MedGen

Phenylketonuria (commonly known as PKU) is an inherited disorder that increases the levels of a substance called phenylalanine in the blood. Phenylalanine is a protein building block (an amino acid) that is obtained from eating certain foods (such as meat, eggs, nuts, and milk) and in some artificial sweeteners. If PKU is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.

The signs and symptoms of PKU vary from mild to severe. The most severe form of this disorder is known as classic PKU. Infants with classic PKU appear normal until they are a few months old. Without treatment, these children develop permanent intellectual disability. Seizures, delayed development, behavioral problems, and psychiatric disorders are also common. Untreated individuals may have a musty or mouse-like odor as a side effect of excess phenylalanine in the body. Children with classic PKU tend to have lighter skin and hair than unaffected family members and are also likely to have skin disorders such as eczema.

Less severe forms of this condition, sometimes called variant PKU and non-PKU hyperphenylalaninemia, have a smaller risk of brain damage. People with very mild cases may not require treatment.

PKU can often be managed by following a diet that is low in phenylalanine. Since phenylalanine is found in all proteins, the PKU diet consists of avoiding meat, dairy, nuts, tofu, and other foods that are high in protein. Infants with PKU need to be fed with a low-protein formula. Affected individuals are often limited to certain fruits and vegetables and foods containing fats and sugars (such as butter, jelly, pasta, and potato chips). The artificial sweeter aspartame, which is found in diet soda and many other low-calorie items, should be avoided as it contains high amounts of phenylalanine. The amount of phenylalanine that is safe to consume is different for each person. Affected individuals should work with a health care professional to develop an individualized diet. 

Babies born to mothers who have PKU and are not following a low-phenylalanine diet have a significant risk of intellectual disability because they are exposed to very high levels of phenylalanine before birth. These infants may also have a low birth weight and grow more slowly than other children. They may also have heart defects or other heart problems, an abnormally small head size (microcephaly), and behavioral problems. Women with PKU who are not following a low-phenylalanine diet (and may have high levels of phenylalanine) also have higher risk of pregnancy loss.

 [from MedlinePlus Genetics]

Phenylalanine hydroxylase (PAH) deficiency results in intolerance to the dietary intake of the essential amino acid phenylalanine and produces a spectrum of disorders. The risk of adverse outcome varies based on the degree of PAH deficiency. Without effective therapy, most individuals with severe PAH deficiency, known as classic PKU, develop profound and irreversible intellectual disability. Affected individuals on an unrestricted diet who have phenylalanine levels above normal but below 1,200 µmol/L (20 mg/dL) are at much lower risk for impaired cognitive development in the absence of treatment. [from GeneReviews]

A rare form of phenylketonuria, an inborn error of amino acid metabolism, characterized by blood phenylalanine (Phe) concentrations of 120-600 micromol/L with or without clinical manifestations of impaired cognitive function, and behavioral and developmental disorders. [from ORDO]

A mild to moderate form of phenylketouria (PKU), an inborn error of amino acid metabolism, characterized by blood phenylalanine concentrations of 600-1,200 micromol/L and manifests with reduced cognitive function and behavioral and developmental disorders. Dietary phenylalanine tolerance is 400-600 mg/day. [from ORDO]