You may recall that DNA consists of a 64-letter (codon) alphabet and that a mutation involves a change in the 'spelling' of one or more genes. ENIGMA researchers screened millions of 'spelling differences' in the genetic codes they analyzed trying to identify which ones impacted the size of key parts of the brain. They used magnetic resonance images (MRIs) from 30,717 individuals. This MRI analysis focused on genetic data from seven regions of the brain that coordinate movement, learning, memory, and motivation. The researchers identified eight genetic variants associated with decreased brain volume. Apparently, individuals who carry one of those eight mutations had, on average, smaller brain regions than brains without a mutation but of comparable age. Some of the genes appear to be implicated in cancer and mental illness.