Variation in GRM3 affects cognition, prefrontal glutamate, and risk for schizophrenia

No evidence for association between polymorphisms in GRM3 and schizophrenia

BACKGROUND

Three studies have previously reported data that were interpreted by the authors as supportive of association between schizophrenia and polymorphisms in the gene encoding the metabotropic glutamate receptor GRM3.

METHODS

In a bid to examine this hypothesis, we examined seven SNPs spanning GRM3 in a UK case-control sample (schizophrenic cases n = 674, controls n = 716). These included all SNPs previously reported to be associated, alone or in haplotypes, with schizophrenia in European or European American samples.

RESULTS

Our data showed no evidence for association with single markers, or 2, 3, 4 and 5 marker haplotypes, nor did any specific haplotypes show evidence for association according to previously observed patterns.

CONCLUSION

Examination of our own data and those of other groups leads us to conclude that at present, GRM3 should not be viewed as a gene for which there is replicated evidence for association with schizophrenia.

The neurodevelopmental model of schizophrenia: update 2005

Neurodevelopmental models of schizophrenia that identify longitudinal precursors of illness have been of great heuristic importance focusing most etiologic research over the past two decades. These models have varied considerably with respect to specificity and timing of hypothesized genetic and environmental 'hits', but have largely focused on insults to prenatal brain development. With heritability around 80%, nongenetic factors impairing development must also be part of the model, and any model must also account for the wide range of age of onset. In recent years, longitudinal brain imaging studies of both early and adult (to distinguish from late ie elderly) onset populations indicate that progressive brain changes are more dynamic than previously thought, with gray matter volume loss particularly striking in adolescence and appearing to be an exaggeration of the normal developmental pattern. This supports an extended time period of abnormal neurodevelopment in schizophrenia in addition to earlier 'lesions'. Many subtle cognitive, motor, and behavioral deviations are seen years before illness onset, and these are more prominent in early onset cases. Moreover, schizophrenia susceptibility genes and chromosomal abnormalities, particularly as examined for early onset populations (ie GAD1, 22q11DS), are associated with premorbid neurodevelopmental abnormalities. Several candidate genes for schizophrenia (eg dysbindin) are associated with lower cognitive abilities in both schizophrenic and other pediatric populations more generally. Postmortem human brain and developmental animal studies document multiple and diverse effects of developmental genes (including schizophrenia susceptibility genes), at sequential stages of brain development. These may underlie the broad array of premorbid cognitive and behavioral abnormalities seen in schizophrenia, and neurodevelopmental disorders more generally. Increased specificity for the most relevant environmental risk factors such as exposure to prenatal infection, and their interaction with susceptibility genes and/or action through phase-specific altered gene expression now both strengthen and modify the neurodevelopmental theory of schizophrenia.

Psychiatric genetics--the new era: genetic research and some clinical implications

Impressive advances in the last decade have been made in the genetics and neuroscience of neuropsychiatric illness. Synergies between complex genetics, elaboration of intermediate phenotypes (Egan et al. (2004) Schizophrenia. London: Blackwell) and novel applications in neuroimaging (Bookheimer et al. (2000) N Engl J Med, 343, 450-456) are revealing the effects of positively associated disease alleles on aspects of neurological function. Genes such as NRG-1, DISC1, RGS4, COMT, PRODH, DTNBP1, G72, DAAO, GRM3 (Harrison and Weinberger (2005) Mol Psychiatry, 10, 40-68) and others have been implicated in schizophrenia along with 5-HTTPR (Ogilvie et al. (1996) Lancet, 347, 731-733; Caspi et al. (2003) Science, 301, 386-389) and BDNF (Geller et al. (2004) Am J Psychiatry, 161, 1698-1700) in affective disorders. As the genetics and complex neurocircuits of these and disorders are being untangled, parallel applications in pharmacogenomics and gene-based drug metabolism are shaping a drive for personalized medicine. Genetic research and pharmacogenomics suggest that the subcategorization of individuals based on various sets of susceptibility alleles will make the treatment of neuropsychiatric and other illnesses more predictable and effective.