Case Study: Phenylketonuria (PKU)

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Transcript Case Study: Phenylketonuria (PKU)

Case Study: Phenylketonuria
(PKU)
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
– Stay away from nutra sweet, meats, dairy
products