Hereditary Nasal Parakeratosis (HNPK)
Hereditary nasal parakeratosis (HNPK) is an inherited skin disorder that affects Labrador retriever dog breed. The disorder is characterized by development of crusts and fissures on the affected dog’s nose pad. Generally, parakeratosis is a benign skin condition which causes dry and scaly skin. The disease is not contagious and some forms of it are hereditary, just like hereditary nasal parakeratosis in Labrador retriever
Characteristics and symptoms
Stratum corneum is the upper layer of the skin. It is composed of dead cells and as such contributes greatly to skin’s barrier function. The cells in this layer lack nuclei and are high in keratin, an important protein for moisture retention, which keeps the skin flexible and strong. These cells are peeled off with time and replaced with new cells which are constantly being produced in the layer underneath.
In parakeratosis, the cells of stratum corneum retain their nuclei and are not completely keratinized, which causes loss of moisture and dry skin. With time, the condition progresses and dry scales start to form, which can result in deep cracks and fissures. Symptoms develop on the nose pad of affected dogs between 6 to 12 months of age. Fissures can be a source of inflammation and bacterial infection of the nasal skin. The condition can be painful and irritating, but the affected dogs are otherwise healthy. With the progression of the disorder, changes in the nose pigmentation occur, fading from its natural dark colour to a lighter pink shade.
There is no cure for hereditary nasal parakeratosis in Labrador retrievers. In order to preserve the dog’s quality of life, lifelong maintenance and treatment of condition will be needed.
The disorder is caused by a point mutation in SUV39H2 gene. The mutation causes a delay in the differentiation of the keratinocytes in the nasal epidermis. Hereditary nasal parakeratosis is inherited in an autosomal recessive pattern. Healthy parents of an affected puppy are obligate heterozygotes and therefore carry one mutant allele. Heterozygotes have no symptoms. When mating two carriers, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
Jagannathan et al., (2013) A Mutation in the SUV39H2 Gene in Labrador Retrievers with Hereditary Nasal Parakeratosis (HNPK) Provides Insights into the Epigenetics of Keratinocyte Differentiation. PLOS Genetics, 9, e100384.