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

42sec

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Can patients with phenylketonuria eat fish and shrimp?

Children with phenylketonuria cannot eat fish and shrimp because phenylketonuria is caused by a deficiency of phenylalanine hydroxylase in the phenylalanine metabolic pathway, leading to metabolic disorder of phenylalanine in the liver. Phenylketonuria is the first hereditary metabolic disease that can be controlled by diet, as natural foods contain certain amounts of phenylalanine. Therefore, once diagnosed, children with phenylketonuria should stop consuming a natural diet and should be treated with a low phenylalanine diet. Fish and shrimp contain rich protein and high levels of phenylalanine, hence children with phenylketonuria cannot eat fish and shrimp.

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Written by Hu Qi Feng

Pediatrics

40sec

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Phenylketonuria inheritance mode

Phenylketonuria is an autosomal recessive genetic disorder, caused by a mutation in the phenylalanine hydroxylase gene leading to reduced enzyme activity. This results in the accumulation of phenylalanine and its metabolic products in the body, causing the disease. It is the most common congenital amino acid metabolism disorder and is clinically characterized by delayed intellectual development, changes in skin and hair pigmentation, and a mousy urine odor. The incidence of this disease in China is approximately 1 in 11,000, and it is inherited in an autosomal recessive manner.

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Written by Zeng Hai Jiang

Pediatrics

45sec

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Can phenylketonuria be breastfed?

Once a child with phenylketonuria is diagnosed, natural diets should be ceased and a low-phenylalanine diet treatment should be initiated. Treatment with a low-phenylalanine formula should continue at least until the age of 12. Breast milk is the ideal natural food for infants; therefore, although breastfeeding should be temporarily halted after diagnosis, it should not be completely stopped so that it can be promptly reintroduced once blood phenylalanine levels are controlled. When blood phenylalanine levels are controlled to an ideal concentration, gradually reintroduce small amounts of natural diet, preferably starting with breast milk, as it contains only one-third the phenylalanine content of cow's milk.

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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 Zeng Hai Jiang

Pediatrics

40sec

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Does phenylketonuria require a lifetime of special milk consumption?

Phenylketonuria does not require a lifetime of special milk consumption. It is the first genetically inherited metabolic disorder that can be treated through dietary control. Once diagnosed with phenylketonuria, one must stop a natural diet and begin treatment with a low-phenylalanine diet. The low-phenylalanine milk formula should be consumed at least until the age of 12. When the concentration of phenylalanine in the blood is controlled within the ideal range, it is possible to appropriately add a small amount of natural diet, adhering to principles of low protein and low phenylalanine.