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Insights into individual differences in gene expression and its heritability (h²) can help in understanding pathways from DNA to phenotype. We estimated the heritability of gene expression of 52,844 genes measured in whole blood in the largest twin RNA-Seq sample to date (1497 individuals including 459 monozygotic twin pairs and 150 dizygotic twin pairs) from classical twin modeling and identity-by-state-based approaches. We estimated for each gene h²_total, composed of cis-heritability (h²_cis, the variance explained by single nucleotide polymorphisms in the cis-window of the gene), and trans-heritability (h²_res, the residual variance explained by all other genome-wide variants). Mean h²_total was 0.26, which was significantly higher than heritability estimates earlier found in a microarray-based study using largely overlapping (>60%) RNA samples (mean h² = 0.14, p = 6.15 × 10⁻²⁵⁸). Mean h²_cis was 0 …