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Genetic Disorders of Parson Russell Terriers

"We need to quit whispering about defects, and gossiping about defects, and instead set up a sound program that allows the standard selection procedures to go on so that we breed good dogs and avoid major defects."

-- Dr. George A. Padgett, DVM*

According to the Guide to Hereditary and Congenital Diseases in Dogs, the following genetic defects occur in Parson Russell Terriers:

Progressive ataxia: a condition where the animal's sense of coordination deteriorates.

Spinal cord demyelination (ataxia): an abnormality of the nervous tissue of the spinal cord leading to incoordination.

Factor X deficiency: a rare clotting disorder. An autosomal trait (affects both sexes).

Lens luxation: a condition where the lens in the eye is displaced into an abnormal position.

Myasthenia gravis: a syndrome characterized by muscle fatigue due to an autoimmune disease, which produces chemical abnormalities of the muscles and nerves. An enlarged esophagus called megaesophagus can result and causes regurgitation of food.

von Willebrand's disease: a type of bleeding disorder caused by defective blood platelet function. An autosomal trait affecting both sexes.

The Jack Russell Terrier Club of America lists 45 disorders that can occur in this breed:

EYE DISEASES

Cataract: Lens opacity which obscures vision and may cause blindness.

Congenital Cataract and Microphthalmia: Cataracts associated with a small eye globe.

Distichiasis: Abnormal location of eyelashes on the margin of the eyelid, causing irritation.

Glaucoma: Increased pressure in the globe which can damage the eye causing blindness.

Glaucoma (pigmentary): Glaucoma in which a dark pigment is also present in the globe and which apparently blocks the drainage angle.

Lens Luxation: Dislocation of the lens from its normal site behind the cornea (partial or complete).

Persistent Pupillary membranes: Failure of blood vessels in the anterior chamber to regress normally; there may be impaired vision or blindness.

Progressive Retinal Atrophy: Degeneration of the retinal vision cells which progresses to blindness.

Trichiasis: Abnormal placement of the eyelashes on the eyelid.

NEUROLOGIC DISEASES

Cerebellar Ataxia: Degeneration of the cortex of the cerebellum leading to a staggering gait; it may or may not progress.

Congenital Myasthenia Gravis: Severe muscle weakness may cause megaesophagus, fatigue and collapse due to a failure of neuromuscular transmission of nerve impulses.

Bilateral Deafness: Inability to hear; i.e., completely deaf, both ears affected.

Unilateral Deafness: Partial deafness; one ear affected.

Epilepsy: Seizures commonly called fits; they recur generally closer together.

Hydrocephalus: Accumulation of fluid in the brain causing severe pressure and degeneration of the brain.

Myelodysplasia: Lack of development of the brain causing incoordination.

Scotty Cramp: Muscle cramps triggered by excitement or exercise; you may see a rabbit hopping gait.

Trembling: Excessive shaking or trembling, particularly of the rear limbs.

Wobbler Syndrome: Abnormality of the neck vertebrae causing rear leg ataxia which may progress to paralysis.

Ceroid-Lipofuscinosis (ATP subunit C storage): Causes night blindness, confusion, unpredictable aggressiveness, and ataxia late in the course of the disease.

Congenital Vestibular Disease: Causes loss of balance/incoordination, dog appears to try to keep from falling.

HARD TISSUE DISEASES

Achondroplasia (Appendicular): Lack of normal development of the skeleton, particularly of the appendages (limbs); dwarfism.

Cleft Lip/Cleft Palate: A fissure in the roof of the mouth and upper lip, may be present together or separately.

Hemivertebra: Abnormal formation of the body of the vertebra, can cause posterior ataxia and paralysis. It causes the twisted tail in the screw tailed breeds.

Legg-Calve-Perthes: Aseptic necrosis of the head and neck of the femur, causes rear leg lameness.

Overshot: Upper jaw extends beyond the lower jaw.

Patellar Luxation: Poor development of structures holding patella (knee cap) in place, usually medial (inward) in small breeds.

Premature Closure of the Ulna: Ulna stops growing sooner than radius, causes wrists to turn in and front feet to turn out.

Radial Agenesis: Radius stops growing sooner than the ulna causing bowed front legs.

Undershot: Lower jaw extends beyond the upper jaw.

RESPIRATORY DISEASES

Laryngeal Hypoplasia: Failure of development of the larynx (voice box) causing breathing difficulties.

Tracheal Collapse: Improper formation of cartilaginous rings of the trachea causing mild to severe breathing problems.

Tracheal Hypoplasia: A small trachea due to improper development causes mild to severe breathing difficulties.

ALIMENTARY DISEASES

Oligodontia: Absence of most if not all teeth.

Pyloric Stenosis: Abnormally small opening between the stomach and the duodenum, prevents food from passing and causes sharp projectile vomiting.

BEHAVIORAL DISEASES

Aggressiveness (Excessive): Excessively assertive or forceful with other dogs or people, may attack or bite without reasonable provocation.

BLOOD DISEASES

Von Willebrand's Disease: Reduced factor VIII in the blood resulting in a prolonged bleeding time; may be mild, moderate, or severe and can cause death.

HEART DISEASES

Cardiomyopathy: Abnormality of heart muscle may cause edema of the lung, weakness at exercise and sudden death.

Patent Ductus Arteriosus: Failure of the fetal vessel between the aorta and pulmonary artery to close around the time of birth, causes heart murmurs, exercise weakness, and may cause death.

DERMATOLOGIC DISEASES

Inguinal Hernia: Outpouching of skin in the area of the inguinal ring which may contain viscera; a scrotal hernia is a type of inguinal hernia.

Umbilical Hernia: Outpouching of skin over belly button; may contain abdominal viscera, and regress spontaneously.

ENDOCRINE DISEASES

Diabetes Mellitus: Excessive sugar in the blood and urine due to a lack of insulin.

Growth Hormone Deficiency: Lack of production of or inability to use growth hormone causes dwarfism.

Hypothyroidism: Destruction of the thyroid gland due to an attack from the animal's own immune system causes rough, scaly skin; hair loss; weight gain.

REPRODUCTIVE DISEASES

Cryptorchidism: Absence of testicles due to retention in the abdomen or inguinal region, may be one or both sided or may slide in and out of the scrotum.

Hermaphrodite: Presence of gonadal tissue for both sexes due to the presence of a full compliment of both male and female chromosomes.

MISCELLANEOUS

Short or "High" Toes. This is a developmental condition where the outside toes, usually on one or both front feet, do not grow to normal length, giving the appearance of being a "short" or "high" toe that does not touch the ground when full the terrier is full grown.

Absence of premolars (one or more). Terrier is missing one or more pre-molars; does not have full denture.

* Dr. George A. Padgett, DVM is a veterinary pathologist at Michigan State University with a special interest in canine genetics. He recommends open record keeping and that breeders should report ALL evaluations to databases, including abnormal and normal. Without such open and honest reporting, we cannot expect to improve the genetic health of our breed as a whole.