To date, more than 60 different causal genes have been identified in approximately 50% of CHH/KS cases: KAL1 (ANOS1), which is X-linked; FGFR1 (encoding fibroblast growth factor receptor 1), FGF8, CHD7, HS6ST1 (encoding heparan-sulfate 6-O-sulphotransferase 1), SOX10, SEMA3A (encoding semaphorin-3A), WDR11 (encoding WD repeat-containing protein 11), IL17RD (encoding interleukin-17 receptor D), which follow autosomal dominant inheritance, PROKR2, PROK2, and FEZF1 with autosomal recessive inheritance. Here, IL17RD is linked to cartilage-hair hypoplasia.