Phenylketonuria (PKU)


What Is The Phenylketonuria?

Phenylketonuria, abbreviated as PKU, is a genetic disease that usually occurs in infants. PKU is a disease caused by excessive accumulation of a substance called phenylalanine due to gene mutation. It can be manifested as mental retardation, pale skin and hair color, and the odor like rat urine.

PKUs are not common. Approximately 1 in 10,000 infants have a PKU.


What Is The Cause Of Phenylketonuria?

The cause of phenylketonuria is very clear and is related to genetic defects. If the parents are consanguineous, the risk of sufferring from PKU for their babies is significantly higher than that of the general population.

Phenylketonuria may be hereditary. It is an autosomal recessive genetic disease.


What Symptom Does Phenylketonuria Have?

Babies with phenylketonuria may have few abnormalities at birth and usually begin to have the following symptoms 3 to 6 months after birth:

  • Neurological abnormalities: mental retardation, IQ lower than their peers. May be accompanied by excitement, hyperactivity, depression, withdrawn and other behavioral abnormalities, may also be accompanied by seizures.
  • Skin and hair abnormalities: Children with PKU have a dark yellow hair, fair skin, and often skin eczema several months after birth.
  • Abnormal body odor: sweat and urine have obvious odor of rat urine.

How To Check For Phenylketonuria?

The follow tests are need to determine whether a baby have the Phenylketonuria or not:

  • Neonatal screening

Because of the greater harm of PKU and the identified etiology, all neonates should be screened for PKU 3–7 days after birth. Early treatment after the discovery of PKU can significantly improve the quality of life of the child in the future.

Initial screening for PKU was achieved by measuring phenylalanine concentration after blood collection from the heel.

  • Measured value of phenylalanine concentration

PKU could be ruled out if phenylalanine concentration was < 120 μmol/L (equivalent to 2mg/dl).

  • Which diseases are similar to phenylketonuria

Coenzyme tetrahydrobiopterin (BH4) deficiency is similar to phenylketonuria, but BH4 deficiency is more damaging to the nervous system and untreated children often die before the age of 1 year.

  • How does PKU differ from BH4 deficiency

The BH4 deficiency can be distinguished from PKU by the collection of urine and the analysis of uropterin chromatograms.


How To Prevent Phenylketonuria?

  • Phenylketonuria can effectively prevented

If one of the couple's relatives has phenylketonuria, or one of the couple has PKU, the couple can have DNA analysis and genetic counseling before deciding whether to get pregnant. Necessary prenatal genetic diagnosis during pregnancy can also prevent the birth of a diseased baby.


How To Treat Phenylketonuria?

Infants with phenylketonuria should be treated in a regular hospital in the neonatal department and pediatrics. The earlier treatment starts, the better the result will be. The main treatment for phenylketonuria is a low-phenylalanine diet:

  • For Infancy

Children are fed with low-phenylalanine formula first and then are gradually added with breast milk or other natural milk after the phenylalanine in the baby's blood is reduced. Breast milk is superior to milk and other natural milk because breast milk has less phenylalanine than other milk.

If breastfeeding, do not exceed 250mL per day. If you are feeding it with milk, do not take more than 100ml per day. The rest is made up with low phenylalanine formula.

Other nutrients that do not contain protein should be replenished like normal children.

  • After 1 Year Old

Give your child a sufficient amount of low-phenylalanine formula after the age of 1 year, but stop drinking natural milk.

At this time, children can already eat a variety of food, should pay attention to choose low protein food, such as green vegetables, fruits, potatoes, lotus root starch, vermicelli, noodles, steamed bread, sugar, etc. The protein content of rice is slightly higher, not more than 50 grams per day.

  • For Adolescence

Treatment with a low-phenylalanine diet should last at least until adolescence (about 12 years of age), when dietary control can be appropriately reduced. Of course, if you can stick to diet control for a lifetime, it will be more beneficial to the patient's body.

In addition to a low-phenylalanine diet, supplementation with tetrahydrobiopterin may be an alternative treatment in patients with mild hyperphenylalaninemia.

Does Phenylketonuria need reexamination?

Phenylketonuria requires reexamination, especially in infancy, and frequent reexamination. The interval of reexamination can be appropriately extended with age.

Since phenylalanine is a necessary amino acid for the human body, concentrations too high or too low are harmful. Blood phenylalanine concentrations should be monitored during the low-phenylalanine diet to assess the reasonableness of the dietary regimen and to try to control blood phenylalanine concentrations within the desired range.

Specific reexamination time: Blood phenylalanine concentration should be checked once a week within one year old, twice a month at the age of 1–12 years old, and once a month after 12 years old.

Can Phenylketonuria be cured completely?

Phenylketonuria is not completely curable. Phenylketonuria is caused by genetic defects, which cannot be cured with the existing medical technology, and can only be controlled by long-term dietary treatment.

What sequela can Phenylketonuria have?

If the treatment is not timely, children with phenylketonuria will have mental retardation, repeated epileptic seizures, decreased mobility and other sequelae.


What Should Phenylketonuria Patient Notice In Life?

  • Does Phenylketonuria affect reproduction?

Phenylketonuria can interfere with fertility. Therefore, women with phenylketonuria in preparation for pregnancy, to restart the low phenylalanine diet until delivery, at least three months before pregnancy to control the blood phenylalanine concentration in 120 ~ 360 μmol/L, to avoid the mother's hyperphenylalaninemia caused by fetal malformations.

Blood phenylalanine concentrations should be monitored twice a week or at least once a week during pregnancy.

  • Does Phenylketonuria affect daily activities

As long as the diet is well controlled and the blood phenylalanine concentration is in the ideal range, daily activities will not be affected.

If the treatment is not timely, and there are sequelae such as mental retardation, repeated epileptic seizures, and low motor ability, it is not suitable for high-intensity exercise or long-distance travel.

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