Identification of Genetic Susceptibility Factors Associated with Canine Gastric Dilatation-Volvulus

New insights into the physiology and pathophysiology of the atypical sodium leak channel NALCN

Cell excitability and its modulation by hormones and neurotransmitters involve the concerted action of a large repertoire of membrane proteins, especially ion channels. Unique complements of coexpressed ion channels are exquisitely balanced against each other in different excitable cell types, establishing distinct electrical properties that are tailored for diverse physiological contributions, and dysfunction of any component may induce a disease state. A crucial parameter controlling cell excitability is the resting membrane potential (RMP) set by extra- and intracellular concentrations of ions, mainly Na+, K+, and Cl-, and their passive permeation across the cell membrane through leak ion channels. Indeed, dysregulation of RMP causes significant effects on cellular excitability. This review describes the molecular and physiological properties of the Na+ leak channel NALCN, which associates with its accessory subunits UNC-79, UNC-80, and NLF-1/FAM155 to conduct depolarizing background Na+ currents in various excitable cell types, especially neurons. Studies of animal models clearly demonstrate that NALCN contributes to fundamental physiological processes in the nervous system including the control of respiratory rhythm, circadian rhythm, sleep, and locomotor behavior. Furthermore, dysfunction of NALCN and its subunits is associated with severe pathological states in humans. The critical involvement of NALCN in physiology is now well established, but its study has been hampered by the lack of specific drugs that can block or agonize NALCN currents in vitro and in vivo. Molecular tools and animal models are now available to accelerate our understanding of how NALCN contributes to key physiological functions and the development of novel therapies for NALCN channelopathies.

GWAS using low-pass whole genome sequence reveals a novel locus in canine congenital idiopathic megaesophagus

Congenital idiopathic megaesophagus (CIM) is a gastrointestinal disorder of dogs wherein the esophagus is dilated and swallowing activity is reduced, causing regurgitation of ingesta. Affected individuals experience weight loss and malnourishment and are at risk for aspiration pneumonia, intussusception, and euthanasia. Great Danes have among the highest incidences of CIM across dog breeds, suggesting a genetic predisposition. We generated low-pass sequencing data for 83 Great Danes and used variant calls to impute missing whole genome single-nucleotide variants (SNVs) for each individual based on haplotypes phased from 624 high-coverage dog genomes, including 21 Great Danes. We validated the utility of our imputed data set for genome-wide association studies (GWASs) by mapping loci known to underlie coat phenotypes with simple and complex inheritance patterns. We conducted a GWAS for CIM with 2,010,300 SNVs, identifying a novel locus on canine chromosome 1 (P-val = 2.76 × 10-10). Associated SNVs are intergenic or intronic and are found in two clusters across a 1.7-Mb region. Inspection of coding regions in high-coverage genomes from affected Great Danes did not reveal candidate causal variants, suggesting that regulatory variants underlie CIM. Further studies are necessary to assess the role of these non-coding variants.

Common Orthopedic Traits and Screening for Breeding Programs

Orthopedic diseases are complex traits, meaning genetics and environmental factors affect risk, making identification of genetic associations difficult. In the United States, hip and elbow scores, patellar luxation scores, Legg-Calvé-Perthes disease, and shoulder osteochondrosis affectedness are available in the Orthopedic Foundation for Animals registry. Distraction indices and extended, ventrodorsal hip conformation scores are recorded by PennHIP. Application of estimated breeding values for hip and elbow dysplasia in breeder selection reduces the severity and prevalence of these traits. Genomic prediction and whole-genome sequence technologies and methods should improve knowledge of genetics underlying orthopedic diseases, leading to improved canine orthopedic genetic quality.

FATAL GASTRIC DILATATION AND VOLVULUS IN THREE CAPTIVE JUVENILE LINNAEUS'S TWO-TOED SLOTHS (CHOLOEPUS DIDACTYLUS)

Linnaeus's two-toed sloth (Choloepus didactylus) is one of two extant neotropical species of the family Megalonychidae. Despite their being commonly kept under managed care, the digestive physiology of sloths remains poorly understood. Gastrointestinal disease has been reported as a primary or contributing cause of morbidity and mortality in captive two-toed and three-toed (Bradypus spp.) sloths. Gastric dilatation due to gas accumulation ("bloat") has been reported in sloths; however, a literature search failed to yield any published mention of gastric volvulus in any sloth species. Following an inquiry sent to the electronic mailing lists of the American Association of Zoo Veterinarians, the European Association of Zoo and Wildlife Veterinarians, and the LatinVets community, three cases of fatal gastric dilatation and volvulus (GDV) were identified in one male and two female Linnaeus's two-toed sloths from institutions in the United States, Canada, and Germany. All cases occurred in juvenile sloths <1 yr of age. Two animals were primarily hand reared, whereas one was reared primarily by its dam. Two animals were found dead with no overt premonitory signs, whereas one animal died following a 3-wk course of waxing and waning clinical signs consistent with gastric gas accumulation. In all cases, GDV was diagnosed on postmortem examination. Similar to other species, the condition is likely subsequent to a combination of host- and husbandry-related contributing factors. Further research into sloth husbandry is required in order to take an evidence-based approach to their management.

Association between Human Genetic Variants and the Vaginal Bacteriome of Pregnant Women

The influence of human genetic variants on the vaginal bacterial traits (VBTs) of pregnant women is still unknown. Using a genome-wide association approach based on the 16S rRNA bacteriome analysis, a total of 72 host genetic variant (single nucleotide polymorphisms [SNPs], indels, or copy number variations [CNVs])-VBT associations were found that reached the genome-wide significance level (P < 5 × 10^-8) with an acceptable genomic inflation factor λ of <1.1. The majority of these SNPs that reached the genome-wide significance level had a relatively low minor allele frequency (MAF), and only seven of them had MAFs greater than 0.05. rs303212, located at the IFIT1 gene on chromosome 10, was the most eye-catching variant, which had a genome-wide association with the relative abundance (RAB) of Actinobacteria and Bifidobacteriaceae and also had a suggestive association with the RAB of a few common vaginal bacteria including Actinobacteriota, Firmicutes, Lactobacillus, and Gardnerella vaginalis and the beta diversity weighted UniFrac (P < 1 × 10^-5). The findings of the study suggest that the vaginal bacteriome may be influenced by a number of genetic variants across the human genome and that interferon signaling may have an important influence on vaginal bacterial communities during pregnancy. IMPORTANCE Knowledge about the influence of host genetics on the vaginal bacteriome in pregnancy is still limited. Although a number of environmental and behavioral factors may exert influences on the structure of vaginal bacterial communities, the vaginal bacteriome often undergoes a relatively fixed transition to a more stable and less diverse state as the menstrual cycle stops, which raises questions on the effects of human genetics. We utilized a genome-wide approach to identify the associations between genetic variants and multiple VBTs and performed enrichment analyses. The human genetics during pregnancy may be involved in multiple pathways. The results may disclose innate functional factors involved in shaping the vaginal bacteriome during pregnancy and provide insight into the establishment of specific strategies for prevention and clinical treatment of pregnancy complications.