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 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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How is phenylketonuria diagnosed?

How is phenylketonuria diagnosed? Firstly, we start with screening, which is usually done when the newborn is 3 to 7 days old by heel prick to collect peripheral blood, which is then dropped onto specialized filter paper for the determination of phenylalanine concentration. If the concentration of phenylalanine is above the cutoff value, further determination of phenylalanine concentration is conducted. The normal concentration is less than 120 umol/L. If the concentration of phenylalanine is greater than 1200 umol/L, it suggests severe phenylketonuria. Moderate levels are above 360 umol/L, and mild levels are above 120 umol/L but less than 360 umol/L. Furthermore, diagnosis can be confirmed through DNA analysis, currently available tests include screening for mutations in the phenylalanine hydroxylase gene.

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Written by Yao Li Qin

Pediatrics

1min 4sec

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Is phenylketonuria often misdiagnosed?

Phenylketonuria belongs to congenital hereditary metabolic disorders and is caused by enzyme deficiencies in the phenylalanine metabolic pathway. Misdiagnosis of phenylketonuria is not common; if the disease develops, meaning that the child has typical clinical manifestations, it is relatively easy to diagnose. However, once a child exhibits the typical clinical manifestations of phenylketonuria such as blood phenylalanine levels, by the time of diagnosis the child may already have varying degrees of neurological damage, meaning the child might already have intellectual disabilities. Therefore, in such cases, we cannot rely solely on clinical symptoms for diagnosis but should instead carry out newborn disease screening promptly after birth. By diagnosing and treating before any clinical symptoms appear, we can prevent the occurrence of neurological complications, allowing the child to grow and develop like a normal child.

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Written by Tong Peng

Pediatrics

1min 1sec

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Does phenylketonuria easily cause a cold?

Phenylketonuria does not easily cause a cold, as a cold is a type of infectious disease mainly caused by various pathogen infections and stimuli, leading to symptoms such as cough, fever, and runny nose. Phenylketonuria is a common amino acid metabolism disorder caused by a deficiency of the enzyme required for phenylalanine to convert into tyrosine, resulting in excessive excretion of phenylalanine in urine. This disease is a recessive hereditary disorder, which can lead to intellectual disability, neuropsychiatric symptoms, and pigment loss. Due to the lack of melanin, affected children often present with yellow hair, pale skin and sclera, and their urine has a mousy odor. They may also suffer from eczema, vomiting, and diarrhea. Phenylketonuria is one of the few treatable hereditary metabolic diseases, so it generally does not cause symptoms of a cold.

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Written by Wu Ben Rong

Pediatrics

52sec

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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.