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Phenylketonuria
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.
Does phenylketonuria require lifelong dietary control?
Theoretically, phenylketonuria requires lifelong dietary control. Phenylketonuria is caused by a deficiency in phenylalanine hydroxylase in the metabolic pathway of phenylalanine, leading to disordered metabolism of phenylalanine in the liver. Phenylketonuria is the first genetic metabolic disease that can be managed through diet. Since natural foods all contain certain amounts of phenylalanine, once diagnosed, affected children should cease consuming natural diets and should be treated with a low-phenylalanine diet. Treatment with a low-phenylalanine formula should continue at least until the age of 12. When the concentration of phenylalanine in the blood is controlled at an ideal level, natural foods can gradually be reintroduced in small amounts. The reintroduction of food should still follow the principles of low protein and low phenylalanine. The types and amounts of food that each child can add vary individually and are related to the severity of the enzyme deficiency.
Can phenylketonuria be cured?
Phenylketonuria is one of the few treatable genetic metabolic diseases. It strives for early diagnosis and treatment to avoid irreversible damage to the nervous system. Once diagnosed, aggressive treatment should be given. The younger the age at which treatment starts, the better the effect. The main approach is to use a low-phenylalanine formula milk. When the blood concentration drops to a normal level, natural diet can gradually be added in small amounts, with breast milk being the preferred choice, as it contains only one-third the phenylalanine of cow's milk. Larger infants can add cow's milk, porridge, noodles, eggs, etc. The added foods should also follow the principle of being low in protein and low in phenylalanine, because concentrations of phenylalanine that are too high or too low will affect growth and development. Low-phenylalanine treatment should continue at least until after puberty. Lifelong treatment is more beneficial for patients. This disease can only control symptoms, and lifelong treatment is the best; it cannot be completely cured.
"Phenylketonuria weakly positive" means what?
The indication of weakly positive phenylketonuria suggests a re-examination of blood phenylalanine levels. Generally, there are no obvious specialized clinical symptoms of phenylketonuria in the newborn period. Some newborns may experience feeding difficulties, vomiting, or irritability, and the manifestations of phenylketonuria gradually appear after three months of age. Currently, hospitals routinely screen newborns for phenylketonuria. This screening is conducted 72 hours after birth and must be completed by no later than 20 days post-birth. If the result of the blood phenylalanine test is weakly positive or positive, further testing is generally recommended to determine whether the infant has phenylketonuria or if other factors are affecting the phenylalanine levels.
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.
Do adults with phenylketonuria need to eat special food?
Phenylketonuria may not necessarily require a special diet in adulthood. It is the first genetic metabolic disorder that can be treated through dietary control. Natural foods all contain a certain amount of phenylalanine, so once children with phenylketonuria are diagnosed, they should stop their natural diet and instead be given a low-phenylalanine diet. Low-phenylalanine formula treatment should continue at least until the age of 12. When the concentration of phenylalanine in the blood is controlled at an ideal level, a gradual addition of natural foods can be made. Larger infants and children can add foods such as milk, porridge, noodles, and eggs. However, these added foods should still primarily be low in protein and low in phenylalanine.
What foods should children with phenylketonuria eat?
Phenylketonuria is a common amino acid metabolic disorder, an autosomal recessive genetic disease, and a type of hereditary metabolic disease that can be treated through dietary control. All natural foods contain certain amounts of phenylalanine. Therefore, once diagnosed, children should stop consuming natural diets and start treatment with a phenylalanine-restricted diet, including low-phenylalanine yogurt. Treatment should continue at least until the age of 12. When the concentration of blood phenylalanine is controlled at an ideal level, gradually add small amounts of natural food, adhering to the principle of low protein and low phenylalanine in the added foods.
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.
Can phenylketonuria cause hair to turn white?
Phenylketonuria is caused by a mutation in the phenylalanine hydroxylase gene, resulting in reduced or lost enzyme activity, and a metabolic disorder of phenylalanine in the liver. Children with phenylketonuria lack phenylalanine hydroxylase, leading to reduced tyrosine and normal metabolic products. The content of phenylalanine in the blood increases, secondary metabolic pathways are enhanced, producing phenylpyruvic acid, phenylacetic acid, and phenyllactic acid, which are excreted in large amounts in the urine. High concentrations of phenylalanine and its abnormal metabolic products inhibit tyrosinase, leading to disturbances in melanin synthesis. Therefore, untreated children will gradually show changes in hair color from black to yellow and skin lightening after three months.
What is the normal value for phenylketonuria?
Phenylketonuria is a common autosomal recessive genetic disorder and the most common congenital amino acid metabolism disorder. It primarily manifests as intellectual disability, light skin and hair pigmentation, and a mousey urine odor. Newborn screening includes routine screening for phenylketonuria as it is a treatable hereditary metabolic disorder, emphasizing the importance of early diagnosis and treatment. Nowadays, newborn screening systems are widely implemented. Generally, this involves collecting a blood sample through a heel prick, dropping the blood on specialized filter paper, and then air drying before sending it to a screening laboratory to measure the phenylalanine concentration. Typically, a normal concentration should be less than 120 micromoles per liter. If the phenylalanine concentration exceeds 1200 micromoles per liter, it can be diagnosed as classical phenylketonuria.