Genetic and physiological. There are no clear differences in  illness development, course,
or family history between DSM-IV dysthymi c disorder and chronic major depressive dis-
order. Earlier findings pertaining to either disorder are therefore likely to apply to per-
sistent depressive disorder. It is thus likel y that individuals with persistent depressive
disorder will have a higher pr oportion of first-degree relatives with persistent depressive
disorder than do individuals with major de pressive disorder, and more depressive disor-
ders in general.
A number of brain regions (e.g., prefrontal  cortex, anterior cing ulate, amygdala, hip-
pocampus) have been implicated in persiste nt depressive disorder. Possible polysomno-
graphic abnormalities exist as well.
Functional Consequences of 
Persistent Depressive Disorder
The degree to which persistent depressive diso rder impacts social and occupational func-
tioning is likely to vary widely, but effects can be as great as or greater than those of major
depressive disorder.
Differential Diagnosis
Major depressive disorder. If there is a depressed mood plus two or more symptoms
meeting criteria for a persistent depressive ep isode for 2 years or more, then the diagnosis of
persistent depressive disorder is made. Th e diagnosis depends on the 2-year duration,
which distinguishes it from episodes of depressi on that do not last 2 years. If the symptom