Bio-social interaction amplifies risk for self-harm/suicidal behavior in adolescents: Family history screening can improve public health practice

Self-harm/suicidal behavior (SH/SB) runs in families and is linked with harsh treatment during childhood, but little is known about comorbidity among these risk factors or synergies between them. Such synergies, superadditive increases in risk associated with comorbidity among risk factors, are suggested by studies of bio-social interaction in the etiology of SH/SB-linked psychopathology. Bio-social interactions can amplify otherwise modest risk factors and are therefore relevant to public health practice. Our study used data from a nationally representative birth cohort of 2,232 British twins followed prospectively over ages 5-12 years. We investigated synergies in risk for mother reported SH/SB at age-12 years (N=62) between family history of SH/SB or psychiatric hospitalization (N=565) and harsh treatment during childhood: history of physical maltreatment (N=93) and maternal negative expressed emotion toward the child at age-5 years (coded from speech samples by trained raters). Biometric modeling techniques were used to partition variance in SH/SB into components due to additive genetic factors, environments shared by twins in a family, and environments not shared by twins in a family. We tested for unmeasured confounding using comparisons of twins within families. We assessed synergies using the 4x2 table method. Harsh treatment during childhood was more common among children with positive family history. Positive family history and harsh treatment during childhood were associated with excess risk for SH/SB at age-12 years individually and, when comorbid, exhibited synergy consistent with bio-social interaction. Family history information can help identify youth at higher risk for SH/SB following exposure to harsh treatment.