#3020 A novel copy number analysis identifies human patients with NPHP1 whole gene deletions in previously genetically unsolved cases

Genome sequencing is rapidly becoming a routine approach to investigating inherited human diseases in clinical practice. Nevertheless, data generated from genome sequencing requires extensive bioinformatic analysis and filtering of variants to determine pathogenicity and remains challenging. Despite well-established workflows and software in place to process raw data, the analysis of genome sequencing data is still complex. Copy Number Variations (CNVs) are increasingly recognised to be pathogenic, especially where this leads to a whole gene being deleted. Software tools to decipher CNVs across genome sequencing datasets are being utilised but are not completely accurate.

Using a bespoke CNV analysis of Genomics England 100,000 Genomes Project (100 kGP) WGS data from 11754 parent-child trios, we searched for homozygous deletions overlapping with annotated genes, across the 22 autosomes.

Homozygous ∼150 kb whole gene deletion of NPHP1-MALL on chromosome 1, which aligned with a known region containing segmental duplications (SD), was the most frequent observation among all autosomal recessive (AR) OMIM-morbid genes. Clinical phenotypes were consistent with this genotype including nephronophthisis and retinal dystrophy. We extended our analysis to look for NPHP1 whole gene deletions in 18877 additional singletons within the 100 kGP. This reverse genetics approach identified additional patients, up to this point genetically unsolved, with whole gene deletions and matching phenotypes. The frequency of heterozygous NPHP1 whole gene deletion was assessed in a control cohort of 15440 cancer patients within 100 kGP and was found to be 0.35%.

In conclusion, NPHP1 was the most frequently observed AR OMIM-morbid gene knockout in our analysis. Homozygous whole gene deletions in NPHP1 may be easily missed using standard WGS pipelines which don't assess fully for CNVs and a targeted read-depth approach to identify CNVs in parent-patient trios and singletons is valuable in identifying these deletions.