Over the past few decades, the 5‐HT hypothesis has driven research on the underlying cause of depression; with reports that depressed patients may have low brain 5‐HT levels and altered 5‐HT receptors, such as upregulated 5‐HT2 and downregulated 5‐HT1A receptors.26 The gene discussed is HTR1A; the disease is depressive symptom measurement.