- Phenylketonuria (PKU) Center
- Patient Comments: Phenylketonuria (PKU) - Symptoms
- Patient Comments: Phenylketonuria - Experience
Phenylketonuria (PKU) definition and facts*
*Phenylketonuria (PKU) medically edited by: Charles Patrick Davis, MD, PhD
- Phenylketonuria (PKU) is a disease that's inherited that increases the levels of phenylalanine in the blood. If left untreated, high phenylalanine levels can cause intellectual disability and other problems. Phenylketonuria disease was discovered in 1934 by Dr. A. Folling.
- Signs and symptoms of PKU vary from
mild to severe depending upon phenylalanine levels. Infants appear normal until
a few months old when they start to show
- intellectual disability,
- delayed development,
- behavior problems, and
- psychiatric disorders.
- Children with untreated PKU also may have lighter skin and hair than other family members, and also may develop a musty or mouse-like odor due to excess phenylalanine. These are classic PKU symptoms.
- Less severe forms of PKU (sometimes termed variant PKU and non-PKU hyperphenylalaninemia may develop less severe symptoms with a smaller risk of brain damage.
- Women with PKU that have uncontrolled phenylalanine levels can have babies that are at significant risk for intellectual disability, low birth weight, heart defects, microcephaly, behavior problems, and slow growth.
- PKU occurs in about 1/10,000 to15,000 births, but classic PKU symptoms are rarely seen because of newborn screening tests for the disease.
- Mutations in the PAH gene cause phenylketonuria. Some mutations in this gene allow the enzyme to retain some activity resulting in variant PKU and/or non-PKU hyperphenylalaninemia.
- PKU is inherited in an autosomal recessive pattern so that both copies of the gene in the cell have mutations. Consequently, the autosomal recessive condition in both parents carry one copy of the mutated gene and parents typically do not show symptoms. Symptoms of PKU develop in their children when both parents donate one autosomal recessive condition to the newborn.
- PKU has many different names, for example, phenylketonuria, PKU, Folling Disease, Folling's Disease, and phenylalanine hydroxylase deficiency disease.
- PKU does not shorten a person's life expectancy, with or without treatment.
- Blood tests for PKU is required for infants (newborns) in all 50 states.
- There is a 1 in 4 chance of having a PKU infant when both parents are genetic carriers. The approximate incident rate of PKU in the US is 0.01%. This means about 74 infants every day are diagnosed with PKU.
- PKU patients usually are treated in a special metabolic disease clinic with restrictions on foods that contain phenylalanine and are given amino acids, vitamins, minerals, and other micronutrients along with close monitoring of phenylalanine levels.
- A PKU diet bans meat, fish, chicken, eggs, nuts, beans, milk, and other dairy products. People with PKU also need to avoid aspartame, a type of peptide composed of aspartic acid and phenylalanine.
What is phenylketonuria?
Phenylketonuria (commonly known as PKU) is an inherited disorder that increases the levels of a substance called phenylalanine in the blood. Phenylalanine is a building block of proteins (an amino acid) that is obtained through the diet. It is found in all proteins and in some artificial sweeteners. If PKU is not treated, phenylalanine can build up to harmful levels in the body, causing intellectual disability and other serious health problems.
How common is phenylketonuria?
The occurrence of PKU varies among ethnic groups and geographic regions worldwide. In the United States, PKU occurs in 1 in 10,000 to 15,000 (newborns. Most cases of PKU are detected shortly after birth by newborn screening, and treatment is started promptly. As a result, the severe signs and symptoms of classic PKU are rarely seen.
What genes are related to phenylketonuria?
Mutations in the PAH gene cause phenylketonuria.
The PAH gene provides instructions for making an enzyme called phenylalanine hydroxylase. This enzyme converts the amino acid phenylalanine to other important compounds in the body. If gene mutations reduce the activity of phenylalanine hydroxylase, phenylalanine from the diet is not processed effectively. As a result, this amino acid can build up to toxic levels in the blood and other tissues. Because nerve cells in the brain are particularly sensitive to phenylalanine levels, excessive amounts of this substance can cause brain damage.
Classic PKU, the most severe form of the disorder, occurs when phenylalanine hydroxylase activity is severely reduced or absent. People with untreated classic PKU have levels of phenylalanine high enough to cause severe brain damage and other serious medical problems. Mutations in the PAH gene that allow the enzyme to retain some activity result in milder versions of this condition, such as variant PKU or non-PKU hyperphenylalaninemia.
Changes in other genes may influence the severity of PKU, but little is known about these additional genetic factors.
