Similar submicroscopic variations and rearrangements appear in the genetic material of individuals with schizophrenia, autism and mental retardation, suggesting that the three disorders may share a developmental pathway, according to a report in the September issue of Archives of General Psychiatry, one of the JAMA/Archives journals.
New technologies to compare genomes have enabled researchers to detect genetic alterations known as copy number variations—deletions or duplications that change the number of copies of specific DNA segments, according to background information in the article. “Recently, this approach has been widely used in neurologic and psychiatric disorders, including mental retardation, autism spectrum disorders and schizophrenia,” the authors write. “Findings from these studies suggested that several genes involved in similar neurodevelopmental pathways may be associated with these conditions. However, so far only rare structural variants, sometimes present in a single case, have been identified.”
Audrey Guilmatre, Ph.D., of Institut Hospitalo-Universitaire de Recherche Biomédicale, Rouen, France, and colleagues analyzed genetic material from 247 individuals with mental retardation, 260 with autism spectrum disorders, 236 with schizophrenia and 236 controls with no psychiatric diagnoses. They focused on 28 candidate loci (points on a chromosome where a gene is located) found to be associated with these conditions in previous studies.
Among the 743 individuals with one of the disorders, recurrent or overlapping copy number variations were found in 11 of the 28 candidate loci (39.3 percent). One of the 28 variations was found in 10 of 236 individuals with schizophrenia (4.2 percent), 16 of 260 individuals with autism spectrum disorders (6.2 percent) and 13 of 247 cases with mental retardation (5.3 percent), compared with one of 236 controls (0.4 percent).
Only one copy number variation—related to autism spectrum disorders—was potentially found to be more specifically associated with one condition as opposed to all three. In addition, many of the individuals with a copy number variation had more than one disorder; one-third of those with schizophrenia and 83.3 percent of those with autism also had a level of cognitive functioning placing them in the range of mental retardation.
The study “confirms and extends recent evidence suggesting that many candidate copy number variations are not disease specific but are involved in the expression of different behavioral phenotypes, including mental retardation, autism spectrum disorders and schizophrenia. This implies the existence of shared biologic pathways in these three neurodevelopmental conditions,” the authors conclude. These pathways appear to affect the formation and maintenance of the synapses or gaps between nerve cells, as well as the function of specific neurotransmitters. “The dysfunction of specific neuronal networks underlying the particular symptoms of each clinical condition most likely depends on additional genetics, epigenetics and environmental factors that remain to be characterized.”