We add new weight to our previous suggestion [20] to seriously consider the assessment of sleep when analyzing BDNF as a marker in stress-related mood disorders, since several studies have found decreased levels of serum BDNF in various stress-related mental disorders, such as depression [14], [49], posttraumatic stress disorder [50] and burnout syndrome [46], all of which are associated with sleep-related problems. This evidence concerns the gene BDNF and major depressive disorder.