These results imply that stronger purifying selection is operating at the fem gene in the presence of csd.

Previous studies showed that fem retained its sex determination function, whereas the rise of csd established a new primary signal of sex determination.

Methods: A national CSD surveillance study is conducted in Israel since 1991.

Results: There were 846 immunocompetent patients with CSD included in this study.

CSD: She's a joy to behold and the funniest woman I know.