Autosomal recessive ichthyosis in golden retriever dogs: distribution and frequency of the PNPLA1 mutant allele in different populations
Background – Ichthyoses are genodermatoses that mainly occur in dogs and humans. To date four genes have been identified in dogs; all are also involved in homologous human ichthyoses. A new autosomal recessive ichthyosis gene, PNPLA1, was recently identified in the golden retriever breed.
Objective – The aim of this study was to report the allele frequency and penetrance of the PNPLA1 gene mutation causing ichthyosis in golden retriever dogs from Europe, Australia and the USA.
Animals – Blood or cheek swab samples were collected from 1600 healthy or affected golden retriever dogs.
Methods – Golden retriever dogs were tested for the PNPLA1 mutation using a commercially available genetic test.
Results The results showed that in the French population of golden retrievers the mutation is almost fully penetrant. Moreover, the PNPLA1 mutation has a high frequency in France and is generally more frequent in European dogs compared to dogs in the USA and Australia, occurring in approximately 30% of homozygous affected dogs and 40% of heterozygous (carrier) dogs. Interestingly, the first estimates showed that the mutation frequency is lower in the USA and Australia.
Conclusion and clinical importance – A commercially available genetic test for the PNPLA1 mutation can be used to identify affected, homozygous healthy and carrier dogs, and helps with the diagnosis of mild ichthyosis cases. Moreover, it assists breeders to rationally decrease the frequency of the disease in golden retriever dogs.
Ichthyoses encompass a heterogeneous group of genodermatoses characterized by abnormal desquamation over the entire body due to defects of terminal keratinocyte differentiation and desquamation.1–3 This disease occurs in people and in animals (dogs, horses, cattle). Breed-associated ichthyoses have been identified in the Norfolk terrier (KRT10 gene4), Jack Russell terrier (TGM1 gene5) and cavalier King Charles spaniel (FAM83H gene6). Lamellar ichthyosis has been reported in the golden retriever breed,7–10 and the genetic cause has been recently identified.1 Affected golden retriever dogs have a homozygous insertion-deletion in the PNPLA1 gene that leads to a premature stop codon and a 74 amino-acid shortened PNPLA1 protein. This protein belongs to a family of enzymes regulating lipid metabolism.11 The consequence of this mutation in the homozygous state is an impairment of the cutaneous-barrier lipid metabolism that affects normal differentiation of keratinocytes and ultimately leads to a dysfunction of epidermal desquamation.
The goal of this study was to determine the frequency and penetrance of the PNPLA1 mutation in geographically distinct golden retriever populations using a recent commercially available genetic test.