Does the Transmissible Liability Index (TLI) Predict MDD and Suicidal Symptoms?

Introduction: Our previous work demonstrated that Transmissible Liability Index (TLI), a measure designed to assess liability for substance use disorder (SUD), as measured at age 10-12, is associated with an increased risk of subsequent substance use and of substance use disorder.   The current study was designed to assess whether TLI also predicts subsequent development of major depressive disorder (MDD) and suicidal symptoms.  We hypothesized that TLI would predict MDD, and would also predict an increased risk of lifetime suicidal symptoms.

Methods: The subjects in this ongoing study were male offspring of men with a lifetime history of a SUD (SUD + probands, N=250, called the HAR group) and offspring of men with no lifetime history of a SUD (SUD –  probands, N=250, called the LAR group).  These subjects had been recruited for participation in a longitudinal project designed to elucidate the etiology of SUD, which was conducted at the Center for Education and Drug Abuse Research (CEDAR).  Probands were considered to have a lifetime history of SUDs if they met DSM-III-R dependence or abuse criteria for any substance other than nicotine, caffeine, or alcohol.  The participants were initially recruited when they were 10-12 years of age, and subsequent assessments were conducted at age 12-14, 16, 19, and then annually until age 30.  DSM criteria were utilized to assess the diagnostic criteria for major depressive disorder, and suicidal symptoms were assessed using the Suicidal Symptom Inventory (SSI).  Statistical analyses were conducted using ANOVA, chi-square tests, negative binomial, and logistic regression.

Results: The sample included 500 males, including 76% white, 21% black, and 3% other subjects.  By the age 25 assessment, 28% of the HAR subjects versus 18% of the LAR subjects had been diagnosed with MDD (chi-square=7.1, df=1, p=.005).  The DSM symptom count for MDD was significantly higher in the HAR group than in the LAR group (F=10.6, df=1, p=.001).  The number of lifetime suicidal symptoms on the SSI was significantly higher in the HAR group than in the LAR group (F=5.9, df=1, p=.001).  TLI was significantly higher in the HAR group than the LAR group (F=18.7, df=1, p<.001). Furthermore, TLI predicted number of lifetime depressive symptoms, but not lifetime depressive disorder diagnosis.  TLI also predicted lifetime suicidal ideation, plan, threat, gesture, and attempt on the SSI at an alpha level of .05.

Conclusions: These findings confirmed both of our hypotheses in showing that TLI predicts MDD and also predicts an increased risk of lifetime suicidal symptoms.  These findings demonstrate that TLI predicts not only SUD but also predicts other serious clinical disorders.

Supported by P50 DA05605, K02 DA017822, K24 AA015320, K05 DA031248