Hereditary Fructose Intolerance
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Reasons why a person suffering from Hereditary Fructose Intolerance is not able to metabolize fructose
Hereditary fructose intolerance is a disease caused by the deficiency of aldolase B enzyme. A person suffering from HFI should not ingest fructose nor sucrose as this may lead to a severe disease called hypoglycemia and also the build-up of other dangerous substances in the liver. According to Bouteldia & Timson1, Mutations in the ALDOB gene cause this condition. These genes are inherited in a recessive manner. The gene also provides the directives for making the aldolase B enzyme. The enzyme is located in the liver and helps in fructose breakdown into energy. The alterations of ALDOB gene then reduce the capability of aldolase B enzyme to metabolize fructose.
Fructose digestion starts in the small intestines and because the body cannot absorb solid molecules then it is broken down into fructose and sucrose particles by sucrose enzyme. Fructose molecules then enter the small intestines lining through a channel into the bloodstream. Bouteldia & Timson1 also explained that after fructose enters the bloodstream, it then travels with all the other absorbed nutrients for metabolism in the liber. Metabolism then occurs in the liver. The process of metabolism of fructose in the liver is called fructolysis.
Fructose metabolism is started by its phosphorylation in the liver to D-fructose 1- phosphate. This is characterized via an enzyme called fructokinase. According to Goudsmit2 ,when there is the deficiency aldolase, D-fructose 1-phosphate accumulates in the liver and therefore inhibiting a kinase reaction. This results in a slower removal of fructose in the bloodstream. Goudsmit2 also explained that fructose may be phosphorylated in the muscle or as adipose tissue when their concentration goes high.2 This is done by an enzyme called hexokinase. D-fructose 6-phosphate produced then enters the catabolic pathways or can be changed to glycogen. To avoid hypoglycemia, it’s therefore released into the blood.
Human liver aldolase works together with D-fructose 1-phosphate and D-fructose 1, 6-biphosphate substrates. Patients with hereditary fructose intolerance indicate a significant functioning of fructose 1,6-biphosphate than the fructose 1-phosphate in the liver tissues. There is also the increase in enzyme elevation due to ingestion of D-fructose. Liver cirrhosis and fibrosis are some of the chronic diseases that are accompanied by hereditary fructose disorder. There are histologic changes from 1 to 1.5h in the liver hepatocytes after fructose ingestion. The amount of AST and GPT released then increases.
Parents of individuals with hereditary fructose intolerance disease carry a copy of the mutated gene. According to Lenaspa et al3, there are several symptoms of HFI disorder, for example, poor feeding in case the patient is a baby, vomiting, convulsions, excessive sleepiness, avoidance of fruits, irritability, and prolonged jaundice. Continuous ingestion of fructose-containing fruits may lead to the damage of the kidney and liver. When the infants are affected, they fail to gain weight and grow. It also may lead to low blood sugar. The liver of the affected may also enlarge. Lenaspa et al3 reported that continuous exposure to fructose may lead to coma and death due to kidney and liver failures. Symptoms vary from one person to another. According to coffee4, eliminating fructose and sucrose from the diet helps in the treatment of the disease though when severe it may not intestines in treating the liver disease. Therefore, a person suffering from hereditary fructose intolerance is not able to metabolize fructose.
Mode of a function of mutagenesis agent
A gene is a distinct stretch of a DNA that shows something about who someone is. Genetics is the study of genes and genetic variations and inheritance. Genes vary from one individual to another and are often inherited. According to Guichard et al5 genes are made of DNA which is made of a chain of nucleotides. There are four types of nucleotides namely adenine, cytosine, guanine and thymine. Genetic information is found in the nucleotides. Guichard et al5 also explained that genes are part of the DNA sequence and there are two types of DNA sequence namely introns and exons. DNA often replicates itself, therefore, changing the structure of the gene.
Mutation is the change in the DNA sequence during replication according to Maruyama et al6. This causes the change in genes and chromosomes. The change in mutation could be harmful beneficial or even silent in some cases as explained by Maruyama et al6. There are different types of mutations and vary according to the region in which the sequence of the genetic material has been changed as explained by Pane et al7. Mutations are classified according to the cause of mutation, the kind of change caused to the gene or its effect on the function of the gene.
The first type of mutation is called substitution mutations. In this mutation, a single nucleotide mapped onto another. The corresponding base pair is altered for organisms with double-stranded DNA or RNA. It can have different effects depending on the position of the change. Insertions and deletion is another type of mutation and this involves the removal and addition of stretches in the nucleotide sequence. According to Pane et al7 they cause frame sheet mutations and therefore, altering the sequence downstream of amino acids of the mutation site. They also lead to change in polypeptide length, therefore, creating proteins causing aggregates that are non-functional. Large-scale mutation is a third type of mutation. This is where changes in the nucleotide sequence occur on a large scale. This involves many base pairs and nucleotides. Amplification is one type of this mutation where segments of genetic materials are present in multiple copies and another I deletions where a large chunk of genetic material is removed.
According to Kostoff & Lau8 there are different types of mutagenesis agents which include electromagnetic radiation. Ultra-Violet light causes the formation of pyrimidine dimers called TT and CC, therefore, causing point mutations. If two dimer occur in one strand of the DNA this causes, the UV light causes the fusion leading to the formation of thymine dimer. UV light is absorbed by nitrogenous bases and is maximum at 260nm. The duplication error rate at the site of thymine dimer because the confirmation of the DNA is changed. For dimers to form the DNA sequence must have an adjacent pyrimidine in order. Kostoff & Lau8 also ascertained that a change in a DNA sequence of a gene for example, in addition of a gene, could cause an exaggeration of a certain characteristic in an organism. Cancer is also another consequence of ultra-violet light. It can eventually cause death.
References
Bouteldja N, Timson DJ. The biochemical basis of hereditary fructose intolerance. Journal of inherited metabolic disease. 2010 Apr 1;33(2):105-12.
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