For example, a duplication of three fibroblast growth factor (FGF) genes causes the dorsal hair ridge in Rhodesian and Thai Ridgeback dogs and predisposes to dermoid sinus [23], a duplication upstream of Hyaluronic acid synthase 2 (HAS2) is responsible for the characteristic wrinkled skin of Chinese Shar-Pei dogs and predisposes to periodic fever syndrome [24], and an insertion of an FGF4 retrogene is responsible for chondrodysplasia typical of certain breeds [25]. Here, HAS2 is linked to periodic fever syndrome.