Corneal epithelial inclusion cysts in 12 dogs (13 eyes) from 2010 to 2019: A multicentric retrospective study

OBJECTIVE

The aim of this retrospective study was to review the clinical data and outcomes of patients that suffered corneal epithelial inclusion cysts (CEIC). Animals studied Thirteen eyes from 12 dogs from multiple private practices in France and Belgium, with a strong clinical of CEIC were included in the study.

RESULTS

The mean age of affected dogs was 9 years. There were 9 females and 3 males. Two out of 12 dogs were Shih Tzus. Where identified, etiology was traumatic. Eleven dogs were affected unilaterally, 1 bilaterally. The cysts were single, bi-lobulated, or tri-lobulate, and cyst size ranged from 1 to 6 mm in diameter. Keratectomy alone was performed in seven cases, in conjunction with a conjunctival graft in three cases, a porcine small intestine mucosa graft in two cases, or an amniotic membrane graft in one case. Histopathologic findings were consistent in all eyes with a cyst located in the corneal stroma, composed of a nonkeratinized squamous epithelium delineating a lumen filled with neutrophils and desquamated epithelial cells. Surgery was curative in all cases but one, where the removal was incomplete and recurrence occurred several weeks after the surgery.

CONCLUSION

Corneal epithelial inclusion cysts is a rare condition, secondary to corneal trauma, which can be treated successfully with conventional keratectomy alone or in conjunction with graft procedures.

A Point Mutation in a lincRNA Upstream of GDNF Is Associated to a Canine Insensitivity to Pain: A Spontaneous Model for Human Sensory Neuropathies

Human Hereditary Sensory Autonomic Neuropathies (HSANs) are characterized by insensitivity to pain, sometimes combined with self-mutilation. Strikingly, several sporting dog breeds are particularly affected by such neuropathies. Clinical signs appear in young puppies and consist of acral analgesia, with or without sudden intense licking, biting and severe self-mutilation of the feet, whereas proprioception, motor abilities and spinal reflexes remain intact. Through a Genome Wide Association Study (GWAS) with 24 affected and 30 unaffected sporting dogs using the Canine HD 170K SNP array (Illumina), we identified a 1.8 Mb homozygous locus on canine chromosome 4 (adj. p-val = 2.5x10^-6). Targeted high-throughput sequencing of this locus in 4 affected and 4 unaffected dogs identified 478 variants. Only one variant perfectly segregated with the expected recessive inheritance in 300 sporting dogs of known clinical status, while it was never present in 900 unaffected dogs from 130 other breeds. This variant, located 90 kb upstream of the GDNF gene, a highly relevant neurotrophic factor candidate gene, lies in a long intergenic non-coding RNAs (lincRNA), GDNF-AS. Using human comparative genomic analysis, we observed that the canine variant maps onto an enhancer element. Quantitative RT-PCR of dorsal root ganglia RNAs of affected dogs showed a significant decrease of both GDNF mRNA and GDNF-AS expression levels (respectively 60% and 80%), as compared to unaffected dogs. We thus performed gel shift assays (EMSA) that reveal that the canine variant significantly alters the binding of regulatory elements. Altogether, these results allowed the identification in dogs of GDNF as a relevant candidate for human HSAN and insensitivity to pain, but also shed light on the regulation of GDNF transcription. Finally, such results allow proposing these sporting dog breeds as natural models for clinical trials with a double benefit for human and veterinary medicine.

In this study, we present a canine neuropathy characterized by insensitivity to pain in the feet, sometimes combined with self-mutilation described in four sporting breeds. This particular phenotype has the clinical hallmarks of human Hereditary Sensory Autonomic Neuropathies (HSAN). As we hypothesized that a monogenic recessive disorder was shared between these breeds, we performed a Genome Wide Association Study (GWAS) to search for the genetic causes and found one homozygous chromosomal region in affected dogs. High-throughput sequencing of this region allowed the identification of a point mutation upstream to the GDNF gene and located in the last exon of a long non-coding RNA, GDNF-AS. We confirmed the perfect association of this variant with the disease using more than 900 unaffected dogs that do not present with this mutation. Functional analyses (qRT-PCR, EMSA) confirmed that the mutation alters the binding of regulatory complex, leading to a significant decrease of both GDNF and GDNF-AS mRNA expression levels. This work in canine spontaneous forms of human neuropathies allowed the identification of a novel gene GDNF and its regulation mechanism, not yet described in human HSAN, opening the field of clinical trials to benefit both canine and human medicine.