Abetalipoproteinemia or ABL is a genetic disease that results into increased blood cholesterol levels. It is characterized by the presence of only HDL as plasma lipoprotein and the absence of apoB from the plasma. The significance of the increase or decrease in values of HDL or apoB-containing lipoprotein in the plasma is that there will be a direct effect in there interlinked metabolism and also the transfer of apolipoproteins and lipids inside the plasma compartment(Katsunori Ikewaki, 1994).
Reservoir for excess phospholipids, cholesterol, and apolipoproteins that are freed during the lipolysis of the surface of triglyceride-rich proteins; receiver of excess cholesterol from cells; and carrier of cholesterol in the reverse cholesterol transport are the functions of HDL. A decrease in the level of HDL apolipoproteins will alter the performance of this functions hence the accumulation of cholesterol in the blood. This lipoprotein has two major apolipoproteins which are the Apolipoproteins A-I (apoA-I) and Apolipoproteins E.
In the case of Abetalipoproteinemia, aside from the absence of apolipoproteins B in the plasma the levels of HDL and apoA-I are significantly below the normal value. Increased catabolism rate and decrease anabolism of apoA-I are the causes of its decline in blood plasma of ABL patients(Katsunori Ikewaki, 1994). Familial hypercholesterolemia is a genetic disorder that is due to any mutations of the gene that codes for the proteins that are involved in the functions and metabolism of cholesterol.
Other terms of this genetic disorder are Type II hyperlipoproteinemia, Hypercholesterolemic xanthomatosis, and Low density lipoprotein receptor mutation. Patients with this disease have heart attacks at an early age due to increased level of cholesterol starting at birth(Health, 2007). Heterozygous familial hypercholesterolemia (HeFH) is an inherited genetic condition wherein there a mutation of the allele of the LDL receptor (LDL-R) gene into a heterozygous state. A normal gene for LDL-R gene from a parent and abnormal gene for LDL-R from the other is transmitted to the individual.
The individual’s LDR-R proteins are not all dysfunctional but rather just only half of it. The accumulation of blood cholesterol level is because only half the LDR receptors in the liver are removing the LDL particles thus reducing the function rate by fifty percent. Cholesterol buildup begins at birth then eventually leads to tendon xantomas, corneal stroma and arterosclerosis(DESCAMPS, 2007). Another type of gene mutation that results to familial hypercholesterolemia is those with mutations in the apolipoproteins B (apoB) or familial defective apolipoprotein B. Glutamine is substituted for arginine in the codes for apolipoproteins B.
Heterozygous familial hypercholesterolemia is more severe in terms of LDL cholesterol elevation when compared to familial defective apolipoproteins B(DESCAMPS, 2007). The next type of familial hypercholesterolemia is a mutation that originates from the mutation of the nucleotide 836 in Exon 9 of the Cholesteryl Ester Transfer Protein (CETP) gene. Functions of CETP are the following: catalysis of hetero-exchange and net mass transfer of cholestyl esters and triacylglycerols between different densities of lipoprotein in the plasma; and contributes to the reverse cholesterol transport pathway in coordination with plasma enzyme lecithin.
The latter function returns cholesterol back to the liver either for reuse or excretion. Large portion of the patients that have this type of mutation are of Japanese ancestry. Manifestations of the condition are: moderate hypercholesterolemia with low LDL cholesterol(Dolphin, 1998).
References
DESCAMPS, O. S. (2007). Familial hypercholesterolemia in Belgium Genetic, clinical and epidemiologic aspects. Unpublished Thesis for the obtention of the PhD degree in Public Health Orientation: genetic epidemiology., UNIVERSITE CATHOLIQUE DE LOUVAIN. Dictionary, S. s. M. (Ed. ) (2006) Stedman’s Medical Dictionary (28 ed. ). Lippincott Williams & Wilkins. Dolphin, P. J. (1998). A Novel Mutation in the Human Plasma Cholesteryl Ester Transfer Protein (CETP) Gene Leading to CETP-Deficiency in a Nova Scotian Patient: A Review of CETP Deficiency The Dalhouse Medical Journal. Health, U. N. L. o. M. a. N. I. o. (2007). Medical Encyclopedia. Retrieved October 29, 2007, from http://www. nlm. nih. gov/medlineplus/ency/article/000392. htm
Katsunori Ikewaki, D. J. R. , * Loren A. Zech, and H. Bryan Brewer, Jr. (1994). In vivo metabolism of apolipoproteins A-I and E in patients with abetalipoproteinemia: implications for the roles of apolipoproteins B and E in HDL metabolism. NHLBI, N. H. L. a. B. I. (2006). High blood cholesterol. Diseases and Conditions Index Retrieved October 29 2007, from http://www. nhlbi. nih. gov/health/dci/Diseases/Hbc/HBC_WhatIs. html NIH, N. I. o. H. (2005 ). High Blood Cholesterol: What You Need To Know. NIH Publication.