Brain vs behavior: an effect size comparison of neuroimaging and cognitive studies of genetic risk for schizophrenia

Abstract

Genetic variants associated with increased risk for schizophrenia (SZ) are hypothesized to be more penetrant at the level of brain structure and function than at the level of behavior. However, to date the relative sensitivity of imaging vs cognitive measures of these variants has not been quantified. We considered effect sizes associated with cognitive and imaging studies of 9 robust SZ risk genes (DAOA, DISC1, DTNBP1, NRG1, RGS4, NRGN, CACNA1C, TCF4, and ZNF804A) published between January 2005-November 2011. Summary data was used to calculate estimates of effect size for each significant finding. The mean effect size for each study was categorized as small, medium, or large and the relative frequency of each category was compared between modalities and across genes. Random effects meta-analysis was used to consider the impact of experimental methodology on effect size. Imaging studies reported mostly medium or large effects, whereas cognitive investigations commonly reported small effects. Meta-analysis confirmed that imaging studies were associated with larger effects. Effect size estimates were negatively correlated with sample size but did not differ as a function of gene nor imaging modality. These observations support the notion that SZ risk variants show larger effects, and hence greater penetrance, when characterized using indices of brain structure and function than when indexed by cognitive measures. However, it remains to be established whether this holds true for individual risk variants, imaging modalities, or cognitive functions, and how such effects may be mediated by a relationship with sample size and other aspects of experimental variability.

Fig. 1.

The relationship between “effect size,” “sample size,” and “power.”

Fig. 2.

Percentage of results in each effect size category (ie, small, medium, or large) for (A) cognitive and (B) imaging studies.

Fig. 3.

Forest plot (random effects) showing Hedge’s g, SE and relative weight for meta-analysis in (A) cognitive and (B) imaging investigations.

Fig. 4.

The linear regression of sample size (N) against observed mean effect size (d) in (A) imaging and cognitive studies (Note: for visualization purposes investigations where N > 1200 (ie, 3 studies) have been excluded from this graph) (B) imaging investigations, and (C) cognitive investigations.

Fig. 5.

Funnel plots of log OR against the SE of the log OR for each study in (A) cognitive studies and (B) imaging studies. Since all effect size estimations were considered positive, these plots have been cropped at OR = 0.