GPER1 and attention deficit-hyperactivity disorder: Elevated GPER serum levels were also found in patients with major depressive disorder (Findikli et al., 2017) and bipolar disorder (Orhan et al., 2018), but reduced levels in patients with attention deficit hyperactivity disorder (ADHD; Sahin et al., 2018) and autism spectrum disorder (ASD; Altun et al., 2017).