Congenital ichthyosis in American Bulldogs

Congenital ichthyosis is an inherited autosomal recessive skin disorder in American Bulldogs. In the affected dogs, the outermost layer of the skin (the stratum corneum) is not formed correctly. This layer is the final product of skin cornification process.  The stratum corneum consists of overlapping layers of keratinocytes (corneocytes) encased in bilayers of lipid.  It plays an important role as a primary protective barrier against entry of pathogens, allergens and other foreign matter into the body. Further, thanks to the bilayers of lipid and its hydrophobic properties it helps to ensure skin hydration.

The typical signs of congenital ichthyosis are recognizable as early as 1 to 2 weeks of age. Compared to normal littermates, the affected dogs have a dishevelled pelage and the glabrous skin of the abdomen is reddened and discoloured light brown resulting in wrinkly appearance (Mauldin, 2013).  The clinical signs either do not change into adulthood or can worsen slightly. Complications due to infection caused by fungi of Malassezia genus, naturally found on the skin surface of many animals, happen quite often. However, the main problem is the impairment of the skin barrier function as nothing can combat the   Malassezia overgrowth.  Together with the growth of the fungi, the inflammation of acoustic duct and itching infection of skin folds or paws develop and even hyperkeratosis (excessive skin cornification) may develop in adult dogs.

The congenital ichthyosis is caused by mutations in NIPAL4 gene that encodes for the ichthyin protein having an essential effect on the lipid metabolism in the skin. A deletion of one base pair g.52737379delC was localized in exon 6. The frequency of occurrence of this disease is 23.2 % (Mauldin et al., 2015).

Congenital ichthyosis is autosomal recessive inherited disease. That means the disease affects dogs with P/P (positive / positive) genotype only. The dogs with P/N (positive / negative) genotype are clinically without any symptom. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

.

Reference:

Casal ML, Wang P, Mauldin EA, Lin G, Henthorn PS (2017) A Defect in NIPAL4 Is Associated with Autosomal Recessive Congenital Ichthyosis in American Bulldogs. PLoS ONE 12(1): e0170708. https://doi.org/10.1371/journal.pone.0170708

Mauldin, E.A., Wang, P., Evans, E., Cantner, C.A., Ferracone, J.D., Credille, K.M., Casal, M.L. : Autosomal Recessive Congenital Ichthyosis in American Bulldogs Is Associated With NIPAL4 (ICHTHYIN) Deficiency. Vet Pathol 52:654-62, 2015.

Mauldin, E.A. : Canine ichthyosis and related disorders of cornification. Vet Clin North Am Small Anim Pract 43:89-97, 2013.