deCODE-led Mega-study Finds new Genetic Clues to Causes of Schizophrenia
News Jul 02, 2009
The largest study of the genetics of schizophrenia ever undertaken has revealed several new common single-letter variants in the sequence of the human genome (SNPs) linked to risk of the disease.
The study, by a multinational consortium of scientists led by a team from deCODE genetics, analyzed the genomes of more than 50,000 patients and control participants from fourteen countries. It is published in the online edition of Nature.
One of the SNPs is located near the neurogranin gene (NRGN) on chromosome 11. NRGN may be a candidate drug target, as it appears to play an important role in regulating both memory and cognition, processes that are often perturbed in schizophrenics. Another SNP is in the transcription factor 4 (TCF4) gene on chromosome 18, which is involved in brain development.
Five of the SNPs are located very closely together in the Major Histocompatibility Complex, a region on chromosome 6 densely packed with genes regulating immune response. This lends support to previous research suggesting a possible environmental link between schizophrenia immune response.
It has long been known, for example, that a disproportionately large number of schizophrenics are born in the winter and spring, when influenza rates are usually highest. All of the variants found in this study are very common and each is associated with a modest increase in risk.
“Genetics offers a unique window for better understanding diseases like schizophrenia because the brain and cognition are so little understood and so difficult to study. Discoveries such as these are crucial for teasing out the biology of the disease and making it possible for us to begin to develop drugs targeting the underlying causes and not just the symptoms of the disease. One of the reasons this study was so successful is its unprecendented size. Pooling our resources has yielded spectacular results, which is what the participants from three continents hoped for. At the same time, this study underscores the fact that rare variants may well carry a significant part of the genetic risk of schizophrenia, so our next task is to use the ever more affordable sequencing technologies to find more of them,” said Kari Stefansson, CEO of deCODE and corresponding author on the paper.
In the first phase of the study, the deCODE-led SGENE consortium conducted a genome-wide scan of more than 300,000 SNPs in a total of 17,000 patients and controls from England, Finland, Germany, Iceland, Italy and Scotland.
The 1500 SNPs with the best signal were then analyzed in 11,000 patients and controls from the International Schizophrenia Consortium (ISC) and the European-American portion of the Molecular Genetics of Schizophrenia studies (MGS).
Twenty-five SNPs with strong suggestive correlation were then followed up in more than 20,000 patients and controls from the Netherlands, Denmark, Germany, Hungary, Norway, Russia, Finland and Spain. Bringing together the results of different consortia established he association between the total of seven markers on chromosomes 6, 11, and 18 with increased risk of schizophrenia.