The Burden of Abetalipoproteinemia and Nutrition Therapy
Abstract
Abetalipoproteinemia is an autosomal recessive genetic disorder that affects approximately <1 in 100,000 individuals, especially those of European or Central Ashkenazi Jewish descendance. The affected individuals are not able to express apolipoproteinB associated with chylomicrons, which play an important role in lipid metabolism. These individuals carry a single nucleotide polymorphism in the MTTP gene responsible for the synthesis of the microsomal triglyceride transfer protein, which produces β-lipoproteins. If this condition is left untreated, it can have detrimental consequences in an individual such as peripheral neuropathy, and in severe cases permanent blindness. However, nutrition therapy has been an effective tool to ameliorate the negative side effects of this condition.
Keywords: abetalipoprotenemia, MTTP gene, polymorphism
A rare genetic disease known as abetalipoproteinemia is a condition characterized by reduced plasma levels of LDL-cholesterol and apolipoproteinB (apoB) (Levy, 2015). This condition would inhibit a person from being able to absorb fats and fat-soluble vitamins (A, D, E and K), which would result in damage to the eyes, gastrointestinal system, blood, and nervous system. The apoliporoteinB is associated with newly formed chylomicrons and play an important role in lipid metabolism. The chylomicrons are large triglyceride-rich spherical particles containing triglycerides, cholesteryl esters, phospholipids, vitamins A and E, free cholesterol, and apolipoproteins on the surface (Gropper and Smith, 2012). Mutations to the MTTP gene responsible for the synthesis of apoB can have adverse effects to affected individuals. This review paper will explore the causes, inheritance pattern, frequency, signs, symptoms, and the treatment for abetalipoproteinemia.
When an MTTP gene mutation occurs, it results in aberrant formation of apolipoprotein. The cytogenic location of the MTTP gene is 4q23, which represents the long (q) arm of chromosome 4 at position 23 in Homo sapiens, and its molecular location is found between base pairs 99,564,078 and 99,623,997. This single nucleotide polymorphism may occur when the amino acid glycine is replaced with a premature stop signal at position 865 (G865X) in the MTTP gene, which provides instructions for making the microsomal triglyceride transfer protein (MTT) (Shoulders et al., 1993). When MTT is mutated, a cell is no longer able to produce β-lipoproteins, which are molecules made up of apoB, cholesterol, phospholipids, and triglycerides (Sharp et al, 1993).
Abetalipoproteinemia is genetically transferred in an autosomal recessive manner, meaning that both parents are carriers of the mutated gene but do not show any manifestations of the condition. However, the parents carrying the mutation have a 25% probability of having an affected offspring. This rare metabolic disorder has a frequency of <1 in 100,000 and the most affected population are Ashkenazi Jewish descendants from Eastern and Central Europe (Rola et al., 2008).
Different individuals affected by abetalipoproteinemia show physiological manifestations that if left untreated can have detrimental consequences to health. Some of the most common signs of the disease are failure to thrive in infancy, diarrhea, steatorrhea, acanthocytosis (abnormal erythrocytes), slower intellectual development, peripheral neuropathy, poor muscle coordination, ataxia, intention tremors, decreased night and color vision, and in severe cases permanent blindness (Zemel et al. 2008). However, the symptoms will vary from one person to another. According to the Human Phenotype Ontology database, 80 to 99% of affected individuals show symptoms of intestinal malabsorption. Whereas 30 to 79% of affected individuals show the other symptoms previously mentioned except for intestinal malabsorption. The best way to test for this condition is by having the affected subject undergo a genetic test by reaching out to a health care provider or genetic specialist. In addition, parents have the option to do a prenatal test during pregnancy to assess any potential risks of genetic mutations.
The good news is that there are dietary modification treatments for this condition to alleviate the negative effects of the disease. A nutritionist or qualified medical professional should be reached out to obtain the proper dietary counseling. It is recommended that the affected individuals have a low-fat diet to allow the absorption of other vital nutrients. In addition, it is recommended to take high doses of oral vitamin E supplementation, ranging in doses from 2400 to 12000 IU (Kayden, 2001). High doses of vitamin A ranging from 100 to 400 IU per kilogram are recommended to ameliorate any deficiencies; however, some patients have reported toxicity from high intakes. Given that in some cases patients are diagnosed with low serum ionized calcium and bony abnormalities, vitamin D supplements are recommended with daily doses of 1000 mg per day. Other supplementary nutrients that some individuals should consider are vitamin K, iron, and folic acid. However, a well-balanced diet should be a priority for any affected individuals with abetalipoproteinemia (Zamel et al., 2008).
Even though Abetalipoproteinemia is a rare genetic condition, it is important to understand its causes, prevalence, symptoms, and nutritional interventions. Nutrition therapy has been an effective tool to improve the quality of life of affected individuals. It is important to obtain counseling from professionals such as registered dietitians or nutrition scientists.
References
Kayden HJ. (2001). The genetic basis of vitamin E deficiency in humans. Nutrition, 17:797-798.
Levy, E. (2015). Insights from human congenital disorders of intestinal lipid metabolism. J. Lipid Res. 56: 945–962.
Sharp, D.L. Blinderman, K.A. Combs, et al. (1993). Cloning and gene defects in microsomal triglyceride transfer protein associated with abetalipoproteinaemia. Nature. 365: 65–69.
Shoulders, C.C., Brett, D.J., Bayliss, J.D., et al. (1993). Abetalipoproteinemia is caused by defects of the gene encoding the 97 kDa subunit of a microsomal triglyceride transfer protein. Hum. Mol. Genet. 2: 2109–2116.
Zamel, R., R. Khan, R.L., Pollex, et al. (2008). Abetalipoproteinemia: two case reports and literature review. Orphanet J Rare Dis. 3:19.
