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94 Cards in this Set

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Is screening a diagnostic test? What does a screen tell you?
No, screened individulas are generally health and not seeking medical care

tells that there is an increased risk for a disorder, which justifies further diagnositic procedures
Why are screens done?
routine testing as predictive medicine to target interventions to individual patients in order to improve their health and prevent disease
What is required for a screening program?
1 well defined disorder
2 medically important disorder that has a treatment
3. cost effective
4. Simple and safe
5. Procedures following a positive test are acceptable for patients and doctors
6. Distribuitionof test values in affected AND unaffected individuals is known AND the extent of overlap is sufficiently small and suitable cut off is defined
What are 3 characteristics of a screening test?
1. Detection Rate (DR)
2. False Positive Rate (FPR)
3. Odds of being affected given a positive result (OAPR)
What is a detection rate?
The number of people whith the disease who screen positive
What is a false positive rate?
The number of people without the disease who screen positive
What are the detection rate and false positive rate independent of?
prevalence of disease being screened for
What are DR and FPR related to algebraically?
DR = a/ (a+c)
FPR = b/ (b+d)
What is odds of being affected given a positive result (OAPR) dependent on ?
prevalence of disorder in population being studied
What is OAPR a ratio of ?
Affected to unaffected individuals who screen POSITIVE
Which prenatal screening test must be offered to patients? What does it screen for?
Must offer maternal serum screening for neural tube defects, trisomy 18 and downs syndrome
What are the types of screening?
prenatal
newborn
carrier-- tay-sachs, cystic fibrosis
disease--presymptomatic like heart disease and cnacer
drug susceptibility
infectious disease
Which matenal serum screening disorder is most frequent in live births?
Trisomy 18: 1 in 6500

Least is Down Syndrome
Do most neural tube defects result in spontaneous abortion? What are some common neural tube defects?
Yes
1. anencephaly
2. enchephalocele
3. spina bifida
What are characteristics of anencephaly?
--absence of skull vault, cerebellum absent, brain stem hypoplastic
ALWAYS FATAL
What are the characteristics of encephalocele?
Herniation of brain tissue and or meninges through a BONY defect in skull

80 % closed defects

Hydrocephalus in 50%

often have other syndromes
What are the characteristics of spina bifida? What are the two subsets of spina bifida? What % are closed? open?
Defective closure of vetebral column

Meningocele involves MENINGES ONLY

Myelomeningocele involves MENINGES AND SPINAL CORD TISSUE

Closed: 20%
Open: 80%
What are the characteristics of open spina bifida? What is disability dependent on?
higher morbitity and mortality

94% survivors are SEVERELY disabled

Disability dependent on open or closed and location of lesion and presence or absence of hydrocephaly
What are the characteristics of closed spina bifida?
clinical sequelae are variable

less severely affected
What is spina bifida occulta and what are the symptoms?
incomplete ossification of the POSTERIOR vertebral laminae (L5 S1 most common)

NO CLINICAL OR GENETIC consequences

Normal variant in kids less than 2

Occurs in about 20% of adults
What are ventral wall defects? What are the two types? How prevelant are they?
Abdominal wall defects

OMPHALOCELE 1 in 4000 intestine protrudes into umbilical cord...associated wtiht trisomy 13 or 18

GASTROSCHISIS--Opening to right of umbilical cord 1 in 10,000.
Down Syndrome is a trisomy of which chromosome? What are the symptoms?
21

Short, epicanthal folds, flat nasal bridge, transverse palmar crease, mental retardation, gypotonia, congenital heart defect in 40%
What increases a mother's risk of producing DS child?

What % of DS babies are born to women under 35?

What % spontaneously abort?
Age

under 35 55%

23% spontaneously abort
How likely are Trisomy 18 babies to survive to their 1st birthday?

What % miscarry?

What are the symptoms?
5-10% survive to 1st b. day

70% miscarry before birth

severe mental retardation, heart and kidney defects, NTD's and VWD's (neural tube and ventral wall defects)
What does the triple screen check for?
1 alpha fetoprotein (AFP)
2 hcG human chorionic gonadotropin
3 unconjugated estriol (uE3)
What does a quad screen check for?
Same as triple screen and add dimeric inhibin A (DIA)
Why test for AFT alpha feto protein
producted by fetal liver and ylok sac, values increase in the 2nd trimester (15% per week)
What would affect maternal serum levels of alpha fetal protein?
gestational age dating (ultrasound) maternal weight, # fetuses, maternal race, IDDM
Where is hCG produced and When are levels increasing? What type of subunits? Which is most unique to hCG? When is most hcG intact? What factors must be corrected for?
hormone synthesized and secreted by placenta, levels increase rapidly in early pregnancey and DECREASE between 10-20 weeks gestation

