I am a functional medicine physician utilizing a protocol for depression and all mood disorders that looks at key markers that reflect neurotransmitter activity. Based on extensive research, as many as 95% of persons with mood disorders are experiencing one or more of 5 major biotypes; these nutrient conditions are highly responsive to proper supplementation. Markers tell us about nutrient status, oxidative stress and methylation. Methylation with respect to SERT and DERT is highly useful as it impacts levels of serotonin and dopamine activity. Overmethylators are high in these nuerotransmitters. Undermethylators are low. This is because their reuptake enzymes are either over or under active.