Technique for Evaluation of Gravity-Assisted Esophageal Transit Characteristics in Dogs with Megaesophagus

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.

Extraesophageal reflux and reflux aspiration in dogs with respiratory diseases and in healthy dogs

BACKGROUND

Salivary bile acids are used to diagnose extraesophageal reflux (EER) and to evaluate the risk of reflux aspiration that is associated with respiratory diseases in dogs.

OBJECTIVES

To study total bile acid (TBA) concentrations in saliva and in bronchoalveolar lavage fluid (BALF) to investigate EER and reflux aspiration in dogs with respiratory diseases and in healthy dogs.

ANIMALS

 Thirty-one West Highland White Terriers (WHWTs) with idiopathic pulmonary fibrosis (IPF), 12 dogs with inflammatory airway disease (IAD), 6 dogs with recurrent pneumonia (RP), 26 brachycephalic dogs (BD), 27 healthy WHWTs (HW), 52 healthy dogs (HD). All privately-owned dogs.

METHODS

Saliva and BALF were collected from dogs in each group.

RESULTS

Salivary TBA concentrations were higher in IPF (median 0.1692 μM, interquartile range [IQR] 0.1115-0.2925 μM, Cohen's d 3.4, 95% confidence interval [CI] 2.2-4.0, P < .001) and BD (0.0256 μM, IQR 0.0086-0.0417 μM, d 0.5, CI -0.1 to 1.1, P = .003) compared to HD (0 μM, IQR not quantifiable [n.q.]-0.0131 μM). Bronchoalveolar lavage fluid TBA concentrations were higher in IPF (0.0117 μM, IQR 0.0048-0.0361 μM, d 0.5, CI 0-1.1, P < .001) compared to HD (0 μM, IQR n.q.-0.0074 μM).

CONCLUSION AND CLINICAL IMPORTANCE

Extraesophageal reflux and reflux aspiration occur in healthy dogs and those with respiratory diseases.

A Comparative Assessment of the Diagnosis of Swallowing Impairment and Gastroesophageal Reflux in Canines and Humans

Swallowing impairment is a highly prevalent and clinically significant problem affecting people and dogs. There are myriad causes of swallowing impairment of which gastroesophageal reflux is the most common in both species. Similarities in anatomy and physiology between humans and canines results in analogous swallowing disorders including cricopharyngeus muscle achalasia, esophageal achalasia, hiatal herniation, and gastroesophageal reflux with secondary esophagitis and esophageal dysmotility. Accordingly, the diagnostic approach to human and canine patients with swallowing impairment is similar. Diagnostic procedures such as swallowing fluoroscopy, high-resolution manometry, pH/impedance monitoring, and endolumenal functional luminal imaging probe can be performed in both species; however, nasofacial conformation, increased esophageal length, and the difficulty of completing several of these procedures in awake dogs are inherent challenges that need to be considered. Human patients can convey their symptoms and respond to verbal cues, whereas veterinarians must rely on clinical histories narrated by pet owners followed by comprehensive physical examination and observation of the animal eating different food consistencies and drinking water. Dogs may also be unwilling to drink or eat in the hospital setting and may be resistant to physical restraint during diagnostic procedures. Despite the species differences and diagnostic challenges, dogs are a natural animal model for many oropharyngeal and esophageal disorders affecting people, which presents a tremendous opportunity for shared learnings. This manuscript reviews the comparative aspects of esophageal anatomy and physiology between humans and canines, summarizes the diagnostic assessment of swallowing impairment in both species, and discusses future considerations for collaborative medicine and translational research.

Use of a videofluoroscopic feeding evaluation to guide management of dogs with congenital idiopathic megaoesophagus

Background

Evidence‐based guidelines for determining dietary management in dogs with megaoesophagus are lacking.

Objectives

This study looked to compare oesophageal clearance times (ECT) of liquid and two food consistencies using a contrast videofluoroscopy feeding evaluation, and to assess if recommendations made based on findings could improve regurgitation and quality of life in dogs with congenital megaoesophagus.

Methods

Twenty‐one dogs with congenital megaoesophagus and nine healthy dogs received liquid, slurry, and meatball diets containing barium while in an upright position. Follow‐up was performed to determine response to recommendations.

Results

Healthy dogs had significantly shorter median ECT for all consistencies (p < 0.001). In the megaoesophagus group, ECT varied by consistency and individual. The number of dogs in the megaoesophagus group with complete clearance was four (median ECT 10 min) for liquid, five (median ECT 5 min) for slurry, and two (median ECT 5 and 30 min, respectively) for meatballs. Partial clearance was seen in 11 dogs (median clearance 25%) with liquid, seven with slurry (median clearance 50%), and five with meatballs (median clearance 60%). Recommendations included altering current medications (13/21 dogs), diet consistency (6/21), time upright (12/21), water delivery (21/21), and adding activity (7/21). Regurgitation episodes/week decreased significantly from 5.5 to 2.5 (p < 0.001) at follow‐up 3–5 weeks post‐evaluation, with 95% of owners reporting improvement in quality of life. Seventy percent were alive 46–777 days after last recheck. Three dogs died from megaoesophagus associated complications (median survival 461 days after diagnosis).

