Background: The role of the virulence of the infecting cytomegalovirus (CMV) strain in the transmission of the virus from mother to fetus and the outcome of the fetal infection has not received much attention yet. Molecular analysis of the gene coding for the surface glycoprotein B (gB) has been used to investigate the relationship between genotype and virulence in groups of immunosuppressed patients.
Objectives: (1) to assess the prevalence of different gB genotypes in babies with congenital CMV infection; (2) to investigate the possible relationship between genotype and severity of congenital CMV disease; (3) to evaluate the possibility of using dried blood on Guthrie cards (DBS) for genotyping.
Study design: CMV DNA was extracted from DBS and from urine/saliva samples collected in the first two weeks of life of 98 congenitally infected babies, half of which were symptomatic at birth. Genotyping was performed through RFLP analysis of the region corresponding to the cleavage site of the gB protein.
Results: The most prevalent genotype was gB1 (42%) followed by gB3 (26%), gB2 (19%) and gB4 (13%). Rates of disease and CNS damages were higher among children infected by gB1 (35%, 17%) and gB3 (31%, 28%) than in those infected by gB2 and gB4 (20%, 17% and 13%, 15%, respectively). These differences however did not reach the statistical significance. The parallel typing of DBS and urine/saliva strains gave a full concordance of results.
Conclusions: All four major CMV gB genotypes (gB1-4) can cause a congenital infection but none seems to be associated to the development and the severity of disease. The possibility of using the neonatal DBS for genotyping opens a way to the examination of large numbers of cases of congenital CMV infection.