Improved variant detection using long-read sequencing and optical mapping: Illustration in STRC-related hearing loss

Biallelic loss-of-function variants in STRC contribute to mild-moderate hearing loss (DFNB16). Here, we report a female patient with mild hearing loss. Exome sequencing and MLPA analysis revealed STRC biallelic inactivation due to a nonsense and a CKMT1B-STRC deletion. Analysis of the self-reported normal-hearing parents revealed inconsistent Mendelian inheritance. Indeed, the mother was a heterozygous carrier of a CKTM1B-STRC-CATSPER2 deletion, and the father shared the same genotype as his daughter. He was later found to also have mild-moderate hearing loss. To address these discrepancies, we used long-read sequencing and optical genome mapping. We demonstrated that the father, in fact, carried a CKMT1B-STRC-CATSPER2 deletion in trans with the STRC nonsense variant and a tandem duplication of CATSPER2-CKMT1A. The proband inherited this latter haplotype, together with the maternal CKMT1B-STRC-CATSPER2 deletion. Combining these two technologies allowed us to fully elucidate the complex structural rearrangements at the STRC locus and provide appropriate genetic counselling.