Recessive LOXHD1 variants cause a prelingual down-sloping hearing loss: genotype-phenotype correlation and three additional children with novel variants

Background: Biallelic mutations in LOXHD1 have been identified as the cause of DFNB77 (deafness, autosomal recessive 77). It is a new progressive, severe-to-profound, and late-onset nonsyndromic sensorineural hearing loss (NSHL), and is highly heterogeneous genetically and phenotypically. This study aimed to provide an additional three cases of DFNB77.

Methods: We presented three unrelated children diagnosed with prelingual mild-to-severe NSHL, and their audiograms showed mild hearing loss at 250 Hz before downsloping to a moderate-to-severe degree. Trio whole-exome sequencing (WES) was conducted to identify the pathogenic variants. Additionally, we reviewed the literature to further analyze the relationships between the genotype and audiology phenotype of LOXHD1.

Results: Six novel possible pathogenic LOXHD1 variants were identified, including three missense, one nonsense, and two splicing variants. The literature review showed that 68.5% of patients with DFNB77 onset before five years old; Most variants (62%) were associated with a down-sloping audiogram of mild-to-moderate hearing loss at low frequencies (200Hz, 500Hz), particularly variants in the protein domain of PLAT 9. We found that compared with homozygous LOXHD1 variants, individuals with heterozygous compound variants had a significantly milder phenotype, especially individuals carrying one missense and one splicing or bi-allelic missense variants (P < 0.05). Audiometric analysis at different ages showed that the hearing loss degree was aggravated at all frequencies by increasing age.

Conclusions: We report three children with prelingual NSHL carrying six novel LOXHD1 variants. Furthermore, our work indicates that DFNB77 may be milder than previously reported and recommends considering the genotype combination and mutation location of LOXHD1 and race-specificity in DFNB77 molecular diagnoses and management.