Postmortem brain studies have shown deficits in the cortical c-aminobutyric acid (GABA) system in schizophrenic individuals. Expression studies have shown a decrease in the major GABA-synthesizing enzyme (glutamic acid decarboxylase (GAD 67 ) mRNA levels in neurons in dorsolateral prefrontal cortex in schizophrenics relative to controls. In the present study, SNPs in and around the GAD1 gene, which encodes the protein GAD 67 , were tested on a rare, severely ill group of children and adolescents with childhood-onset schizophrenia (COS) (n ¼ 72), in a family-based association analysis. Compared to adult-onset samples, the COS sample has evidence for more salient familial, and perhaps genetic, risk factors for schizophrenia, as well as evidence for frontal cortical hypofunction, and greater decline in cortical gray matter volume on anatomic brain MRI scans during adolescence. We performed family-based TDT and haplotype association analyses of the clinical phenotype, as well as association analyses with endophenotypes using the QTDT program. Three adjacent SNPs in the 5 0 upstream region of GAD1 showed a positive pairwise association with illness in these families (P ¼ 0.022-0.057). Significant transmission distortion of 4-SNP haplotypes was also observed (P ¼ 0.003-0.008). Quantitative trait TDT analyses showed an intriguing association between several SNPs and increased rate of frontal gray matter loss. These observations, when taken together with the positive results reported recently in two independent adult-onset schizophrenia pedigree samples, suggest that the gene encoding GAD 67 may be a common risk factor for schizophrenia. Molecular Psychiatry (2005) 10, 581-588.

Striking loss of cerebral gray matter is seen through adolescence in patients with childhood-onset schizophrenia. The rate of reduction was related to premorbid impairment and baseline symptom severity, but it may also be in part a plastic response to illness.

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The cortical GM volume loss in COS appears diagnostically specific; it was not seen in children and adolescents with atypical psychosis. Because both patient groups had similar early developmental patterns, cognitive functioning, medications, and hospitalizations, this progressive loss appears to be intrinsic to COS. An ongoing neurodevelopmental process and/or brain response specific to the illness could account for these changes.

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Straub et al. (2002) recently identified the 6p22.3 gene dysbindin (DTNBP1) through positional cloning as a schizophrenia susceptibility gene. We studied a rare cohort of 102 children with onset of psychosis before age 13. Standardized ratings of early development, medication response, neuropsychological and cognitive performance, premorbid dysfunction and clinical follow-up were obtained. Fourteen SNPs were genotyped in the gene DTNBP1. Family-based pairwise and haplotype transmission disequilibrium test (TDT) analysis with the clinical phenotype, and quantitative transmission disequilibrium test (QTDT) explored endophenotype relationships. One SNP was associated with diagnosis (TDT p=.01). The QTDT analyses showed several significant relationships. Four adjacent SNPs were associated (p values=.0009-.003) with poor premorbid functioning. These findings support the hypothesis that this and other schizophrenia susceptibility genes contribute to early neurodevelopmental impairment.

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