Genome-wide estimates of heritability and genetic correlations in essential tremor

Introduction Despite considerable efforts to identify disease-causing and risk factors contributing to essential tremor (ET), no comprehensive assessment of heritable risk has been performed to date. Methods: We use GREML-LDMS to estimate narrow-sense heritability due to additive effects (h(2)) and GREMLd to calculate non-additive heritability due to dominance variance (delta(2)) using data from 1,751 ET cases and 5,311 controls. We evaluate heritability per 10 Mb segments across the genome and assess the impact of Parkinson's disease (PD) misdiagnosis on heritability estimates. We apply genetic risk score (GRS) from PD and restless legs syndrome (RLS) to explore its contribution to ET risk and further assess genetic correlations with 832 traits by Linkage disequilibrium score regression. Results: We estimated ET narrow-sense heritability to be h(2) = 75.5% (s.e = +/- 0.075). In contrast, dominance variance showed insignificant effect on the overall estimates. Heritability split by 10 Mb regions revealed increased estimates at chromosomes 6 and 21. The proportion of genetic variance due to PD misdiagnosed cases was estimated to be 5.33%. PD and RLS GRS were not significantly predictive of ET case-control status. Conclusions: We show for the first time that ET is a highly heritable condition in which additive common variability plays a prominent role. Chromosomes 6 and 21 may contain causative risk variants influencing susceptibility to ET. Despite overlapping symptomatology, ET does not seem to share genetic etiologies with PD or RLS. Our study suggests that most of ET genetic component is yet to be discovered and future GWAS will reveal additional risk factors contributing to ET.