Johns Hopkins scientists studying a rare inherited syndrome marked by eye and kidney problems, learning disabilities and obesity have discovered a genetic mutation that makes the syndrome more severe but that alone doesn’t cause it. Their report appears in the advance online edition of Nature (Dec. 4). The new discovery about Bardet-Beidl syndrome (BBS) came from a panoply of studies -- starting with comparative genomics and experiments with yeast, and moving to experiments with zebrafish and genetic analysis of families with the syndrome -- and mirrors what experts expect for the genetically complex common diseases that kill most Americans, like diabetes, heart disease and cancer.