A mobile phone game that tests spatial navigation skills and has been played by 2.4 million people, has become the largest dementia study in history and raised hopes of a breakthrough in diagnosing the disease. Sea Hero Quest, a collaboration between Alzheimer’s Research UK, Deutsche Telekom, game designers Glitchers and scientists, has generated the equivalent of 9,400 years of lab-based research since its launch in May. Experts hope to use the data to create the…