['Carboxylesterase 1 (CES1) appears to play an important role in the control of the metabolism of triglycerides and cholesterol in adipocytes and other cell types including hepatocytes. Therefore, it is relevant to gain insights into the genetic versus non-genetic mechanisms involved in the control of CES1 mRNA expression. Here, we investigated CES1 mRNA expression level in adipose tissue and its association with measures of adiposity and metabolic function in a population of elderly twins. Furthermore, the heritability of CES1 mRNA expression level in adipose tissue and the effect of CES1 gene duplication were assessed.', 'A total of 295 monozygotic and dizygotic twin subjects (62-83 years) with (n\u200a=\u200a48) or without (n\u200a=\u200a247) type 2 diabetes mellitus were enrolled in the study. They were subjected to a standard oral glucose tolerance test and excision of abdominal subcutaneous fat biopsies during the fasting state. Levels of CES1 mRNA and copy number of the gene were assessed by quantitative PCR.', 'CES1 mRNA expression level in adipose tissue was positively associated with body-mass index (P<0.001), homeostasis model assessment-insulin resistance (P\u200a=\u200a0.003) and level of fasting glucose (P\u200a=\u200a0.002), insulin (P\u200a=\u200a0.006), and triglycerides (P\u200a=\u200a0.003). The heritability for the expression of CES1 mRNA in adipose tissue was high. CES1 gene duplication was positively associated with insulin sensitivity (P\u200a=\u200a0.05) as well as glucose tolerance (P\u200a=\u200a0.03) and negatively associated with homeostasis model assessment-insulin resistance (P\u200a=\u200a0.02). Duplication of CES1 was not linked to mRNA level of this gene (P\u200a=\u200a0.63).'] Are carboxylesterase 1 gene duplication and mRNA expression in adipose tissue linked to obesity and metabolic function?