How is phenylketonuria diagnosed?

Written by Hu Qi Feng

Pediatrics

Updated on September 04, 2024

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Phenylketonuria screening is routinely conducted in China for all newborns. This involves pricking the heel to collect peripheral blood, which is then dropped on specialized filter paper and dried. The samples are sent to a screening laboratory for the measurement of phenylalanine concentration. If the concentration exceeds the threshold, further testing for phenylalanine is conducted. Normally, the concentration should be less than 120 micromoles per liter. Additionally, an analysis of the urinary purine profile can be performed.

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Written by Zeng Hai Jiang

Pediatrics

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Can phenylketonuria be breastfed?

Once a child with phenylketonuria is diagnosed, natural diets should be ceased and a low-phenylalanine diet treatment should be initiated. Treatment with a low-phenylalanine formula should continue at least until the age of 12. Breast milk is the ideal natural food for infants; therefore, although breastfeeding should be temporarily halted after diagnosis, it should not be completely stopped so that it can be promptly reintroduced once blood phenylalanine levels are controlled. When blood phenylalanine levels are controlled to an ideal concentration, gradually reintroduce small amounts of natural diet, preferably starting with breast milk, as it contains only one-third the phenylalanine content of cow's milk.

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Written by Yan Xin Liang

Pediatrics

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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 Yan Xin Liang

Pediatrics

1min 21sec

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The pathogenesis of phenylketonuria

Phenylketonuria is an autosomal recessive genetic disorder. Phenylalanine, which is an essential amino acid required by the human body, is partly used for protein synthesis after ingestion and partly converted into tyrosine via the action of phenylalanine hydroxylase, which is necessary for the synthesis of substances such as adrenaline, melanin, and thyroxine. Phenylketonuria is mainly caused by a deficiency of phenylalanine hydroxylase, which prevents the conversion of phenylalanine to tyrosine. This leads to increased levels of phenylalanine in the blood, cerebrospinal fluid, and various tissues. Additionally, as the primary metabolic pathway is blocked, secondary metabolic pathways are enhanced. Under the action of transaminases, phenylalanine undergoes deamination to produce large quantities of phenylpyruvic acid, which is further metabolized to produce phenylacetic acid, phenyllactic acid, and p-hydroxyphenylpyruvic acid, among other byproduct metabolites. These are excreted in large amounts in the urine. The high concentration of phenylalanine and its byproduct metabolites accumulates in brain tissue, leading to damage to brain cells and resulting in a range of clinical symptoms.

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Written by Yan Xin Liang

Pediatrics

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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.

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Written by Zeng Hai Jiang

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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.