Neuronal ceroid lipofuscinosis in a German Shorthaired Pointer associated with a previously reported CLN8 nonsense variant

Two littermate German Shorthaired Pointers, a male and a female, were adopted as puppies from an animal shelter. Both puppies developed normally until approximately 11 months of age when the male began to exhibit neurological signs including ataxia, vision loss, and behavioral changes indicative of cognitive decline. These signs increased in severity over time. The female remained neurologically normal and healthy. The affected dog was euthanized at approximately 21 months of age. Autofluorescent cytoplasmic storage bodies were detected in neurons in unstained tissue sections from the cerebellum, the cerebrum, and the retina. Electron micrographs of these storage bodies showed that they were membrane bound and that most contained tightly packed aggregates of membranous whorls along with a variety of other ultrastructural features. This ultrastructure, along with the autofluorescence and the clinical signs supported a diagnosis of neuronal ceroid lipofuscinosis (NCL). Unlike earlier investigated forms of canine NCL with causal alleles in ATP13A2, TPP1, MFSD8 and CLN5 that had autofluorescent cytoplasmic storage bodies in cardiac muscle, no autofluorescence was detected in cardiac muscle from the affected German Shorthaired Pointer. A 39-fold average coverage whole genome sequence indicated that the affected German Shorthaired Pointer was homozygous for the A allele of a G > A transversion at position 30,895,648 chromosome 37. This 37:30895648G > A mutation created a CLN8 termination codon that had been previously reported to cause NCL in a mixed breed dog with Australian Shepherd and Australian Cattle Dog ancestry. This nonsense allele was heterozygous in the clinically normal female sibling, while archived DNA samples from 512 other German Shorthaired Pointers were all homozygous for the reference allele. The affected German Shorthaired Pointer and the previously diagnosed mixed breed dog with the same nonsense mutation shaired an identical homozygous haplotype that extended for 4.41 Mb at the telomeric end of chromosome 37, indicating the both dogs inherited the nonsense mutation from a common ancestor.