Genetics Flashcards

Question 1

Q

What is variable expressivity?

Answer

A

when individuals have the same genetic condition (even the same genotype) but have varying degrees of the phentoype

Question 2

Q

What is mosaicism?

Answer

A

the presence of > 2 genetically different sets of cells in the same person caused by an error in mitosis

Question 3

Q

What does a quad screen check for, when is it done, and what genetic abnormalities does it screen for?

Answer

A

a-fetoprotein, hcg, estriol, inhibin A
between 15-18 weeks GA
measures likelihood of Trisomy 18, Trisomy 21, neural tube defects, abdominal wall defects

Question 4

Q

How do you prenatally screen from chromosomal disorders?

Answer

A

cell-free fetal DNA

Question 5

Q

What are ways to diagnose genetic disorders prenatally?

Answer

A

ultrasound
amniocentesis
chorionic villus sampling (placenta)
umbilical blood sampling

Question 6

Q

What factor is associated with increased risk of having baby w/ Trisomy 21?

Answer

A

increasing maternal age

Question 7

Q

What prenatal quad screen results are expected for Trisomy 21?

Answer

A

low maternal serum a-fetoprotein
low unconjugated estriol
elevated hcg
elevated inhibin

can also do early U/S screening fort nuchal translucency (neck thickness) to improve sensitivity/specificity of prenatal screening

Question 8

Q

Describe phenotypic presentation of Trisomy 21

Answer

A

hypotonia
poor Moro reflex
intellectual disability
brachydactyly (short, broad fingers and toes; big space between 1st/2nd toes)
upslanted palpebral fissures
flat midface
full cheeks
protruding tongue
epicanthial folds
single transverse palmar crease
Brushfield spots (whitish spots in ringlike configuration of iris)
high-arched palate
hypoplasia of middle phalanx of 5th finger

Question 9

Q

What medical issues can kids w/ Trisomy 21 have?

Answer

A

cardiac: AV canal defect, VSD, ASD
GI: duodenal atresia (double bubble sign), Hirschprung, celiac disease
ocular: cataracts
developmental: intellectual disability, early onset alzheimer/dementia
hypothyroidism
onc: leukemia (ALL), transient myeloproliferative disorder (typically self-resolves but increases risk of ALL development)
atlantoaxial (C1-C2) instability

Question 10

Q

Health Supervision Guidelines for Trisomy 21 patients

Answer

A

all routine immunizations
echocardiogram in newborn period
ophthalmologic eval before 6 mo old
hearing eval as newborn then again at 6 mo old
thyroid studies at newborn, 6 mo, 12 mo then annually
vision screening at 4 yo
only do cervical spine imaging if symptomatic w/ signs of myelopathy

Question 11

Q

What are features of someone with Trisomy 18 (Edwards Syndrome)?

Answer

A

IUGR
intellectual disability
high forehead
microcephaly
small face/mouth
rocker bottom feet
overlapping fingers
short sternum
hypoplastic nails
structural cardiac defects

Most die in first week or within first year.

Question 12

Q

What are features of someone with Trisomy 13 (Patau Syndrome)?

Answer

A

Midline deficiency

orofacial cleft (midline cleft lip)
microphthalmia
low-set dysplastic ears
spinal cord abnormalities
postaxial (aka ulnar) polydactyly of limbs
holoprosencephaly
heart malformations
hypoplastic or absent ribs
genital anomalies
abdominal wall defects
aplasia cutis congenita (absence of layer of skin)
rocker bottom feet
clenched hands

Question 13

Q

What are the Sex Chromosome Syndromes?

Answer

A

47XXY Klinefelter
47 XYY
47 XXX
45 X Turner

Question 14

Q

What are the clinical features of Turner Syndrome?

Answer

A

45, X

short stature w/ ovarian failure/gonadal dysgenesis w/ lack of 2/2 sex characteristics
cardiac anomalies - bicuspid aortic valves, coarcted aorta
renal anomalies - horseshoe kidney, duplicate collecting system, abnormal vasculature
hearing loss (can be progressive sensorineural)
at birth: broad webbed neck, shield-like chest, posteriorly rotated ears, lymphedema of hands/feet, short 4th metacarpals, cubitus valgus
childhood/adulthood: chronic AI thyroiditis (hashimoto), alopecia, carb intolerance, vitiligo, GI disorders (ex celiac)
if have some Y material - ⇡ risk for gonadoblastoma (need to be removed)

Question 15

Q

What are the clinical features of Klinefelter Syndrome?

Answer

A

47, XXY

male phenotype
tall
gynecomastia
delayed 2/2 sex characteristic development
azoospermia and small testes → infertile

Question 16

Q

What are the clinical features of someone born 47, XYY?

Answer

Study These Flashcards

A

not a true syndrome
taller than average
severe nodular-cystic acne
commonly have developmental delay and behavioral problems
prolonged PR interval

Question 17

Q

How are microdeletion syndromes diagnosed?

Answer

Study These Flashcards

A

too small to detect via karyotype
fluorescence in situ hybridization (FISH) - looks at specific pre-defined region
chromosomal microarray (aka comparative genomic hybridization)
oligonucleotide microarray and SNP array - can find small areas of deletion

Question 18

Q

What are clinical features of Williams Syndrome (7q11.23 deletion)?

Answer

Study These Flashcards

A

broad forehead, medial eyebrow flare, short upturned nose w/ flattened nasal bridge, elongated philtrum w/ downturned lower lip (elfin facies)
friendly personality
stellate pattern of iris
strabismus
supravalvular aortic stenosis
intellectual disability
hypersensitivity to loud sounds
hypercalcemia
connective tissue anomalies (lax joints, soft skin)
growth delay and short stature
perioorbital fullness

Question 19

Q

What are the clinical features of WAGR syndrome (11p13 deletion)?

Answer

Study These Flashcards

A

Wilms tumor - in 50% of cases
Aniridia - no iris
GU abnormalities - male genital hypoplasia (hypospadias, cryptorchidism, small penis, and/or hypoplastic scrotum)
Reduced intellectual abilities - from low IQ to nml
gonadoblastoma
long face
upward-slanting palpebral fissures
ptosis
beaked nose
poorly formed ears