A PNPLA8 frameshift variant in Australian shepherd dogs with hereditary ataxia

Abstract

Hereditary ataxias are common among canine breeds with various molecular etiology. We identified a hereditary ataxia in young-adult Australian Shepherd dogs characterized by uncoordinated movements and spasticity, worsening progressively and leading to inability to walk. Pedigree analysis suggested an autosomal recessive transmission. By whole genome sequencing and variant filtering of an affected dog we identified a PNPLA8:c.1169_1170dupTT variant. This variant, located in PNPLA8 (Patatin Like Phospholipase Domain Containing 8), was predicted to induce a PNPLA8:p.(His391PhefsTer394) frameshift, leading to a premature stop codon in the protein. The truncated protein was predicted to lack the functional patatin catalytic domain of PNPLA8, a calcium-independent phospholipase. PNPLA8 is known to be essential for maintaining mitochondrial energy production through tailoring mitochondrial membrane lipid metabolism and composition. The Australian Shepherd ataxia shares molecular and clinical features with Weaver syndrome in cattle and the mitochondrial-related neurodegeneration associated with PNPLA8 loss-of-function variants in humans. By genotyping a cohort of 85 control Australian Shepherd dogs sampled in France, we found a 4.7% carrier frequency. The PNPLA8:c.[1169_1170dupTT] allele is easily detectable with a genetic test to avoid at-risk matings.

Keywords: Weaver syndrome; canine; cattle; mitochondria; neurodegeneration; patatin domain; phospholipase.

FIGURE 1

Hereditary ataxia in a young‐adult Australian shepherd is governed by a recessive PNPLA8:C.[1169_1170dupTT] frameshift allele. (a, b) ataxia in two affected dogs. (a) Picture of an affected Australian shepherd dog showing wide‐based stance (static ataxia, yellow arrows). (b) Picture of the proband dog showing bunny‐hopping (dynamic ataxia, red arrows). (c) Autosomal recessive inheritance pattern of the disease. Partial pedigree tree of the proband family. Circles represent females and squares represent males. Affected dogs are depicted with fully filled symbols and the proband is shown with an arrow. When available, the result of the genotyping assay for the PNPLA8:C.1169_1170dupTT variant is mentioned: +, wild‐type allele; dup, mutant allele. Two affected female littermates were euthanized and no DNA samples were available (barred symbols). (d) The canine frameshift variant is predicted to produce a truncated PNPLA8 protein. Alignment of protein sequences of PNPLA8 translated from the wild‐type (WT) alleles reported in human, cow and dog and from mutant alleles of Weaver cow and ataxic Australian shepherd dog. Residues that have been evolutionarily conserved are represented by dots in the animal sequences, compared with the reference human sequence. Non‐conserved residues are represented by letters in animal sequences, while dashes represent deletions. The functional patatin domain of PNPLA8 is depicted in green. It starts with amino acid number 445 and ends with amino acid number 640 in human PNPLA8. Red arrow heads point out the two conserved serin 484 (S484) and aspartic acid 627 (D627) residues of the phospholipase catalytic dyad (Appendix S1)