The pronounced 4 to 1 boys to girls ratio reported in autism had long led scientists to speculate that the X chromosome, present in two copies in girls and only one in boys, may hold clues to the genetic component of the disorder. Using the latest ”gene chip” technology, Dr. Vincent and his colleagues have recently identified 15 novel copy number variants (CNV), or submicroscopic DNA insertions and deletions, on the X chromosome of some individuals with autism that appear absent in control samples. Building on this preliminary finding, Dr. Vincent plans to examine these CNVs in a larger collection of affected and a variety of control samples in order to validate them as specific to autism, and if so, whether they are de novo or inherited in origin. What this means for people with autism: Since some of these CNVs span genes known to be involved in mental retardation, neuronal development, and synaptic plasticity and signaling, this study may help identify new autism susceptibility candidate genes quickly. Such discovery may inform us about the disease mechanism and allow subtyping of the population that has important implications for diagnosis as well as treatment.