Viral Infectious Disease: Phenylketonuria


Phenylketonuria is the most frequently diagnosed condition of genetic error of amino acid metabolism that is caused by damaged capacity to metabolize vital amino acid phenylalanine. Shortage of the phenylalanine hydroxylase enzyme (PAH) results in the increase of phenylalanine in the organism. In the majority of countries, including, the United States, Phenylketonuria is diagnosed by urine screening of the newborn baby. This condition is treatable, and if timely diagnosed, people can preserve normal intellectual development and life. Treatment is primarily oriented on keeping low levels of phenylalanine in the body with the help of specially developed diet and inclusion of supplements in the to daily food consumption.

Remainder of the paper is organized in the following way. First, structure of the Phenylketonuria virus is described with further description of the infection cycle. Next, pathology of the disease is presented with potential vaccines and prospects for antiviral drugs. Finally, paper summary is given in the discussion and conclusion sections.

Structure of the Virus

Phenylketonuria is a genetic recessive condition that is transmitted genetically. It is caused by the mutation in the gene of the hepatic enzyme phenylalanine hydroxelase (PAH) that converts it to tyrosine (Figure 1). This deficiency brings dysfunctions to the metabolic system and further development issues. Severe reduction of enzyme phenylalanine hydroxelase results in the accumulation of phenylalanine that is further converted into phenylpyruvate in the human body (Gonzalez & Willis, 2010).

Infectious Cycle

Effective functioning of gene responsible for the hepatic enzyme phenylalanine hydroxelase largely depends on the BH4 co-factor. Latter is synthesized endogenously (Wong, 2009). Synthesis of BH4 starts from synthesis of guanosine triphoshate (GTP) through the prerequisite action of 6-pyruvoltetrahydrobiopterin synthase (PTPS), sepiapterin reductase (SR), and GTP cyclohydrolase I (GTPCH). It is continued by further recycling of dihydropteridine reductase (DHDR).

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Accumulation of phenylalanine in the organism above 360 μmol per liter creates preconditions for the slowdown in the mental development. Moreover, it brings failure of growth, convulsions and microencephaly. The following up reduction of tyrosine results in the drop of hypopigmentation as well as fall in melanin biosynthesis (Argyros, & Wong, 2010).

Pathology and Disease

In the majority of cases, people are diagnosed to have classic type of Phenylketonuria. It entails dysfunctions of PAH that results in the increased levels of phenylalanine in the body with further secretion of phenylacetic acid and phenylpyruvic acid in the urine. For successful conversion of phenylalanine to tyrosine, non proteine cofactor BH4 is required. Inspection of the transformation causing Phenylketonuria reveals that classic type mutations are positioned However, there are other pathological forms of Phenylketonuria, including Phenylketonuria originated from the harmful synthesis of GTP-CH I, BH4, dihydropteridine reductase (DHPR) and/or 6-pyruvoyl tetrahydropterin (6-PTS). This condition is also known as biopterin metabolism (Steiner, 2011).

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Vaccine or Prospects for Vaccine

Phenylketonuria is a treatable condition. Treatment primarily includes a special diet to maintain low levels of phenylalanine in the organism, especially during early period of life when a child is developing and growing. In particular, people with Phenylketonuria are prohibited to consume a lot of eggs, milk and other diary products. There is a specially developed food for newborns, Lofenalac. At the same time it can be used by adults as a source of protein with low levels of phenylalanine. Moreover, addition of supplements into diet is also essential, including iron, fish oil, and carnitine (Behrman, Kliegman & Nelson, 2006).

Potential for Antiviral Drug

Recent pharmaceutical research has found that oral in-take of tetrahydrobiopterin (or BH4) may decrease level of this amino acid in the blood. Produced tetrahydrobiopterin in the form of pills, called Kuvan, is the first medicine for BH4-reponsive people with Phenylketonuria. This drug lowers levels of phenylalanine in the organism to the allowed levels. At the same time, there are other therapies that are currently studied. They include large neutral amino acids, enzyme substitution therapy with phenylalanine ammonia lyase (PAL) as well as gene therapy (Burton, Grange, & Milanowski, 2007).

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Prevalence of Phenylketonuria in the world varies from country to country. In the United States, its prevalence constitutes 4 cases per 100,000 of population. Incidence of the newly detected cases is 350 per 1 million of live births. At the same time, low rates of Phenylketonuria incidence are reported in poor countries, like African countries (1 case per 50,000 of population). Comparatively higher rates of incidence are notified in Turkey with around 1 case per 2600 births. At the same time Hungary, Estoni,a, Scotland, Denmark, France, Norway, Italy and some other countries also have high rates of incidence (Steiner, 2011). Numerous neonatal screening programs allow detection and diagnosis of Phenylketonuria among newborn babies. This prevents severe mental retardation and normal human development of individuals in case of following special diet. There is no evidence about gender preconditions for this disease. However, Phenylketonuria is more common among white and Asian population and fewer cases are detected among people with black color of skin.


A lot of improvements and advances in the knowledge of genetic background and treatment of Phenylketonuria have been made over the past few years. Diagnosis of Phenylketonuria at the early days of a newborn child allows introduction of the diet for a patient with low levels of phenylalanine. This prevents development of the neurological damages. Moreover, several therapies and medicines that modify disease are already available or on the stage of clinical trials. Finally, a forthcoming promising treatment of Phenylketonuria is developed based on the genetic therapy. 

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