Whole-genome discovery of pathogenic snRNA variants and efficient extended-exome screening.

Pathogenic variants in small nuclear RNA genes (RNU4-2, RNU2-2, RNU5B-1, RNU4ATAC), loci not captured by conventional exome designs and therefore invisible in routine diagnostics.

Variants in small nuclear RNA (snRNA) genes are an emerging cause of Mendelian disease, particularly neurodevelopmental disorders, but remain out of reach of conventional WES, which does not capture these loci. The authors reanalysed WGS data from 1,578 unsolved probands and identified pathogenic variants in several snRNA genes — RNU4-2, RNU2-2, RNU5B-1 and RNU4ATAC — accounting for 1.2% of cases (19 patients). They then developed an snRNA-extended WES approach by adding capture probes targeting 50 snRNA genes to a standard exome design. Benchmarking showed robust, uniform coverage across all targeted loci without increasing sequencing depth, and the approach reliably detected snRNA variants previously identified by WGS.

Synthesis written by Geno'X. For the full original abstract, please refer to the source publication.

This is precisely the kind of paper a laboratory can act on: a documented WES blind spot, quantified at 1.2% yield in unsolved cases, and a technical fix that is simple to implement on an existing capture design. The deeper answer remains WGS, which covers these loci without added probes, but for laboratories still on exome the gain is immediate and inexpensive. The number of patients tested on the new capture is limited, so prospective analytical performance needs confirmation.

Analysis by Dr Thibaut Benquey