Frontotemporal dementia (FTD) is the leading cause of dementia in individuals less than 65 years old. Currently, there is no approved treatment of FTD and no diagnostic tests for predicting disease onset or measuring progression. Increasing evidence suggests that inflammation and immune system dysfunction play an important role in the pathogenesis of FTD.
We used summary data from genome-wide association studies to investigate genetic overlap, or “pleiotropy,” between FTD and a variety of immune-mediated diseases. Through this approach, we found extensive FTD–immune genetic overlap within the HLA region on Chromosome 6, an area rich in genes related to microglial function, as well as in 3 genes not previously identified as contributing to the pathophysiology of FTD. Pointing to the functional relevance of these genetic results, we found that these candidate FTD–immune genes are differentially expressed in postmortem brains from patients with FTD compared to controls, and in microglia/macrophages compared with other central nervous system cells. Using bioinformatics tools, we explored protein and genetic interactions among our candidate FTD–immune genes. These results suggest that rather than a few individual loci, large portions of the HLA region may be associated with increased FTD risk. Immune dysfunction may play a role in the pathophysiology of a subset of FTD cases. For a subset of patients in whom immune dysfunction in general—and microglial activation in particular—is central to disease pathophysiology, anti-inflammatory treatment is an important area for further investigation.
The authors thank the IFGC for providing phase I summary statistics data for these analyses. Further acknowledgments for the IFGC are provided in S1 Acknowledgments.