Following a series of papers in the past two years, what seems irrefutable is that copy number variations ― in which a particular stretch of DNA is either deleted or duplicated ― are important in autism.

Stylianos Antonarakis still vividly remembers the thorny statistical problem that had vexed him for several months in 1982. Antonarakis, then a postdoctoral fellow at Johns Hopkins University, had turned to his colleagues at Hopkins, but none of them had been able to solve the problem.