Phenylketonuria (PKU) is a rare condition in which a baby is born without the ability to properly break down an amino acid called phenylalanine.
Phenylketonuria (PKU) is inherited, which means it is passed down through families. Both parents must pass on a nonworking copy of the gene in order for a baby to have the condition. When this is the case, their children have a 1 in 4 chance of being affected.
Babies with PKU are missing an enzyme called phenylalanine hydroxylase. It is needed to break down the essential amino acid phenylalanine. Phenylalanine is found in foods that contain protein.
Without the enzyme, levels of phenylalanine build up in the body. This buildup can harm the central nervous system and cause brain damage.
Phenylalanine plays a role in the body’s production of melanin. The pigment is responsible for skin and hair color. Therefore, infants with the condition often have lighter skin, hair, and eyes than brothers or sisters without the disease.
Other symptoms may include:
- Delayed mental and social skills
- Head size much smaller than normal
- Jerking movements of the arms or legs
- Mental disability
- Skin rashes
If PKU is untreated, or if foods containing phenylalanine are eaten, the breath, skin, ear wax, and urine may have a «mousy» or «musty» odor. This odor is due to a buildup of phenylalanine substances in the body.
Exams and Tests
PKU can be easily detected with a simple blood test. All states in the United States require a PKU screening test for all newborns as part of the newborn screening panel. The test is generally done by taking a few drops of blood from the baby before the baby leaves the hospital.
If the screening test is positive, further blood and urine tests are required to confirm the diagnosis. Genetic testing is also done.
PKU is a treatable disease. Treatment involves a diet that is very low in phenylalanine, particularly when the child is growing. The diet must be strictly followed. This requires close supervision by a registered dietitian or doctor, and cooperation of the parent and child. Those who continue the diet into adulthood have better physical and mental health than those who don’t stay on it. «Diet for life» has become the standard most experts recommend. Women who have PKU need to follow the diet before conception and throughout pregnancy.
There are large amounts of phenylalanine in milk, eggs, and other common foods. The artificial sweetener NutraSweet (aspartame) also contains phenylalanine. Any products containing aspartame should be avoided.
There are several special formulas made for infants with PKU. These can be used as a protein source that is extremely low in phenylalanine and balanced for the remaining essential amino acids. Older children and adults use a different formula that provides protein in the amounts they need. People with PKU need to take formula every day for their entire life.
The outcome is expected to be very good if the diet is closely followed, starting shortly after the child’s birth. If treatment is delayed or the condition remains untreated, brain damage will occur. School functioning may be mildly impaired.
If proteins containing phenylalanine are not avoided, PKU can lead to mental disability by the end of the first year of life.
Severe mental disability occurs if the disorder is untreated. ADHD (attention-deficit hyperactivity disorder) appears to be a common problem in those who do not stick to a very low-phenylalanine diet.
When to Contact a Medical Professional
Call your health care provider if your infant has not been tested for PKU. This is particularly important if anyone in your family has the disorder.
An enzyme assay or genetic testing can determine if parents carry the gene for PKU. Chorionic villus sampling or amniocentesis can be done during pregnancy to test the unborn baby for PKU.
It is very important that women with PKU closely follow a strict low-phenylalanine diet both before becoming pregnant and throughout the pregnancy. Buildup of phenylalanine will damage the developing baby, even if the child has not inherited the full disease.
Phenylketonuria (PKU) is a rare genetic condition that causes an amino acid called phenylalanine to build up in the body. Amino acids are the building blocks of protein. Phenylalanine is found in all proteins and some artificial sweeteners.
Phenylalanine hydroxylase is an enzyme your body uses to convert phenylalanine into tyrosine, which your body needs to create neurotransmitters such as epinephrine, norepinephrine, and dopamine. PKU is caused by a defect in the gene that helps create phenylalanine hydroxylase. When this enzyme is missing, your body can’t break down phenylalanine. This causes a buildup of phenylalanine in your body.
Babies in the United States are screened for PKU shortly after birth. The condition is uncommon in this country, only affecting about 1 in 10,000 to 15,000 newborns each year. The severe signs and symptoms of PKU are rare in the United States, as early screening allows treatment to begin soon after birth. Early diagnosis and treatment can help relieve symptoms of PKU and prevent brain damage.
PKU symptoms can range from mild to severe. The most severe form of this disorder is known as classic PKU. An infant with classic PKU may appear normal for the first few months of their life. If the baby isn’t treated for PKU during this time, they’ll start to develop the following symptoms:
- tremors, or trembling and shaking
- stunted growth
- skin conditions such as eczema
- a musty odor of their breath, skin, or urine
If PKU isn’t diagnosed at birth and treatment isn’t started quickly, the disorder can cause:
- irreversible brain damage and intellectual disabilities within the first few months of life
- behavioral problems and seizures in older children
A less severe form of PKU is called variant PKU or non-PKU hyperphenylalaninemia. This occurs when the baby has too much phenylalanine in their body. Infants with this form of the disorder may have only mild symptoms, but they’ll need to follow a special diet to prevent intellectual disabilities.
