Altered gene expression in the liver and small intestine of horses with equine neuroaxonal dystrophy

Background Equine neuroaxonal dystrophy/degenerative myeloencephalopathy (eNAD/EDM) is the second most common diagnosis of spinal ataxia in horses in the United States. The disease develops due to a combination of vitamin E deficiency and an unknown genetic risk factor(s), and there currently is no effective treatment. Objectives We performed transcriptomic profiling of the liver and small intestine of horses with and without eNAD/EDM, as both tissues are the main locations for absorption, metabolism, and delivery of vitamin E to the nervous system. Study Design Case‐control exploratory study. Methods Postmortem‐confirmed cases of eNAD/EDM were compared to horses that had eNAD/EDM excluded at necropsy and were euthanised for either non‐neurologic disease or for cervical vertebral compressive myelopathy (CVCM), which were included due to the logistical challenge of obtaining control horses that have undergone a full neuropathologic review. RNA was isolated from frozen liver (eNAD/EDM n = 34, non‐eNAD/EDM n = 27) and small intestinal (eNAD/EDM n = 18, non‐eNAD/EDM n = 18) samples. Gene expression was compared between groups using a linear model, adjusting for age, breed, and RNA integrity score. Results No genes were differentially expressed at p FDR <0.05 in either tissue between eNAD/EDM and non‐eNAD/EDM horses. However, one of the top genes, NPC1L1 , was upregulated in the liver of horses with eNAD/EDM (log 2 FC = 0.93, p unadjusted < 0.05). In the small intestine, 747 genes were differentially expressed ( p unadjusted <0.05), including two genes that were markedly downregulated in both tissues. These genes have high sequence homology to LGALS9 . Main Limitations Non‐neurologic control numbers were limited. Tissues were collected at the time of euthanasia and therefore may not capture biological processes that were occurring at the time the neurological damage developed. Conclusions Processes related to both cholesterol transport and autophagy may be altered in horses with eNAD/EDM. Two new candidate genes for eNAD/EDM, NPC1L1 and LGALS9 , were identified for further investigation.