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

1min

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Can phenylketonuria be cured?

Once phenylketonuria is diagnosed, immediate treatment is necessary; the younger the age at which treatment is started, the better the prognosis. The main approach is to use a low phenylalanine formula milk for treatment. Once the blood phenylalanine concentration has decreased to the desired level, we can gradually begin adding small amounts of natural diet. For small infants, breast milk is preferred since it contains much less phenylalanine than cow's milk. For older infants, additions such as cow's milk, porridge, noodles, and eggs are acceptable, but supplements should still follow the principle of being low in protein and phenylalanine. The amount and frequency of these additions should be determined based on the phenylalanine concentration, as too high or too low levels can affect growth and development. This condition can only be managed by controlling symptoms and maintaining blood phenylalanine levels. Long-term treatment is required; it cannot be cured, only controlled.

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Written by Hu Qi Feng

Pediatrics

45sec

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Phenylketonuria Clinical Symptoms

Phenylketonuria may appear normal at birth, but symptoms usually start to appear between three to six months, with the symptoms becoming most evident at one year old. These are often manifestations of the nervous system, with prominent developmental delays in intelligence. The IQ is often lower than normal, and there may be abnormal behaviors, minor epileptic seizures, and, in a few children, increased muscle tone and hyperactive tendon reflexes. Due to insufficient melanin synthesis a few months after birth, affected children’s hair color changes from black to yellow, their skin is fair, and skin eczema is relatively common. Due to the elevated excretion of phenylacetic acid in urine and sweat, there is a distinct mouse-like urine smell.

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Written by Zeng Hai Jiang

Pediatrics

49sec

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"Phenylketonuria weakly positive" means what?

The indication of weakly positive phenylketonuria suggests a re-examination of blood phenylalanine levels. Generally, there are no obvious specialized clinical symptoms of phenylketonuria in the newborn period. Some newborns may experience feeding difficulties, vomiting, or irritability, and the manifestations of phenylketonuria gradually appear after three months of age. Currently, hospitals routinely screen newborns for phenylketonuria. This screening is conducted 72 hours after birth and must be completed by no later than 20 days post-birth. If the result of the blood phenylalanine test is weakly positive or positive, further testing is generally recommended to determine whether the infant has phenylketonuria or if other factors are affecting the phenylalanine levels.

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Written by Zeng Hai Jiang

Pediatrics

1min 2sec

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Does phenylketonuria require lifelong dietary control?

Theoretically, phenylketonuria requires lifelong dietary control. Phenylketonuria is caused by a deficiency in phenylalanine hydroxylase in the metabolic pathway of phenylalanine, leading to disordered metabolism of phenylalanine in the liver. Phenylketonuria is the first genetic metabolic disease that can be managed through diet. Since natural foods all contain certain amounts of phenylalanine, once diagnosed, affected children should cease consuming natural diets and should be treated with a low-phenylalanine diet. 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, natural foods can gradually be reintroduced in small amounts. The reintroduction of food should still follow the principles of low protein and low phenylalanine. The types and amounts of food that each child can add vary individually and are related to the severity of the enzyme deficiency.

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Written by Zeng Hai Jiang

Pediatrics

41sec

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How long does it take for phenylketonuria to manifest?

Phenylketonuria is a common amino acid metabolic disease. Most infants appear normal at birth and do not show any specific clinical symptoms during the neonatal period, although some newborns may experience symptoms such as feeding difficulties, vomiting, or irritability. Symptoms of phenylketonuria gradually appear in the first three months after birth, including changes such as hair turning from black to yellow, skin whitening, delayed growth and intellectual development, seizures, hyperactive reflexes, eczema, etc. The sweat and urine of affected children will have a mouse-like odor.