title: Consortium on the Genetics of Schizophrenia (COGS) assessment of endophenotypes for schizophrenia: an introduction to this Special Issue of Schizophrenia Research.
abstract: BACKGROUND
  The COGS is a multi-site NIMH-sponsored investigation of the genetic basis of 12 primary and multiple secondary quantitative endophenotypes in schizophrenia.
  
  
  METHODS
  Since 2003, COGS has completed studies using a family-based ascertainment strategy (COGS-1), and a case-control ascertainment strategy (COGS-2) (cumulative "n">4000).
  
  
  RESULTS
  COGS-1 family study confirmed robust deficits in, and heritability of, these endophenotypes in schizophrenia, and provided evidence for a coherent genetic architecture underlying the risk for neurocognitive and neurophysiological deficits in this disorder. COGS-2 case-control findings, many reported herein, establish a foundation for fine genomic mapping and other analyses of these endophenotypes and risk genes for SZ. Several reports in this Special Issue compare findings of endophenotype deficits generated by fundamentally different COGS-1 vs. COGS-2 ascertainment strategies. Despite the expectation that family-based and case-control designs would establish demographically and potentially biologically distinct patient cohorts, findings generally revealed comparable patterns of endophenotype deficits across studies. The COGS-2 case-control design facilitated the accrual of a larger "n", permitting detailed analyses of factors moderating endophenotype performance. Some COGS-2 endophenotypes not assessed in COGS-1 are also reported, as is a new factor analytic strategy for identifying shared vs. unique factors among the COGS endophenotypes which can be used to develop composite variables with distinct genetic signatures.
  
  
  CONCLUSIONS
  The path to date of COGS-1 endophenotype and genetic findings, followed by replication and extension in COGS-2, establishes benchmarks for endophenotype deficits in SZ and their moderation by specific factors, and clear expectations for informative findings from upcoming COGS-2 genetic analyses.
authors.affiliation: Department of Psychiatry, School of Medicine, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0804, USA. Electronic address: nswerdlow@ucsd.edu.
authors.forename: Neal R
authors.initials: NR
authors.lastname: Swerdlow
authors.affiliation: Departments of Psychiatry, Neurology & Radiology, Perelman School of Medicine, University of Pennsylvania, 10th Floor Gates Building, Philadelphia, PA 19104, USA.
authors.forename: Raquel E
authors.initials: RE
authors.lastname: Gur
authors.affiliation: Department of Psychiatry, School of Medicine, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0804, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Braff
mesh_terms: D058068:Endophenotypes; D005190:Family; D020022:Genetic Predisposition to Disease; D006801:Humans; D015337:Multicenter Studies as Topic; D012559:Schizophrenia / Q000235:genetics* / Q000503:physiopathology*; D014481:United States
keywords: Consortium; Endophenotype; Genetics; Neurocognition; Neurophysiology; Schizophrenia