Module D: Risk Calculation & Genetic Services Flashcards
For recessive conditions, how does the carrier risk decrease for each generation separating the consultand from a known carrier?
carrier risk decreases by 1/2 for each generation separating the consultand from a known carrier
For recessive conditions, how is combined carrier risk calculated?
carrier risk of two parents are multiplied
How can the carrier risk of two parents be used to determine the risk of having an affected child?
carrier risks of two parents are multiplied, and then risk of having affected child is 1/4 of combined carrier risk
How can the carrier rate for autosomal recessive disorders be calculated using the Hardy-Weinberg equilibrium?
carrier rate = twice the square root of disease frequency (q2)
For X-linked conditions, what is the risk for a mother of being a carrier?
2/3 risk of being a carrier (i.e. a heterozygote), if she has an affected male son and no other male family history of the disease
In X-linked conditions, mothers of affected males have a 2/3 risk of being a carrier assuming no other family history of the disease. What accounts for the other 1/3 of risk?
other 1/3 is due to new mutations in the affected son’s X-chromosome
For X-linked conditions, how does the carrier risk decrease for each generation separating the consultand from a known carrier?
each generation of women separating a known heterozygote/carrier from the consultand reduces the carrier risk by 1/2
How is disease frequency for autosomal dominant disorders obtained for the Hardy-Weinberg equilibrium?
disease frequency is frequency of heterozygotes
How is gene frequency for autosomal dominant disorders obtained for the Hardy-Weinberg equilibrium?
gene frequency = 1/2 the frequency of affected individuals
For X-linked disorders, how is the gene frequency obtained?
gene frequency = frequency of affected males
For X-linked disorders, how is the carrier frequency obtained?
carrier frequency = twice the disease frequency
What is the 5% rule? (2)
if disease frequency (q) is less than 5%, then use 1 for the frequency of the normal gene
if population carrier rate is less than 5%, ignore contribution of possible carriers from outside the family (unless affected individual is removed from consultand by >4 generations)
What are teratogens?
agents or conditions that can give rise to birth defects
What is chorionic villus sampling?
prenatal testing method that retrieves fetal cells from placenta at 10-12 weeks gestation
What is amniocentesis?
retrieves fetal cells from amniotic fluid at 14-20 weeks gestation
How is fetal DNA retrieved?
from maternal blood
How is fetal imaging performed?
by ultrasound or MRI
Describe the steps of preimplantation genetic diagnosis.
embryo from in-vitro fertilizaiton allowed to grow to 8-16 cell stage
single cell removed and tested for genetic disorder
only embryos without the disorder are implanted
What is dysmorphology?
genetic subspecialty area concerned with syndrome identification for individuals w/ congenital abnormalities
A dysmorphology evaluation includes (4)
family hx
pregnancy hx
physical exam
labs/imaging
What are the seven most common treatment methods for genetic disorders?
remove toxic substance
enzyme replacement therapy
dietary restriction
supply missing small molecule
transplant
block synthesis of toxic substance
gene therapy
[mnemonic: RED-STBG — think of BA 77W G-STBG]

Define empiric risk.
risk estimate based on observation