A Missense Change in the ATG4D Gene Links Aberrant Autophagy to a Neurodegenerative Vacuolar Storage Disease

Abstract

Inherited neurodegenerative disorders are debilitating diseases that occur across different species. We have performed clinical, pathological and genetic studies to characterize a novel canine neurodegenerative disease present in the Lagotto Romagnolo dog breed. Affected dogs suffer from progressive cerebellar ataxia, sometimes accompanied by episodic nystagmus and behavioral changes. Histological examination revealed unique pathological changes, including profound neuronal cytoplasmic vacuolization in the nervous system, as well as spheroid formation and cytoplasmic aggregation of vacuoles in secretory epithelial tissues and mesenchymal cells. Genetic analyses uncovered a missense change, c.1288G>A; p.A430T, in the autophagy-related ATG4D gene on canine chromosome 20 with a highly significant disease association (p = 3.8 x 10-136) in a cohort of more than 2300 Lagotto Romagnolo dogs. ATG4D encodes a poorly characterized cysteine protease belonging to the macroautophagy pathway. Accordingly, our histological analyses indicated altered autophagic flux in affected tissues. The knockdown of the zebrafish homologue atg4da resulted in a widespread developmental disturbance and neurodegeneration in the central nervous system. Our study describes a previously unknown canine neurological disease with particular pathological features and implicates the ATG4D protein as an important autophagy mediator in neuronal homeostasis. The canine phenotype serves as a model to delineate the disease-causing pathological mechanism(s) and ATG4D function, and can also be used to explore treatment options. Furthermore, our results reveal a novel candidate gene for human neurodegeneration and enable the development of a genetic test for veterinary diagnostic and breeding purposes.

Initial characterization of stiff skin‐like syndrome in West Highland white terriers

“…Whole genome sequencing information at 30× coverage was obtained using an HiSeq3000 instrument (Illumina, San Diego CA, USA) and 2 × 150‐bp paired‐end reads. The sequence data analysis was performed as described previously . The sequence data of the affected WHWTs were compared to a boxer reference genome and 172 control dogs of various breeds.…”

Neuronal vacuolation and spinocerebellar degeneration associated with altered neurotransmission

“…Intraneuronal vacuoles with a similar distribution pattern as in NVSD have been recently reported in a spontaneous neurodegenerative disease in Lagotto Romagnolo dogs associated with abnormal autophagosome maturation and a mutation in the autophagy-related gene ATG4D [28]. There are a variety of studies, either in transgenic mice or canine hereditary ataxias providing compelling evidence that a primary defect in autophagy can induce neurodegenerative disease.…”

Focal epilepsy with fear‐related behavior as primary presentation in Boerboel dogs

“…A neurodegenerative storage disease characterized by progressive cerebellar ataxia and profound vacuolization of neuronal cytoplasm affecting both the peripheral and central nervous system (especially the cerebellar cortex) has been described in Lagotto Romagnolo dogs. The disease is associated with a missense variant in the autophagy‐related ATG4D gene . Lastly, abundant small neuronal cytoplasmic vacuoles have been reported in animals with viral infections, intoxications, and lysosomal storage diseases such as fucosidosis and GM1‐gangliosidosis .…”