Description phenylketonuria

Phenylketonuria is an inherited disorder of metabolism of aromatic acids with a complete deficit of phenylalanine hydroxylase, the enzyme converting the amino acid phenylalanine to tyrosine, or its cofactor (cofactor is basically a “helper” enzyme), tetrahydrobiopterin (BH 4), which is necessary to transform these amino acids and the proper operation phenylalaninhydroxylase.

Enzymes generally help speed up the majority of metabolic processes (or chemical reactions) in the body and their absence may mean the cessation of these processes and the accumulation of certain substances, which can not be metabolized and then acts problems in terms of its excess and for example, toxicity.

In our case, phenylalanine is converted to tyrosine and accumulates in body fluids. This condition is called HPA.

HPA causes severe physical and psychological harm to the child with phenylketonuria few months after birth. Today it is known several biochemically and clinically distinct forms of hyperphenylalaninemia.


Prevention phenylketonuria – screening

The only possible prevention is screening. In the Czech Republic, newborn screening of phenylketonuria conducted since 1969. The screening test for phenylketonuria Neonatal capillary blood taken from the footer 4- 5 days after birth.

It is recommended that the day of abrasion was already newborn least three days on a milk diet. If the child is released from the hospital for the second or third day after birth, newborn screening is done at the hospital, but after the release of the child provides a general practitioner for children and adolescents collection and transportation of capillary blood control examination to the relevant regional laboratories.

Prospects for the health of children, which were found in time this disease are good. A prerequisite, however, are high-quality food products and insufficient cooperation from parents initially, and later by the very people with phenylketonuria.


Classical phenylketonuria

Progress and symptoms of phenylketonuria

Classical PKU is inherited in an autosomal recessive manner with the localization of a gene on chromosome 12q. The gene in the population occurs in about 2%. Disease affects 1 in 10,000 births.Phenylketonuria is a hereditary disorders most common cause of mental retardation.

Symptoms begin to develop around the second month of life. Among the first symptoms include frequent burping and vomiting, which arouses suspicion of pyloric stenosis (narrowing of the stomach). Urine has a typical mouse (some authors indicate wolf) odor.

The skin is dry, rough, eczematous. Hair of children with phenylketonuria are 90% fair. Light color is accompanied by the overall appearance of individual irises are pale blue and pale complexion.Children are generally paler than their siblings. Part of the children has a protruding upper jaw, broad hryzáky with spaces, weakened tooth enamel, flat feet, and growth retardation.

Child with phenylketonuria since the 9th month of psychomotor significantly lagging and image končívá imbecility (IQ 30-35) or idiocy (IQ 60-65). It is reported that the PKU inteligenní quotient reduces by about half.

There are also frequent cramps, changes in EEG (electroencephalography, the device records the electrical activity of the brain), nightmares, increased muscle tension, increased tendon reflexes, purposeless movements. Only early treatment in the first days of life can prevent mental retardation.

Treatment of PKU and its complications

The aim is to reduce the concentration of phenylalanine and its metabolites in blood and tissues and thus prevent or at least reduce to a minimum the damage of brain disorder and mental development.

The treatment consists of continuous administration of a diet low in phenylalanine. The daily requirement of protein in the diet must be replaced by an artificial mixture of essential amino acids without phenylalanine, which is enriched with trace elements, ions, minerals and vitamins, and always depending on the age of the child being treated. They are therefore protein preparations devoid of phenylalanine. The need for dietary treatment for individuals with phenylketonuria islifelong.

In the treatment of phenylketonuria it is necessary to regularly monitor the concentration of phenylalanine in the blood. The optimum is considered to 120 to 500 mmol / l.

Excessive reduction in phenylalanine levels can lead to a deficiency with the image of appetite,fatigue and lethargy, the incidence of skin eczema and anemia (anemia). It is not clear unified view of when to stop treatment and certain restrictions in diet are needed throughout life. Changes in diet can only be decided by an expert.

Phenylketonuria disease and pregnancy

Pregnant mothers with phenylketonuria have a chance to give birth to a baby intact only if already at the time of conception and even throughout pregnancy nízkofenylalaninovou strictly follow the diet. Even moderately elevated levels of phenylalanine in the blood of pregnant women with phenylketonuria or other forms of HPA increased risk of impaired fetal growth retardation, mental retardation and developmental disabilities hearts.


other hyperphenylalaninaemia

Other HPA form a group of genetically inherited metabolic diseases in which a deficiency induced hyperphenylalaninemia other enzymes, and require different treatment.

Fenylketnurie deficiency of tetrahydrobiopterin (BH4) occurs in 2% of children with hyperphenylalaninemia. Tetrahydrobiopterin cofactor of phenylalanine hydroxylase is not only but also other amino acids hydroxylases tyrosine and tryptophan. These enzymes are essential for the synthesis of substances necessary for the proper functioning of the nervous system – serotonin and dopamine.

In the first months of life symptoms are the same as for classical phenylketonuria, is dominated by digestive tract problems and neurological problems, one of which is mainly convulsions.

The most important difference is the fact that even when starting nízkofenylalaninové diets neurological symptoms worsen severely. It is not enough just alone nízkofenylalaninová diet, but it is also necessary to timely treatment comprising the administration of L-dopa (a substance from which it is formed dopamine) and serotonin. It just saves patients from permanent neurological damage. They must be all newborns in whom screening hyperphenylalaninemia captured, examined and timely to tetrahydrobiopterin deficiency.

Permanent HPA. Some children have only moderately elevated levels of phenylalanine in the blood, and therefore do not exclude its exhausts, pimelic phenylpyruvic, urine. These patients have only a reduced activity of phenylalanine hydroxylase. Children are free of clinical signs and their psychological development is adequate even without special diets. It is recommended that they reduce protein intake.

HPA transient occurrences during late ripening enzyme fenylalantransferázy. In this group of patients sufficient to temporarily reduce the intake of protein.

Other names: PKU, Follingova disease, oligophrenia fenylpyruvica

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