Synkinesia and renal agenesis areparticularly associated with ANOS1 mutations, hearing losswith CHD7 and SOX10 mutations, andmidline, digital and dental defects with mutations of FGFR1or its cognate ligand FGF8. Given that X-linked KS(ANOS1) comprises only around 10% of KS cases (5% oftotal CHH), the genetic architecture of CHH provides no clues as why it isaround 3-4-times less common in females (15). This evidence concerns the gene CHD7 and cartilage-hair hypoplasia.