Phenylketonuria II

This type of phenylketonuria is atypical. For the first time, atypical phenylketonuria was described in 1974. The disease is transmitted by an autosomal recessive type. The difference of this form of phenylketonuria from the above is that the disruption of the conversion of the amino acid phenylalanine to the amino acid tyrosine is localized at a different level in the chain of chemical reactions. As a result, a large amount of phenylalanine and its derivatives accumulate in the body, but in this case no longer acids but other compounds. In this form of phenylketonuria, there is a deficiency in the body of tetrahydropterin, which takes part in the exchange of phenylalanine.

In the clinical picture of phenylketonuria II severe mental retardation, convulsions, signs of increased excitability, increased reflexes, violation of muscle tone, spastic paresis of all limbs predominate. The course of the disease is progressive and often leads to death at the age of 2-3 years. Patients are identified due to mass screening of newborns for phenylketonuria. The level of phenylalanine in the blood in these children is naturally increased. Early started dietary treatment can normalize the amount of phenylalanine in the blood, but does not prevent the appearance of symptoms that can be noted in the child at the beginning of the second half of life.

The diagnosis is established based on the definition of the child's symptoms of the disease, increasing the amount of amino acid phenylalanine in the blood and massive excretion in the urine of its derivatives. Great diagnostic value has a load test with tetrahydropterin, which is given to the patient through the mouth. After 4-6 hours after a single intake of the substance in a certain dose, a sharp decrease in the level of phenylalanine in the blood takes place, up to the complete normalization of the index. At the same time there is a simultaneous increase in the content of the amino acid tyrosine, the level of which decreases with phenylketonuria.

There is the possibility of prenatal diagnosis of phenylketonuria II.The object of investigation in this case is the cells of the amniotic fluid.

Treatment of for this type of phenylketonuria also consists in compliance with a protein restriction diet and products containing phenylalanine. It is necessary to take vitamin preparations, as well as additional administration of tetrahydropterin. The effectiveness of the treatment depends on the timing of its onset.