Conclusions

The findings of this study suggest that a videofluoroscopic feeding evaluation may help guide management of dogs with congenital megaoesophagus.

Congenital idiopathic megaesophagus in the German shepherd dog is a sex-differentiated trait and is associated with an intronic variable number tandem repeat in Melanin-Concentrating Hormone Receptor 2

Congenital idiopathic megaesophagus (CIM) is a gastrointestinal (GI) motility disorder of dogs in which reduced peristaltic activity and dilation of the esophagus prevent the normal transport of food into the stomach. Affected puppies regurgitate meals and water, fail to thrive, and experience complications such as aspiration pneumonia that may necessitate euthanasia. The German shepherd dog (GSD) has the highest disease incidence, indicative of a genetic predisposition. Here, we discover that male GSDs are twice as likely to be affected as females and show that the sex bias is independent of body size. We propose that female endogenous factors (e.g., estrogen) are protective via their role in promoting relaxation of the sphincter between the esophagus and stomach, facilitating food passage. A genome-wide association study for CIM revealed an association on canine chromosome 12 (P-val = 3.12x10^-13), with the lead SNPs located upstream or within Melanin-Concentrating Hormone Receptor 2 (MCHR2), a compelling positional candidate gene having a role in appetite, weight, and GI motility. Within the first intron of MCHR2, we identified a 33 bp variable number tandem repeat (VNTR) containing a consensus binding sequence for the T-box family of transcription factors. Across dogs and wolves, the major allele includes two copies of the repeat, whereas the predominant alleles in GSDs have one or three copies. The single-copy allele is strongly associated with CIM (P-val = 1.32x10^-17), with homozygosity for this allele posing the most significant risk. Our findings suggest that the number of T-box protein binding motifs may correlate with MCHR2 expression and that an imbalance of melanin-concentrating hormone plays a role in CIM. We describe herein the first genetic factors identified in CIM: sex and a major locus on chromosome 12, which together predict disease state in the GSD with greater than 75% accuracy.

German shepherd dogs (GSDs) are predisposed to an inherited motility disorder of the esophagus, termed congenital idiopathic megaesophagus (CIM), in which swallowing is ineffective and the esophagus is enlarged. Affected puppies are unable to properly pass food into their stomachs and consequently regurgitate their meals and show a failure to thrive, often leading to euthanasia. Here, we discovered that male GSDs are affected at a ratio of almost 2-to-1 over females, suggesting a protective biological advantage in females. In humans, estrogen is thought to play a role in the male predominance of esophageal disorders like reflux esophagitis and esophageal cancer. In a genome-wide scan, we identified an association with CIM on chromosome 12 and, within this region, a repetitive sequence in MCHR2. This gene encodes a receptor for melanin-concentrating hormone, a signaling molecule that is linked to appetite, weight, and gut motility. Together, sex and the MCHR2 repeat sequence accurately predict affection status in over 75% of dogs, and a genetic test is now available to facilitate breeding decisions aimed at reducing disease incidence.

A randomized crossover study of compounded liquid sildenafil for treatment of generalized megaesophagus in dogs

OBJECTIVE

To determine whether delivery of compounded liquid sildenafil directly to the stomach of dogs with megaesophagus (ME) would affect esophageal clearance, regurgitation frequency, body weight, or quality of life.

ANIMALS

10 client-owned otherwise healthy dogs with stable ME.

PROCEDURES

A randomized crossover study was performed. Dogs received either sildenafil (1 mg/kg, PO, q 12 h) or a placebo for 14 days, followed by a 7-day washout period, then the opposite treatment for 14 days. Esophageal clearance time was assessed by means of videofluoroscopy prior to treatment and on day 1 of each treatment period. Owners maintained logs of regurgitation episodes and quality of life.

RESULTS

Compounded liquid sildenafil moved into the stomach during 21 of 30 (70%) videofluoroscopy sessions. Sildenafil resulted in a significant reduction in the number of regurgitation episodes (median, 3.5 episodes/wk; range, 0 to 14.5 episodes/wk), compared with baseline (median, 6.5 episodes/wk; range, 1.5 to 19.5 episodes/wk) and the placebo (median, 4 episodes/wk; range, 0 to 28 episodes/wk), and a significant increase in body weight (median, 22.05 kg; range, 6 to 26.3 kg), compared with baseline (median, 21.55 kg; range, 5.1 to 26.2 kg) and the placebo (median, 22.9 kg; range, 5.8 to 25.9 kg). There were no differences in esophageal clearance times or quality-of life-scores between sildenafil and placebo.

CLINICAL RELEVANCE

Although significant differences with placebo administration were identified, clinically relevant improvements were not seen with the use of compounded liquid sildenafil in dogs with ME.