GALT Gene and Occurrence of Galactosemia - Essay Example

Download file to see previous pages A person with classic galactosemia is unable to metabolize galactose sugar into glucose in the liver and is susceptible to various diseases mostly of the liver and central nervous system (The New York Times). This paper attempts to explore the organization, structure, history, and regulatory elements associated with the GALT gene, and understand how a mutation will lead to the occurrence of galactosemia.

GALT is the official symbol for the galactose-1-phosphate uridyl transferase gene. The position of GALT is 13 on the shorter p arm of chromosome 9. The more exact molecular positioning of GALT on chromosome 9 can be described as starting at base pair 34,646,585 till ending at base pair 34,650,594 (Genetics Home Reference). The organization of GALT encompasses 11 exons spanning approximately 4-4.3 kb. The GALT gene encodes proteins with a 43 kDa molecular mass, consisting of about 379 amino acids in length. Two molecules or a dimer make up an active GALT enzyme and contain a molecular mass of around 88 kDa. It has been found that disruption in the Q188R region is the most common mutation found to cause classic galactosemia with a relative frequency of 60%. It is because a His-Pro-His motif is present at exon 6 in the functional site, which significantly impairs the entire gene functioning if a mutation occurs proximal to this region of the gene (Calderon, 939-40). People with classic galactosemia have been identified with over 180 mutations in the GALT gene. The structural illustration of the GALT gene is presented in fig 01.

The genetic deficiency is inherited in an autosomal recessive manner requiring a copy of the GALT sequence from both carrier parents (Elsas). Though the incidence rate of GALT deficiency is different among nations, about 1 in every 62 000 has been estimated in pan-ethnic populations. The incidence rate in travelers from the Irish population is also significant (Murphy et al., 550). The GALT gene is responsible for the synthesis of the GALT enzyme in the liver. The GALT enzyme catalyzes the breakdown of galactose-1-phosphate into available glucose as an energy source in the second step of the Leloir metabolism pathway (Reichardt, 194). Galactose is a product of the larger sugar Lactose found in all milk and dairy products. The reaction also produces UDP-galactose which is further employed in the formation of sugar-containing proteins and fats. These galactose-containing proteins and fats have multiple roles in various body functions such as chemical signaling pathways, construction of cell structure, molecule transportation, and energy production (Genetics Home Reference).

The GALT enzyme reveals a ping-pong, bi-bi kinetics that describes the binding of one domain of enzyme with uridine diphosphate (UDP) glucose, which forms an enzyme-UDP-glucose intermediate. The uridine monophosphate stays attached to GALT and the glucose-1-phosphate becomes free. The GALT uridine monophosphate then binds galactose-l-phosphate to develop GALT-UDP-galactose. The UDP-galactose becomes free of the GALT and allows it to cycle the next reaction (Elsas and Lai, 40). The failure of the GALT enzyme to metabolize galactose results in the building up of Galactose-1-phosphate to toxic levels in the body, which can give rise to several health issues such as jaundice, feeding issues, weight faltering, liver damage, bleeding, hyperammonemia, sepsis, infections, cataracts, dyspraxia, ovarian failure, and neural abnormalities (Elsas).

Von Ruess was the first to report a case of galactosemia in breastfeed infants in his publication in 1908. By 1917, galactosemia had been widely recognized as an inherited disorder, and ingestion of milk and milk products was prohibited for patients. However, Mason and Turner were the first ones to describe galactosemia as a syndrome in 1935. Later, Leloir and co-researchers explained the metabolic pathways for galactose in the early 1950s. In 1956, the defective gene was identified for galactosemia and the newborn screening method developed by Guthrie and Paigen detected it in 1963 Bolivia, 2011). The evaluation of patients for outcomes began in the 1980s, and genotype/phenotype associations were determined by the  1990s when the cDNA and GALT genes were cloned and sequenced by using probes similar to recognized microbial amino acid sequences. As the amino acid sequence of Escherichia coli was significantly similar to the GALT gene in humans, understanding of the mutation impact on enzymatic activity made significant progress (Elsas and Lai, 40). ...Download file to see next pages Read More