Copy numbers of 45S and 5S ribosomal DNA arrays lack meaningful correlation in humans

The ribosomal DNA genes are tandemly arrayed in most eukaryotes and exhibit vast copy number variation. There is growing interest in integrating this variation into genotype-phenotype associations. Here, we explored a possible association of rDNA copy number variation with autism spectrum disorder and found no difference between probands and unaffected siblings. However, rDNA copy number estimates from whole genome sequencing are error-prone, so we sought to use pulsed-field gel electrophoresis, a classic gold-standard method, to validate rDNA copy number genotypes. The electrophoresis approach is not readily applicable to the human 45S arrays due to their size and location on five separate chromosomes; however, it should accurately resolve copy numbers for the shorter 5S arrays that reside on a single chromosome. Previous studies reported tightly correlated, concerted copy number variation between the 45S and 5S arrays, which should enable the validation of 45S copy number estimates with CHEF-gel-verified 5S copy numbers. Here, we show that the previously reported strong concerted copy number variation is likely an artifact of variable data quality in the earlier published 1000 Genomes Project sequences. We failed to detect a meaningful correlation between 45S and 5S copy numbers in the large, high-coverage Simons Simplex Collection dataset as well as in the recent high-coverage 1000 Genomes Project sequences. Our findings illustrate the challenge of genotyping repetitive DNA regions accurately and call into question the accuracy of recently published studies of rDNA copy number variation in cancers and aging that relied on diverse publicly available resources for sequence data.Competing Interest StatementThe authors have declared no competing interest.View Full Text