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Clinical relevance of small copy-number variants in chromosomal microarray clinical testing

2016-09-15 13:44:15

Genetics inMedicine; 15 September 2016: DOI:10.1038/gim.2016.132

Dana Hollenbeck MPH, MS, Crescenda L. Williams MS, Kathryn Drazba MPH, MS, Maria Descartes MD, Bruce R. Korf MD, PhD, S. Lane Rutledge MD, Edward J. Lose MD, Nathaniel H. Robin MD, Andrew J. Carroll PhD & Fady M. Mikhail MD, PhD



Abstract


 

Purpose


The 2010 consensus statement on diagnostic chromosomal microarray (CMA) testing recommended an array resolution ≥400 kb throughout the genome as a balance of analytical and clinical sensitivity. In spite of the clear evidence for pathogenicity of large copy-number variants (CNVs) in neurodevelopmental disorders and/or congenital anomalies, the significance of small, nonrecurrent CNVs (<500 kb) has not been well established in a clinical setting.



Methods


We investigated the clinical significance of all nonpolymorphic small, nonrecurrent CNVs (<500 kb) in patients referred for CMA clinical testing over a period of 6 years, from 2009 to 2014 (a total of 4,417 patients). We excluded from our study patients with benign or likely benign CNVs and patients with only recurrent microdeletions/microduplications <500 kb.



Results


In total, 383 patients (8.67%) were found to carry at least one small, nonrecurrent CNV, of whom 176 patients (3.98%) had one small CNV classified as a variant of uncertain significance (VUS), 45 (1.02%) had two or more small VUS CNVs, 20 (0.45%) had one small VUS CNV and a recurrent CNV, 113 (2.56%) had one small pathogenic or likely pathogenic CNV, 17 (0.38%) had two or more small pathogenic or likely pathogenic CNVs, and 12 (0.27%) had one small pathogenic or likely pathogenic CNV and a recurrent CNV. Within the pathogenic group, 80 of 142 patients (56% of all small pathogenic CNV cases) were found to have a single whole-gene or exonic deletion. The themes that emerged from our study are presented in the Discussion section.



Conclusions


Our study demonstrates the diagnostic clinical relevance of small, nonrecurrent CNVs <500 kb during CMA clinical testing and underscores the need for careful clinical interpretation of these CNVs.



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Key Words

CMA clinical testing | intragenic deletion | single-gene deletion |small CNV