Genetically predicted complement component 4A expression: effects on memory function and middle temporal lobe activation

Background The longstanding association between the major histocompatibility complex (MHC) locus and schizophrenia (SZ) risk has recently been accounted for, partially, by structural variation at the complement component 4 (C4) gene. This structural variation generates varying levels of C4 RNA expression, and genetic information from the MHC region can now be used to predict C4 RNA expression in the brain. Increased predicted C4A RNA expression is associated with the risk of SZ, and C4 is reported to influence synaptic pruning in animal models. Methods Based on our previous studies associating MHC SZ risk variants with poorer memory performance, we tested whether increased predicted C4A RNA expression was associated with reduced memory function in a large (n = 1238) dataset of psychosis cases and healthy participants, and with altered task-dependent cortical activation in a subset of these samples. Results We observed that increased predicted C4A RNA expression predicted poorer performance on measures of memory recall (p = 0.016, corrected). Furthermore, in healthy participants, we found that increased predicted C4A RNA expression was associated with a pattern of reduced cortical activity in middle temporal cortex during a measure of visual processing (p < 0.05, corrected). Conclusions These data suggest that the effects of C4 on cognition were observable at both a cortical and behavioural level, and may represent one mechanism by which illness risk is mediated. As such, deficits in learning and memory may represent a therapeutic target for new molecular developments aimed at altering C4’s developmental role.The authors have no conflict of interest to declare. The authors wish to thank all patients and their support staff, and all healthy volunteers for participating in the data collection on which this manuscript is based. Recruitment, genotyping and analysis were supported by the European Research Council (grant 677467) Science Foundation Ireland (grants 12/IP/1670, 12/IP/1359 and 08/IN.1/B1916) and the Wellcome Trust Case Control Consortium 2 project (grants 085475/B/08/Z and 085475/Z/08/Z) and the Wellcome Trust (grants 072894/Z/03/Z, 090532/Z/09/Z and 075491/Z/04/B). The authors thank Dr Avery Davis and Dr Steven A. McCarroll at Harvard Medical School for generating the predicted C4A RNA expression data from chromosome 6 SNP data for all samples. The authors also thank Lucinda Hopkins and Lesley Bates for assistance in generating genotype data at Cardiff University. They also thank Dr Davis and Dr McCarroll for their helpful comments on the manuscript. The Wellcome Trust Case Control Consortium 2 investigators include: Peter Donnelly, Lesley Bates, Ines Barroso, Jenefer M. Blackwell, Elvira Bramon, Matthew A. Brown, Juan P. Casas, Aiden Corvin, Panos Deloukas, Audrey Duncanson, Janusz Jankowski, Hugh S. Markus, Christopher G. Mathew, Colin N. A. Palmer, Robert Plomin, Anna Rautanen, Stephen J. Sawcer, Richard C. Trembath, Ananth C. Viswanathan, Nicholas W. Wood, Chris C. A. Spencer, Gavin Band, Céline Bellenguez, Colin Freeman, Garrett Hellenthal, Eleni Giannoulatou, Lucinda Hopkins, Matti Pirinen, Richard Pearson, Amy Strange, Zhan Su, Damjan Vukcevic, Cordelia Langford, Sarah E. Hunt, Sarah Edkins, Rhian Gwilliam, Hannah Blackburn, Suzannah J. Bumpstead, Serge Dronov, Matthew Gillman, Emma Gray, Naomi Hammond, Alagurevathi Jayakumar, Owen T. McCann, Jennifer Liddle, Simon C. Potter, Radhi Ravindrarajah, Michelle Ricketts, Matthew Waller, Paul Weston, Sara Widaa and Pamela Whittaker.2019-06-0