Shares in GameStop, the American computer games retailer, surged from $17 at the start of the year to a peak of $483, a 2,700pc rise, as members of Reddit's WallStreetBets forum piled into the shares. Those who bought the shares close to the peak were left nursing huge losses, however, as momentum faded and the stock crashed 90pc from its high. MSCI, the index provider, said there were five crucial metrics investors could examine to spot whether a stock was trading in a bubble – all of which were flashing warning signs during GameStop's boom and bust.