Case Study: Phenylketonuria
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
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
In some cases, treatment can reduce or
reverse the mental retartadtion
The Guthrie Test:
determines the phenylalanine level in the
should be done on the second or third day of
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.
• Inherited as autosomal recessive disorder.
• Variation to classical symptoms is result of
• 65 allelic variants make compound
heterogeneity more common then
homogeneity for the same allele.
Treatment of PKU:
• Phenylketonuria is
treatable with a low
• phenylalanine levels
should be kept below
15 mg per deciliter
• Nutra sweet is
especially high in
Tell the parents that the baby will be normal
if they follow the prescribed dietary
The child is normally out of danger of the
disease after puberty
Phenylalanine should be avoided
– Stay away from nutra sweet, meats, dairy