Jack Russell Terrier Club of America - JRTCA Preserve, Protect and Work the Jack Russell Terrier

Disorders in Jack Russells: A Brief Definition


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

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

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

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

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

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

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

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

  9. Trichiasis: Abnormal placement of the eyelashes on the eyelid.


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

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

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

  13. Unilateral Deafness: Partial deafness; one ear affected.

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

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

  16. Myelodysplasia: Lack of development of the brain causing incoordination.

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

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

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

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

    c. Ceroid-Lipofuscinosis: Causes visual impairment, confusion, erratic temperaments, and apparent loss of memory for previously learned tasks.

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


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

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

  22. 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.

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

  24. Overshot: Upper jaw extends beyond the lower jaw.

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

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

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

  28. Undershot: Lower jaw extends beyond the upper jaw.


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

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

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


  32. Oligodontia: Absence of most if not all teeth.

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


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


  35. 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.


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

  37. 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.


  38. 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.

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


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

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

  42. 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.


  43. 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.

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


  45. 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.

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