The pathogenesis of phenylketonuria

Written by Hu Qi Feng

Pediatrics

Updated on September 02, 2024

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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

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 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 Yan Xin Liang

Pediatrics

48sec

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The earliest manifestation of phenylketonuria

Children with phenylketonuria usually start showing symptoms within 3 to 6 months after birth: Firstly, the nervous system is affected, which can be seen in developmental delays in intelligence, often with IQs lower than normal. Symptoms may include restlessness, depression, hyperactivity, or minor epileptic seizures. A few may exhibit increased muscle tone or heightened tendon reflexes. A few months after birth, due to insufficient melanin synthesis, the skin and hair undergo changes. Hair color may shift from black to yellow, the skin may appear very pale, and eczema is also more common. Additionally, because of the excretion of greater amounts of phenylacetic acids in urine and sweat, there may be a distinct mouse-like urine odor.

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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.

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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.