When do people with phenylketonuria need to eat a special diet until?

Written by Zeng Hai Jiang

Pediatrics

Updated on January 07, 2025

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Phenylketonuria is the first genetic metabolic disease that can be treated through dietary control. Since natural foods contain certain amounts of phenylalanine, once children with phenylketonuria are diagnosed, they should stop consuming a natural diet and start a low-phenylalanine diet treatment. Treatment with a low-phenylalanine formula should continue at least until the age of 12. When the concentration of phenylalanine in the blood is controlled at an ideal level, gradually small amounts of natural diet can be reintroduced. The food added should adhere to the principles of being low in protein and phenylalanine.

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Written by Yan Xin Liang

Pediatrics

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How is phenylketonuria tested?

Phenylketonuria is a treatable inherited metabolic disease, and early diagnosis is essential for early treatment. Currently, we have generally implemented a newborn disease screening system that requires collecting peripheral blood by pricking the heel of newborns after three days of breastfeeding, dropping the blood onto specialized filter paper and sending it to a screening laboratory for phenylalanine concentration measurement. If the concentration exceeds the confirmed value, further differential diagnosis and confirmation are needed. If treatment can begin early, especially within two to three weeks after birth, the prognosis is generally good. Normally, the concentration is less than 120 µmol/L; a fetal concentration of 1200 µmol/L would be considered mild phenylketonuria.

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Written by Wu Ben Rong

Pediatrics

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Can phenylketonuria be treated with surgery?

Phenylketonuria (PKU) in children cannot be treated surgically. PKU is an autosomal recessive genetic disorder caused by a deficiency in the enzyme needed for the metabolic pathway of phenylalanine. Typically, there are no obvious symptoms in newborns, although some children may experience non-specific symptoms such as vomiting and feeding difficulties. If no relevant treatment is pursued, the child may gradually show signs of developmental delays in movement and intellect, and the hair might change from black to yellow while the skin tends to be paler. As the child grows older, the intellectual delays become more pronounced, and in severe cases, they might develop cerebral palsy. This disease can be treated in its early stages through dietary methods, and the younger the age at which treatment begins, the better the outcomes.

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Written by Yan Xin Liang

Pediatrics

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The earliest manifestation of phenylketonuria

Children with phenylketonuria usually start showing symptoms within 3 to 6 months after birth: Firstly, the nervous system is affected, which can be seen in developmental delays in intelligence, often with IQs lower than normal. Symptoms may include restlessness, depression, hyperactivity, or minor epileptic seizures. A few may exhibit increased muscle tone or heightened tendon reflexes. A few months after birth, due to insufficient melanin synthesis, the skin and hair undergo changes. Hair color may shift from black to yellow, the skin may appear very pale, and eczema is also more common. Additionally, because of the excretion of greater amounts of phenylacetic acids in urine and sweat, there may be a distinct mouse-like urine odor.

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Written by Zeng Hai Jiang

Pediatrics

38sec

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Phenylketonuria treatment duration before discontinuation

Phenylketonuria is the first genetic metabolic disease that can be treated through dietary control. Once diagnosed with phenylketonuria, active treatment must be given, ceasing a natural diet and implementing a low-phenylalanine diet. Generally, a low-phenylalanine milk formula should be administered at least until the age of three. When the concentration of phenylalanine in the blood is adjusted to an ideal range, a small amount of natural diet can gradually be reintroduced. The reintroduced diet should still adhere to low-protein and low-phenylalanine standards.

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Written by Yan Xin Liang

Pediatrics

53sec

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If phenylketonuria is not treated, what will happen?

Phenylketonuria (PKU) is an amino acid metabolic disorder primarily caused by a deficiency in phenylalanine hydroxylase. This deficiency prevents phenylalanine from being converted to tyrosine, leading to a significant accumulation of phenylalanine, which is then excreted in large quantities in the urine. It is a common genetic metabolic disorder. If not treated, it can lead to developmental delays in children, particularly in intellectual development, with markedly lower IQ than peers, especially noticeable in language development disorders. Additionally, it can also present with neurological and psychiatric symptoms such as agitation, hyperactivity, increased muscle tone, and hyperreflexia. There is also depigmentation of the skin and hair, and the urine may have a mousy odor.