Do children with mild phenylketonuria need treatment?

Written by Yan Xin Liang
Pediatrics
Updated on May 06, 2025
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Phenylketonuria is a common amino acid metabolic disease, primarily due to the deficiency of phenylalanine hydroxylase, preventing phenylalanine from being converted into tyrosine. This leads to the accumulation of phenylalanine and its keto acids in the body, which are then excreted in large amounts in the urine. It is a relatively common genetic amino acid metabolic disorder and is inherited as an autosomal recessive trait. Even in cases of mild symptoms, treatment is still required. The main treatment is a low-phenylalanine diet, which involves dietary control, as phenylalanine is an essential amino acid for protein synthesis. Special phenylalanine-formula milk powder is fed to infants, and at this stage, it is appropriate to add some complementary foods such as starchy vegetables and fruits, focusing on low-protein foods. The goal of dietary treatment is to maintain an appropriate concentration of phenylalanine in the blood.

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Written by Yan Xin Liang
Pediatrics
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Why does phenylketonuria lead to intellectual disability?

Phenylketonuria is a common amino acid metabolic disease, mainly due to the deficiency of phenylalanine hydroxylase, which prevents phenylalanine from being transformed into tyrosine, leading to the accumulation of phenylalanine and its keto acids. Due to the lack of tyrosine in the body, it affects the growth and development of the brain, resulting in intellectual developmental delays. Therefore, children with phenylketonuria often exhibit intellectual disabilities, as well as some psychiatric and neurological symptoms, such as increased muscle tone, restlessness, hyperactivity, abnormal behavior, and heightened excitability.

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Written by Yan Xin Liang
Pediatrics
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How to diagnose phenylketonuria?

Phenylketonuria is a treatable hereditary metabolic disease, where our primary goal is early diagnosis and treatment. Currently, a universal newborn screening system has been widely implemented. The standard procedure requires that after three days of breastfeeding, peripheral blood is collected from the newborn's heel, dropped onto specialized blood collection filter paper, and, once dried, sent to a screening laboratory to measure the phenylalanine concentration. If the phenylalanine concentration exceeds the cutoff value, further differential diagnosis and confirmation are conducted. Treatment typically starts two to three weeks after birth, and the prognosis is good. Additionally, diagnostic tests for phenylketonuria include urine ferric chloride, 2,4-dinitrophenylhydrazine tests, urinary purine profile analysis, and tetrahydrobiopterin loading test. Another method is through DNA analysis.

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Written by Yan Xin Liang
Pediatrics
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Is the incidence of phenylketonuria high?

Phenylketonuria is an autosomal recessive hereditary disease and is the most common congenital amino acid metabolic disorder. The main clinical manifestations include distinctive features such as intellectual disability, light skin and hair pigmentation, and a mouse-like urine odor, which is named after the large amounts of phenylketone acid metabolites excreted in the urine. The incidence of this disease varies by race and region, and the overall incidence in China is approximately 1:11,000, meaning one in eleven thousand. The incidence is higher in the northern population than in the southern population, though it is not particularly high.

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Written by Zeng Hai Jiang
Pediatrics
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What foods should children with phenylketonuria eat?

Phenylketonuria is a common amino acid metabolic disorder, an autosomal recessive genetic disease, and a type of hereditary metabolic disease that can be treated through dietary control. All natural foods contain certain amounts of phenylalanine. Therefore, once diagnosed, children should stop consuming natural diets and start treatment with a phenylalanine-restricted diet, including low-phenylalanine yogurt. Treatment should continue at least until the age of 12. When the concentration of blood phenylalanine is controlled at an ideal level, gradually add small amounts of natural food, adhering to the principle of low protein and low phenylalanine in the added foods.

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Written by Zeng Hai Jiang
Pediatrics
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Can people with phenylketonuria not eat things high in protein?

Phenylketonuria patients should avoid foods high in protein, as phenylketonuria is a common amino acid metabolism disorder caused by a deficiency of phenylalanine hydroxylase in the metabolic pathway of phenylalanine, leading to disordered metabolism of phenylalanine in the liver. Phenylketonuria is a hereditary metabolic disease that can be managed through diet. Natural foods contain certain amounts of phenylalanine. Once diagnosed, the patient should cease consuming natural diets and switch to a phenylalanine-restricted diet. Foods rich in protein have higher amounts of phenylalanine, thus, those with phenylketonuria should not consume foods high in protein.