Genetic screening Flashcards
genetic screening is a
population based approach for identifying individuals with increased susceptibility to or risk for a genetic disease in themselves and their offspring.
newborn screening purpose
screening of all babies just after birth.
it identifies genetic diseases that can be treated early in life.
It is performed by state public health deparments and commercial laboratories.
general criteria for newborn screening
treatment is available
early initiation of treatment before symptoms become manifest, reduces or prevents severe illness
routine observation of newborn will not reveal the disorder.
condition is frequent and severe enough to justify screening.
follow up and counseling are available.
prototype for newborn screening is
phenylketouria (PKU) screening
today newborn screening is done by
tandem mass spectrometry (MSMS)
federal government recommends that every newborn screen program in the US include a uniform screening panel of
31 primary and 26 secondary conditions.
this panel is the recommended uniform screening panel.
carrier screening is used to
identify individuals who are carriers for recessive disease in specific ethnic populations.
It is also used to identify couples in which both individuals are carriers for the same genetic disease.
prototype for carrier screening: tay sachs disease
first done with enzyme assay
now performed with DNA and/or enzyme
tay sachs disease symptoms
progressive mental and motor degeneration
macular degeneration
paralysis
uncontrollable seizures
tay sachs disease carrier frequency
ashkenazi Jewish 1:25
french Canadian 1:25
maternal serum screening is done on woman ages
35 and older
maternal serum screens for
alpha fetoprotein (detects neural tube defects and chromosomal abnormalities)
quad screening (four sserum markers increase detection rate of NTD and chromsome abnormalities)
alpha fetoprotein (AFP)
a fetal protein which is produced initially by the yolk sac and then the fetal liver.
it is elevated in fetuses with neural tube defects
it is decreased in fetuses with chromosome defects.
alpha fetoprotein (AFP) is elevated in maternal serum because AFP
diffuses across the placenta.
accuracy of screening for chromosome abnormalities is improved by measuring maternal serum levels of
unconjugated estriol
human chorionic gonadotropin
inhibin
second trimester maternal serum screening
the test result is very dependent on accurate determination of the gestational age of the fetus. If the gestational age of the fetus has not been accurately determined, the results may be either falsely high or low.
triple screen for down syndrome
AFP, estradiol, hCG
69% all ages
49% <35, 88% >35
quad screen for down syndrome
AFP, estriol, hCG, inhibin
77% all ages
69% <35, 91% >35
however, if a patient tested for triple and quad screen has an ultrasound, then the detection of fetuses with down syndrome increases from
69% to over 95%
maternal serum screening: of the positive test reslts, a significant percentage of these babies
will not have any anomalies.
There may be other benign reasons for the elevated or low levels of the hormones, specifically gestational age or multiple pregnancies.
advanced maternal age
women >35 years have a higher risk of having a down syndrome child or other chromosomal abnormalities.
recommended that women >35 years have
CVS or amniocentesis:
prenatal chromosome screening
measurement of fetal alpha-fetoprotein
70% of all kinder mit major autosomal trisomies are born to women younger than 35 years who
usually do not have CVS or amnios.
therefore, maternal serum protein markers are important in identifying children with autosomal trisomies of younger mothers.
considerations for carrier screening in some religious communities
prenatal diagnosis not feasible, abortion not permitted
AID or birth control not options
marriages aranged
compatibility testing (genetic screening prior to matches)
