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

43sec

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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

37sec

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Can phenylketonuria eat corn?

People with phenylketonuria can eat corn. Phenylketonuria is a hereditary metabolic disease that can be treated through dietary control. Once diagnosed with phenylketonuria, one must stop a natural diet and switch to a low-phenylalanine diet. When the concentration of phenylalanine in the blood drops to an ideal level, natural foods can be gradually reintroduced in small amounts, but the diet must still adhere to low-protein and low-phenylalanine standards. Corn mainly consists of starch and does not contain phenylalanine, so individuals with phenylketonuria can eat corn.

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Written by Yan Xin Liang

Pediatrics

1min 13sec

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How is phenylketonuria cured?

Phenylketonuria is an autosomal recessive genetic disease, primarily due to a mutation in the phenylalanine hydroxylase gene which leads to reduced enzymatic activity, causing the accumulation of phenylalanine and its metabolites in the body, thereby leading to this disease. The main manifestations include developmental intellectual disabilities, light skin and hair pigmentation, and a musty urine odor. Once diagnosed, immediate treatment is necessary, mainly using a low-phenylalanine formula milk. Generally, when orally administering low-phenylalanine formula milk, it is essential to monitor the phenylalanine levels in the blood. Since each patient has a different tolerance level for phenylalanine, periodic determination of blood phenylalanine concentration is required in the dietary treatment. Such patients can only be treated long-term in this way; it is not curable nor can it be completely eradicated; treatment can only alleviate the symptoms and involves long-term administration of a low-phenylalanine diet.

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Written by Yan Xin Liang

Pediatrics

1min 34sec

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The causes of phenylketonuria

Phenylketonuria is a common autosomal recessive genetic disorder, the most frequent primary clinical manifestation among congenital amino acid metabolic disorders. It is characterized by intellectual disability, pale skin and hair pigmentation, and a mouse urine-like odor. The main cause is that phenylalanine is an essential amino acid for the human body. The phenylalanine ingested is partly used for protein synthesis and partly converted to tyrosine by the action of phenylalanine hydroxylase, which is necessary for the synthesis of substances like adrenaline, melanin, and thyroxine. The disease is mainly due to a deficiency of phenylalanine hydroxylase, which inhibits the conversion of phenylalanine to tyrosine, resulting in increased concentrations of phenylalanine in the blood, cerebrospinal fluid, and various tissues. At the same time, due to the predominance of the main pathway, the enhancement of the secondary metabolic pathway leads to the deamination of phenylalanine by transaminase, producing a large amount of phenylpyruvic acid, which through oxidation produces a large amount of phenylacetic acid, phenyllactic acid, and p-hydroxyphenylpyruvic acid. These metabolic by-products are excreted in large quantities in the urine, and the high concentrations of phenylalanine and its by-products accumulate extensively in brain tissue, thereby causing damage to brain cells.

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Written by Zeng Hai Jiang

Pediatrics

1min 1sec

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Does phenylketonuria require chromosome testing?

Phenylketonuria is usually screened during the neonatal period through routine blood testing, where the level of phenylalanine in the blood is measured to screen each newborn. This enables early diagnosis and treatment, hence reducing the occurrence of intellectual disabilities. Phenylketonuria can also be screened prenatally before the birth of the newborn. It is an autosomal recessive genetic disorder, closely related to chromosomal abnormalities. Therefore, prenatal screening can be conducted by amniocentesis between the 16th to 20th weeks of pregnancy. Chromosomal abnormalities detected through the amniocentesis indicate that the fetus carries the pathogenic gene, meaning the child will be born with phenylketonuria. If both parents carry related genes, it is crucial to undergo prenatal screening and chromosomal analysis to eliminate the risk of the fetus developing the condition.