The protein p11 (also known as S100A10), a member of the S100 EF-hand protein family, is widely expressed in several brain regions that are implicated in the pathophysiology of depression, including the hippocampus and frontal cortex.20, 21, 22 Accumulating evidence suggests a key role of p11 in the pathophysiology of depression. This evidence concerns the gene S100A10 and depressive symptom measurement.