What is PKU?
Phenylketonuria is a Condition that Can Cause Neurological Damage
PKU, or phenylketonuria, is a genetic disorder that can cause neurological as well as behavioral problems in infants and children. Learn about diagnosis and treatments.
Phenylketonuria (PKU) is a genetic disorder that can cause neurological as well as behavioral problems. Mental retardation, seizures, attention deficit/hyperactivity disorder, and spasticity and tremors are some of the consequences of not treating a PKU newborn.
The physiology of PKU is pretty simple: it is a body chemistry disorder in which phenylalanine, a protein, cannot be processed. Affected individuals do not possess or have low levels of an enzyme (phenylalanine hydroxylase) which is needed to break down phenylalanine in the body.
Diagnosis
Since PKU is genetic, those who already have the disorder have a chance of passing it on to offspring. The disorder is passed on in a defective gene, and both parents must carry the mutated gene in order for the child to inherit PKU. There is a 25% chance that a child born to parents who both carry the defective gene will be born with PKU.
Given these statistics, it is possible for someone who had PKU to give it to his or her child. Other people don't even know that they are carriers. To answer this dilemma, a test was developed in the 1960s to screen all newborns in the US and in many other countries before they leave the hospital. Carrier tests to determine if potential parents carry the defective gene can be done at special PKU treatment centers.
Treatment
For babies born with PKU, a special diet must be started immediately. This diet can include a formula, Lofenalac, which is high in protein but low in phenylalanine. Lofenalac may be consumed after infancy and into adulthood because of its health benefits for people with PKU.
Infants may also consume breast milk or regular formula at levels that do not increase their phenylalanine levels. Eventually they may have particular fruits, vegetables, and grains. Things to avoid include regular milk, meat, fish, eggs, cheese, and other foods high in protein.
It used to be thought that PKU patients could end their special diets just before puberty (around age 9 or 10), but in recent years doctors agree that to maintain optimal health, PKU patients should continue to follow a very low phenylalanine diet.
Maternal PKU
A major reason to continue the PKU diet is to prevent devastating birth defects in offspring. Mothers who have PKU but no longer follow the diet often have dangerously high levels of phenylalanine in their blood. Although they may have outgrown the risks of developing neurological and behavioral problems, their children very likely will be born with brain damage, small head circumferences, and/or heart defects. These children do not necessarily have PKU, so the low phenylalanine diet will not help them after they are born. Potential mothers who have PKU should therefore be put back on a low phenylalanine diet before trying to conceive.
- For related neurological information, check out the Neurological ARTICLE INDEX and Blog
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