The IL17RD gene (Interleukin 17 Receptor D) encodes a 739 amino acid membrane protein, member of the interleukin 17 receptor protein family, that also regulates the signaling pathway of FGF8/FGFR1, and its pathogenic variants have been associated with CHH with or without anosmia and delayed puberty and in some cases with deafness [59,61]. This evidence concerns the gene IL18RAP and cartilage-hair hypoplasia.