The new study identifies 27 loci that have rare copy number variations, where there are more or fewer repeated DNA segments than expected, common to the genomes of several children with autism spectrum disorder. These variations are not present in controls without autism spectrum disorder.
The peer reviewed paper is available in the Open Access journal PLoS Genetics.
The sample included 2,832 individuals distributed among 912 families that had multiple autistic children. The control group consisted of 1,070 samples of disease-free children who presumably are not clustered from a smaller number of family groups.
Note the apparent imbalance in sample size. Actually, it is not as big of a difference as one might think, as the 2,832 individuals samples do not represent 2,832 cases because they come from a set of under 1,000 families. In effect, the sample size of autism-related individuals in 912.