Table 6.

Residual Risk (%) of a Relative Being a CFTR Mutation Carrier if Molecular Genetic Testing Does Not Detect a Mutation

Prior Risk of Being a CarrierMutation Detection Rate (%)
30%40%50%60%70%75%80%85%90%95%
2/3
(66.7%) 1
58.3%54.5%50.0%44.4%37.5%33.3%28.6%23.1%16.7%9.1%
1/2
(50.0%) 2
41.2%37.5%33.3%28.6%23.1%20.0%16.7%13.0%9.1%4.8%
1/4
(25.0%) 3
18.9%16.7%14.3%11.8%9.1%7.7%6.3%4.8%3.2%1.6%

1. Unaffected sib of a proband

2. Unaffected sib of a carrier

3. Unaffected cousin of a proband

See Table 6a (pdf) for residual risk of being a carrier for other values of prior risk.

From: CFTR-Related Disorders

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