The understanding of complex heritable psychiatric disorders such as schizophrenia could be clarified by examining endophenotypes within genetically isolated populations, such as the one found in the Central Valley of Costa Rica. The reduction of familial variability within a sample could allow the relationship between the cognitive and symptomatic manifestations of the illness and the genetic underpinnings to become more observable. This study investigates the neuropsychological test performances of 41 family members from four extended multiplex families within the Spanish origin population of the Central Valley of Costa Rica as potential endophenotypes for genetic studies.
Individuals with a diagnosis of schizophrenia or schizoaffective disorder were compared with unaffected relatives and 15 unrelated controls with no family history of schizophrenia.
Although the sample size is small, the results confirm previous reports in the literature of deficits in working memory, executive function, processing speed, and verbal fluency in individuals with schizophrenia compared with controls and intermediate performance in nonpsychotic family members compared with controls. We also found several suggestive quantitative cognitive trait loci with log of the odds greater than 1.75.
These findings suggest that the cognitive deficits in schizophrenia are consistent aspects of the illness, although their usefulness as endophenotypes for genetic studies remains unclear.