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Classification and external resources
ICD-10 E70.0
ICD-9 270.1
OMIM 261600 261630
DiseasesDB 9987
MedlinePlus 001166
eMedicine ped/1787 derm/712
MeSH D010661

Phenylketonuria (PKU) is a genetic disorder (a disease a person is born with) where a person's body cannot break down an amino acid called phenylalanine. Amino acids are necessary to make proteins, an important part of the human body. Phenylalanine only comes from the food we eat; our bodies do not make any by themselves.

How it works

People without PKU produce an enzyme called phenylalanine hydroxylase in their bodies. When they ingest phenylalanine, the body cannot use it, so this enzyme changes phenylalanine into tyrosine, which the body can use. In people with PKU, very little or no enzyme is made. Since the phenylalanine they eat is not being changed into tyrosine, it builds up in their bodies. This can cause problems with the way their bodies work.


Symptoms vary from person to person. Because of the rarity of PKU, many symptoms go undiagnosed or unrecognized. In addition, there are variations in the categories of PKU individual's. There are untreated, early treated, those returning to diet, Hyperphe, uncontrolled, and highly controlled. For your average infant a doctor will diagnose PKU with a quick blood test. Their symptom will be high PHE levels. If that infant goes undiagnosed for weeks or months, he/she may start to exhibit some or all of the following symptoms for uncontrolled PKU.

  • focus/concentration problems
  • seizures
  • lowered intelligence
  • tremors
  • problems with memory
  • gate problems
  • anxiety
  • skin problems
  • depression
  • mousy odor
  • aggression
  • irritability
  • phobias
  • mental fog
  • slower thinking and response
  • hyperactivity
  • lethargy
  • social anxiety
  • decreased motor function and hand/eye coordination
  • fatigue
  • psychotic symptoms
  • mild paralysis
  • autisic behaviors
  • social withdrawals
  • lack of autonomy
  • social maturity deficits
  • decreased positive emotions
  • low self-esteem


In the past, children with PKU almost always died from having too much phenylalanine in their bodies. Today, scientists know what foods have phenylalanine in them, and they have created a special diet for people with PKU. Since they cannot use it, people with PKU cannot eat foods that have a lot of phenylalanine, like eggs, meat and milk. An artificial sweetener called aspartame, which is used to favour take a lot of vitamins to make up for the foods they cannot eat, especially vitamins B6 and B12.

Babies with PKU are fed a special formula called Lofenelac. It has everything babies need to stay healthy, but with very little phenylalanine. There are also other formulas for older children and young adults, PhenylAde and other types are available, As well as Low Protein breads and flour (Made from corn instead of regular wheat)

Women with PKU who are pregnant or trying to get pregnant have to be especially careful to follow this diet. If they do not follow the diet, Their babies could be born with severe birth defects and mental retardation. Babies born to women with PKU who have followed the PKU diet throughout their pregnancy are usually healthy and do not necessarily but may develop PKU. Whether or not they have PKU themselves depends on the mother and father's genes. As well as the Fact that Genetics may play a part, But in fact there are people who are Carriers instead of hosts (Dormant Genes) that can be passed on until they resurface in the future generations. These are so far undetectable and random at best, However it is subject to debate whether it is the mother or fathers genes that are dominant.

While PKU kids are generally small in size and are usually attributed with blond hair and blue eyes, They also tend to have very fair skin (Noted only in female PKU currently) and tend to burn easily. Solar protection is a must for those who wish to work, play, or engage in activities outdoors.


Most people with PKU can live as long and healthy as anyone else if the low-phenylalanine diet is started when they are babies and continued for the rest of their lives. The symptoms will usually disappear after the diet is started.

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