Therefore, the expression of the circadian-clock (PER1, PER2, BMAL1 and CRY2), TRPV1 and NGF genes in the esophagus shows a diurnal rhythmic pattern and is correlated with the severity of GERD in patients (Table 3, Figure S1 and Fig. 3A). Here, PER1 is linked to gastroesophageal reflux disease.