Expression pattern of PER2 mRNA in the subjects with Grade A GERD was similar to that in the patient controls (Fig. 1B, P < 0.001); however, expression of PER2 mRNA in the subjects with Grades B-D GERD was severely affected and not detected the rhythmic pattern (Fig. 1B, P > 0.05). This evidence concerns the gene PER2 and gastroesophageal reflux disease.