To investigate the mutation of HBV preS/S gene in patients with occult hepatitis B virus (OBI) infection, and to explore its effect on the progress of severe liver function injury.

Total of 689 patients with negative HBsAg were collected from Shiqiao Hospital of Panyu District, Guangzhou. The serum samples were detected by fluorescence quantitative PCR amplification. Among the 689 patients, 76 patients with OBI were selected as research group, while 87 patients with HBsAg positive were selected as control group. The preS/S gene of HBV was sequenced of patients in both groups. The positive rates of HBcAb, HBeAb, HBeAg and HBcAb/HBsAb were calculated, respectively. The load of HBV DNA and gene mutation frequency in preS/S region between the two groups were compared, respectively.

Total of HBsAg negative serum samples from 76 cases with OBI with OBI were detected, among which, 14 samples (18.42%), 9 samples (11.84%), 27 samples (35.53%) and 26 samples (34.21%) were positive for HBcAb, HBeAb, HBeAg and HBcAb/HBsAb, respectively. There were 11 cases (14.5%) detected with HBV genotype B and 65 cases (85.5%) with genotype C in preS/S region; but no genotype D of HBV was detected in both groups, without significant difference in genotypes between the two groups (χ² = 1.794, P = 0.180). The load of HBV DNA in research group was 76-1 989 IU/ml (the median was 186.6 IU/ml), significantly lower than that of the control group [573.7 (108-5 689) IU/ml], with significant difference (Z = 25.775, P < 0.001). HBV DNA load of patients with OBI and severe liver function injury in research group was 76-1 989 IU/ml (median was 193 IU/ml), significantly higher than that of those patients without severe liver function injury in this group [178.6 (77-1 325) IU/ml], with significant difference (Z = 14.638, P < 0.001), however, it was significantly lower than that of control group with severe liver function injury [623.7 (217-5 689) IU/ml], with significant difference (Z = 21.396, P < 0.001). The frequencies of G185R, T118R/K/A/M, L175S, I126s and preS deletion mutations in preS/S region of patients in research group were significantly higher than those of the control group (all P < 0.05). The mutation frequency of I126s in patients with OBI and severe liver function injury was slightly lower than those of the cases without severe liver function injury in research group, but without significant difference (χ² = 0.508, P = 0.476). The deletion of L175S and preS in G185R, T118R/K/A/M and L175S were significantly higher than those of patients without severe liver function injury (all P < 0.05). The I126S of patients with severe liver function injury in research group were slightly higher than those of the control group, but without significant difference (χ² = 3.287, P = 0.070); but the frequencies of G185R, T118R/K/A/M, L175S and preS were significantly higher than those of cases with severe liver function injury in control group (all P < 0.05).

HBeAg and HBcAb/HBsAb positive dection were the most among patients with OBI, and the mutant genotype was basically consistent with the positive rate of HBsAg. However, the difference of HBV DNA load and gene mutation between patients with OBI and patients with HBsAg positive was significant. The deletion of G185R, T118R/K/A/M, L175S and preS may be important detection indexes for patients with OBI and severe liver function injury.