Pedigree Analysis

Question 1

Autosomal Dominant Criteria

Answer 1

• phenotype appears in every generation
• each affected person has an affected parent
• recurrence risk for any child is 50%
• phenotypically normal family members do not transmit the trait to their children
• trait can be transmitted by both sexes & both sexes are equally at risk
• MALE-TO-MALE TRANSMISSION

Question 2

AD considerations

Answer 2

• reduced penetrance
• variable expressivity
• later age of onset
• new mutations
• germline mosaicism

Question 3

Autosomal Recessive Criteria

Answer 3

• phenotype is usually found only in siblings
• recurrence risk for each sibling of the proband is 25%
• Both sexes are equally likely to be affected
• many cases are sporadic
• Unaffected siblings have a 2/3 risk of BEING A CARRIER

Question 4

AR considerations

Answer 4

• consanguinity
• quasidominant or pseudodominant
• quasidominant: individual affected with an AR condition mating with a carrier & having affected children

Question 5

X-linked Recessive Criteria

Answer 5

• incidence of the trait is higher in males
• daughters of affected males are obligate carriers
• no male-to-male transmission
• affected males related through unaffected carrier females
• a carrier female has:
• -50% chance for affected son
• -25% chance for an affected child

Question 6

X-linked Dominant Criteria

Answer 6

• affected males have no affected sons and all daughters affected
• no male-to-male transmission
• both male and female children of affected female shave a 50% risk of inheriting the condition
• affected females are about twice as common as affected males, but may have milder phenotype

Question 7

X-linked Dominant Considerations

Answer 7

• new mutation
• germline mosaicism
• manifesting carriers (lyonization/X-linked inactivation)