They include some of the genes responsible for Bardet–Biedl syndrome (BBS1 [175], BBS4 [175], MKKS (BBS6) [175] and TTC8 (BBS8) [132]) (see [66] for review), genes responsible for Meckel–Gruber syndrome (Mks1 [44]), and genes responsible for Alström syndrome (Alms1 [89]). Here, TTC8 is linked to Down syndrome.