Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats. It is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trait, with the exception of the Siberian Husky (inherited as an X chromosome linked trait) and the Bullmastiff (inherited as an autosomal dominant trait). There is no treatment. PRA is similar to retinitis pigmentosa in humans.
Progressive vision loss in any dog in the absence of canine glaucoma or cataracts can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia. Other symptoms include dilated pupils and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus, increased reflection from the tapetum due to thinning of the retina, and later in the disease a darkened, atrophied optic disc. Secondary cataract formation in the posterior portion of the lens can occur late in the disease. In these cases diagnosis of PRA may require electroretinography (ERG). For many breeds there are specific genetic tests of blood or buccal mucosa for PRA.
Types of PRA
Generalized PRA is the most common type and causes atrophy of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED).
Generalized PRA can be divided into either dysplastic disease, where the cells develop abnormally, and degenerative, where the cells develop normally but then undergo a damaging change. PRA can be further divided into affecting either rod or cone cells. Rod cells detect shape and motion, and function in dim light. Cone cells detect color and definition, and function in bright light.
Commonly affected breeds:
- Akita - Symptoms at one to three years old and blindness at three to five years old.
- Miniature longhaired Dachshund - Symptoms at six months old.
- Papillon - Slowly progressive with blindness at seven to eight years old.
- Tibetan Spaniel - Symptoms at three to five years old.
- Tibetan Terrier - Symptoms at less than one year old, often blind by two years old, and cataract formation by four years old.
- Samoyed - Symptoms by three to five years old.
This type of PRA has an early onset of severe vision loss. It is caused by a defect in the gene for cGMP-phosphodiesterase, which leads to retinal levels of cyclic guanosine monophosphate ten times normal.
Rod-cone dysplasia type 1
- Irish Setter - Rod cell response is nearly absent. Night blindness by six to eight weeks old, often blind by one year old.
- Sloughi - A DNA test can identify whether Sloughis have the mutated recessive gene. This has enabled breeders to breed away from PRA, and the disease is now rare in the breed.
Rod-cone dysplasia type 2
- Collie - Rod cell response is nearly absent. Night blindness by six weeks old, blind by one to two years old.
Rod-cone dysplasia type 3
- Norwegian Elkhound - Characterized by dysplasia of the rod cell unit and subsequent degeneration of the cone cell unit. Rod cell response is nearly absent. Night blindness by six months old, blind by three to five years old. Rod dysplasia has now been bred out of this breed.
Early retinal degeneration
- Norwegian Elkhound - Night blindness by six weeks old, blind by twelve to eighteen months old.
This is caused by an abnormal development of both rod and cone cells. Dogs are initially night blind and then progress to day blindness.
- Alaskan Malamute - Temporary loss of vision in daylight (hemeralopia) at eight to ten weeks old. There is a purely rod cell retina by four years old.
Progressive rod-cone degeneration (PRCD)
This is a disease with normal rod and cone cell development but late onset degeneration of the rod cells that progresses to the cone cells. It is inherited as an autosomal recessive trait and has been linked to the ninth canine chromosome.
This condition is linked to the X chromosome.
- Siberian Husky - Night blindness by two to four years old.
- Samoyed - More severe disease than the Husky.
- Abyssinian - Two forms exist. One is inherited as an autosomal dominant trait and has an early age onset. The other is inherited as an autosomal recessive trait and has a middle age onset.
- Early onset PRA has also been reported in the domestic shorthaired cat and Persian. The Siamese also likely has a hereditary form of PRA. Despite belief among breeders to the contrary, there is apparently no link between coat color in Persians and the development of PRA.
Central progressive retinal atrophy (CPRA)
CPRA is also known as retinal pigment epithelial dystrophy (RPED). The cause of this condition is the loss of the retinal pigment epithelium's ability to effectively process the photoreceptor outer segment (POS) and subsequent accumulation of POS material in the RPE and loss of function. The loss of function of the RPE leads to photoreceptor degeneration. Vitamin E deficiency may play a role in the development of CPRA. It is characterized by accumulation of pigment spots in the retina surrounded by retinal atrophy and a mottled appearance of the pigmented nontapetal fundus. The pigmented spots eventually coalesce and fade as the atrophy of the retina increases. It is an inherited condition (in the Labrador Retriever it is inherited as an autosomal dominant trait with variable penetrance). CPRA occurs in older dogs. Peripheral vision is retained for a long time. Vision is better in low light and better for moving or distant objects. Not all affected dogs go blind. Secondary cataracts are common.
Commonly affected breeds
It can also be found in the poodle varieties
Hereditary retinal dysplasia
There is another retinal disease in Briards known as hereditary retinal dysplasia. These dogs are night blind from birth, and day vision varies. Puppies affected often have nystagmus. It is also known as lipid retinopathy.
Welcome to Microbiology Spring 2010
T/F 8:30-9:40 Irene Newton
Laboratory Instructors: Tucker Crum and Janet McDonough
Labs: L302- Tues. 12:30-4 McDonough; Wed. 2:15-5:45 Crum
The labs for BISC 209, Microbiology, are designed to familiarize you with how research investigation in microbiology is designed, performed and communicated. Over the course of the semester, you will investigate the diversity and identity of enviromental microbes and assess their impact. Your job will be to think like microbiologists when designing and executing experiments to identify and characterize bacteria from the soil. Your instructor does not know what's in the specimen you will collect; therefore, the successful outcome of the investigation is in your hands alone. You will learn to take ownership of the project, perform the experiments properly, keep good records of your results, and to communicate effectively the results and conclusions of your work, both orally and in written reports.
These are ambitious goals for an introductory microbiology course. Since this course only has one prerequisite, BISC110, we expect that some of you will have had extensive experience in cellular biology and research investigation, but that just as many of you will have had little previous investigative research experience or related course work. Our goal is to bring everyone up to a working level of expertise in the tools and techniques of microbiologists and then to build our invesgation from there.
GENERAL LABORATORY DIRECTIVES
1. Please familiarize yourself in advance with the exercise(s) to be performed. Before coming to lab each week, read thoroughly the exercise and any accompanying technical material. In your lab notebook outline or create a flow chart of any experimental procedures to be performed, leaving blank space for rethinking or reworking each.
2. Your instructor will give preliminary instructions and/or demonstrations at the beginning of each lab. Please make sure that you understand the purpose and execution of each exercise and ask any clarifying questions at that time. Do not attempt to start work before receiving instructions.
3. Accurate and detailed results are to be recorded in a lab notebook. Draw all of your microscopic findings. In making your drawings, do not attempt to draw everything in the microscopic field; simply select a few representative specimens (i.e. a few cells), their arrangements or relevant sub-structures and label everything clearly, including total magnification, how the specimen was processed, and the goal of the procedure. Please keep your lab notebook up to date and be prepared to hand it in at any time.
4. Creating a permanent slide collection is helpful. Save a representative slide in your slide box after each exercise that includes staining or microsopy. Make sure all your slides are properly labeled. This collection will prove useful in reviewing or analyzing the body of your work.
POLICY ON LATE ASSIGNMENTS AND LAB MAKE-UP:
Make up of laboratory work is very difficult and must be avoided except for extreme illness or serious family emergeny.
All late work and missed examinations, whether or not excused, must be submitted within the week. All late work is subject to a penalty of 5% per day late and is not accepted for point credit after one week.
Links to Labs