Mechanism of phenylketonuria

Written by Hu Qi Feng
Pediatrics
Updated on September 03, 2024
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Phenylketonuria is characterized by reduced activity of phenylalanine hydroxylase, which fails to convert phenylalanine to tyrosine, causing extremely elevated levels of phenylalanine in the blood, cerebrospinal fluid, and tissues. This leads to the production of large amounts of phenylpyruvic acid, phenylacetic acid, phenyllactic acid, and p-hydroxyphenylacetic acid via alternative pathways. High concentrations of phenylalanine and its metabolic products can cause brain damage, which manifests as developmental intellectual disabilities, changes in skin and hair pigmentation, and a mousy urine odor, all part of a clinical syndrome.

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Written by Wu Ben Rong
Pediatrics
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Can phenylketonuria be treated with surgery?

Phenylketonuria (PKU) in children cannot be treated surgically. PKU is an autosomal recessive genetic disorder caused by a deficiency in the enzyme needed for the metabolic pathway of phenylalanine. Typically, there are no obvious symptoms in newborns, although some children may experience non-specific symptoms such as vomiting and feeding difficulties. If no relevant treatment is pursued, the child may gradually show signs of developmental delays in movement and intellect, and the hair might change from black to yellow while the skin tends to be paler. As the child grows older, the intellectual delays become more pronounced, and in severe cases, they might develop cerebral palsy. This disease can be treated in its early stages through dietary methods, and the younger the age at which treatment begins, the better the outcomes.

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Written by Yan Xin Liang
Pediatrics
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The pathogenesis of phenylketonuria

Phenylketonuria is an autosomal recessive genetic disorder. Phenylalanine, which is an essential amino acid required by the human body, is partly used for protein synthesis after ingestion and partly converted into tyrosine via the action of phenylalanine hydroxylase, which is necessary for the synthesis of substances such as adrenaline, melanin, and thyroxine. Phenylketonuria is mainly caused by a deficiency of phenylalanine hydroxylase, which prevents the conversion of phenylalanine to tyrosine. This leads to increased levels of phenylalanine in the blood, cerebrospinal fluid, and various tissues. Additionally, as the primary metabolic pathway is blocked, secondary metabolic pathways are enhanced. Under the action of transaminases, phenylalanine undergoes deamination to produce large quantities of phenylpyruvic acid, which is further metabolized to produce phenylacetic acid, phenyllactic acid, and p-hydroxyphenylpyruvic acid, among other byproduct metabolites. These are excreted in large amounts in the urine. The high concentration of phenylalanine and its byproduct metabolites accumulates in brain tissue, leading to damage to brain cells and resulting in a range of clinical symptoms.

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Written by Zeng Hai Jiang
Pediatrics
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Can people with phenylketonuria not eat things high in protein?

Phenylketonuria patients should avoid foods high in protein, as phenylketonuria is a common amino acid metabolism disorder caused by a deficiency of phenylalanine hydroxylase in the metabolic pathway of phenylalanine, leading to disordered metabolism of phenylalanine in the liver. Phenylketonuria is a hereditary metabolic disease that can be managed through diet. Natural foods contain certain amounts of phenylalanine. Once diagnosed, the patient should cease consuming natural diets and switch to a phenylalanine-restricted diet. Foods rich in protein have higher amounts of phenylalanine, thus, those with phenylketonuria should not consume foods high in protein.

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Written by Hu Qi Feng
Pediatrics
43sec home-news-image

Mechanism of phenylketonuria

Phenylketonuria is characterized by reduced activity of phenylalanine hydroxylase, which fails to convert phenylalanine to tyrosine, causing extremely elevated levels of phenylalanine in the blood, cerebrospinal fluid, and tissues. This leads to the production of large amounts of phenylpyruvic acid, phenylacetic acid, phenyllactic acid, and p-hydroxyphenylacetic acid via alternative pathways. High concentrations of phenylalanine and its metabolic products can cause brain damage, which manifests as developmental intellectual disabilities, changes in skin and hair pigmentation, and a mousy urine odor, all part of a clinical syndrome.

doctor image
home-news-image
Written by Hu Qi Feng
Pediatrics
48sec home-news-image

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.