A whole-genome scan for recurrent airway obstruction in Warmblood sport horses indicates two positional candidate regions

Abstract

Recurrent airway obstruction (RAO), or heaves, is a naturally occurring asthma-like disease that is related to sensitisation and exposure to mouldy hay and has a familial basis with a complex mode of inheritance. A genome-wide scanning approach using two half-sibling families was taken in order to locate the chromosome regions that contribute to the inherited component of this condition in these families. Initially, a panel of 250 microsatellite markers, which were chosen as a well-spaced, polymorphic selection covering the 31 equine autosomes, was used to genotype the two half-sibling families, which comprised in total 239 Warmblood horses. Subsequently, supplementary markers were added for a total of 315 genotyped markers. Each half-sibling family is focused around a severely RAO-affected stallion, and the phenotype of each individual was assessed for RAO and related signs, namely, breathing effort at rest, breathing effort at work, coughing, and nasal discharge, using an owner-based questionnaire. Analysis using a regression method for half-sibling family structures was performed using RAO and each of the composite clinical signs separately; two chromosome regions (on ECA13 and ECA15) showed a genome-wide significant association with RAO at P < 0.05. An additional 11 chromosome regions showed a more modest association. This is the first publication that describes the mapping of genetic loci involved in RAO. Several candidate genes are located in these regions, a number of which are interleukins. These are important signalling molecules that are intricately involved in the control of the immune response and are therefore good positional candidates.

Evaluation of Coughing and Nasal Discharge as Early Indicators for An Increased Risk to Develop Equine Recurrent Airway Obstruction (RAO)

“…This is likely because of genetic effects, the most important predisposing factor for the development of RAO besides hay feeding 8, 9, 11, 25, 26. Family history of RAO is itself an important predictor for developing the disease with risks estimated at 3–5 fold when one of the parents is affected 11, 26.…”

“…RAO, in contrast, affects middle‐aged to older horses and provokes more severe respiratory signs. A strong genetic basis was shown for RAO7, 8, 9 and hay feeding is the most important environmental factor for its development4, 10, 11 and exacerbation 12, 13…”

Recurrent respiratory disorders in Polish Konik horses - clinical and laboratory findings

“…Considering the origin of the Polish Konik horse from a small number of progenitors (21), namely their close relationship, a higher incidence of genetic diseases can be suspected. Several studies have demonstrated a predisposition for RAO in families, and it is now proven that this disease has a genetic background (6,(14)(15)(16)18). In offspring the risk of developing recurrent airway obstruction is three times higher, when one parent is affected with this disease, and increases almost five times, when both parents have RAO.…”

“…In offspring the risk of developing recurrent airway obstruction is three times higher, when one parent is affected with this disease, and increases almost five times, when both parents have RAO. Moreover, Swinburne et al (6), recognised locations in the genome responsible for the higher prevalence of RAO in Warmblood sport horses, which are two chromosome regions on ECA13 and ECA15 (18). However, genetic testing can be done after the basic research indicating the pathophysiology of chronic respiratory problems in horses.…”

Genetics of equine insect bite hypersensitivity and genetic diversity in horses

“…RAO, or heaves, is a hypersensitivity reaction to inhaled stable dust, including mold spores (Swinburne et al, 2009). It is one of the most common disorders of the lower respiratory tract of mature horses and is influenced by multiple genes.…”