Is there a relationship between sex of cystic fibrosis carriers and sex ratio of their offspring?

Data on the offspring of 198 aunts and 179 uncles of 100 cystic fibrosis index cases were analyzed. Aunts showed higher average number of liveborn sons than uncles. No significant difference was observed in the number of liveborn female offspring. When the sample was subdivided with respect to family size, the proportion of liveborn sons of aunts appeared higher than that of uncles in all classes. The present observations suggest that a female carrier may have a higher probability of male offspring than a male carrier and that she may be mainly responsible for the sex ratio deviations previously reported in sibships of cystic fibrosis patients.