The first group, led by Michele Pergadia, Ph.D., carried out genetic linkage analyses of DSM-IV-diagnosed major depressive disorder in two samples that are part of the Nicotine Addiction Genetics (NAG) project, an international
consortium focused on tobacco dependence. "We used an affected sibling-pair design, in which at least two adult offspring
per family reported a history of DSM-IV major depressive disorder, and tested for linkage," said the group in its report. "Results appear to confirm a genomewide
significant linkage signal at chromosome 3p25-3p26."