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Phenylketonuria
Phenylketonuria smells like mouse urine.
Phenylketonuria is a common amino acid metabolic disorder primarily caused by a deficiency of phenylalanine hydroxylase. This deficiency prevents phenylalanine from being converted to tyrosine, leading to the accumulation of phenylalanine and ketone bodies, which are then excreted in large amounts in the urine. This disease is relatively common among genetic amino acid metabolic disorders and is inherited as an autosomal recessive trait. Additionally, due to the lack of phenylalanine hydroxylase, phenylalanine is metabolized through another pathway, resulting in increased production of phenyllactic acid and phenylacetic acid, which are excreted through sweat and urine, giving off a mouse-like urine odor.
Early symptoms of phenylketonuria
Phenylketonuria is a hereditary metabolic disease caused by a deficiency or low activity of phenylalanine hydroxylase. Its main clinical manifestations include very obvious developmental delays in children and significantly lower IQ than their peers, severely affecting the child's growth and development. Due to the lack of this enzyme, the increase of abnormal metabolic products affects brain function, leading to symptoms such as seizures, convulsions, increased muscle tone, as well as hyperactivity and restlessness in children. The skin becomes particularly dry, prone to eczema, appears pale, and the hair turns yellow. The urine has a distinct mouse-like odor. Once diagnosed, early treatment is essential to reduce the sequelae of brain damage. The earlier the treatment, the better the prognosis. For these children, a special formula is needed, which is low in phenylalanine.
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.
Does phenylketonuria require chromosome testing?
Phenylketonuria is usually screened during the neonatal period through routine blood testing, where the level of phenylalanine in the blood is measured to screen each newborn. This enables early diagnosis and treatment, hence reducing the occurrence of intellectual disabilities. Phenylketonuria can also be screened prenatally before the birth of the newborn. It is an autosomal recessive genetic disorder, closely related to chromosomal abnormalities. Therefore, prenatal screening can be conducted by amniocentesis between the 16th to 20th weeks of pregnancy. Chromosomal abnormalities detected through the amniocentesis indicate that the fetus carries the pathogenic gene, meaning the child will be born with phenylketonuria. If both parents carry related genes, it is crucial to undergo prenatal screening and chromosomal analysis to eliminate the risk of the fetus developing the condition.
The causes of phenylketonuria
Phenylketonuria is a common autosomal recessive genetic disorder, the most frequent primary clinical manifestation among congenital amino acid metabolic disorders. It is characterized by intellectual disability, pale skin and hair pigmentation, and a mouse urine-like odor. The main cause is that phenylalanine is an essential amino acid for the human body. The phenylalanine ingested is partly used for protein synthesis and partly converted to tyrosine by the action of phenylalanine hydroxylase, which is necessary for the synthesis of substances like adrenaline, melanin, and thyroxine. The disease is mainly due to a deficiency of phenylalanine hydroxylase, which inhibits the conversion of phenylalanine to tyrosine, resulting in increased concentrations of phenylalanine in the blood, cerebrospinal fluid, and various tissues. At the same time, due to the predominance of the main pathway, the enhancement of the secondary metabolic pathway leads to the deamination of phenylalanine by transaminase, producing a large amount of phenylpyruvic acid, which through oxidation produces a large amount of phenylacetic acid, phenyllactic acid, and p-hydroxyphenylpyruvic acid. These metabolic by-products are excreted in large quantities in the urine, and the high concentrations of phenylalanine and its by-products accumulate extensively in brain tissue, thereby causing damage to brain cells.
Phenylketonuria should be treated in which department?
Phenylketonuria is a common autosomal recessive genetic disorder due to a deficiency in the enzymes involved in the metabolic pathway of phenylalanine. It is a genetic metabolic disease. After the birth of a child, newborn screening is conducted for this disease. If a child is diagnosed with phenylketonuria or suspected of having the condition, it is common to visit a pediatric neurology department at a children's hospital. Phenylketonuria mainly causes varying degrees of intellectual disability, and some children may even experience epileptic seizures. Additionally, about 90% of affected children gradually develop lighter skin and hair, reduced iris pigmentation, dry skin, eczema, and a distinctive mouse-like urine odor, which is due to the excretion of phenylacetic acid in urine and sweat. It is a challenging genetic metabolic disorder to treat, requiring special dietary management. It is advisable to bring the child to the pediatric neurology department. Some hospitals may have a specialized department for genetic metabolic diseases. If such a department is available, it is recommended to consult there; otherwise, pediatric neurology is the appropriate alternative.
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.
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.
Causes of Phenylketonuria
The cause of phenylketonuria is that phenylalanine is an essential amino acid for the human body. Some of the phenylalanine ingested is used for protein synthesis, while another part is converted into tyrosine by the action of phenylalanine hydroxylase. Only a small amount of phenylalanine undergoes a secondary metabolic pathway and is converted into phenylpyruvate under the action of transaminase. Due to the reduced activity of phenylalanine hydroxylase in affected children, phenylalanine cannot be converted into tyrosine, leading to an extremely high concentration of phenylalanine in blood, cerebrospinal fluid, and tissues. This, through a bypass metabolic pathway, results in the production of a large amount of phenylpyruvate, phenylacetate, phenyllactate, and p-hydroxyphenylacetate. The high concentration of phenylalanine and its metabolic products then leads to brain damage, which is the cause of the disease.
Is the incidence of phenylketonuria high?
Phenylketonuria is an autosomal recessive hereditary disease and is the most common congenital amino acid metabolic disorder. The main clinical manifestations include distinctive features such as intellectual disability, light skin and hair pigmentation, and a mouse-like urine odor, which is named after the large amounts of phenylketone acid metabolites excreted in the urine. The incidence of this disease varies by race and region, and the overall incidence in China is approximately 1:11,000, meaning one in eleven thousand. The incidence is higher in the northern population than in the southern population, though it is not particularly high.