Easychip 8x15k: A New Tool for Detecting Chromosome Anomalies in Low Risk Pregnancies, Supporting and Integrating Standard Karyotype

Over last decade chromosome microarray analysis has become a routine test, but its use as first tier in prenatal diagnosis still raises disputes specially when applied to low risk pregnancies. In order to limit the identification of incidental findings (IF) and variants of unknown significance (VOUS) we designed EasyChip, a low-resolution oligonucleotide array CGH platform with a functional resolution of 3 Mb in genomic backbone, 300 Kb in sub-telomeric regions, and 150 Kb in 43 regions associated with syndromic disorders, selected considering morbidity, penetrance, and etiological mechanisms. After an “in silico” evaluation, which showed that Easychip would not uncover most of VOUS (24% vs 3%) and any IF, we have validated EasyChip on 169 patients samples, 57 retrospective samples with known imbalances and 112 prospective samples as part of the prenatal diagnosis process. All the known rearrangements were detected and 7 further pathogenic imbalances were detected on the still undiagnosed cohort. To evaluate false positive/negative rate, thirty-eight out of the 112 prospective samples were also processed on an high resolution array CGH, allowing comparing the results in term of diagnostic utility and impact on detection rate. Two positive and pathogenic results were detected by both platforms. EasyChip did not detect 10 of the 11 VOUS nor 2 IF discovered by the high-resolution platform. In conjunction with karyotype, EasyChip is a useful tool in prenatal diagnosis for screening purposes on low risk pregnancies, it enables the detection of cryptic imbalanced subtelomeric rearrangements, microdeletions/duplications within 43 syndromic regions and supports standard cytogenetic analysis at whole genome level. Finally, this tool, differently from higher resolution platforms, significantly reduces the detection rate of VOUS and IF, which represent a major drawback during genetic counselling specially for low risk pregnancies, significantly reduces the time to spend on analysis and limit the need of additional confirmation.