A proof-of-principle spike-in experiment was performed using a synthetic construct to explore the digital array's feasibility as a robust platform for the CNV study. A 65-base oligonucleotide that is identical to a fragment of the human RPP30 was ordered from Integrated DNA Technologies (Coralville, IA, USA). RNase P, a single copy gene, is used as reference in this study (20, 21) .