Familial aggregation of delusional depression: re-examination in a recent family study

Delusional (D-MDD) and nondelusional depression (ND-MDD) differ in clinical presentation, biological abnormalities, course of illness, and treatment response. Family data, however, have been less consistent regarding differential risk both for any major depression (MDD) and specifically D-MDD in relatives of D-MDD probands. In an earlier family study, we observed a 1.5-fold increase in rates of any MDD, specificity of transmission of D-MDD, and increased rates of bipolar disorders in relatives of D-MDD compared to relatives of ND-MDD probands. In a new family study, we attempted to replicate these findings.

A family study of 361 directly interviewed adult first-degree relatives (FDRs) of 163 probands (118 with MDD and 45 screened normal controls) was used to examine familial aggregation of any MDD, D-MDD, and bipolarity by proband delusional status.

Compared to FDRs of ND-MDD probands, FDRs of D-MDD probands were at modestly increased risk for any MDD. These results were unaffected by adjustment for proband ascertainment source, comorbidity, or whether probands had chronologically primary MDD. There was a trend toward increased rates of broadly defined bipolarity (bipolar I, bipolar II, or cyclothymia) in FDRs of D-MDD compared to FDRs of ND-MDD probands.

Results from the present study were broadly consistent with those from our previous work. While other lines of evidence for D-MDD as a distinct subtype are more compelling than family data, it would be of methodologic interest to identify sources of inconsistency across studies in findings concerning the familial aggregation of delusional depression.