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

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 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 Hu Qi Feng

Pediatrics

48sec

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The pathogenesis of phenylketonuria

Phenylketonuria is an amino acid metabolic disease caused by a deficiency of phenylalanine hydroxylase. Phenylalanine is an essential amino acid for the human body, and it is partially converted into tyrosine by phenylalanine hydroxylase. Due to the reduced activity of phenylalanine hydroxylase, phenylalanine cannot be transformed into tyrosine. This leads to extremely high concentrations of phenylalanine in the blood, cerebrospinal fluid, and tissues. Through alternative metabolic pathways, large amounts of phenylpyruvic acid, phenylacetic acid, phenyllactic acid, and others are produced. High concentrations of phenylalanine and its metabolic products can cause brain damage.

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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.

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Written by Quan Xiang Mei

Pediatrics

1min 2sec

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Does phenylketonuria cause liver dysfunction?

Phenylketonuria generally does not cause abnormalities in liver function. Phenylketonuria is a common amino acid metabolic disorder, mainly due to a deficiency of an enzyme in the phenylalanine metabolic pathway, preventing phenylalanine from being converted into tyrosine. This leads to the accumulation of phenylalanine and its keto acids, which are then excreted in large amounts in the urine. This disease is a relatively common genetic amino acid metabolic defect. Once diagnosed with phenylketonuria, the main treatment is a dietary therapy, which includes a low-phenylalanine diet. It is important during the upbringing of children to ensure that the child's living environment is quiet and comfortable. Therefore, in terms of prevention of the disease, it is important to avoid consanguineous marriage, conduct newborn screening, and focus on early detection and early treatment.