[Clinical evaluation of the new coat colour macchiato in a male Franches-Montagnes horse].

This research article explores the case of a Franches-Montagnes colt born with a unique coat color and physical features never before seen in its breed, accompanied by impairment in its hearing believed to be caused by a spontaneous mutation in a specific gene called MITF. The confirmation of the mutation’s role through experimental mating could not be achieved due to the colt’s castration.

Unusual Phenotype and Genetic Mutation in a Franches-Montagnes Colt

• The study starts with the birth of a Franches-Montagnes colt in April 2008 who displayed notable physical characteristics: extensive white markings on the body and legs, a white head, and blue eyes, not seen previously in the breed.
• Given the normal bay coat color of its parents, the research team suspected a new, or “de novo,” mutation in the colt. Extensive genetic testing identified the mutation, specifically in the Microphthalmia Associated Transcription Factor Gene (MITF).

Impaired Hearing Capacity Possibly Linked to MITF Mutation

• This was explored further since, in the American Paint Horse breed, unusual features such as significant white facial markings and blue eyes are associated with deafness. A more detailed auditory examination was carried out using brainstem auditory-evoked responses (BAER).
• The BAER examination confirmed that the Franches-Montagnes colt was indeed suffering from bilateral deafness.
• The researchers hypothesize that this hearing impairment is caused by a deficiency in melanocytes (pigment-producing cells) stemming from the identified MITF gene mutation.

Unable to Confirm Mutation’s Role Due to Colt’s Castration

• Verifying the direct link between the MITF gene mutation, the unusual coat color, and hearing deficiency could ideally be done through experimental mating. However, it was not possible in this case because of the colt’s castration.
• Despite this, the study offers significant insights into unusual phenotypes potentially linked to new genetic mutations and the broader scope of their impacts on health and physiological characteristics in animals.