LMP301H1 Lecture Notes - Lecture 21: Newborn Screening, Sickle-Cell Disease, Mass Spectrometry
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14 Sep 2016
School
Department
Course
Professor
LMP301
Introduction to the Biochemistry of Human Disease
Lecture 21 – Newborn screening
o Screened within 24-48 hrs
o Blood collected at heel
PKU
o Mutation causing decreased function of phenylalanine hydroxylase (PAH)
o Normal Phe from diet (proteins) is converted to tyrosine
o Lack of PAH results in accumulation of Phe (xs interferes with brain development),
formation of phenylketones, less tyrosine (decreased pigmentation), seizures
o 1:10,000 incidences and 1:50 carrier
o Biopterin is a cofactor of PAH
Deficiency in any of the pathway impairs PAH
GTPCH
PTPS
DHPR
PCD
Diagnosis for biopterin defects: Phe decreases in response to biopterin but not
Phe-restricted diet
o Testing for PKU
Chromatography
Mass spectroscopy – sensitive and specific
Tandem mass spectroscopy, newer, screen 40+ diseases including: congenital
hypothyroidism, sickle cell, MCAD, cystic fibrosis
Screening vs. testing
o Everyone is screened (unless parents wish not to)
o Testing only on suspected individuals
o Principles of NBS
Frequency of disease is high
Untreated natural history is well-defined
Untreated high morbidity/mortality
Treated significant better outcome
Testing is safe, simple, and sensitive (will catch all instances of disease)
Specific confirmatory testing available (to rule out false positives)
Everything is cost-effective
Diseases
Name
Causes
Characteristics
Diagnosis
Treatments
PKU
PAH deficiency-autosomal
recessive
Biopterin pathway defects
(5%)
Mental
retardation
Blond appearance
Urine smell
Phe > 1300 µM
Biochemical
tests (see
above)
Measure urine
and CSF pterins
Dietary