Myotonia (MYT) is a rare disorder involving a slowed relaxation of muscles after contraction. The most well-known example of myotonia is “fainting goats,” a breed that is characterized by sudden rigidy and/or falling over when startled. In the single documented horse, this resulted in a protruding third eyelid when excited, as well as problems with muscle stiffness.

Naked Foal Syndrome (NFS) is a recessive trait that results in the birth of foals with little to no hair and a general weakness. Death occurs early in life (weeks to months).

Occipitoatlantoaxial Malformation 1 (OAAM1) is an inherited developmental condition predominantly found in Arabian horses, characterized by abnormal development of the cervical vertebrae leading to compression of the upper cervical cord and subsequent neurological damage.

Polysaccharide Storage Myopathy (PSSM) is a glycogen storage disorder in which affected horses have chronic episodes of exertional rhabdomyolysis (“tying-up”). Acute symptoms are an unwillingness to move and muscle damage following exercise. Moderate symptoms can usually be managed through a low-sugar/starch diet and exercise.

Recurrent Laryngeal Neuropathy (RLN) is a disease that results in loss of the neurons that open the larynx, significantly affecting performance in Thoroughbreds and other sport horses. It is an important issue for horses in competitive events because the resultant paralysis of the larynx leads to obstruction of air flow during intense exercise, creating the abnormal inspiratory noise that gives RLN its common name: “roaring”.

Severe Combined Immunodeficiency Disease (SCID) is a condition in which affected foals are unable to mount an effective immune response after infection and are unable to recover from infections that unaffected foals would easily resist. The disease is universally fatal in horses, usually within 4-6 months of life.

Squamous Cell Carcinoma (SCC) is the most common cause of eye cancer in horses. It is also responsible for a large percentage of tumors throughout other parts of the equine body.

West Nile Virus (WNV) is a mosquito-borne virus that can infect multiple types of mammals, including horses. Infection can lead to a series of severe symptoms, most commonly encephalitis – acute inflammation of the brain. Severe neurological symptoms develop in ~8% of exposed horses, and once symptoms manifest, the fatality rate ranges from 20-40% and is higher in older horses.