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Re: MSTS RiskFrom: Richard M. Roberts (gene@vol.com)Tue Feb 13 18:12:52 2001
Odds are different from actual risk, with one exception: when they are 1:1. If the odds are "even", or 1 to 1, you have a total of 2 different outcomes, and the risk is 1 out of 2, or 50%. So, the risk of recurrence for an autosomal dominant trait and the odds of another affected child are identical: 1 out of 2. A bookie would pay you one dollar in addition to every dollar you wagered. NOW, if the odds are 1 to 3 (the bookie pays you 3 dollars for every dollar wagered, if you win), you have a total of 4 different outcomes, so the recurrence risk is 1 out of 4, or 25%. The odds of an autosomal recessive recurring to carrier parents are 1 to 3, but their recurrence risk is 1 out of 4. This concept is used whenever Bayesian analysis is employed for more complicated analysis of recurrence risk, such as a women whose brother had Duchenne, she has never been tested, and wants to know what her risk is. Well, using Bayesian analysis, her risk is NOT as high as you think, because each normal male child she has reduces her risk of being a carrier. Cheers.At Tue, 13 Feb 2001, Wayne Persutte wrote: > >Friends, > >Can anyone explain to me why a Maternal serum triple screen that provides a >odds ratio of 1:1 is actually a risk of 50%? As was explained by a >geneticist, a 1:1 risk means that for every one affected child there is one >normal child. I find this counter-intuitive and think that this should >represent a 100% risk. Does anyone else find this odd? . . . or have I been >misinformed? >-Wayne > >-- >Wayne H. Persutte, B.S., R.D.M.S. >Director of Ultrasound, Reproductive Genetics Center >Assistant Professor, Obstetrics and Gynecology >University of Colorado Health Sciences Center >Denver, Colorado >(303) 399-5393 >FAX (303) 399-6190 >
-- Richard M. Roberts, PhD, MD, FACMG
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