Obstetric Genetics Flashcards
Inheritance patterns
autosomal dominant
autosomal recessive
X-linked recessive
Autosomal dominant
heterzygotes with one copy of the abnormal gene are affected
Autosomal recessive
homozygotes with two copies of the abnormal gene are affected
X-linked recessive
males with one copy of the abnormal gene on the X chromosome are affected
carrier females unaffected
all men who inherit mutation are affected
Example of X-linked recessive
Duchenne Muscular Dystrophy
most common, 3-5 years, learning difficulties, Gower sign
Also: Haemophilia
Example of autosomal recessive
CF
progressive lung disease, affects lungs, pancreas, male infertility
Also: beta-thalassaemia
What information is needed to calculate carrier risk?
risk figure for both parents being a carrier
How to calculate risk for offspring
parent CR x parent CR x probability child will inherit 2 copies of mutation
How to calculate carrier rate for recessive condition
Hardy-Weinberg principle: can calculate once incidence is known
What is needed for H-W principle to work?
gene frequency in equilibrium
large, randomly mating population
no outside influences
2 alleles for autosomal condition
Equation
if autosomal recessive condition
p2 + q2 + 2pq = 1
AA aa Aa
p2 = homo unaffected 2pq = carriers q2 = affected
Factors affecting H-W principle
assortative mating, tendency to choose similar mate consanguinity - rs with close relatives selection founder effect migration (gene flow)
Routine prenatal screening
ultrasound - date baby, dating, single/twins
NT scan - thickness of neck in US, detect anomalies such as Down’s, major congenital heart disease
ultrasound - more detail, cleft lip
Targeted tests
family history
abnormalities in pregnancy
Non-invasive tests
US, fetal MRI, molecular testing on fetal cells/DNA in mother’s blood
