Genetic diseases affecting Arabian horses & their Partbreds

There are six known genetic diseases in Arabian horses, two inevitably fatal, two not always fatal but usually result in euthanasia of the affected animal, the remaining conditions can be treated. Three are thought to be autosomal recessive conditions, which means that the flawed gene is not sex-linked and has to come from both parents for an affected foal to be born. The others currently lack sufficient research data to determine the precise mode of inheritance. Arabians are not the only breed of horse to have problems with inherited diseases; fatal or disabling genetic conditions also exist in many other breeds.
The genetic diseases that can occur in purebred Arabians, or in Partbreds with Arabian ancestry in both parents are:

Severe Combined Immunodeficiency (SCID). Affected foals are born with no immune system, and thus generally die of an opportunistic infection, usually before the age of five months. There is a DNA test that can detect healthy horses who are carriers of the gene causing SCID, therefore testing and careful, planned matings can now eliminate the possibility of an affected foal ever being born.

Cerebellar abiotrophy (CA or CCA). An affected foal is usually born without symptoms, but at some point, usually after the age of six weeks, develops severe in-coordination, a head tremor, wide-legged stance and other symptoms related to the death of the purkinje cells in the cerebellum. Such foals are frequently diagnosed only after they have crashed into a fence or fallen over backwards, and often are misdiagnosed as a head injury caused by an accident. Severity varies, with some foals having fast onset of severe coordination problems, others showing milder symptoms. Mildly affected horses can live a full lifespan, but most are euthanized before adulthood because they are so accident-prone as to be dangerous. Clinical signs are distinguishable from other neurological conditions, but a diagnosis of CA can also be verified by examining the brain after euthanasia. As of 2008, there is also a genetic test that uses DNA markers associated with CA that can detect both carriers and affected animals.

Lavender Foal Syndrome (LFS), also known as Coat Color Dilution Lethal (CCDL). The condition gets its name because most affected foals are born with a coat color dilution that lightens the tips of the coat hairs, or even the entire hair shaft. Foals with LFS are unable to stand at birth, often have seizures, and are usually euthanized within a few days of birth. In November, 2009, Cornell University announced that a DNA test has been developed to detect carriers of LFS. Simultaneously, the University of Pretoria also announced that they had also developed a DNA test.

Occipital Atlanto-Axial Malformation (OAAM). Is a condition where the cervical vertebrae fuse together in the neck and at the base of the skull. Symptoms range from mild in-coordination to the paralysis of both front and rear legs. Some affected foals cannot stand to nurse, in others the symptoms may not be seen for several weeks. This is the only cervical spinal cord disease seen in horses less than 1 month of age, and a radiograph can diagnose the condition. There is no genetic test for OAAM, and the hereditary component of this condition is not well researched at present.

Equine juvenile epilepsy, or Juvenile Idiopathic Epilepsy, sometimes referred to as "benign" epilepsy, is not usually fatal. Foals are born normal and appear normal between epileptic seizures. Seizures usually stop occurring between 12 and 18 months of age. Affected foals may show signs of epilepsy anywhere from two days to six months from birth. Symptoms of the condition can be treated with traditional anti-seizure medications, which may reduce the severity of symptoms. Though the condition has been studied since 1985 at the University of California, Davis, the genetic mode of inheritance is unclear, though the cases studied were all of one general bloodline group. Some researchers have suggested that epilepsy may be linked in some fashion to Lavender Foal Syndrome due to the fact that it occurs in similar bloodlines and some horses have produced foals with both conditions.

Guttural Pouch Tympany (GPT) occurs in horses ranging from birth to 1 yr of age and is more common in fillies than in colts. It is thought to be genetic in Arabians, possibly polygenic in inheritance, but more study is needed. Foals are born with a defect that causes the pharyngeal opening of the eustachian tube to act like a one-way valve. Air can get in, but it cannot get out. The affected guttural pouch is distended with air and forms a characteristic nonpainful swelling. Breathing is noisy in severely affected animals. Diagnosis is based on clinical signs and radiographic examination of the skull. Medical management with NSAID and antimicrobial therapy can treat upper respiratory tract inflammation. Surgical intervention is needed to correct the malformation of the guttural pouch opening to provide a route for air in the abnormal guttural pouch to pass to the normal side and be expelled into the pharynx. Foals that are successfully treated should grow up to have fully useful lives.