitamins A and E. This eye disorder affects the retina, the part of the eye that receives light. For patients with retinitis pigmentosa, retinal cells slowly deteriorate, resulting in a progressive loss of vision. One of the first symptoms of this eye condition is nighttime vision loss, and this is typically noticeable in childhood. As the disorder advances, patients start to have blind spots in their peripheral vision, and this eventually produces tunnel vision. Over the course of years or decades, central vision is also impacted, making it difficult to perform daily tasks such as writing, reading, and driving. Some patients may also have difficulty with facial recognition. The majority of patients with retinitis pigmentosa become legally blind by the time they are adults. Optical aids, retinal prostheses, and some surgical interventions may be useful for patients with this condition.

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Failure To Thrive

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Failure to thrive is often seen in infants with abetalipoproteinemia. It is caused by inadequate nutrition that may develop as a result of the insufficient fat and vitamin absorption that characterizes this syndrome. Clinically, doctors define failure to thrive as height and weight measurements below the third or fifth percentiles. Infants and children who are struggling to thrive typically have a lack of appropriate weight gain, excessive sleepiness, delayed development of motor skills, and difficulties with learning and behavior in later childhood. They might also display a lack of vocal sounds, a lack of age-appropriate social responses such as smiling, and fatigue or irritability. For patients with abetalipoproteinemia, treatment for failure to thrive normally focuses on vitamin supplementation and adequate intake of appropriate dietary fats. Since abetalipoproteinemia causes problems with the absorption of long-chain saturated fatty acids, doctors recommend infants with this condition to be given plenty of medium-chain fatty acids to support normal growth patterns; these medium-chain fats can be carried through the bloodstream without the need for apoB-containing lipoproteins.

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Developmental Delays

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Developmental delays in infants and children with abetalipoproteinemia may vary in severity. As the name suggests, developmental delays occur when a child does not reach a recognized developmental milestone at the expected time. To be classified as a developmental delay, the delay must be an ongoing delay in the child's developmental process, and it can be either major or minor in severity. Developmental delays are not diagnosed if a child is only temporarily behind in reaching milestones. Delays in development can affect fine and gross motor skills and language abilities, social skills, and cognition. Screening for developmental delays is typically performed periodically by a child's pediatrician, and pediatric neurologists and developmental specialists can also provide assessment and support. If a delay is identified, early intervention can help minimize its impact on the child's life and enable them to build skills to adapt to or work around these delays. For example, physical, occupational, and behavioral therapies may all be beneficial as forms of early intervention. School systems can provide resources and individualized education plans for children with developmental delays.

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Scoliosis

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Scoliosis, an abnormal curvature of the spine, is a possible complication that may occur for children with abetalipoproteinemia. For patients with scoliosis, the spine curves sideways, and the degree of the curve may become more severe as a child grows. Patients with this spinal problem may have uneven shoulders, and one hip might be higher than another. The condition may lead to chronic back pain, even in adults. In particularly advanced cases, patients may have breathing difficulties and cardiac symptoms if the rib cage begins to press on the lungs or heart. To treat scoliosis, patients sometimes wear a special brace that can prevent further curvature of the spine. For patients with advanced forms of the condition, surgical intervention may be required to straighten the spine.

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