The differences in NGF levels between the control groups in figures 1B and 1C may reflect the underlying differences between the two groups, since the nonsmoking group (figure 1B) had other comorbid medical conditions, such as obesity, that have been associated with elevated NGF levels which were absent in the healthy control group (figure 1C) [35]. Here, NGF is linked to obesity due to melanocortin 4 receptor deficiency.