Twin studies also allow calculation of the proportion of phenotypic variation attributable to familial non-genetic factors, i.e. the shared common environment. Notably, we found that as much as 32% of expressed LCL transcripts have a common environment component that explains over30% of the total variance compared to 2% and 8% in adipose and skin tissue (Fig. 1B). This larger shared environmental effect in LCLs most likely reflect the impact of additional correlated sample handling steps not applicable for tissue biopsies such as blood sampling, cell isolation, EBV transformation and cell culture procedures as the study subjects visited the clinic in pairs.
