© 2005 Oxford University Press
CORRESPONDENCE |
RESPONSE: Re: Detection of Hypermethylated Genes in Women With and Without Cervical Neoplasia
Affiliation of authors: Department of Pathology, University of Washington, Seattle, WA
Correspondence to: Qinghua Feng, PhD, Department of Pathology, University of Washington, 815 Mercer St., Seattle, WA 98109 (e-mail: qf{at}u.washington.edu).
We agree with Murty and Narayan's comment that it is premature to conclude that the specific panel of genes that we reported to be associated with increasing severity of cervical cancer among Senegalese women to be generalizable to other populations. Studies in lung, liver, and gallbladder cancer from different geographic sites suggest that the methylation profile seen in cancers may vary by population and environmental exposures (1–3). Clearly, the sensitivity and specificity of our panel of genes need to be assessed in cancer and normal tissues from various populations.
Although Murty and Narayan suggest that the high frequency of methylation of HIC1, APC, and SFN we observed in normal cervical samples is unusual and may have obscured an association with cervical cancer, others have also reported observing methylation of these genes in other benign tissues. For example, HIC1 was methylated in 30% of benign breast tissues (5). APC methylation was also observed in 30% of normal liver tissues (6), although the level of methylation was lower than what was seen in liver cancer tissues. Moreover, SFN is known to be methylated in normal lymphoid cells (4). Because many of our normal samples contained inflammatory infiltrates as well as blood, the high frequency of promoter methylation observed in this gene may be attributable to these noncervical cells.
Another explanation for the difference in our respective results may be due to the different methods used to detect methylation in the two studies. Because the methylation-specific polymerase chain reaction assay we used is not a quantitative assay, there may have been a difference in methylation levels of APC and HIC methylation between normal and cancer tissues that could not be distinguished. However, unmethylated (U)-DNA (human sperm DNA) and methylated (M)-DNA (in vitro methylated human sperm DNA) were included as positive and negative controls in all experiments. Furthermore, methylation of a specific gene was considered to be present only if both the specimen and the M-DNA but not the U-DNA were amplified by methylation-specific primers after sodium bisulfate modification. By taking such measures, which have not been incorporated in many other studies, we are confident of the specificity of our findings. Finally, the differences observed between our study and that of Narayan et al. (7) may be related to the use of different primers detecting different CpGs within the same CpG island.
REFERENCES
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J Natl Cancer Inst 2005 97: 1548.
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