Although, generally, we observed no statistically significant interactions between GST genotypes, obesity, or SHS exposure and time-domain parameters, there was a suggestion for an elevated decrease in SDNN and SDANN among subjects exhibiting both GSTM1 deletion genotype and high SHS exposure or obesity [see Supplemental Material, Table 2 (http://www.ehponline.org/members/2008/11402/suppl.pdf)]. The gene discussed is GSTM1; the disease is obesity due to melanocortin 4 receptor deficiency.