Neuroaxonal dystrophy in Merino-Border Leicester × Polled Dorset lambs

Compound heterozygous PLA2G6 loss-of-function variants in Swaledale sheep with neuroaxonal dystrophy

Sporadic occurrences of neurodegenerative disorders including neuroaxonal dystrophy (NAD) have been previously reported in sheep. However, so far no causative genetic variant has been found for ovine NAD. The aim of this study was to characterize the phenotype and the genetic aetiology of an early-onset neurodegenerative disorder observed in several lambs of purebred Swaledale sheep, a native English breed. Affected lambs showed progressive ataxia and stiff gait and subsequent histopathological analysis revealed the widespread presence of axonal spheroid indicating neuronal degeneration. Thus, the observed clinical phenotype could be explained by a novel form of NAD. After SNP genotyping and subsequent linkage mapping within a paternal half-sib pedigree with a total of five NAD-affected lambs, we identified two loss-of-function variants by whole-genome sequencing in the ovine PLA2G6 gene situated in a NAD-linked genome region on chromosome 3. All cases were carriers of a compound heterozygous splice site variant in intron 2 and a nonsense variant in exon 8. Herein we present evidence for the occurrence of a familial novel form of recessively inherited NAD in sheep due to allelic heterogeneity at PLA2G6. This study reports two pathogenic variants in PLA2G6 causing a novel form of NAD in Swaledale sheep which enables selection against this fatal disorder.

A Missense Mutation in the Vacuolar Protein Sorting 11 (VPS11) Gene Is Associated with Neuroaxonal Dystrophy in Rottweiler Dogs

Canine neuroaxonal dystrophy (NAD) is a recessive, degenerative neurological disease of young adult Rottweiler dogs (Canis lupus familiaris) characterized pathologically by axonal spheroids primarily targeting sensory axon terminals. A genome-wide association study of seven Rottweilers affected with NAD and 42 controls revealed a significantly associated region on canine chromosome 5 (CFA 5). Homozygosity within the associated region narrowed the critical interval to a 4.46 Mb haplotype (CFA5:11.28 Mb – 15.75 Mb; CanFam3.1) that associated with the phenotype. Whole-genome sequencing of two histopathologically confirmed canine NAD cases and 98 dogs unaffected with NAD revealed a homozygous missense mutation within the Vacuolar Protein Sorting 11 (VPS11) gene (g.14777774T > C; p.H835R) that was associated with the phenotype. These findings present the opportunity for an antemortem test for confirming NAD in Rottweilers where the allele frequency was estimated at 2.3%. VPS11 mutations have been associated with a degenerative leukoencephalopathy in humans, and VSP11 should additionally be included as a candidate gene for unexplained cases of human NAD.

Primary, congenital neuroaxonal dystrophy with peripheral nerve demyelination in Merino-Border Leicester × Polled Dorset lambs

CASE REPORT

Clinicopathological features of neuroaxonal dystrophy (NAD) in newborn, Merino-Border Leicester × Polled Dorset lambs are described. The affected lambs were unable to walk at birth and microscopic examination of brainstem and spinal cord sections revealed bilaterally symmetrical accumulations of axonal swellings (spheroids), the histological hallmark of primary NAD. The neurological deficit was also exacerbated by myelin loss and secondary axonal degeneration, particularly in the spinal cord and sciatic nerves, but also, to a more limited extent, in brainstem and spinal nerves.

CONCLUSIONS

Although lambs previously diagnosed with NAD have ranged in age from 2 days to 7 months, this is believed to be the first report of congenital NAD in this species. Moreover, the present cases are the only ones in which peripheral nerve demyelination has been found.

Axonal spheroids in ovine neuroaxonal dystrophy are immunopositive to kinesin and dynein

Neuroaxonal dystrophy (NAD) is a neurologic disorder of sheep characterized by accumulation of numerous axonal swellings (spheroids) in specific regions of the brainstem and spinal cord. Disruption of axonal transport, which is driven in anterograde and retrograde directions by the molecular motors, kinesin and dynein, respectively, is believed to contribute to spheroid development. Accordingly, we examined spheroids in ovine NAD cases immunohistochemically for kinesin and dynein and found both motor proteins, with dynein more strongly expressed than kinesin. Further investigations of the kinesin and dynein content of axonal spheroids in NAD, and other neurodegenerative disorders of domestic animals, could assist in better understanding the pathogenesis of these diseases.

Axonal Spheroid Accumulation In the Brainstem and Spinal Cord of A Young Angus Cow with Ataxia

CASE REPORT

An 18-month-old Angus cow presented with rapidly developing ataxia and subsequently died. The finding of large numbers of axonal spheroids in brainstem nuclei and spinal cord grey matter, bilaterally symmetrical in distribution, was consistent with a histopathological diagnosis of neuroaxonal dystrophy (NAD). Most of the axonal swellings were immunopositive to amyloid precursor protein, suggesting that interruption to axonal flow was important in their genesis.

CONCLUSIONS

The topographical distribution of axonal spheroids in the brain and spinal cord in this bovine case closely resembled that found in the ovine neurodegenerative disorder termed NAD, in which axonal swellings are the major pathological feature. This appears to be the first reported case of this type of NAD in cattle. The aetiology of the spheroidal aggregations in this case was not determined. There was no evidence from the case history or neuropathology to indicate whether the axonal spheroids in this case involved an acquired or heritable aetiology.