Phenylketonuria
Basic Information
Phenylketonuria (PKU) is a rare, genetic disorder that affects the body's metabolic system. The metabolic system maintains body chemistry, and is a critical part of the body's ability to break down food into usable energy. Approximately one out of every 15,000 newborns is born with PKU. If left untreated, this condition can lead to mental retardation. Fortunately, most instances of PKU are detected early, and treatment is able to prevent the onset of mental retardation and other neurological problems. PKU affects all ethnic groups, though it is more common in people of Northern European descent.
When a person has this condition, their body is unable to properly process food. Specifically, newborns with PKU are unable to break down an essential amino acid called "phenylalanine". Amino acids are the basic components that the body uses to build proteins. Children with PKU are unable to use phenylalanine because the enzyme that typically breaks down this amino acid is missing in their body. Eventually, toxic amounts of phenylaline accumulate in the bloodstream and body tissues. The result is brain damage.
PKU is a genetic disorder. It is inherited when both parents give the PKU gene to their offspring. A person can be a carrier of this disease. A carrier is a person who has one normal PKU gene and one defective PKU gene. Carriers do not have symptoms and their health is not affected by the disease. However, if two carriers mate, there is a one in four chance that each of their offspring will have PKU. The incidence of carriers in the general population is around one out of every 50 people.
Symptoms
At first, children born with PKU appear normal. They typically will not show signs of having PKU until the three to five month point. The onset of symptoms occurs in a very rapid manner. The child may begin showing a disinterest in its immediate surroundings. At the same time, children with this disorder are often irritable, restless and destructive. They may vomit regularly, and their skin and urine can have a musty odor. They may have dry skin or eczema-like rashes.
They may also have nervous system problems. For instance, they may have abnormally well-developed muscle tone, or involuntary muscle reflexes (convulsions). Other often observed features of newborns with PKU include:
- Blue eyes or hair and skin that is more fair than that of their relatives
- An unusually small head
- Prominent cheek and upper jaw bones
- Widely spaced teeth
- Underdeveloped tooth enamel
In most cases of untreated PKU, children will show signs of mental retardation within one year of the onset of other symptoms.
Diagnosis
The screening process for PKU is highly developed. In fact, all newborns in the United States are tested for PKU before they leave the hospital. During this test, the newborn's heel is pricked with a needle and a few drops of blood are obtained. These drops of blood are then sent to a laboratory for testing. If the test results find that there is an excessive amount of phenlalanine in the blood, a series of other tests are done to determine if the baby has PKU. The diagnostic tests for PKU are extremely accurate. It is recommended that they are performed at about three days of age.
Treatment
The early detection of PKU is an essential part of the treatment process. When the treatment of PKU begins immediately after early detection, brain damage can be prevented and the affected person tends to have a completely healthy life. For the most part, treatment consists of a special diet that is low in phenylalanine. This means that the high protein foods are avoided. These foods include: meat, fish, poultry, eggs, cheese, milk, peas, dried beans, ice cream, lgumes, nuts, and breast milk. Instead, the child is given a formula that serves as a nutritional substitute for the avoided foods. Although this formula is expensive, most states have financial aid programs to benefit families that have affected children. Eventually, the affected child will move on to a solid food diet that consists of cereals, starches, fruits, vegetables and milk substitutes. All of these foods have a low phenylalanine content. At the same time, the child will continue to use the formula in order to get the basic proteins that are an essential part of the body's physical development.
It is important to realize that the diet should be individualized for each affected child. Some children with PKU can tolerate foods with high levels of phenylalanine, and as a result, do not need to follow strict dietary restrictions. On the other hand, some children must adhere to a very regimented diet. In most cases, a qualified nutritionist will determine the type of diet that a child must follow.
As time goes on, the nutritionist may make changes in the diet. However, it is common for people with PKU to remain on a restricted diet throughout childhood, and often for life. Some problems that are associated with stopping the diet after childhood include: learning disabilities, decrease in IQ, behavioral problems, seizures, hyperactivity, irritability, eczema, skin problems, panic attacks, schizophrenia and agoraphobia. At the same time, it is very important that women remain on the diet during pregnancy.
A person with PKU should continually undergo blood screening throughout their lifetime. Periodic monitoring will allow for the early detection of any PKU-related complications. Information regarding the location of PKU screening sites can be obtained through every state's newborn screening program.