PKU Webquest

PHENYLKETONURIA: A METABOLIC DISORDER

Metabolic disorders are genetic diseases that affect the body's ability to perform its normal chemical reactions. Many metabolic disorders result from enzyme defects. Recall that a metabolic pathway is a stepwise sequence of enzyme-mediated reactions. If one enzyme in a metabolic pathway is defective, that enzyme's substrate may accumulate and the pathway may not be completed. This may result in a buildup of harmful substances or a shortage of required molecules.

Activity

In this exercise, you will use the Web links below to gather information about the metabolic disorder phenylketonuria (PKU). Use what you learn to answer the questions at the bottom of the page.


Your Genes, Your Health: Phenylketonuria
http://www.ygyh.org

NSPKU Home Page
http://www.nspku.org

Texas Department of Health Genetic Disorders
http://www.dshs.state.tx.us/newborn

Phenylketonuria - The Genetics
http://willroberts.com/pku/


Questions

1. What enzyme is most commonly defective in people with phenylketonuria?
The most common defective enzyme is called phenylalanine hydroxylase which is needed to break down essential amino acid callednphenylalanine into a different amino acid called tyrosine.

2. What reaction does this enzyme catalyze? (What is the substrate and what product is produced?) This reaction causes a build up of high body levels called hyperphenylalaninaemia  which can damage the brain.
3. Describe the symptoms of phenylketonuria.
The symptoms of phenylketonuria vary from mild to very serious:
Seizures, delayed development, behavioral problems, and psychiatric disorders are also common.
Children with classic PKU tend to have lighter skin and hair than unaffected family members and are also likely to have skin disorders such as eczema.
Some cases aslo cause brain damage to the child.

4. What causes the symptoms of PKU, the lack of a substance or the buildup of one?
Phenylalanine is found in proteins of the food that we eat, and reacts badly with the PKU because the hindered enzyme is one of a metabolic nature.


5. How common is phenylketonuria? How is it treated?
PKU is not very common. Rates in Asian and Caucasians are rare but come up more in Irish and Turkish heritage families. It is treatable and is treated by a low protein diet that is carried out throughout the patient’s lifetime.