The subtypes of major depression in a twin registry.

The subtypes of major depression (MD) remain incompletely understood. While there is consensus about the existence of MD with 'typical' vegetative features, further data are required to evaluate the existence of MD with atypical features. Assessment of MD symptomatology in year prior to interview was available in 6846 individual twins from a population-based twin registry. The nine 'A' criteria for DSM-IV MD were unpacked so that the nature of sleep disturbance, appetite and weight changes, and motoric alterations were recorded. Latent class analysis was used to create an empirical typology of MD. Seven latent classes appeared to provide the best representation of the data. The most severe of these classes had interpretable profiles corresponding to typical MD, atypical MD, and 'minor' but seemingly important depressive states. These classes were generally more deviant than a comparison group for nearly all available validators. There tended to be a gradient with the typical class being most extreme, minor depressive classes the least extreme, and the atypical class having an intermediate position. Our findings support the existence of atypical depression as a phenomenological subtype of MD. Besides the differences in symptom patterns, there are many more similarities than differences across a range of external validators. Similar to other reports, we found evidence of the importance and morbidity of depressive symptomatology that does not meet the DSM-IV MD thresholds.