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 Wu Ben Rong
Pediatrics
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Is phenylketonuria related to a baby's face turning dark?

Baby's dark complexion is not directly related to phenylketonuria (PKU). Phenylketonuria is a relatively common amino acid metabolism disorder caused by a deficiency in the enzyme needed for the metabolic pathway of phenylalanine, preventing it from being converted into tyrosine. This leads to the accumulation of phenylalanine and keto acids in the body, which are then excreted in large amounts through urine. Children with phenylketonuria may have lighter hair and skin color within months of birth due to insufficient melanin synthesis. Typically, their skin is very pale; therefore, if a child has darker facial skin, it is not related to phenylketonuria. This condition might be due to genetic factors or prolonged exposure to the sun among other reasons.

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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.

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Written by Wang Lin Zhong
Pediatrics
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Early symptoms of phenylketonuria

Phenylketonuria is a hereditary metabolic disease caused by a deficiency or low activity of phenylalanine hydroxylase. Its main clinical manifestations include very obvious developmental delays in children and significantly lower IQ than their peers, severely affecting the child's growth and development. Due to the lack of this enzyme, the increase of abnormal metabolic products affects brain function, leading to symptoms such as seizures, convulsions, increased muscle tone, as well as hyperactivity and restlessness in children. The skin becomes particularly dry, prone to eczema, appears pale, and the hair turns yellow. The urine has a distinct mouse-like odor. Once diagnosed, early treatment is essential to reduce the sequelae of brain damage. The earlier the treatment, the better the prognosis. For these children, a special formula is needed, which is low in phenylalanine.

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Written by Zeng Hai Jiang
Pediatrics
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Can phenylketonuria be detected before a newborn is born?

Phenylketonuria can be screened prenatally before the birth of a newborn. The procedure involves genetic screening using amniotic fluid drawn through amniocentesis between the 16th and 20th week of pregnancy. Phenylketonuria is an autosomal recessive hereditary disease, greatly associated with chromosomal abnormalities. If chromosomal abnormalities are detected through amniocentesis, indicating the presence of pathogenic genes, it confirms that the fetus will be born with phenylketonuria. If both parents carry the relevant genes, prenatal screening is still necessary to rule out the risk of the disease in the fetus.

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Written by Yan Xin Liang
Pediatrics
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Is phenylketonuria characterized only by pale facial skin?

Phenylketonuria is a common amino acid metabolic disorder. It is primarily due to the deficiency of phenylalanine hydroxylase, which prevents the conversion of phenylalanine to tyrosine, leading to a series of clinical symptoms. These can manifest as intellectual disability, neuropsychiatric symptoms, eczema, skin scratching, pigment loss, and a musty odor. The skin whiteness mentioned is not merely facial pallor; it affects the entire skin because the benefits of tyrosine are reduced, leading to decreased melanin synthesis. Consequently, the hair of affected children can also be lighter and tend to be brown.