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Phenylketonuria: Symptoms, Effects, and Prognosis

An Overview of Phenylketonuria (PKU)

Phenylketonuria is a genetic condition that causes an increases in the levels of a substance known as phenylalanine in the blood. This disorder is commonly known as PKU and the name was derived from the presence of a phenylketone in the urine. In addition, in 1943, Asbjörn Fölling discovered PKU while living in Norway (Hozyasz, 2020). It has been the model of inherited metabolic disorder. Asbjörn Fölling discovered the disorder by performing an analysis on two serious mentally retarded children.

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Phenylketonuria commonly referred to as PKU is a disorder caused by the accumulation of phenylalanine in the body. This occurs due to the lack of phenylalanine Hydroxylase (PAH) gene on chromosome 12. The disorder is hereditary, meaning that it can be passed from parent to child. If both parents have a faulty PAH gene, their child is at risk of developing the condition as shown in the figure above (Mayo Clinic, 2018). The main factor is that both parent must have the faulty gene. A mutation in both alleles of phenylalanine hydroxylase causes phenylketonuria.

Genetic Information

Genetic information provide details of the PAH gene causing the disorder. First, the PAH gene is situated on chromosome 12 within the bands 12q22-q24.1. Second, PKU is a single gene disorder because it is caused by changes in the DNA in a given gene and have predictable inheritance pattern. Third, the autosomal nature of the PAH gene means that it is not located in either X or Y sex chromosomes. Fourth, PKU is considered a point mutation because it is caused by a change in a single nucleotide of a DNA. Lastly, PKU is a recessive disorder, which means that both parents must have in order to pass it to offspring (Hozyasz, 2020).

Symptoms of PKU

There are various symptoms of phenylketonuria which can observed by a health provider. The first symptom is a bad smell in the breath, urine or skin. This smell is as a result of a build-up of phenylalanine in the body. The second symptom is intellectual disability, where an individual has limited cognitive functioning and skills. The third symptom is neurological problems, because of the structural and biochemical defects in the nervous system organs. The fourth symptom is the presence of rashes in an individual skin. The rashes are noticeable changes in the texture and color of the skin (Mayo Clinic, 2018).

The Effects of PKU

The effects of phenylketonuria on an individual ranges from physical, emotional and social aspects. First, phenylketonuria causes irreversible brain damage, which interferes with the manner in which the brain functions. Second, the disorder can result into delayed development and permanent intellectual disability. Third, PKU can cause behavioral, emotional and social problems. Fourth, PKU can also result in hyperactivity, which is characterized by impulsiveness, increased movements, short attention plan and many more (Mayo Clinic, 2018). Finally, it can lead to skin rashes, which are characterized by emergence of skin lesions

Diagnosis of PKU

A doctor can determine an individual has PKU using two mechanisms. First, he or she can focus on clinical manifestation presented by the patient. For example, an individual with more than half of the listed symptoms is likely to have the disorder. However, this is considered inaccurate because of the possibility of errors. Second, the doctor can also run a series of tests designed for PKU (Ceberio et al., 2019). The tests that can be used are Plasma phenylalanine screening, Guthrie inhibition assay test, Urine tests, and assess Magnetic resonance imaging (MRI) changes in patients. This is the most preferred test because of its accuracy during diagnosis.

Prognosis of Individuals with PKU

PKU is a genetic disorder that occurs gradually disorder and lacks a specific life expectancy. It does not reduce life expectancy with or without treatment. If it is discovered and treated promptly, one can lead a normal life. However, if it is not treated, the disorder can cause brain damage, behavioral issues and many more. People with PKU who stopped eating the PKU diet may benefit once they start the process again (Ceberio et al., 2019). Also, PKU can cause a stressor on family members with an individual with the disorder especially on the area of additional support and treatment adherence.

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Medication of PKU

The following are treatment options for PKU:

  1. Low-protein diet: This is due to the fact that individuals with PKU lack an enzyme allows them to effectively digest the phenylalanine, which is a component of protein.
  2. The current treatment involve eating of specialized diet that limits foods containing phenylalanine.
  3. Gene therapy: the process utilizes an injectable version of phenylalanine ammonium lyase, an enzyme that can replace phenylalanine hydroxylase (Ceberio et al., 2019).

Current Research

The National PKU Alliance is an organization established to improve the lives of individuals and families who have PKU. They are an important voice to the PKU community to assist solve some of the issues they experience. In addition, they are using peer-reviewed and targeted research in order to advance PKU research and accelerate the timeline for a cure. People with PKU receive education on issues experienced by individuals and families and offer necessary support.


One of the interesting stories about PKU is that of Bailey. He was diagnosed with PKU at birth and have managed to live with the disorder. When growing up, Bailey had to be conscious of his diet. He tagged along with his specially-prepared meals when going to school and other events. In addition, he had to drink his formula every morning, which contains all amino acid except phenyl (BioMarin Pharmaceutical Inc., 2020). After all this, Bailey is now an aspiring pilot and he is almost through with first-pilot license.


BioMarin Pharmaceutical Inc. (2020). Bailey – PKU: patient stories. BioMarin. Web.

Ceberio, L., Hermida, Á., Venegas, E., Arrieta, F., Morales, M., Forga, M., & Gonzalo, M. (2019). Phenylketonuria in the adult patient. Expert Opinion on Orphan Drugs, 7(6), 265-276. Web.

Harding, C. O. (2019). Prospects for cell-directed curative therapy of phenylketonuria (PKU). Molecular Frontiers Journal, 3(02), 110-121. Web.

Hozyasz, K. K. (2020). Atypical phenylketonuria: Over 60 years from the discovery of tetrahydrobiopterin. Pielęgniarstwo i Zdrowie Publicize Nursing and Public Health, 10(4), 277-282. Web.

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Mayo Clinic. (2018). Phenylketonuria (PKU) – Symptoms and causes. Web.

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