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Phenylketonuria
Why does phenylketonuria lead to intellectual disability?
Phenylketonuria is a common amino acid metabolic disease, mainly due to the deficiency of phenylalanine hydroxylase, which prevents phenylalanine from being transformed into tyrosine, leading to the accumulation of phenylalanine and its keto acids. Due to the lack of tyrosine in the body, it affects the growth and development of the brain, resulting in intellectual developmental delays. Therefore, children with phenylketonuria often exhibit intellectual disabilities, as well as some psychiatric and neurological symptoms, such as increased muscle tone, restlessness, hyperactivity, abnormal behavior, and heightened excitability.
Why can't people with phenylketonuria eat vitamin C?
Phenylketonuria is a common amino acid metabolic disorder. It primarily occurs because the patient's liver lacks phenylalanine hydroxylase, leading to the inability of phenylalanine to convert into tyrosine. This causes phenylalanine to accumulate in large amounts in the body, and it cannot be excreted through urine, presenting some corresponding clinical symptoms. The diet for phenylketonuria mainly involves avoiding high-protein foods, such as dairy, eggs, and soy products. Additionally, spicy, raw, and greasy foods should be avoided as they can negatively impact the health of the child. It is also beneficial to include starch-rich foods in the diet, such as potato starch, vermicelli, pumpkin, and Chinese yam, as these foods are low in phenylalanine and high in carbohydrates. Furthermore, vitamin C can be consumed without restrictions in cases of phenylketonuria, and it should be taken in moderation.
How to determine if phenylketonuria is mild
Phenylketonuria severity is generally determined by clinical manifestations and blood phenylalanine concentration. Mild phenylketonuria is characterized by mild or asymptomatic intelligence, motor, and developmental delays, light hair and skin color, and a musty odor in urine and sweat. It includes clinical features such as seizures accompanied by abnormal mental and behavioral symptoms, with blood phenylalanine levels less than 120 to 360 micromoles per liter. This is primarily seen in a very small number of newborns or premature infants, or in cases where there is higher residual activity of phenylalanine hydroxylase enzyme.
How to diagnose phenylketonuria?
Phenylketonuria is a treatable hereditary metabolic disease, where our primary goal is early diagnosis and treatment. Currently, a universal newborn screening system has been widely implemented. The standard procedure requires that after three days of breastfeeding, peripheral blood is collected from the newborn's heel, dropped onto specialized blood collection filter paper, and, once dried, sent to a screening laboratory to measure the phenylalanine concentration. If the phenylalanine concentration exceeds the cutoff value, further differential diagnosis and confirmation are conducted. Treatment typically starts two to three weeks after birth, and the prognosis is good. Additionally, diagnostic tests for phenylketonuria include urine ferric chloride, 2,4-dinitrophenylhydrazine tests, urinary purine profile analysis, and tetrahydrobiopterin loading test. Another method is through DNA analysis.
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.
Does phenylketonuria easily cause a cold?
Phenylketonuria does not easily cause a cold, as a cold is a type of infectious disease mainly caused by various pathogen infections and stimuli, leading to symptoms such as cough, fever, and runny nose. Phenylketonuria is a common amino acid metabolism disorder caused by a deficiency of the enzyme required for phenylalanine to convert into tyrosine, resulting in excessive excretion of phenylalanine in urine. This disease is a recessive hereditary disorder, which can lead to intellectual disability, neuropsychiatric symptoms, and pigment loss. Due to the lack of melanin, affected children often present with yellow hair, pale skin and sclera, and their urine has a mousy odor. They may also suffer from eczema, vomiting, and diarrhea. Phenylketonuria is one of the few treatable hereditary metabolic diseases, so it generally does not cause symptoms of a cold.
Can phenylketonuria be prevented?
Phenylketonuria belongs to a recessive hereditary metabolic disease; how can we take preventive measures? First, we must avoid consanguineous marriages. Second, we need to conduct newborn screening to achieve early diagnosis, early detection, and early treatment. Third, for pregnant women with a family history of this disease, it is mandatory to use DNA analysis or methods like amniotic fluid testing for prenatal diagnosis of their fetuses. Prevention is better than cure. By taking preventive measures early, the chances of complications occurring are greatly reduced. If a baby shows symptoms of newborn phenylketonuria, parents should not take it lightly and should actively cooperate with the treatment.
Does phenylketonuria definitely cause intellectual disabilities when one grows up?
Phenylketonuria is a common amino acid metabolic disorder that is due to a deficiency of phenylalanine hydroxylase in the phenylalanine metabolic pathway, leading to metabolic disorder of phenylalanine in the liver. Phenylketonuria is the first genetic metabolic disorder that can be controlled and treated through diet. Once diagnosed, natural diet should be discontinued for the patient, and a low-phenylalanine diet should be administered. If phenylketonuria is diagnosed and treated early, intelligence can be normal. However, if not controlled, it can lead to delayed growth and development, especially in terms of intellectual development.
Does phenylketonuria have a distinctive facial appearance?
Phenylketonuria is characterized by a specific facial appearance, primarily presenting with pale skin and yellow hair. Some affected children may develop eczema due to a disruption in melanin synthesis, which results in a distinctive skin color. Additionally, there are neuropsychiatric abnormalities, such as intellectual disability, increased excitability, and heightened muscle tone. The urine of patients has a plastic-like smell, largely because phenylketonuria is a hereditary metabolic disease. Newborns exhibit hyperphenylalaninemia, but as harmful metabolites of phenylalanine are not present in high concentrations before feeding begins, initial conditions at birth are often normal. However, as diet is introduced and metabolite concentrations increase, specific clinical symptoms, including severe cases of epileptic seizures manifested as infantile spasms, nodding seizures, or other forms, become evident. Therefore, dietary management is essential in treatment.
If phenylketonuria is not treated, what will happen?
Phenylketonuria (PKU) is an amino acid metabolic disorder primarily caused by a deficiency in phenylalanine hydroxylase. This deficiency prevents phenylalanine from being converted to tyrosine, leading to a significant accumulation of phenylalanine, which is then excreted in large quantities in the urine. It is a common genetic metabolic disorder. If not treated, it can lead to developmental delays in children, particularly in intellectual development, with markedly lower IQ than peers, especially noticeable in language development disorders. Additionally, it can also present with neurological and psychiatric symptoms such as agitation, hyperactivity, increased muscle tone, and hyperreflexia. There is also depigmentation of the skin and hair, and the urine may have a mousy odor.