Canine Cone Degeneration
Achromatopsia, also called rod monochromacy, is an inherited condition characterized by decreased visual acuity, absent color vision, photophobia, and nystagmus. Achromatopsic humans report that colored objects appear in shades of gray. Two forms of this condition have been described in humans.
Complete achromatopsia is a congenital vision disorder in which all cone function is absent or severely diminished. The incomplete (atypical) form is defined as dyschromatopsia, in which the symptoms are similar to those of the complete achromatopsia (typical) form but with less visual dysfunction.
In dogs, the condition is referred to as canine cone degeneration. Cones are light-sensitive retinal photoreceptors in the vertebrate eye. Although cone cells account for only 5% of photoreceptors, they are essential for high-acuity daylight-vision and discrimination of color. Canine cone degenration is caused by mutation in the canine GNGB3 gene. In the Alaskan Malamute, the complete gene is deleted, while in the German Shorthaired Pointer, the gene has substituted amino acids.
The disorder has also been described in the Miniature Poodle and other breeds of dogs. Affected dogs do not lose eyesight and remain normal throughout life.2 Puppies develop day-blindness and photophobia between 8 and 12 weeks. You will know that a dog has day-blindness when you notice him colliding with obstacles in daylight. Symptoms are present only in bright light, while vision in dim light is normal.
Acromegaly
Acromegaly is a type of musculoskeletal disorder marked by progressive enlargement of the head, face, hands, and feet due to excessive secretion of growth hormone (GH) somatotropin. Chronic overproduction of growth hormone in man and cat is most often caused by a GH-producing tumor of the pituitary gland. In dogs the usual cause is quite different and the disorder is reversible.
Signs include gait abnormalities consisting of chronic progressive stiffness and rigidity. Other symptoms are increased appetite associated with weight gain, excess urination (polyuria) and increased thirst (polydipsia), excessive panting, progressive thickening of the skin, prominent skin folds, noisy breathing and enlargement of the tongue. A definitive diagnosis requires measurement of increased plasma growth hormone or insulin-like growth factor 1 (IGF-1) concentrations in suspected cases.
Acromegaly is encountered in intact female dogs that were treated with progestagens to prevent estrus and in dogs during diestrus, or period of sexual inactivity. Progestagen withdrawal and/or ovariohysterectomy will result in a reduction of plasma GH and GH-dependent insulin-like growth factor concentrations and appreciable clinical improvement.
Acromegaly is encountered in intact female dogs that were treated with progestagens to prevent estrus and in dogs during diestrus, or period of sexual inactivity. Progestagen withdrawal and/or ovariohysterectomy will result in a reduction of plasma GH and GH-dependent insulin-like growth factor concentrations and appreciable clinical improvement.
Feline acromegaly is most commonly caused by a functional pituitary tumor. Definitive diagnosis can be difficult because of the gradual disease onset, subtle clinical signs, unavailability of relevant laboratory tests, and client financial investment. The most significant clinical finding of acromegaly is the presence of insulin-resistant diabetes mellitus. Diagnosis is currently based upon brain imaging and measurement of serum GH and/or insulin-like growth factor-1 concentrations. Definitive treatment in cat is not well described, but radiation therapy appears promising.