Case Study: Phenylketonuria (PKU)

Case Study: Phenylketonuria (PKU)
By: Bobby Orr
Adam Edwards
Danielle Heinbaugh

Introduction: What is PKU?
* PKU (Phenylketonuria) is a disorder defined as the inability to metabolize the essential amino acid phenylalanine
* This can cause mental retardation, if untreated, although sufficient treatment can occur immediately after birth

Symptoms:
* The main symptom consists of mild to moderate mental retardation, but this is easily prevented through treatment
* However, other side effects include seizures, vomiting, a “mousy odor”, and behavioral self-mutilation
* In some cases, treatment can reduce or reverse the mental retartadtion

The Guthrie Test:
* determines the phenylalanine level in the blood
* should be done on the second or third day of life
* is a screening test done to identify elevated phenylalanine levels it is not diagnostic
* PKU babies’ phenylalanine level is usually 20-40 mg/dl in comparison with normal levels of 4-6 mg/dl.

How the Guthrie Test works:
* Blood on filter paper is placed on agar plates with a strain of bacillus subtilis that requires phenylalanine for growth.
* The presence of growth is indicated by a halo surrounding the filter paper.
* If positive, blood phenylalanine and tyrosine levels are determined, and if elevated, a confirmatory assay for phenylalanine hydroxylase is done.

PKU Inheritance:
* Inherited as autosomal recessive disorder.
* Variation to classical symptoms is result of compound heterogeneity.
* 65 allelic variants make compound heterogeneity more common then homogeneity for the same allele.

Treatment of PKU:
* Phenylketonuria is treatable with a low phenylalanine diet.
* phenylalanine levels should be kept below 15 mg per deciliter
* Nutra sweet is especially high in phenylalanines

Genetic Counseling:
* Tell the parents that the baby will be normal if they follow the prescribed dietary guidelines
* The child is normally out of danger of the disease after puberty
* Phenylalanine should be avoided
o Stay away from nutra sweet, meats, dairy products

Case Study: Phenylketonuria (PKU)