Multiple threshold models for the affective disorders: the Yale-NIMH collaborative family study

Area of Science:

• Psychiatric Genetics
• Behavioral Genetics
• Clinical Psychology

Background:

• Investigating the genetic architecture of major psychiatric disorders is crucial for understanding their etiology.
• Previous research has explored shared genetic underpinnings for bipolar disorder and major depressive disorder.

Purpose of the Study:

• To test the hypothesis that bipolar 1 disorder and major depression share a single underlying genetic liability.
• To evaluate the fit of multifactorial-polygenic and single-major-locus models to family data for these disorders.

Main Methods:

• Analysis of 1482 first-degree relatives from families with probands diagnosed with bipolar 1 disorder (n=90) and major depression (n=163).
• Application of multifactorial-polygenic and single-major-locus multiple threshold models, accounting for sex and illness severity.
• Comparison of findings with previous studies, considering variations in assumptions and analytical approaches.

Main Results:

• Marginal support was found for models positing a single underlying genetic liability for bipolar 1 and major depression.
• Differences in model fit were not primarily explained by age adjustment methods, disorder placement in a liability continuum, or sex thresholds.
• Key factors influencing genetic transmission models include sample rate variability, potential genetic heterogeneity, and secular trends in affective illness.

Conclusions:

• The hypothesis of a single genetic liability for bipolar 1 and major depression received limited support from this family study.
• Genetic heterogeneity and significant secular increases in affective illness over generations are important considerations for genetic transmission models.
• Current genetic threshold models may not fully accommodate the complex interplay of factors contributing to the development of these disorders.