The most frequent pathogenic genetic variants in selected primary ciliary dyskinesia genes and their regional distribution. The most common variants in DNAH5, CCDC40, DNAI1, SPAG1 and CCNO show regional clusters. a) The most common DNAH5 variant c.10815del (×46) is prevalent in northern Europe. b) The most common CCDC40 variant c.248del (×69) is also frequently reported in the northern parts of Europe. c) The most common DNAI1 variant c.48+2dup (×60) predominantly occurs in northern Europe and neighbouring countries. d) The most common SPAG1 variant c.2014C>T (×56) shows a dominant regional distribution in the Slavic countries Poland, Czech Republic and Slovakia. e) In CCNO, there are two frequent genetic variants: c.248_252dup (×18) mainly occurs in Turkey, whereas c.258_262dup (×16) is mainly reported in Israel. NA: not available.