Once a specific diet and other necessary treatments are started, symptoms start to diminish. People with PKU who properly manage their diet usually don’t show any symptoms.
PKU is an inherited condition caused by a defect in the PAH gene. The PAH gene helps create phenylalanine hydroxylase, the enzyme responsible for breaking down phenylalanine. A dangerous buildup of phenylalanine can occur when someone eats high-protein foods, such as eggs and meat.
Both parents must pass on a defective version of the PAH gene for their child to inherit the disorder. If just one parent passes on an altered gene, the child won’t have any symptoms, but they’ll be a carrier of the gene.
Since the 1960s, hospitals in the United States have routinely screened newborns for PKU by taking a blood sample. A doctor uses a needle or lancet to take a few drops of blood from your baby’s heel to test for PKU and other genetic disorders.
The screening test is performed when the baby is one to two days old and still in the hospital. If you don’t deliver your baby in a hospital, you’ll need to schedule the screening test with your doctor.
Additional tests may be performed to confirm the initial results. These tests search for the presence of the PAH gene mutation that causes PKU. These tests are often done within six weeks after birth.
If a child or adult shows symptoms of PKU, such as developmental delays, the doctor will order a blood test to confirm the diagnosis. This test involves taking a sample of blood and analyzing it for the presence of the enzyme needed to break down phenylalanine.
People with PKU can relieve their symptoms and prevent complications by following a special diet and by taking medications.
The main way to treat PKU is to eat a special diet that limits foods containing phenylalanine. Infants with PKU may be fed breast milk. They usually also need to consume a special formula known as Lofenalac. When your baby is old enough to eat solid foods, you need to avoid letting them eat foods high in protein. These foods include:
To make sure that they still receive an adequate amount of protein, children with PKU need to consume PKU formula. It contains all the amino acids that the body needs, except for phenylalanine. There are also certain low-protein, PKU-friendly foods that can be found at specialty health stores.
People with PKU will have to follow these dietary restrictions and consume PKU formula throughout their lives to manage their symptoms.
It’s important to note that PKU meal plans vary person to person. People with PKU need to work closely with a doctor or dietitian to maintain a proper balance of nutrients while limiting their intake of phenylalanine. They also have to monitor their phenylalanine levels by keeping records of the amount of phenylalanine in the foods they eat throughout the day.
Some state legislatures have enacted bills that provide some insurance coverage for the foods and formulas necessary to treat PKU. Check with your state legislature and medical insurance company to find out if this coverage is available for you. If you don’t have medical insurance, you can check with your local health departments to see what options are available to help you afford PKU formula.
The United States Food and Drug Administration (FDA) recently approved sapropterin (Kuvan) for the treatment of PKU. Sapropterin helps lower phenylalanine levels. This medication must be used in combination with a special PKU meal plan. However, it doesn’t work for everyone with PKU. It’s most effective in children with mild cases of PKU.
MOLECULAR-GENETIC STUDY OF THE PHENYLALANINE HYDROXYLASE GENE IN PATIENTS WITH PHENYLKETONURIA
Phenylketonuria (PKU) is a aminoacid metabolic disorder caused by heritable phenylalanine hydroxylase activity deficiency, which is due to different mutations of either the ferment gene (classical PKU, PKU-I), or its co-factor biosynthesis pathway genes(PKU-II, PKU-III). The incidence of PKU varies widely in different human populations.
98 affected families live in Novosibirsk region.
Aim of work: Identification of phenylalanine hydroxylase gene mutations in patients with PKU, residing in the territory of the Siberian and Far East federal district. Study of the PAH gene mutation frequency and spectrum and analysis of possible combination of PKU-causing alleles.
Applied problem : To completely rule out PKU-assosiated mutation carrier state; in the case of this carrier state to pinpoint type of PKU-assosiated mutations.
DNA samples studied: of PKU patients and members of their families:
4 families residing in the Altai territory;
5 families residing in the Sakha Republic;
15 families residing in the Far East district;
24 families residing in the Saratov region;
48 families residing in the Kemerovo region;
98 families residing in the Novosibirsk region.
In all 551 patients
Example of the genodiagnostics for the family of PAH-carriers:
The son inheriting parent «bad» genes suffer from PKU. He has heterozygous mutant genotype R408W/ INS12+1G>A. But future child doesn’t have these mutations.
As a result of the studing PKU-patients there were identified PKU-I assosiated mutations including the early unknown mutations, which are very important for family planning, prenatal diagnostics and the birth of healthy children.