Why does it occur
Phenylalanine comes from protein foods and is normally converted to tyrosine by the enzyme phenylalanine hydroxylase. In phenylketonuria, the gene for this enzyme is changed, and the conversion does not occur. The amino acid accumulates in the blood and tissues, and its byproducts are excreted in the urine, giving it a characteristic musty odor. Excess phenylalanine is toxic to nerve cells and interferes with the formation of the myelin sheath. The disease is inherited in an autosomal recessive manner: both parents are healthy, but each passes on the altered gene, and the chance for each child is one in four.
- Phenylalanine hydroxylase enzyme deficiency
- Autosomal recessive inheritance
- Both parents are healthy carriers
- The risk for each child is one in four.
- Increased frequency in consanguineous marriages
- There are rarer forms associated with a cofactor
How does it manifest without treatment?
In the first weeks of life there are no signs, and this is precisely why the disease is dangerous: the time when treatment is most effective passes unnoticed. From the second or third month, lethargy or, conversely, anxiety, vomiting, persistent eczema, and convulsions appear. Gradually, a developmental delay becomes obvious: the child later holds his head up, does not follow objects, and does not roam. Light skin, blond hair and blue eyes are characteristic even in dark-skinned parents, because the formation of pigment is impaired. A peculiar musty odor emanates from urine and skin. Without a diet, severe mental retardation develops.
- Complete absence of symptoms in the first weeks
- Vomiting and persistent eczema
- Convulsions
- Delay in psychomotor development
- Lightening of skin, hair and iris
- Musty odor of urine and skin
- Increased muscle tone, behavioral disorders
Newborn screening
Screening is the only way to detect the disease before irreversible changes occur. Blood is taken from the heel on a special form, usually on the third to fifth day of life, when the child has already received nutrition, otherwise the result may be false negative. A positive result does not mean a definitive diagnosis: repeated quantitative determination of phenylalanine is required. If screening was not carried out, for example during home birth or early discharge, it needs to be done later, and parents should check this with the clinic. The earlier treatment is started, the better the prognosis.
- Blood sampling from the heel on days 3–5 of life
- Confirmation by quantitative determination of phenylalanine
- Genetic research to clarify the form
- Exclusion of more rare forms of metabolic disorders
- Mandatory examination in case of missed screening
- Examination of the child's siblings
Diet is the basis of treatment
Treatment consists of sharply limiting natural protein and replacing it with special mixtures of amino acids without phenylalanine. These mixtures provide the child with everything necessary for growth and development, including vitamins and microelements, and are prescribed for life. The doctor calculates the usual amount of protein individually, focusing on the level of phenylalanine in the blood, age and growth rate. Breastfeeding in a limited volume is possible in combination with formula according to the scheme given by the doctor. Meat, fish, eggs, cottage cheese, cheese, nuts, legumes, regular bread and sweeteners with aspartame are prohibited.
- Special amino acid mixtures without phenylalanine
- Strict calculation of natural protein by a doctor
- Eliminate meat, fish, eggs, dairy products, nuts and legumes
- Low-protein specialty foods instead of regular bread and pasta
- Avoiding sweeteners with aspartame
- Regular monitoring of phenylalanine levels in the blood
- Keeping a food diary
- Monitoring the height, weight and development of the child
Adulthood and pregnancy
Previously, it was believed that the diet could be stopped after the end of brain formation, but today it is recommended to continue it for life: with high levels of phenylalanine in adolescents and adults, attention, memory and mood decrease. Diet is of particular importance for women planning pregnancy. A high level of phenylalanine in the mother damages the fetus, even though the child has inherited only one altered gene and will not be sick himself: heart defects, microcephaly, and developmental delay are possible. Therefore, strict control begins even before conception.
- Lifelong diet
- Control of attention, memory and mood in adolescents
- Strict control of phenylalanine before conception and throughout pregnancy
- Observation by a geneticist and obstetrician-gynecologist during pregnancy
- Teaching teenagers to independently calculate their diet
- Psychological and social support for families