Phenylketonuria - What is It?

Phenylketonuria, or PKU as it is most commonly known, is a genetic disorder where the body is unable to utilize the essential amino acid phenylalanine. Amino acids are important and necessary for the body's proteins. Essential amino acids are only obtained from food we eat as our bodies do not produce them.

With PKU, the enzyme that breaks down phenylalanine hydroxylase is not present or is not fully present. This enzyme is needed to convert phenylalanine to tyrosine, another amino acid. Without this enzyme, phenylalanine and the chemicals that break it down accumulate in the blood and body tissues causing many problems.

Normally, a blood phenylalanine level is about 1 mg/dl. With PKU, the levels may range from 6 to 80mg/dl, but are typically higher than 30mg/dl.

If phenylalanine levels are consistently high, some of its breakdown products can cause severe brain problems. Illnesses and fever can cause the body to break down proteins and cause a rise of phenylalanine levels.

PKU cases affect about one of every 10,000 to 20,000 Caucasian or Asian births. PKU is seen in African Americans much less. PKU is seen in males and females equally.

PKU is an inherited recessive gene. Someone with PKU has inherited two traits for the disorder, one from each parent. Carriers, those with one trait for PKU, do not have symptoms of PKU.

At birth, babies with PKU appear normal and will usually have blue eyes and lighter colored hair and skin than other family members. PKU is one of many things babies are screened for at birth. So in most cases, it is detected very early on.

Those few babies that aren't detected for PKU and have PKU will see symptoms such as: vomiting, instability, eczema like rashes, and off smelling urine. Others may see signs of increased muscle tone and over active muscle tendon reflexes. If continued on without treatment severe brain problems can occur such as mental retardation and seizures. Untreated children might also have microcephaly (small head) or prominent cheeks and upper jaw bones as well as widely spaced teeth, tooth enamel problems and a decreased bodily growth.

Treating PKU requires that the blood level of phenylalanine is between 2 and 10 mg/dl. Some phenylalanine is needed for normal growth and so requires a diet with some phenylalanine, but in smaller than normal amounts. Foods such as: meat, fish, poultry, eggs, cheese, milk, dried beans, peas and other high-protein foods are avoided. Foods such as cereals, starches, fruits and vegetables along with a milk substitute are recommended. For babies and older children phenylalanine free formulas are available. This type of diet is usually required for life.

Rechecks of the levels of phenylalanine in the blood and consulting with a nutritionist can help to keep those with PKU at the desired range.

While PKU can be very serious, it is highly treatable and manageable with the proper diet and staying in close contact with your doctor and dietician. A new medication is also on the market for PKU but, as with any medication, has its risks and benefits.

Phenylketonuria - What is it?

Phenylketonuria - Signs, Symptoms, Causes, and Prognosis