Missense variant in LOXHD1 is associated with canine nonsyndromic hearing loss

LOXHD1 is indispensable for coupling auditory mechanosensitive channels to the site of force transmission

Hearing is initiated in hair cells by the mechanical activation of ion channels in the hair bundle. The hair bundle is formed by stereocilia organized into rows of increasing heights interconnected by tip links, which convey sound-induced forces to stereocilia tips. The auditory mechanosensitive channels are complexes containing at least four protein-subunits - TMC1/2, TMIE, CIB2, and LHFPL51-16 - and are located at the tips of shorter stereocilia at a yet-undetermined distance from the lower tip link insertion point17. While multiple auditory channel subunits appear to interact with the tip link, it remains unknown whether their combined interaction alone can resist the high-frequency mechanical stimulations owing to sound. Here we show that an unanticipated additional element, LOXHD1, is indispensable for maintaining the TMC1 pore-forming channel subunits coupled to the tip link. We demonstrate that LOXHD1 is a unique element of the auditory mechanotransduction complex that selectively affects the localization of TMC1, but not its close developmental paralogue TMC2. Taking advantage of our novel immunogold scanning electron microscopy method for submembranous epitopes (SUB-immunogold-SEM), we demonstrate that TMC1 normally concentrates within 100-nm of the tip link insertion point. In LOXHD1's absence, TMC1 is instead mislocalized away from this force transmission site. Supporting this finding, we found that LOXHD1 interacts selectively in vitro with TMC1 but not with TMC2 while also binding to channel subunits CIB2 and LHFPL5 and tip-link protein PCDH15. SUB-immunogold-SEM additionally demonstrates that LOXHD1 and TMC1 are physically connected to the lower tip-link complex in situ. Our results show that the TMC1-driven mature channels require LOXHD1 to stay coupled to the tip link and remain functional, but the TMC2-driven developmental channels do not. As both tip links and TMC1 remain present in hair bundles lacking LOXHD1, it opens the possibility to reconnect them and restore hearing for this form of genetic deafness.

An Overview of Canine Inherited Neurological Disorders with Known Causal Variants

Hereditary neurological conditions documented in dogs encompass congenital, neonatal, and late-onset disorders, along with both progressive and non-progressive forms. In order to identify the causal variant of a disease, the main two approaches are genome-wide investigations and candidate gene investigation. Online Mendelian Inheritance in Animals currently lists 418 Mendelian disorders specific to dogs, of which 355 have their likely causal genetic variant identified. This review aims to summarize the current knowledge on the canine nervous system phenes and their genetic causal variant. It has been noted that the majority of these diseases have an autosomal recessive pattern of inheritance. Additionally, the dog breeds that are more prone to develop such diseases are the Golden Retriever, in which six inherited neurological disorders with a known causal variant have been documented, and the Belgian Shepherd, in which five such disorders have been documented. DNA tests can play a vital role in effectively managing and ultimately eradicating inherited diseases.

De-novo and genome-wide meta-analyses identify a risk haplotype for congenital sensorineural deafness in Dalmatian dogs

Congenital sensorineural deafness (CSD) has been reported to affect up to 30% of Dalmatian dogs world-wide and while unilaterally deaf dogs can live a close to normal life, dogs suffering bilateral deafness are frequently euthanized. Extreme-white coat patterning as encoded by the gene Melanocyte Inducing Transcription Factor (MITF) has long been postulated as the major risk factor for CSD in the Dalmatian breed. While attempts to identify causative risk variants associated with CSD have been numerous, no genome-wide association study has positively identified MITF as a risk locus for either bilateral or unilateral deafness in the Dalmatian breed to date. In this study, we identified an association with CSD on CFA20 in the vicinity of MITF within Australian Dalmatian dogs. Although not genome-wide significant, the association signal was validated by reanalysing publicly available data and merging the wider data resource with the local data to improve statistical power. The merged data, representing three major global populations of Dalmatian dogs, enabled us to identify a single, well-defined genome-wide significant risk haplotype for CSD. The haplotype was formed by three genome-wide significant associated markers (BICF2G630233852T>C, BICF2G630233861T>C, BICF2G630233888G>A) on CFA20 with 62% of bilaterally deaf dogs homozygous for the risk haplotype (CCA), while 30% of bilaterally deaf and 45% of hearing dogs carried one copy of the risk haplotype. Animals homozygous or heterozygous for the low-risk haplotype were less likely to be unilaterally deaf. While the association between the risk haplotype and deafness is incomplete, animals homozygous for the risk haplotype were 10-times more likely to be bilaterally deaf. Although the underlying causative variants are yet to be discovered, results from this study can now assist with reducing deafness in Dalmatian dogs.

Dog-human translational genomics: state of the art and genomic resources

Innovative models for medical research are strongly required nowadays. Convincing evidence supports dog as the most suitable spontaneous model for several human genetic diseases. Decades of studies on dog genome allowed the identification of hundreds of mutations causing genetic disorders, many of which are proposed as counterparts responsible for human diseases. Traditionally, the murine model is the most extensively used in human translational research. However, this species shows large physiological differences from humans, and it is kept under a controlled artificial environment. Conversely, canine genetic disorders often show pathophysiological and clinical features highly resembling the human counterpart. In addition, dogs share the same environment with humans; therefore, they are naturally exposed to many risk factors. Thus, different branches of translational medicine aim to study spontaneously occurring diseases in dogs to provide a more reliable model for human disorders. This review offers a comprehensive overview of the knowledge and resources available today for all the researchers involved in the field of dog-human translational medicine. Some of the main successful examples from dog-human translational genomics are reported, such as the canine association studies which helped to identify the causal mutation in the human counterpart. We also illustrated the ongoing projects aiming to create public canine big datasets. Finally, specific online databases are discussed along with several information resources that can speed up clinical translational research.