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Cone Rod Dystrophy type 2         CRD2 Test       Code 203


For breeds: American Pit Bull Terrier

What is crd2? crd2 is one of several cone rod dystrophies that have been recognized in multiple breeds of dogs.  All forms of CRD are characterized by the initial loss of cones, the cells in the retina that are responsible for vision in bright light/daylight, followed by the degeneration of rods, the retinal cells that operate during night vision. Clinical symptoms of crd2 are typically evident early in a pupís life and the severe retinal degeneration that characterizes this disease usually results in complete blindness by 1 year of age.

What breeds of dog carry crd2? To date, the mutation causing crd2 has only been observed in one breed of dog, the APBT.  Researchers were somewhat surprised to learn that this mutation was not the cause of a very similar disease that occurs in a closely related breed, the American Staffordshire Terrier (1).  The Am.Staff.ís disease has been termed Cone Rod Dystrophy 1 (crd1) and later renamed crd1/ rcd1b.  Because Pit Bulls and Am. Staffs share many common ancestors and interbreeding among these and other bull-type dogs is quite common, OptiGen will accept samples from any of these breeds for crd2 testing.  Owners of pedigreed dogs that have been diagnosed by a veterinary ophthalmologist as having retinal degenerations (e.g. PRA or CRD) are encouraged to contact OptiGen to inquire about our Free DNA testing/Research program (http://www.optigen.com/opt9_research.html).

Breeding recommendations: crd2 is inherited in an autosomal recessive mode, meaning that offspring need to inherit the mutation from both parents (i.e. have two copies of/be homozygous for the mutation) for disease to occur. Carriers of one copy of the mutation (heterozygotes) will not show disease but they can pass the mutation on to their offspring.  In order to avoid producing crd2-affected offspring, at least one dog of any breeding pair should be homozygous Normal/Clear (See chart below).

 

Expected results for breeding strategies using the
OptiGen crd2 test
Parent 1
Genotype
Parent 2 Genotype
Normal/ClearCarrierAffected
Normal/ClearAll = Normal/Clear1/2 = Normal/Clear
1/2 = Carrier
All = Carrier
Carrier1/2 = Normal
1/2 = Carrier
1/4 = Normal/Clear
1/2 = Carrier
1/4 = Affected
1/2 = Carrier
1/2 = Affected
Affected All = Carrier
1/2 = Carrier
1/2 = Affected
All = Affected

 

Research leading to the discovery of the crd2 mutation was conducted at Cornell University and the University of Pennsylvania, with collaboration by OptiGen. 

References: 

1.  Goldstein O, Mezey JG, Schweitzer PA, Boyko AR, Gao C, Bustamante CD, Jordan JA, Aguirre GD, Acland GM. 2013. IQCB1 and PDE6B mutations cause similar early onset retinal degenerations in two closely related terrier dog breeds. Invest Ophthalmol Vis Sci. Oct 25; 54(10):7005-19.

 

 


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Tel: 607 257 0301 · Fax: 607 257 0353 · email: genetest@optigen.com or optigen@clarityconnect.com
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