Genetic Disorders

Equine severe combined immunodeficiency is an autosomal recessive immunological disorder found in Arabian horses. It is characterized by a complete absence of B-and T-lymphocytes which results in severe and generally fatal infectious diseases in foals.
A deletion mutation (= loss of base) of the DNA-PK gene has been found to be the cause of that disease.
Affected foals which carry two copies of the SCID gene (SCID-ss) can result from the mating of two carriers of the deletion (SCID-Ss). Those heterozygous carriers themselves can transmit the disease-causing mutation but show no clinical signs of the disease and therefore cannot be distinguished from homozygous SCID healthy horses (SCID-SS).
SCID gene testing allows for unambiguous identification of carriers and is highly recommended for Arabian horses before mating.
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Please note: Due to current provisions from patent law, we SCID gene testing is not available for customers in the United States, Great Britain and Australia.

Hyperkalemic Periodic Paralysis in horses is an autosomal dominant inherited disease of the muscles. It is associated with episodic muscular paralysis and/or tremor which can lead to collapse and death of the animal. HYPP is also known as 'Impressive Syndrome', due to its occurrence in offspring of the American stallion Impressive. Nowadays, the disease can be foundin Quarter Horse, Paint, Appaloosa und US-Pony.
HYPP is caused by a point mutation in the genome of affected animals and leads to dysfunction of the sodium channels of muscle cells. Clinical symptoms of this defect are exaggerated and unintended contractions of the muscles. Such attacks can be stimulated by stress (transportation, convalescence, etc.) and high levels of potassium ions in the blood (low-potassium diet needs to be maintained). Heterozygous animals (h /H) frequently show milder symptoms than homozygous horses (H/H).
Genetic testing enables a clear distinction of affected homo- or heterozygous carriers (H/H and h/H, respectively) from healthy individuals (h/h) for diagnostic, treatment and mating objects.

The Overo Lethal White Syndrome describes an autosomal recessive lethal defect in Overo dappled American Paints caused by a mutation in the endothelin-B receptor gene. In homozygous animals (OO) the mutation leads to congenital dysfunctional innervation of certain sections of the intestine (intestinal aganglionosis). Due to the impaired intestinal motility, affected foals suffer from severe colic and die within the first days of life. The available DNA test detects the mutation of the endothelin-receptor B gene and identifies possible carriers. Breeders can use the test to avoid affected offspring in Overos but also in Tobiano Paints, Quarter Horses and Thoroughbreds.

Equine Cerebellar Abiotrophy (CA) of Arabian thoroughbreds is a hereditary neurological disorder with autosomal recessive inheritance. Affected animals appear normal at birth; however develop neurological symptoms within of a few weeks or months due to abnormal death of cerebellar neurons.
Affected foals may show a variety of cerebellar deficiencies, e.g. head tremor (intention tremor), ataxia or tendency for a higher startle response. In addition, those horses often have difficulties in rising and/or moving backwards or may collide with other horses or obstacles due to an insufficient coordination. Finally, affected horses have a higher risk for severe accidents and injuries and thus often need to be euthanized.
Genetic testing of a specific mutation in the TOE-1 gene which is associated with CA, allows identifying affected animals as well as potential carriers of the disease gene.

The terms "Lavender Foal Syndrome" (LFS) or "Coat Colour Dilution Lethal" (CCDL) describe a hereditary neurological disease of the Arabian horse which is most commonly thought to be inherited in an autosomal recessive manner.
Lavender foals typically show a brightened coat colour (dull lavender) and suffer from a variety of neurological symptoms, such as opisthotonos, nystagmus as well as convulsive seizures. All clinical signs manifest shortly after birth. Due to the massive neurological deficits, LFS-affected foals usually are unable to stand or to ingest colostrum. Therefore, they often die within a few days after birth or have to be euthanized. According to the autosomal recessive inheritance of this trait, heterozygous carriers do not show any neurological deficits but can produce homozygous LFS-affected foals. LFS results from a specific mutation of the MYO5A gene in horses. Genetic testing for this mutation enables a clear distinction between homozygous non-carriers and clinically normal LFS-carriers.

