MKKS and McKusick-Kaufman syndrome: BBS2 and BBS4 mutations cause BBS (Mykytyn et al., 2001; Nishimura et al., 2001), whereas BBS6 (or MKKS) gene defects are associated with McKusick-Kaufman syndrome (abnormalities in finger, heart and genitals) in addition to BBS (Katsanis et al., 2000; Slavotinek et al., 2000).