The article by Duffy et al ^{Reference Duffy, Horrocks, Doucette, Keown-Stoneman, McCloskey and Grof1} in the February issue tests evidence for a clinical staging model of bipolar disorder for the offspring of parents with lithium-responsive illness and the offspring of parents with lithium-non-responsive illness.

In their analyses, Duffy et al were unable to show a statistically significant difference for the risk of any psychiatric disorder between both subgroups of offspring. Yet they still conclude that the offspring of parents with lithium-non-responsive illness manifest neurodevelopmental disorders in childhood and psychotic disorders in young adulthood. A second problem is that the neurodevelopmental disorder category included cluster A traits, which do not readily fit with the others (attention deficit hyperactivity disorder (ADHD) and learning disabilities). A third problem is that schizoaffective disorder was included among the bipolar spectrum disorders in the analyses, a decision that requires further justification.

A fourth problem is that, as described in a previous article,^{Reference Duffy, Alda, Crawford, Milin and Grof2} a diagnosis of bipolar affective disorder not otherwise specified was given to participants who presented with manic symptoms meeting threshold DSM-IV diagnostic criteria but not minimal duration criteria. It is possible that this was the reason for a statistically significant difference in the cumulative incidence of bipolar spectrum disorders between the offspring of well parents and the offspring of parents with a bipolar disorder. Finally, 23% of participants in the group of offspring of a parent with bipolar disorder 1 were recruited within families, making it unclear how many participants had a parent who did not have the disorder.