HCRTR2 and Cluster headache: Nonetheless, other studies (Baumber et al., 2006; Weller et al., 2015; Zarrilli et al., 2015; Fan et al., 2018; Fourier et al., 2019; Papasavva et al., 2020), did not support the association between G1246A polymorphism of the HCRTR2 gene and the risk of cluster headache in diverse populations.