Hereditary Equine Regional Dermal Asthenia (HERDA) describes a degenerative skin disease in American Quarter Horses which is inherited in an autosomal recessive manner.
Horses suffering from HERDA are usually born without any clinical signs. However, at a later stage affected animals develop localized skin defects which often appear along the horse’s back. In most cases, on the course of the disease, progressing lesions prohibit any further use of affected animals for riding purposes.
The diagnostic DNA test for HERDA detects the causal mutation in the cyclophilin B (PPIB) gene and thus enables identification of horses that are affected or carry the mutation.

Junctional epidermolysis bullosa (JEB) is an autosomal recessive inherited trait which is observed in Belgian Draft as well as in American Saddlebred horses. JEB-affected foals are born with moderate to severe skin defects like blisters, erosions or ulcera on the skin (fetlocks, hips, etc.) and mucocutaneous epithelia (mouth, anus, vulva, etc.). In the long run, affected foals are not viable and usually need to be euthanized at an early age.
Due to its autosomal recessive inheritance, JEB foals can arise from mating of two JEB-carriers, which themselves do not show any clinical signs of the skin disease.
JEB gene testing provides the possibility to distinguish not only between clear and affected animals, but also enables identifying carriers for this disease. Therefore, gene testing offers an instrument for avoiding production of affected and unviable foals.

Please note: The offered test detects the mutation associated with JEB in American Saddlebred horses, only. In Belgian Draft horses, JEB originates from a different mutation not located in the LAMA3 gene.

Hoof Wall Separation Disease (HWSD) describes a genetic hoof disease found in Connemara ponies.
First symptoms of the disease develop in foals of early age and get worse during the first years of life. Due to an unstable and brittle hoof wall weight bearing structures do not fulfil their function thus leading to weight overload of the sole of the hoof. The associated chronic inflammation often leads to laminitis and clinical symptoms such as hoof pain and lameness. Symptoms can vary from subtile to severe pain for the animal, which in worst case may lead to the necessity of euthanasia.
HWSD is a disease which is inherited in autosomal recessive manner. The causal mutation responsible for the disease was identified in the SERPINB11 gene and genetic testing can be performed in order to avoid affected foals.

Polysaccharide storage myopathy (PSSM) is a hereditary disorder affecting the carbohydrate metabolism and causing abnormal accumulation of carbohydrates (polysaccharides) in the muscles. PSSM is widespread and occurs in various horse breeds, e.g.. Quarter Horse, Paint Horse, Appaloosa, but also draft horses and warmbloods as well as crossbreeds.
Clinical signs of the disease are reluctance to move, increased sweating, muscle tremors, alternating lameness, painful muscle stiffness, etc. The clinical signs result from a damage of the muscles cells and usually appear after physical work. In severe cases, the damage of the muscle cells leads to a release of muscle proteins, which subsequently are urinated (myoglobinuria). This can cause additional damage of the kidneys and impair renal function.
Due to legal restrictions we offer this test in cooperation with our laboratory.

Warmblood Fragile Foal Syndrome (WFFS) is a hereditary acquired disease of the connective tissue in wormblood horses. The disease is characterised by extremely brittle skin which easily tears and thus resulting in wounds all over the body. Besides regions of hairy skin also the gums and mucous membranes can show lesions. Symptomes become apparent relatively soon after birth. Affected foals usually cannot stand normally because their limb joints are highly hyperextendable. The disease may result in premature births or miscarriages of affected foals. Due to a poor prognosis, foals which are born alive are often euthanised shortly after birth.
The underlying mutation of WFFS was published at Cornell University. Due to legal restrictions we offer this test in cooperation with different partner laboratories.