RESUMO
Studies of clonality have been essential for understanding the hierarchy of hematopoiesis and the biology of malignancies. Most clonality assays are based on the X chromosome inactivation phenomenon in females; these assays detect protein polymorphisms, differences in DNA methylation, or transcripts of the active X chromosome. Assays based on protein polymorphisms or DNA methylation have significant shortcomings. The major disadvantage of transcriptional assays is their limited applicability since only approximately half of females are informative for these studies. We have developed a new transcriptional assay based on an exonic polymorphism of the X-chromosome gene IDS. This gene is located in the same X-chromosome region (Xq28) as G6PD and p55, two genes with exonic polymorphisms for which we previously developed transcriptional assays. We developed non-radioactive PCR-based assays for rapid screening of genotype and determination of clonality. We also report reaction conditions for a quantitative ligase detection assay of IDS allelic transcripts. The frequency of the IDS polymorphism is 46% in Caucasian females and 39% in African-American females; in combination with G6PD and p55, 76% of Caucasian females and 62% of African-American females are informative for these assays. While this gene is highly polymorphic in Caucasian and African-American females, it is not informative in Oriental females. We established that the IDS gene is in linkage equilibrium with G6PD and p55. Unlike methylation-based assays, this assay is suitable for studying clonality in non-nucleated cells such as platelets and reticulocytes. With the discovery of exonic polymorphisms of other X-chromosome genes, all females should eventually be suitable for X-chromosome transcriptional clonality analysis.
