Phenylketonuria is the most common metabolic disorder. On average, 1 in 8,000 people are subject to phenylketonuria.
The basis of the disease is the lack of an enzyme that converts phenylalanine into tyrosine (tyrosine prevents the deposition of fat, reduces the level of appetite, improves the function of the pituitary, thyroid and adrenal glands).
Phenylketonuria appears in the first year of life. The main symptoms at this age are:
- lethargy child;
- lack of interest in the environment;
- sometimes irritability;
- disorders of muscle tone (usually muscle hypotonia);
- signs of atopic dermatitis;
- there is a characteristic “mouse” smell of urine.
At a later age, patients with phenylketonuria are characterized by delayed psychoverbal development, microcephaly is often noted.
Phenylketonuria is characterized by the following phenotypic features: hypopigmentation of the skin, hair, iris. In some patients, one of the manifestations of pathology may be scleroderma .
Epileptic seizures occur in almost half of patients with phenylketonuria, and in some cases may be the first sign of illness.
The diagnosis of suspected phenylketonuria is based on a combination of genealogical data, results of clinical and biochemical examination:
- possible related marriage of parents of a sick child;
- similar pathology in siblings or siblings (brothers or sisters);
- convulsions, muscle tone disorder;
- eczematous skin changes;
- hypopigmentation of hair, skin, iris;
- a kind of “mouse” smell of urine;
- elevated blood phenylalanine level> 900 μmol / l;
- the presence in the urine of phenylpyruvic, phenyl milk, phenylacetic acid;
- Felling positive test.
Currently, for the diagnosis of phenylketonuria, molecular genetic methods for detecting a gene defect have been developed and introduced.
Diagnosis in newborns (screening)
Due to the high prevalence of phenylketonuria, the severity of clinical manifestations and the real possibility of preventive treatment, phenylketonuria was among the first hereditary metabolic disorders included in the list of hereditary diseases recommended by the World Health Organization for early detection among newborns.
For the early diagnosis of phenylketonuria in Russia, a mass examination of children in maternity hospitals with the determination of the level of phenylalanine in the blood is carried out.
Blood sampling is performed on newborns aged 4–5 days. Less commonly, the subject is urine.
The main treatment for phenylketonuria is diet therapy, which restricts the intake of protein and phenylalanine.
The main criterion for the adequacy of the diet for phenylketonuria is the level of phenylalanine in the blood, which should:
- at an early age be 120–240 µmol / l;
- in preschool children, do not exceed 360 µmol / l;
- for schoolchildren – not to exceed 480 µmol / l;
- in children of older school age, an increase in blood phenylalanine up to 600 µmol / l is permissible.
The diet is built by sharply limiting the supply of protein products of animal and vegetable origin and, consequently, phenylalanine. To facilitate calculations, it is considered that 1 g of the conditional protein contains 50 mg of phenylalanine.
In the treatment of phenylketonuria, products rich in protein and phenylalanine are completely excluded: meat, fish, cheese, cottage cheese, eggs, legumes, etc. The diet of patients includes vegetables, fruits, juices, and special low protein foods – amylophenes.
For the correction of protein nutrition and replenishment of amino acid deficiencies in phenylketonuria, special therapeutic products are prescribed:
- protein hydrolysates: nofelan (Poland), apone (USA), lofenolak (USA);
- mixtures of L-amino acids, devoid of phenylalanine, but containing all other essential amino acids: phenyl-free (USA), tetrafen (Russia), P-AM universal (UK).
Despite the enrichment of amino acid mixtures and protein hydrolysates with mineral and other substances, patients with phenylketonuria need additional prescription of vitamins, in particular group B, mineral compounds, especially those containing calcium and phosphorus, iron preparations and microelements.
In recent years, the need to use carnitine preparations (L-carnitine, elkar in an average daily dose of 10–20 mg / kg mass for 1-2 months, 3-4 courses per year) for the prevention of its insufficiency was justified for those suffering from phenylketonuria.
In parallel, the treatment of phenylketonuria is carried out by medical pathogenetic and symptomatic treatment with nootropic drugs, drugs that improve vascular microcirculation, according to indications – anticonvulsants.
Therapeutic gymnastics, general massage, etc. are widely used. Comprehensive rehabilitation of children with phenylketonuria provides special methods of pedagogical influences in the process of preparing for school and school education. Patients need the help of a speech therapist, a teacher, in some cases a defectologist.
Great controversy raises the question of the duration of diet in the treatment of phenylketonuria. Recently, most doctors have taken the point of view of the need for continuous implementation of dietary recommendations. Examination of children who stopped dieting at school age, and children who continued to receive diet therapy, clearly showed a significantly higher level of intellectual development of the latter.
In older patients with phenylketonuria, including adolescents, of course, a gradual expansion of the diet is possible due to improved tolerance to phenylalanine. Nutrition correction is usually carried out by introducing into the diet a limited amount of cereals, milk and some other natural products containing relatively moderate amounts of phenylalanine. During the period of expansion of the diet, the neuropsychological status of children is evaluated electroencephalogram , the level of phenylalanine in the blood.
At the age of over 18–20 years, a further expansion of the diet is carried out; however, in the adult period, patients are advised not to use high-protein products of animal origin.
Especially strictly suited to the diet of girls suffering from phenylketonuria, and women in the reproductive period. This kind of patient with phenylketonuria must continue dietary treatment to ensure the birth of healthy offspring.
In recent years, a method has been developed to reduce the level of phenylalanine in the blood by taking a drug containing plant phenylalanine hydroxylase.