Has alpha AND beta subunits

Beta subunit is UNIQUE to hCG

In 2nd trimester most hCG is inact

results must be corrected for maternal weight and race
When is uE3 Unconjugated Estriol 3 found? Where does it come from? When do levels increase? What must be corrected for?
Found in maternal circulation 7-9 weeks gestation,

syntesized by fetal adrenal glands, liver, and placenta,

levels increase throughout the 2nd trimester

results are corrected for maternal weight
What is inhibin and what is dimeric inhibin A (DIA)specificially? Where is it produced?
inhibin is a hererodimeric glycoprotein consisting of an alpha and either beta a or beta b subunits

DIA is the dimer of the alpha subunit and the beta a subunit

Synthesized in the gonads and the placenta
Where is DIA secreted in early pregnancy?

What is significant about increased levels of DIA?
in early pregnancy inhibin is secreted from the corpus luteum AND the palcenta

inhibin A is elevated in Down syndrome (2x non DS)

Levels do not vary much with GA in 2nd trimester
In autosomal dominance what % of childern will inherit the mutation?
50%
What is consanguity?
married blood relatives
Are there skipped generations in autosomal dominant inheritance?
no skipped generations
Who transmits autosomal dominant genes more?
doesn't matter
men and women equally
What types of genes are involved in autosomal dominant inheritance? How common are NEW mutations?
structural genes most often

new mutations ARE COMMON
What type of transmission is observed in autosomal dominant inheritance?
vertical transmission
What causes new mutations in autosomal dominant inheritance?
sperm usually--single mutation

egg age--chromosomal abnormalities
What is the difference between incomplete and complete penetrance?

Give an example of each
incomplete expressed as a phenotype, not as penetrant as complete penetrance.

Ex. of incomplete: BRCA gene not all carriers have breast cancer

complete: achrondoplasia or neurofibromastosis
What is varible expression and what is an example?
different phenotypes from same mutation.

Van der Woude can result in cleft lip OR palate or lip pits

Interfamilial variation
Is consanguity more or less common in recessive inheritance?
More common
What types of genes are affected in autosomal recessive inheritance?
functional

involves enzymes
What are the chance that you are a carrier if you are the sibling of a cystic fibrosis ?
66%
What is the risk assoiated of being affected with an autosomal recessive gene if both parents are carriers?
25%
In X linked recessive disorders how many daughters of affected fathers will be CARRIERS? How many of his sons?
100% daughters

0% sons
When X linked is LETHAL who transmits the gene?

When non lethal?
MOM when lethal

non lethal from both sexes
Give an example of a non lethal and a lethal x linked recessive disease.
non lethal--colorblindness

lethal--duchenne's muscular dystrophy
Sons who's mom carries an x linked recessive have what % likelihood of being affected?
50% mom could give her unaffected X
What happens in anticipation?

What is it due to?

Give an example.
With each generation th edisease gets more and more severe.

Due to triple repeats

myotonic dystrophy and FRAGILE X
What is the parent of origin effect?

Give an example.

What may be the cause?
abnormal allele is active from only one sex.

EX. angelman's syndrome: mother copy is active, paternal is inactive

sister mothers give birth to children with active copy

methylation results in the differences
What is mosaicism?
affects only SOME cells in the body and has a variable phenotype.

Ex. gonadal unaffected parent can lead to more than one affected child

osteogenesis imperfecta II
lethal
Name a disease resulting in a chromosomal translocation.
down syndrome
What is maternal inheritance due to ?
mitochondrial genome passed from mom only
What is the difference between polygenic and multifactorial traits?
polygeneic is many genes resulting in one characteristic

multifactorial is when a few genes make a large contribution. spinabifida, mthfr and folate deficiency
Name some forms of non mendelian inheritance.
polygenic, mulitfactorial, mosaicism, translocations, maternal inheritance
What is genetic heterogenity?

What is genotype/phenotype correlations?
mutatios in different genes cuase the SAME disease.

different mutations in the SAME gene cause a DIFFERENT disease
give an example of genetic heterogeneity?
BRAC1 and BRAC 2 both cause the same disease. Can't differentiate the phenotype
What does the carrier frequency measure?
The prevalence of the altered gene in the population.
Whath is the founder effect?
increased frequency of gene mutation within a population founded by a small group--jew, iceland, poland
How is a karyotype set up?
from largest to smallest

p arm is smaller than q arm
What is CGH?
comparative genome hybridization.

