Health & Nutrition

Canine Color Genetics

BIRTH DEFECTS: CLEFT PALATE WHY AND WHEN

Breeders' Toolbox Library

DNA Testing Available for Norfolk Terrier Ichthyosis" Kelly Credille, DVM, PhD and Robert Dunstan, DVM, MS. Researchers have found the gene that causes it and they now have a test to determine if dogs are carriers,clear, and confirm affected. In 1999 the Comparative Dermatology Laboratory in the College of Veterinary Medicine at Texas A&M University was funded by the Morris Animal Foundation to study an inherited skin disease of the Norfolk Terrier. This disease was brought to the attention of Dr. Bob Dunstan, director of the Dermatology Lab, by a breeder concerned about a mild skin condition affecting one of their dogs. Dr. Dunstan recognized that this canine disease is very similar to a rare inherited skin disease of people called "epidermolytic hyperkeratosis", often included in a family of diseases characterized by scaly or dry skin known as the "ichthyoses". These diseases are associated with a defect in structural proteins of the skin known as keratins. After three years of research that involved the sequencing of three keratin genes, we discovered that keratin 10, a protein important for the integrity of the outer layers of the skin, is mutated in dogs that have this condition. This disease is inherited in a recessive manner in Norfolk Terriers, meaning that two mutated genes are needed to produce clinical symptoms. If a dog has only one copy of the mutated gene, the dog appears normal but is called a carrier because if it mates with another carrier and the defective gene from the sire and the dam are passed to an offspring, the puppy will have the disease. The disease is present at birth but the signs are subtle. You may note that the skin of affected puppies is more grey than pink in color. In our experience, as dogs age the skin changes progress but are always mild. Dandruff and darkening of the skin are the main symptoms in adults, signs that can also occur in a number of skin diseases. There may be a greasy texture to the skin or hair but hair loss is not a feature of this condition. You may note the formation of very thin, fragile blisters in areas that are lightly rubbed. At this time we do not have a good idea how prevalent this altered gene is in the Norfolk Terrier population. The number of affected dogs appears to be low and this suggests the mutation may not be common; however, if a popular sire was a carrier and his offspring were inbred, it is possible that the disease-causing gene could be present in many Norfolk Terrier kennels. In addition, the symptoms of this skin disease are mild and are not very specific, thus some affected dogs may not be recognized. Because we have identified the specific mutation causing this condition, our lab can now perform a simple DNA test to definitively identify Norfolk Terriers that are clear, carriers or are affected with this skin disease. To date, we have diagnosed this disease in seven dogs by examining skin biopsy samples and have subsequently confirmed this diagnosis at the molecular level with the DNA test. We have also confirmed the carrier status of parents of affected dogs and some littermates of affected dogs. All testing will be confidential and our charge will be $85 per dog

"How Are Defects Inherited?