ACKNOWLEDGEMENTS The following shared resources at Albert Einstein College of Medicine were used to generate data for this study: the Bioinformatics Shared Resource, the Genomics Core Facility, as well as resources from the Albert Einstein Cancer Center. This work is supported by a grant from the National Institutes of Health (NIH; NICHD) R01 HD044078 to J.M.G. Both J.L.G. and R.F.T. are supported by NIH MSTP Training Grant GM007288. A.G. is supported by Science Foundation Ireland (Grant Number 05/RFP/CMS0001). G.V.Z. is supported by NIH grants R01 AG022859 and R01 AG024950. The authors thank Ms Carol Swiderski for her expert technical assistance. Funding to pay the Open Access publication charges for this article was provided by R01 HD044078 from the NIH. Conﬂict of interest statement. None declared. REFERENCES 1. Bird,A.P. (1986) CpG-rich islands and the function of DNA methylation. Nature, 321, 209–213. 2. Gardiner-Garden,M. and Frommer,M. (1987) CpG islands in vertebrate genomes. 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