Have an extra amount of DNA,which might not be detected with mircoscope

can compare with a control

map out deletions and duplication
Are all changes in DNA deleterious?
no, some deletions have no effect because they are in the introns
What are the different types of point mutations?
point mutations

Missense (can be neutral or harmful)

nonsense (early stop codon, short protein)

Frameshift due to
deletion or insertion (produces a shorter protein)
What does a splice site mutation result in?
altered RNA sequence
What does ASO require?
allele specific oligonucleotide requires that you KNOW the mutation

1st amplify a gene
2nd add radiolabeled and mutant probes
What is a problem that can arise in PCR
While hybridizing DNA could get technicians dna mixed in
How does linkage anaylsis work?
look for pattern of DNA markers newar the gene of interest.

requires analysis of multiple family members
What is SSCP and how does it work?

Is this technique direct or indirect
single strand conformational polymorphism.

mutant DNA shape is altered
this is an INDIRECT technique
How does CSGE work?
heteroduplex analysis forces a hybridization which leads to 3D changes which affects how it moves thru gel
What is the trouble with DNA sequencing?
cannot detect LARGE deletions

separates 2 strands and compares to each other (one from mom one from dad)
What % of birth defects are caused by known causes?
known: 40%

unknown: 60%
What can cause a disruption? Is it intrinsic or extrinsic?
disruption by teratogens like

retinoic acid--defective programed cell death

thalidomide--meromelia

MATERNAL DISEASE--PKU OR DIABETES

MATERNAL INFECTION

Thromboembolii, amnionic rupture, hypotension

tabacoo--growth retardation, miscarriage

alcohol, mental retardation, heart defect, cleft lip

LACK OF MORPHOGEN--folic acid. W/o get neural tube defects, cardiac anomalies, cleft lip
Are drugs of abuse usually teratogens?
no

alcohol is!!
increased incidence of miscarrabe, facial palsy, aotic arch and ear anomalies are all signs of with embryopathy?
retinoic acid
asymmetric amputations, circumferential constrictions and distal swelling are symptoms of what?

(normal, normal, BOOM)
Amnionic band sequence

Adams oliver syndrome

LOW recurrence
Hypoxia or hypoperfusion of tcord, dimished mm mass, policemans tip are symptoms of what?
vascular disruption or amyoplasia
What is the recommended dosage of folic acid?
400ug/day

Atkins--no folic acid, no grains
What are some malformations?
neural tube defect, ectrodactyly, cleft lip/palate
What is the rate of recurrence of neural tube defect? What can limit this? What type of trait is this?
A multifactorial trait
3% recurrence
folic acid can limit this problem when taken PRIOR to conception
What type of trait is ectrodactyly?
autosomal dominant trait

can be in isolation or with other syndromes

Bree Walker
When does cleft lip form?

What type of trait is it?
during 7 wk gestation

multifactorial trait
What is a syndrome?
What type of trait is it? Which gene is it on?
Give an example.
What type of surgery is needed in 70% of cases?
lots of symptoms from a SINGLE cause

autosomal dominant trait: Gene IRF6 50% of the time

Ex. Van der Woude

need cleft surgery
What type of trait is EEC syndrome? What are the symptoms?
autosomal dominant

extodermal dysplasia, ectrodactyly, cleft lip
What type of trait is Adams Oliver syndrome?

What distinguishes this from amnionic banding?
autosomal dominant

transverse terminal defect--ectrodactyly, scalp and skin defects, SYMMETRIC lesionsn

(not amnionic banding because of symmetry of lesions
What is a dysplasia?
a pattern of malformations that affect the SAME tissue
Which disorder so the following symptoms relate to?

females with thin hair, patchy sweating, poor teeth

males with needle like or missing teeth, absent sweating, alopecia
X linked ectodermal dysplasia

mild in women
What is the most common bone dysplasia? What type of trait is it? Which gene is it on and which parent donates it?
achondroplasia

autosomal disorder--FGFR3 of paternal origin
What do the following symptoms correlate to?

lethal bone dysplasia
rhizomelia
trident hand
telephone receiver femurs
stellate iliac bones
thanatophoric dysplasia
What causes osteogenesis imprefecta Type II?

What type of trait is it?

What are the symptoms?
gonadal mosaicism--recurrence 2-6%
lethal defect of collagen

autosomal dominant trait

severe intrauterine fractrues, accordion femurs, bent long bones, beaded ribs, multiple fractures
What is association?
pattern of anomalies that occur together BUT more often than expected by chance alone

BUT nto necessarily in any patern or with any cause
What is an example of association?
VATER

Vertebral defects
Anus imperforate
Trachea
Esophageal fistula
Radial/Renal defects
What is a sequence?
A pattern of anomalies where the primary defect leads to one or more secondaries--a CASCADE EFFECT
Give an example of association.
holoprosencephaly--face predicts the brain

midline CNS structures induce the premaxillary process. Get premaxillary agenesis

cebocephaly--single nostril
parents may have single central incisor