J.L. Scheidt; M.L. Casal
Matthew J Ryan Veterinary Hospital, Section of Medical Genetics, University of Pennsylvania
Genetic skin diseases exist in many forms and occur in a wide range of dog breeds. A large portion of these diseases are inherited in a recessive pattern which means affected puppies can be born to seemingly normal parents. We are currently studying the skin disorders described below to elucidate the mechanism of disease and determine the mutation. Once the mutations are known, carrier tests can be developed and the mutant allele eliminated from the breeding population.
X-linked ectodermal dysplasia occurs in a variety of dog breeds, mice, cows, and humans. The disease is characterized by sparse or absent hair, a lack of sweat glands, and missing and/or malformed teeth. While ectodermal dysplastic humans have a 30% mortality rate due to hyperthermia from an inability to sweat, affected dogs are able to live quite normally as they pant to thermoregulate. Breeding studies have confirmed an x-linked recessive mode of inheritance.
Epidermolysis bullosa has been described in several dog breeds, sheep, pigs, cows, horses, and humans. In this disorder, minor trauma to the skin/epithelium causes blistering between the dermis and epidermis. The blisters later become evident on the surface of the skin as severe ulcerated lesions. There can be involvement of both skin and mucous membranes including those of the digestive tract and respiratory tract. The disease in our patients is inherited as an autosomal recessive trait.
Lupoid dermatosis or exfoliative cutaneous lupus erythematosus in the German Shorthair Pointer is marked by scaly and crusty lesions on the face, ears, legs, back, and in the male, the scrotum. Both male and female dogs are affected and are born to normal appearing parents, which suggests an autosomal recessive mode of inheritance.
Black hair follicular dysplasia in the Large Munsterlander is noted by grey and white fur at birth instead of black and white as expected in this breed. Over the first few months of life, the grey hair fall out and a bald spot persists for several months after that. While there appears to be no equivalent to this disease in other species, a large number of dog breeds can be affected. Pedigree analysis suggests an autosomal recessive mode of inheritance.
Ichthyosis (or fish scale skin disease) refers to an entire group of severe disorders of keratinization. Dogs with ichthyosis present with dry, extremely scaly, and pruritic skin. Both dominant and recessive forms of the disease have been described.