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 Hu Qi Feng

Pediatrics

34sec

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How is phenylketonuria diagnosed?

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 Yan Xin Liang

Pediatrics

1min 18sec

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Phenylketonuria is caused by how?

Phenylketonuria is caused by how? It is an autosomal recessive genetic disease, mainly due to a mutation in the phenylalanine hydroxylase gene, which leads to a reduction in the activity of phenylalanine hydroxylase. Phenylalanine is an essential amino acid in the human body. The phenylalanine ingested is partly used for protein synthesis, and the rest is converted into tyrosine by the action of phenylalanine hydroxylase, with only a small amount of phenylalanine being converted into phenylpyruvic acid through a minor metabolic pathway under the action of transaminase. Due to the reduced activity of phenylalanine hydroxylase, phenylalanine cannot be converted into tyrosine, resulting in an extremely high concentration of phenylalanine in the blood, cerebrospinal fluid, and tissues. Through a bypass metabolism, a large amount of phenylpyruvic acid, phenylacetic acid, phenyllactic acid, and p-hydroxyphenylacetic acid are produced. High concentrations of phenylalanine and its metabolites thus lead to brain damage. Due to the synthesis disorder of tyrosine, this also leads to symptoms such as light skin and hair pigmentation.

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Written by Zeng Hai Jiang

Pediatrics

40sec

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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

48sec

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Phenylketonuria lacks what enzyme?

Phenylketonuria is an autosomal recessive genetic disorder primarily caused by mutations in the phenylalanine hydroxylase gene. This leads to reduced activity of phenylalanine hydroxylase, accumulation of phenylalanine and its metabolites in the body, and the onset of the disease. Phenylketonuria is the most common congenital amino acid metabolism disorder. Clinically, it is mainly characterized by intellectual developmental delays, light skin and hair pigmentation, and a mousey urine odor. The incidence of this disease varies by ethnicity and region. In China, the incidence is approximately 1 in 11,000.

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Written by Yan Xin Liang

Pediatrics

1min 3sec

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Phenylketonuria has what symptoms?

Phenylketonuria is an autosomal recessive genetic disorder. It is the most common congenital amino acid metabolism disorder. Its main clinical characteristics include intellectual disability, light skin and hair pigmentation, and a mousy urine odor. This name arises from the excretion of large amounts of phenylketonic acid metabolites in children's urine, which leads to the characteristic odor. Typically, affected children appear normal at birth, but symptoms usually begin to appear between three to six months of age, with most significant symptoms evident by one year. The most prominent issue is delayed intellectual development, with intelligence quotients often falling below normal. Skin pigmentation usually becomes lighter several months after birth due to insufficient melanin synthesis, resulting in hair turning from black to yellow and a paler skin complexion. Additionally, a distinct mousy body odor is produced due to the excretion of excessive phenylacetic acid in urine and sweat.