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Phenylketonuria
Phenylketonuria patients lack phenylalanine hydroxylase.
Phenylketonuria is an autosomal recessive genetic disorder caused by mutations in the phenylalanine hydroxylase gene, leading to reduced enzyme activity and resulting in the accumulation of phenylalanine and its metabolic products in the body, causing the disease. Phenylketonuria is the most common congenital amino acid metabolism disorder, clinically presenting with intellectual developmental delays, lighter skin and hair pigmentation, and a musty urine odor. The disease is mainly caused by mutations in the phenylalanine hydroxylase gene, leading to reduced enzyme activity.
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.
Phenylketonuria treatment duration before discontinuation
Phenylketonuria is the first genetic metabolic disease that can be treated through dietary control. Once diagnosed with phenylketonuria, active treatment must be given, ceasing a natural diet and implementing a low-phenylalanine diet. Generally, a low-phenylalanine milk formula should be administered at least until the age of three. When the concentration of phenylalanine in the blood is adjusted to an ideal range, a small amount of natural diet can gradually be reintroduced. The reintroduced diet should still adhere to low-protein and low-phenylalanine standards.
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.
What can be eaten with phenylketonuria?
Phenylketonuria is primarily due to a deficiency of phenylalanine hydroxylase in the body, which prevents the conversion of phenylalanine to tyrosine. Due to the blockage of the metabolic pathway, secondary metabolic pathways are enhanced, leading to the deamination of phenylalanine and the production of large amounts of phenylpyruvic acid. Through oxidation, by-products such as phenylacetic acid, phenyllactic acid, and para-hydroxyphenylpyruvic acid are formed. The treatment mainly involves the use of low-phenylalanine formula milk. When the concentration in the blood reaches the desired level, natural foods can be gradually added in small amounts. Breast milk is the preferred choice as it contains only one-third of the phenylalanine content of cow's milk. For older infants and children, cow's milk, porridge, noodles, and eggs can be added. The principle for introducing foods should be based on low protein and low phenylalanine content, adjusted according to the phenylalanine concentration in the blood. Both too high and too low levels of phenylalanine can affect growth and development.
Is phenylketonuria characterized only by pale facial skin?
Phenylketonuria is a common amino acid metabolic disorder. It is primarily due to the deficiency of phenylalanine hydroxylase, which prevents the conversion of phenylalanine to tyrosine, leading to a series of clinical symptoms. These can manifest as intellectual disability, neuropsychiatric symptoms, eczema, skin scratching, pigment loss, and a musty odor. The skin whiteness mentioned is not merely facial pallor; it affects the entire skin because the benefits of tyrosine are reduced, leading to decreased melanin synthesis. Consequently, the hair of affected children can also be lighter and tend to be brown.
Can people with phenylketonuria eat meat?
Children with phenylketonuria should not eat meat and should try to eat as little as possible. Phenylketonuria is caused by a defect in the phenylalanine hydroxylase enzyme in the phenylalanine metabolic pathway, which results in a metabolic disorder of phenylalanine in the liver. Phenylketonuria is the first hereditary metabolic disease that can be treated by dietary control. All natural foods contain a certain amount of phenylalanine. Once diagnosed, children should stop consuming a natural diet and be given a low-phenylalanine diet for treatment. Meat is rich in protein and also contains a high amount of phenylalanine, thus the intake of meat must be restricted or minimized.
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.
Does phenylketonuria affect intelligence?
Phenylketonuria is a common amino acid metabolic disease, primarily caused by a deficiency of phenylalanine hydroxylase in the metabolic pathway of phenylalanine, preventing phenylalanine from converting into tyrosine. This leads to the accumulation of phenylalanine and its ketones in the body, which are then excreted in large amounts through urine. Its clinical manifestations are not uniform. The main clinical characteristic is intellectual disability, thus it does affect intelligence. Additionally, it can present various neuropsychiatric symptoms such as increased muscle tone, hyperreflexia, agitation, hyperactivity, convulsions, etc. It can also lead to reduced skin pigmentation and yellowing of hair among other symptoms. This disease can impact intelligence.
How is phenylketonuria tested?
Phenylketonuria is a treatable inherited metabolic disease, and early diagnosis is essential for early treatment. Currently, we have generally implemented a newborn disease screening system that requires collecting peripheral blood by pricking the heel of newborns after three days of breastfeeding, dropping the blood onto specialized filter paper and sending it to a screening laboratory for phenylalanine concentration measurement. If the concentration exceeds the confirmed value, further differential diagnosis and confirmation are needed. If treatment can begin early, especially within two to three weeks after birth, the prognosis is generally good. Normally, the concentration is less than 120 µmol/L; a fetal concentration of 1200 µmol/L would be considered mild phenylketonuria.