From Mutation to Manifestation: Evaluation of a PKLR Gene Truncation Caused by Exon Skipping in a Schnauzer Terrier.

A five-month-old, intact, female Miniature Schnauzer Terrier presented with persistent severe hemolytic anemia following an initial infection with Babesia gibsoni and B. vogeli. Despite treatment, severe regenerative anemia persisted, and the patient was unresponsive to antibiotics, as well as antiprotozoal and immunosuppressive agents. Subsequent laboratory tests and diagnostic imaging ruled out persistent hemiparasitic infections, immune-mediated diseases, or neoplasia. Genomic DNA and cDNA sequencing identified a point mutation in exon 8 (g.4978G>T) that introduced a premature termination codon, leading to exon 8 skipping and a single-nucleotide deletion at the exon 7-intron 7 boundary (c.966delG) during splicing. A 151 bp deletion in the coding region of the patient's PKLR cDNA was subsequently detected, which ultimately resulted in pyruvate kinase deficiency. This missplicing results in a premature stop codon and disrupts PKLR tetramer formation owing to the partial loss of domain A and complete loss of domain C. Enzyme activity assays confirmed a complete loss of function in the mutant PKLR protein compared to the wild-type, supporting the causal role of this deletion in non-spherocytic hemolytic anemia. This is the first report as per our knowledge documenting truncated PKLR variant in a dog, and notably, the first such case in a Miniature Schnauzer breed.