William Allan (1881–1943) was an American physician and geneticist who made pioneering studies in human genetics and hereditary diseases.
He established the first course in human genetics, at the Bowman Gray School of Medicine, which is now a part of Wake Forest University Baptist Medical Center.
Prior to this appointment, Allan had been in private practice in Charlotte, North Carolina, where he was nationally recognized for his early work in human and medical genetics.
As chairman of this new department, William Allan also directed the nation's first research program in medical genetics, funded by the Carnegie Foundation.
Allan-Herndon-Dudley syndrome is a rare disorder of brain development that causes moderate to severe mental retardation and problems with movement.