KCNK9 and Birk-Barel syndrome: K2P9.1 is also inhibited by acid pHo with a pKa of ~6 [1006]. Imprinting of the KCNK9 gene is associated with Birk Barel syndrome [66]. K2P9 can form heterodimers with K2P1 [982] or K2P3 [231].