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It's an autosomal recessive disorder caused by a mutation in both alleles of the gene for phenylalanine hydroxylase (PAH).

Usually, each parent of an individual who has PKU carries a copy of the altered gene and don't show symptoms, this can then be passed onto offspring (Bethseda 1998)

Phenotypes can vary from a very mild increase in blood phenylalanine concentrations to a severe classic phenotype with pronounced hyperphenylalaninemia. The incidence of this condition in the UK is around 1 in 10,000 newborns (Bethseda 1998)

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(Mevalia, no date)

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A prevalent disorder caused by an inborn error in amino acid metabolism, it's caused by mutations in the phenylalanine hydroxylase gene (PAH gene). (Nenan, Van Spronsen, Levy 2010)

Due to the gene alterations in the PAH gene, it leads to low levels of phenylalanine and phenylalanine can't be metabolised. Phenylalanine is an essential amino acid which is metabolised in the liver by PAH. (Nenan, Van Spronsen, Levy, 2010)

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Phenylketonuria can be treated from a young age to prevent further health implications in later life (NICHD. 2016).

The ‘main treatment’ for phenylketonuria is a controlled diet with low levels of protein while avoiding ‘high-protein foods’ like ‘meat, eggs and dairy products’  (NHS. 2019). This diet is extremely restrictive, controlling the consumption of lots of other foods like ‘potatoes and cereals’ (NHS. 2019).

Even though this diet is considered ‘successful’ it is ‘very difficult’ to follow in the long term and comes with the risk of ‘nutritional deficiencies’ (Cleary, M. A. et al. 2019) which must be avoided by supplementing with vitamins and ‘amino acid supplement’ (NHS. 2019).

In order to tackle these issues, ‘new treatments’ namely ‘sapropterin (a tetrahydrobiopterin analogue)’ and ‘large neutral amino acids’ are being explored (Cleary, M. A. et al. 2019). Research into ‘enzyme replacement therapy’ is also being conducted, with ‘clinical trials underway’ (Cleary, M. A. et al. 2019). To aid with diet control, ‘low-protein versions of common foods’ are available for people with phenylketonuria through prescription (NHS. 2019).

As well as avoiding foods with high protein content, it is important that people with phenylketonuria also avoid foods containing aspartame. ‘Aspartame is a sweetener’ in foods and drinks including diet fizzy drinks, ‘some alcopops’ and some medicines, and is ‘converted into phenylalanine in the body’ (NHS. 2019). It is important that substances for consumption containing aspartame are avoided so that phenylalanine levels in the body are not increased.

Babies are tested for phenylketonuria by testing blood for high phenylalanine levels if a ‘high phenylalanine level is confirmed’ the patient is put on the specialised diet immediately (NHS. 2019). Regular blood tests are required to monitor phenylalanine levels, and a dietitian will ‘create a detailed dietary plan’ for the patient which can be ‘revised’ as the patient ages (NHS. 2019). Provided that a person with phenylketonuria strictly follows their specialised diet and ‘their phenylalanine levels stay within certain limits’ they will not face changes to, or issues with their ‘natural intelligence’ (NHS. 2019).

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The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) has played a large role in the research of PKU related issues. In the 60s researchers backed by the NICHD, displayed a mass screening test that can screen for PKU. Before long the NICHD had led research on the idea of a restricted diet to treat newborns with PKU, along with the safety implications of this. (NICHD, 2016)

Due to this research in the United States, PKU has almost been eradicated as a cause of intellectual disabilities in newborn babies. (NICHD, 2016)

To this day the NICHD aids in screening access to newborn babies for PKU and other disorders. Moreover, they continue to study in this field for new screening methods, educating healthcare workers on screening and establishing a network of programs for screening babies. (NICHD, 2016)

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As Well as identifying and understanding the disease, NICHD backed researchers aim to improve the life of people with PKU, the highest priority was maternal PKU. Studies of pregnant women with PKU discovered that those with a low-phenylalanine pre and during pregnancy averted intellectual disabilities in their offspring. (NICHD, 2016)

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(azcentral.com, no date)

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In the UK screening of newborns is undertaken by the NHS which tests for PKU as well as many other conditions, if PKU is diagnosed treatment is given instantaneously to prevent complications in the future. (NHS, 2019)

Due to the work of the NICHD PKU rarely leads to any serious damage to people if treatment is started early. It can be controlled with regular blood tests through the course of the life of someone with PKU. (NHS, 2019)

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-Nenan, B, Van Spronsen, F, Levy, H, 2010, Phenylketonuria, The Lancet (British Edition), Vol.376 (9750), p.1417-1427
-Bethseda, MD, 1998, Phenylketonuria, Genes and Diseases [internet], National Centre for Biotechnology Information.
-Cleary, M. A. Skeath, R. 2019. Phenylketonuria. Symposium: Inborn errors of metabolism. 29(3), pp. 111-115.
-NHS. 2019. Phenylketonuria. [Online]. [Accessed 8 February 2021]. Available from: https://www.nhs.uk/conditions/phenylketonuria/
-NICHD. 2016. What are common treatments for phenylketonuria. [Online]. [Accessed 10 February 2021]. Available from: https://www.nichd.nih.gov/health/topics/pku/conditioninfo/treatments#:~:text=There%20is%20no%20cure%20for,disabilities%20and%20other%20health%20problems.&text=A%20person%20with%20PKU%20should,that%20specializes%20in%20the%20disorder.
-NICHD. 2016. Phenylketonuria (PKU): Research Activities and Scientific Advances. [Online]. [Accessed 9 February 2021]. Available from: https://www.nichd.nih.gov/health/topics/pku/researchinfo/activities
-NORD. 2019. Phenylketonuria. [Online]. [Accessed 10 February 2021]. Available from: https://rarediseases.org/rare-diseases/phenylketonuria/
-azcentral. [no date]. PKU is a rare genetic disease that affects one in every 15,000 births. [Online]. [Accessed 10 February 2020]. Available from: https://eu.azcentral.com/story/news/local/phoenix/2016/07/05/pku-one-childs-triumph-one-familys-battle-challenging-disorder/86200560/
-Mevalia. [no date]. autosomal recessive inheritance of PKU. [online]. [Accessed 10 February 2020]. Available from: https://www.mevalia.com/en/a/phenylketonuria
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Phenylketonuria also known as PKU affects from one in 13,500 to 19,000 new-borns in the USA, this disease affects people from the most ethnic backgrounds (NORD, 2019). However “in the United states, PKU is most common in people of European or native American Ancestry.” As stated by (NICHD, 2016).

Babies diagnosed with PKU may be weak and will have a low appetite, other symptoms include rashes, vomiting and irritation (NORD, 2019). Parents of babies born with PKU will start to notice a developmental delay in their child, untreated children will have an average IQ of less then 50 this is due to the breaking down of nerve fibres within the brain (NORD, 2019).

Pregnant females with untreated PKU are at high risk of having a miscarriage and If they are to have a child they are likely to be born with abnormal features and developmental abnormalities (NORD, 2019).

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In the UK it is detected on the newborn heel-prick screening sample, and this early detection can allow a strict low phenylalanine diet.

If undetected and untreated, PKU can lead to progressive intellectual impairment. It can also be identified through neonatal screening and several treatments can also help reduce the neurological complications of phenylketonuria. Examples of this treatment are enzyme substitution with phenylalanine ammonia-lyase that degrades phenylalanine and also gene therapy to restore phenylalanine hydroxylase activity (Cleary, Skeath 2019).

It's the first metabolic disorder to have a successful treatment, the first to be controlled by diet and the first to be detected by newborn screening (Cleary, Skeath 2019).