Identification of an Alu-repeat-mediated deletion of OPTN upstream region in a patient with a complex ocular phenotype

Genetic causes of ocular conditions remain largely unknown. To reveal the molecular basis for a congenital ocular phenotype associated with glaucoma we performed whole-exome sequencing (WES) and whole-genome copy number analyses of patient DNA. WES did not identify a causative variant. Copy number variation analysis identified a deletion of 10p13 in the patient and his unaffected father; the deletion breakpoint contained a single 37-bp sequence that is normally present in two distinct Alu repeats separated by ~181 kb. The deletion removed part of the upstream region of optineurin (OPTN) as well as the upstream sequence and two coding exons of coiled-coil domain containing 3 (CCDC3); analysis of the patient's second allele showed normal OPTN and CCDC3 sequences. Studies of zebrafish orthologs identified expression in the developing eye for both genes. OPTN is a known factor in dominant adult-onset glaucoma and Amyotrophic Lateral Sclerosis (ALS). The deletion eliminates 98 kb of the OPTN upstream sequence leaving only ~1 kb of the proximal promoter region. Comparison of transcriptional activation capability of the 3 kb normal and the rearranged del(10)(p13) OPTN promoter sequences demonstrated a statistically significant decrease for the deleted allele; sequence analysis of the entire deleted region identified multiple conserved elements with possible cis-regulatory activity. Additional screening of CCDC3 indicated that heterozygous loss-of-function alleles are unlikely to cause congenital ocular disease. In summary, we report the first regulatory region deletion involving OPTN, caused by Alu-mediated nonallelic homologous recombination and possibly contributing to the patient's ocular phenotype. In addition, our data indicate that Alu-mediated rearrangements of the OPTN upstream region may represent a new source of affected alleles in human conditions. Evaluation of the upstream OPTN sequences in additional ocular and ALS patients may help to determine the role of this region, if any, in human disease.