Monozygotic Twins Display Different Minor Histocompatibility Antigens.

Albeit it is generally presumed that monozygotic twins are genetically identical and that phenotypic differences between twins are mainly due to environmental factors, large-scale variation in copy number of DNA segments recently evidenced by Bruder et al. (AJHG, 2008) showed presence of genotypic diversity in monozygotic twins. The rationale of this study was to test whether monozygotic twins display disparities of minor Histocompatibility antigens (mHags) which may play role in syngenic HCT. We and others have previously shown that mHags constitute an important immunogenetic factor influencing immune responses following transplantation from HLA-matched allogeneic donors.

mHags HA-1, HA-2, HA-3, HA-8, HB-1, ACC-1, ACC-2, HwA-9, HwA-10, UGT2B17, HY genotypes were defined with use of Dynal AllSet kits by PCR-SSP method in secured DNA samples from 3 monozygotic twins pairs aged 34, 24 and 28, who underwent syngenic allo-HCTs due to different hematological malignancies (NHL, CML, AML) in the Department of Hematology and BMT in Katowice, Poland in years 2000-2004.

In 2 out of 3 syngenic pairs we have found differences in genes encoding mHags: different allele of EB-1 was present in one pair (NHL) (recipient HH, donor HY), and two different alleles of HwA-9 (RR, RG) and HwA-10 (**, R*) were present in second pair (CML). No differences in mHags were observed in the third pair (AML).

Our results question the long-standing belief that monozygotic twins are genetically identical and open up a possibility to further study the role of disparate mHags in disease and transplantation.

No relevant conflicts of interest to declare.