The term rare, or orphan disease can encompass any one of more than 6000 conditions. Some, such as cystic fibrosis or Tourette’s syndrome, are well known, while others, including Acromegaly or Morquio syndrome, are much less well recognised. David James at J+D Forecasting delves into history, showing how historically, patients diagnosed with a disease classified as rare were denied access to effective medicines because prescription drug manufacturers could rarely make a profit from marketing drugs to such small groups.