The genetic load for major depressive disorder (MDD) may be higher in people who develop MDD earlier in life. This study aimed to investigate whether the parents of adolescents with MDD were more likely to have MDD, bipolar disorder (BD), schizophrenic disorder (SZ), alcohol use disorder, or substance use disorder than the parents of adolescents without MDD. We also examined whether the response to antidepressant treatment predicted the likelihood of parental psychiatric disorders.

In all, 1,758 adolescents aged 12–19 years with antidepressant-resistant depression, 7,032 (1:4) age-/sex-matched adolescents with antidepressant-responsive depression and 7,032 (1:4) age-/sex-matched controls were included. Parental psychiatric disorders of individuals enrolled were assessed.

The parents of the adolescents with MDD were more likely to be diagnosed with MDD, BD, SZ, alcohol use disorder, or substance use disorder than the parents of the control group. The parents of adolescents who were antidepressant resistant and the mothers of adolescents who were either treatment resistant or treatment responsive were more likely to be diagnosed with a psychiatric disorder.

Our study demonstrated that parents of adolescents with MDD may be more likely to be diagnosed with MDD, BD, SZ, alcohol use disorder, or substance use disorder than parents of adolescents without MDD, suggesting the within-disorder transmission and cross-disorder transmission of these psychiatric disorders. Furthermore, the parent’s sex and the response to antidepressant treatment may affect the within-disorder transmission of MDD.