Moreover, due to the fact that there are many reports that indicate the potential role of other biochemical substances as markers of stress, anxiety and/or depression in serum, plasma, urine or even hair, it would also be advisable to perform laboratory experiments and determine whether there is a correlation between individual parameters present in other biological materials and their content in saliva, e.g., malondialdehyde [92] or nesfatin-1 [93]. The gene discussed is NUCB2; the disease is major depressive disorder.