In addition, while polydactyly is very common in human BBS patients, none of the BBS mouse models generated so far display polydactyly as is seen in Smo or Shh mutants [2], implying a potential species-specific requirement of BBS proteins or differential threshold in SHH signaling in the limb bud. The gene discussed is BBS2; the disease is Bardet-Biedl syndrome.