Neurogenetic markers were part of the DNA sequence. They were included in the genetic profile of Starfleet personnel. In a Betazoid, abnormal neurogenetic markers might indicate that a person was psychotic.
In 2372, The Doctor found that Lon Suder's neurogenetic markers showed no signs of psychosis. (VOY: "Meld")
Directly thereafter, bipolar disorder was also discussed, but it was unclear from dialog if this was indicated by the neurogenetic markers, or another part of the genetic profile.