Sequence capture and next-generation resequencing of multiple tagged nucleic acid samples for mutation screening of urea cycle disorders.

BACKGROUND

Molecular genetic testing is commonly used to confirm clinical diagnoses of inherited urea cycle disorders (UCDs); however, conventional mutation screenings encompassing only the coding regions of genes may not detect disease-causing mutations occurring in regulatory elements and introns. Microarray-based target enrichment and next-generation sequencing now allow more-comprehensive genetic screening. We applied this approach to UCDs and combined it with the use of DNA bar codes for more cost-effective, parallel analyses of multiple samples.

METHODS

We used sectored 2240-feature medium-density oligonucleotide arrays to capture and enrich a 199-kb genomic target encompassing the complete genomic regions of 3 urea cycle genes, OTC (ornithine carbamoyltransferase), CPS1 (carbamoyl-phosphate synthetase 1, mitochondrial), and NAGS (N-acetylglutamate synthase). We used the Genome Sequencer FLX System (454 Life Sciences) to jointly analyze 4 samples individually tagged with a 6-bp DNA bar code and compared the results with those for an individually sequenced sample.

RESULTS

Using a low tiling density of only 1 probe per 91 bp, we obtained strong enrichment of the targeted loci to achieve ≥90% coverage with up to 64% of the sequences covered at a sequencing depth ≥10-fold. We observed a very homogeneous sequence representation of the bar-coded samples, which yielded a >30% increase in the sequence data generated per sample, compared with an individually processed sample. Heterozygous and homozygous disease-associated mutations were correctly detected in all samples.

CONCLUSIONS

The use of DNA bar codes and the use of sectored oligonucleotide arrays for target enrichment enable parallel, large-scale analysis of complete genomic regions for multiple genes of a disease pathway and for multiple samples simultaneously. This approach thus may provide an efficient tool for comprehensive diagnostic screening of mutations.