In a recent Remuda magazine of the Texas Equine Veterinary Association, Dr. Lee Bulla from Progressive Molecular Diagnostics talks about hereditary diseases. He indicates they are genetic diseases caused by an abnormality in an individual's genome and these abnormalities may be minor or major. Those genetic diseases inherited from the parents are hereditary and those that are caused by acquired changes or mutations in a pre-existing gene or group of genes are genetic but not hereditary. These mutations can occur randomly or from exposure to environmental conditions.

There are several hereditary diseases for which tests are available in horses and one of these diseases is HERDA. HERDA, or hereditary equine regional dermal asthenia, is an autosomal recessive disorder that causes horses to have loose hyperextensible, fragile skin. The skin frequently tears away and results in non-healing wounds and there is no treatment.

Another hereditary condition is hyperkalemic periodic paralysis, which is an autosomal dominant disorder that causes an increase in blood potassium levels. Elevated potassium levels increase muscle contraction and affected horses exhibit violent muscle twitching, weakness and paralysis, sweating and prolapse of the third eyelid; horses are affected for life. Another inherited disease is glycogen branching enzyme deficiency and this syndrome occurs in quarter horses and paint horses. The disease results in muscle weakness and is fatal. There are several other genetic diseases that have been recognized in horses and fortunately DNA testing is available to recognize these diseases and find carriers to decrease recurrence of the diseases in the future.