PROK2 and cartilage-hair hypoplasia: In recent years, a number of gene mutations have been found to cause CHH, including ANOS1 (anosmin 1), FGFR1, FGF8 (fibroblast growth factor 8), PROKR2 (prokineticin receptor 2), PROK2 (prokineticin 2), CHD7 (chromodomain helicase DNA binding protein 7), WDR11 (WD repeat domain 11), TACR3 (tachykinin receptor 3), TAC3 (tachykinin 3), KISS1R (KISS1 receptor), NSMF (NMDA receptor synaptonuclear signaling and neuronal migration factor), HS6ST1 (heparan sulfate 6-O-sulfotransferase 1), SOX2 (SRY-box transcription factor 2), and SEMA3A (semaphorin 3A) [2].