2 Further analysis of additional unsolved CRS cases using WES/WGS, RNA sequencing or targeted resequencing identified heterozygous variants in SIX1 in seven further patients with CRS from six unrelated families. Dominantly inherited SIX1 variants were previously reported in branchio-otic syndrome (BOS; MIM 608389),3 4 non-syndromic HL (MIM 605192)5 and (rarely) in branchio-oto-renal (BOR) syndrome, associated in addition with renal malformation.3 This work uncovers a previously unrecognised role of SIX1 in the maintenance of cranial suture patency. This evidence concerns the gene SIX1 and Branchio-otic syndrome.