If the child is affected due to a new mutation, then the risk of recurrence is very low. If the affected child has an autosomal dominant condition inherited from a clinically normal parent, then the recurrence risk is higher. If there are healthy children in addition to the affected child, then the odds are better than if there were no unaffected siblings.


Conditions for Young's equation:

(1) autosomal dominant condition

(2) both parents clinically unaffected

(3) calculating the risk for the sibling of an affected child

(4) integrates the condition of having normal siblings in addition to the affected child


risk of recurrence =

= (0.5 * (penetrance) * (1 - (penetrance)) * ((1 - ((penetrance) / 2)) ^ (number of unaffected siblings))) / (((1 - (penetrance)) * ((1 - ((penetrance) / 2))^(number of unaffected siblings))) + ((penetrance) * (1 - (fitness of affected heterozygotes))))



• fitness is that of the affected (= penetrant) heterozygote (Friedman's equation uses the fitness of all heterozygotes)

• penetrance and fitness are decimal fractions from 0 to 1.


If only the affected child is present (no healthy siblings), this equation becomes


risk of recurrence =

= (0.5 * (penetrance) * (1 - (penetrance))) / ((1 - ((penetrance) * (fitness of affected heterozygotes))))


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