How do people inherit phenylketonuria?
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
Daily Health News
Subscribe to MedicineNet's Children's Health & Parenting Newsletter
"Phenylketonuria." Genetics Home Reference. 16 Dec. 2013.
Top Phenylketonuria Related Articles
Birth DefectsBirth defects have many causes and currently, are the leading cause of death for infants in the first year of life. Some of the causes of birth defects include genetic or chromosome problems. Exposure of the mother to rubella or German measles during pregnancy, or using drugs or alcohol during pregnancy. The treatment for birth defects depends upon the condition of the effected child.
Children's HealthChildren's health is focused on the well-being of children from conception through adolescence. There are many aspects of children's health, including growth and development, illnesses, injuries, behavior, mental illness, family health, and community health.
Eczema FactsEczema refers to skin inflammation. There are many different types of eczema that produce symptoms and signs that range from oozing blisters to crusty plaques of skin. Treatment varies depending upon the type of eczema the person has.
Genetic CounselingYour health care provider may refer you to a genetic professional. Universities and medical centers also often have affiliated genetic professionals, or can provide referrals to a genetic professional or genetics clinic. Genetic counseling provides patients and family members the tools to make the right choice in regard to test for a disease or condition.
The definition of a genetic disease is a disorder or condition caused by abnormalities in a person's genome. Some types of genetic inheritance include single inheritance, including cystic fibrosis, sickle cell anemia, Marfan syndrome, and hemochromatosis. Other types of genetic diseases include multifactorial inheritance. Still other types of genetic diseases include chromosome abnormalities (for example, Turner syndrome, and Klinefelter syndrome), and mitochondrial inheritance (for example, epilepsy and dementia).
Infant FormulasThough human milk is the preferred feeding for infants, parents may consider formula-feeding if there is an inadequate supply of breast milk, the baby sucks inefficiently, the parents want to monitor how much the baby is receiving, or the mother is taking medications that are unsafe for the baby and may be passed through the breast milk.
MicrocephalyMicrocephaly is a genetic condition where the circumference of the head is smaller than normal due to underdeveloped brain. Microcephaly is caused by genetic abnormalities, abuse of alcohol or drugs, infection (for example, Zika virus, German measles, or chickenpox), exposure to toxins, or PKU while the mother is pregnant. Symptoms of microcephaly depend upon the severity of the accompanying syndrome. There is no treatment for microcephaly.
Miscarriage Causes and SymptomsMiscarriage is the medical term for the spontaneous loss of pregnancy from conception to 20 weeks gestation. Risk factors for a woman having a miscarriage include cigarette smoking, older maternal age, radiation exposure, previous miscarriage, maternal weight, illicit drug use, use of NSAIDs, and trauma or anatomical abnormalities to the uterus. There are five classified types of miscarriage: 1) threatened abortion; 2) incomplete abortion; 3) complete abortion; 4) missed abortion; and (5 septic abortion. While there are no specific treatments to stop a miscarriage, a woman's doctor may advise avoiding certain activities, bed rest, etc. If a woman believes she has had a miscarriage, she needs to seek prompt medical attention.
Pregnancy Planning (Preparing for Pregnancy)
Pregnancy planning is an important step in preparation for starting or expanding a family. Planning for a pregnancy includes:
- Taking prenatal vitamins
- Eating healthy for you and your baby
- Disease prevention (for both parents and baby) to prevent birth defects and infections
- Avoiding certain medications that may be harmful to your baby
- How much weight gain is healthy
- Exercise safety and pregnancy
- Travel during pregnancy
SeizureEpilepsy is a brain disorder in which the person has seizures. There are two kinds of seizures, focal and generalized. There are many causes of epilepsy. Treatment of epilepsy (seizures) depends upon the cause and type of seizures experienced.
Seizures Symptoms and TypesSeizures are divided into two categories: generalized and partial. Generalized seizures are produced by electrical impulses from throughout the brain, while partial seizures are produced by electrical impulses in a small part of the brain. Seizure symptoms include unconsciousness, convulsions, and muscle rigidity.
Tetrahydrobiopterin DeficiencyTetrahydrobiopterin deficiency is a rare genetic disorder that increases the levels of phenylalanine and several other substances in the blood, at birth. Symptoms of Tetrahydrobiopterin deficiency include movement disorders, difficulty swallowing, seizures, and more. Causes of tetrahydrobiopterin deficiency can be from mutations of several genes including GCH1, PCBD1, PTS, and QDPR. Tetrahydrobiopterin deficiency is an inherited condition in an autosomal resessive pattern.