Heritability of Early-Onset Major Depression in Children
The correct answer is A: Twin studies have demonstrated that early-onset major depression is moderately heritable at 40-50%, with environmental stressors and adverse events as major contributors. 1
Evidence from Twin Studies
The heritability of youth-onset depression ranges from 30-80% according to the most recent guideline evidence, with the remaining variance explained by environmental factors 1. However, when examining the specific range provided in your question options, the 40-50% estimate falls squarely within the established moderate heritability range and represents the most commonly cited central estimate 1.
Why Option A is Correct
- The 40-50% heritability estimate accurately reflects moderate genetic contribution, not the extreme high end of the range 1
- This moderate heritability explicitly highlights that environmental stressors and adverse events account for 50-60% of the variance, making them major contributors as stated in option A 1
- Well-documented environmental risk factors include poverty, negative family relationships, parental divorce, and child maltreatment 1
Why Option C is Incorrect
- Option C's claim of 80% heritability represents only the upper extreme of the range, not the typical finding 1
- The 80% figure would suggest depression is "highly heritable" rather than "moderately heritable," which contradicts the consensus characterization 1
- Most twin studies cluster around the moderate range (30-50%), with 80% being an outlier estimate 1
Why Option B is Incorrect
- Sufficient twin studies have absolutely been conducted - multiple large-scale twin registries have examined this question, including Swedish, Finnish, and other national cohorts 2, 3
- The evidence base is robust enough to establish clear heritability estimates 1
Additional Context on Early-Onset Depression
Early-onset major depression (before age 30) shows heritability of approximately 47%, which is actually higher than late-onset depression at only 10% heritability 4. This supports that the genetic contribution is substantial but still moderate, leaving significant room for environmental influences 4.
The genetic correlation between males and females with major depression is 0.75, suggesting largely overlapping but not identical genetic risk factors 2.