Is depression genetic?

Partially, yes. But "genetic" is doing a lot of work in that question - let me unpack it.

Heritability estimates for major depressive disorder cluster around 35 to 40% based on twin studies. That means roughly 35–40% of the variation in who develops depression versus who doesn't is explained by genetic variation in the population. The remaining 60–65% is environmental - trauma, stress, sleep, social context, medical conditions, life events.

What "genetic" doesn't mean here: there is no "depression gene." Hundreds, possibly thousands, of variants each contribute a small amount to risk. A polygenic risk score for depression is real but still has limited predictive value at the individual level - it tells you whether your risk is somewhat above or below average, not whether you'll develop depression.

What it does mean: if a parent or sibling has depression, your own risk is approximately 2 to 3 times higher than the general population. That's meaningful. But it is still a much smaller effect than what your life circumstances and access to support will do.

Genetics loads the dice. Environment rolls them.

One more useful piece of context.

The hunt for "depression genes" had a famously rough decade. Several candidate genes that early studies identified - particularly 5-HTTLPR, the serotonin transporter variant - failed to replicate in larger studies. The field has shifted from looking for individual genes to looking at the cumulative effect of thousands of small-effect variants, which is what polygenic risk scores try to capture.

The current honest summary: depression has a genetic component that is real, complex, distributed across the genome, and not yet useful for personal prediction. The most useful thing to know about your depression risk is still your own history and your family history - not your DNA test.