Objective To investigate the polymorphism of human cytomegalovirus （HCMV） UL150 open reading frame （ORF） in low-passaged clinical isolates

and to study the relationship between the polymorphism and different pathogenesis of congenital HCMV infection. Methods PCR was performed to amplify the entire HCMV UL150 ORF region of 29 clinical isolates

which had been proven containing detectable HCMV-DNA using fluorescence quantitative PCR. PCR amplification products were sequenced directly

and the data were analyzed. Results Totally 25 among 29 isolates were amplified

and 18 isolates were sequenced successfully. HCMV UL150 ORF sequences derived from congenitally infected infants were high variability. The UL150 ORF in all 18 clinical isolates shifted backward by 8 nucleotides leading to frame-shift

and contained a single nucleotide deletion at nucleotide position 226 compared with that of Toledo strain. The nucleotide diversity was 0.1% to 6.8% and the amino acid diversity was 0.2% to 19.2% related to Toledo strain. However

the nucleotide diversity was 0.1% to 6.4% and amino acid diversity was 0.2% to 8.3% by compared with Merlin strain. Compared with Toledo

4 new cysteine residues and 13 additional posttranslational modification sites were observed in UL150 putative proteins of clinical isolates. Moreover

the UL150 putative protein contained an additional transmembrane helix at position of 4-17 amino acid related to Toledo. Conclusion HCMV UL150 ORF and deduced amino acid sequences of clinical strains are hypervariability. No obvious linkage between the polymorphism and different pathogenesis of congenital HCMV infection is found.