Heritability of Early-Onset Major Depression in Children
Twin studies have demonstrated that the heritability of youth-onset depression ranges from 30-80%, with the remaining variance explained by environmental factors. 1
Evidence from Twin Studies
The most comprehensive systematic review addressing this question comes from the Journal of Child Psychology and Psychiatry (2011), which specifically examined gene-environment interactions in youth depression. This guideline-level evidence clearly establishes that early-onset major depression shows moderate to high heritability, not the 80% suggested in option (a), nor is it limited to only 40-50% as suggested in option (c). 1
Key Findings on Heritability Range
The heritability range of 30-80% indicates substantial genetic contribution, but also highlights the critical role of environmental factors in determining who develops depression. 1
The wide range (30-80%) reflects methodological differences across twin studies, including varying definitions of depression, age ranges studied, and assessment methods used. 1
This range is consistent with adult depression studies, where heritability estimates typically fall between 33-45% for most definitions of major depression. 2
Environmental Contributions
Environmental factors account for 20-70% of the variance in youth-onset depression, demonstrating that genes alone do not determine outcome. 1
Well-documented environmental risk factors include poverty, negative family relationships, parental divorce, and child maltreatment. 1
Most environmental experiences of causative importance are unique to the individual rather than shared by family members. 2
Clinical Implications
The correct answer is that twin studies show heritability ranging from 30-80%, making option (c) about "only moderately heritable at 40-50%" the closest to accurate, though it underrepresents the upper range of heritability estimates. 1
Important Caveats
Option (a) claiming 80% heritability represents only the upper bound of estimates and does not reflect the full range of findings. 1
The statement that "insufficient twin studies have been conducted" (option b) is demonstrably false—multiple twin studies have been conducted and systematically reviewed. 1
Early-onset cases may show even higher heritability than adult-onset depression, particularly in highly comorbid presentations. 1, 3
The genetic contribution appears stronger when depression is diagnosed via structured clinical interviews rather than self-report measures, suggesting phenotype definition matters. 1