Phenylketonuria What we need to know

Phenylketonuria (fen-ul-key-toe-NU-ree-uh), also called phenylketonuria (PKU), is a rare inherited disease that causes the body to build up the amino acid phenylalanine. PKU is caused by a mutation in the phenylalanine hydroxylase (PAH) gene. This gene helps make an enzyme needed to break down phenylalanine.

Phenylketonuria is a genetic defect of aromatic carbohydrate metabolism. As you know, our food consists largely of proteins, and proteins, in turn, of amino acids. During phenylketonuria, the child's body lacks the enzyme that must convert one of the amino acids, phenylalanine, and enter it into the food energy chain. Because of this, phenylalanine cannot be fully consumed and accumulates in the blood.

The body tries to get rid of excess phenylalanine and removes it in the wrong way, and the resulting half-life products are toxic to the body and cause various pathologies. The process of myelination in the brain tissue is delayed, neurons first lose their myelin sheath, and then they die altogether, which is manifested by neurological disorders, seizure syndrome and mental retardation.

Symptoms

Often, during the first three months after birth, nothing appears to the child, and only a special analysis can determine anything. Phenylketonuria is characterized by:

  • excessive sweating and a musty smell on the skin;
  • rashes (eczema);
  • light coloring of skin, eyes and hair (melanin deficiency);
  • behavior disorder;
  • hyperactivity;
  • Irritability;
  • unusually small head size (microcephaly);
  • easy excitability;
  • psychotic disorders;
  • impulsiveness;
  • retardation of speech development;
  • Depression is common in adults.

Forms of phenylketonuria

The severity of the disease depends on its type. There are three forms of phenylketonuria:

  • Classic/severe form – The most severe form of the disease is called classic PKU. The enzyme necessary for the breakdown of phenylalanine is absent or significantly reduced. This leads to high levels of phenylalanine, which can cause severe brain damage;
  • Less severe form (malignant) – here the enzyme still has some function, so the phenylalanine level is not as high, but still carries the risk of significant brain damage;
  • Mild form (benign) – phenylketonuria without phenylalaninemia.

Diagnosis

Pregnant women with phenylketonuria are at risk for another form of the disease called maternal phenylketonuria. If during pregnancy, despite the risks for phenylketonuria, screening tests are not performed or if the diagnostics is made, but the pregnant woman does not follow a special PKU diet (before pregnancy and during pregnancy), the level of phenylalanine in the blood can increase and harm the fetus.

All newborns are screened through a blood test. There are also newer tests that can be used to determine whether the fetus has mutated genes at an early stage of pregnancy through safe testing methods (Veragen (100 monogenic diseases)). Also, if there is a risk of transmitting the disease to the child, couples can consult a specialist before the birth and manage the pregnancy properly.

Screening tests – A prenatal screening test can determine if your baby is more or less likely to have birth defects, many of which are genetic disorders. These tests include blood tests, specific ultrasounds, and prenatal cell-free DNA screening. If screening tests show that you or your fetus has a high risk of phenylketonuria, it is recommended that you also have a diagnostic test to determine whether the fetus has the genetic disorder.

Diagnostic tests – After the screening test, the final answer is given by a diagnostic test that examines the genetic material of the fetus and therefore can determine whether the fetus has a genetic disorder. Invasive and non-invasive prenatal diagnostic tests ((NIPT) Verasity, Veragen) are the only, safe and effective way to confirm the diagnostics.

Be aware that some prenatal diagnostic tests, such as chorionic villus sampling and amniocentesis, carry a small risk of miscarriage.

Learn more about prenatal diagnostics → (https://synevo.ge/prenatal-screening/)

Treatment

Phenylketonuria can't be cured, but it's definitely not a doom and gloom. It is a different lifestyle with a different diet. If phenylketonuria is diagnosed early, the affected newborn can grow up with normal brain development, regulation and control of phenylalanine (“Phe”) levels, and a combination of diet and medication.

The only way to treat its classical form is diet therapy. In case of timely and correct diet, the child will develop fully and nothing will bother him. The only distinguishing feature of such patients from other children will be the diet. Previously, it was considered that diet therapy is necessary only until the age of 7, then this age was increased to 12 years. Today, the world has already agreed that people with phenylketonuria should follow a diet for life, although the older the patient, the less permeable the blood-brain barrier and the less damaging the effect.

Malignant phenylketonuria is not only amenable to diet therapy, at this time we have to include other drugs in the treatment, while in case of benign phenylketonuria we simply monitor patients so that the level of phenylalanine does not exceed the permissible limit. They do not need such strict diet therapy as children with classic phenylketonuria.

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