A missense mutation in damage-specific DNA binding protein 2 is a genetic risk factor for ocular squamous cell carcinoma in Belgian horses

BACKGROUND

Belgian horses are commonly affected with ocular squamous cell carcinoma (SCC), the most common cancer of the equine eye. A missense mutation in damage-specific DNA binding protein 2 (DDB2 c.1013C>T, p.Thr338Met) has been established as a recessive genetic risk factor for ocular SCC in the Haflinger breed. A sample of Belgian horses with unknown SCC phenotype was shown to possess this variant at a similar frequency to the Haflinger breed. Retrospective studies indicate that chestnut coat colour may predispose to the development of SCC.

OBJECTIVES

To determine if DDB2 c.1013C>T is a risk factor for ocular SCC in a strictly phenotyped sample of Belgian horses. To investigate associations between coat colour loci genotypes and ocular SCC.

STUDY DESIGN

Retrospective and prospective case identification, genetic investigation.

METHODS

Genomic DNA was isolated from blood, hair or formalin-fixed paraffin-embedded tissue from 25 Belgian horses with histologically confirmed ocular SCC and 18 unaffected Belgian horses. Association testing of 34 single nucleotide variants from 11 genomic loci and genotyping for DDB2 c.1013C>T and coat colour alleles were performed. Exons of DDB2 were sequenced in four cases and two controls. Associations were analysed by Chi-square or Fisher's exact tests and relative risk was calculated.

RESULTS

Homozygosity for DDB2 c.1013C>T was significantly associated with ocular SCC (P = 7.4 × 10^-7 ). Seventy-six per cent of affected horses were homozygous for the variant. Relative risk for homozygous horses developing SCC was 4.0 (P = 1.0 × 10^-4 ). Sequencing DDB2 did not identify a variant more concordant with disease phenotype. An association between disease and coat colour loci was not identified.

MAIN LIMITATIONS

Phenotyping was determined at a single timepoint. Each included horse genotyped as chestnut, so association with this MC1R variant could not be investigated.

CONCLUSIONS

A missense variant, DDB2 c.1013C>T, p.Thr338Met, is a risk factor for ocular SCC in Belgian horses. A genetic risk test is commercially available.

Identification and management of ocular lipid deposition in association with hyperlipidaemia in captive moray eels, Gymnothorax funebris Ranzani, Gymnothorax moringa (Cuvier) and Muraena retifera Goode and Bean

Ocular lipid deposition and its surgical management and possible association with systemic hyperlipidaemia in captive moray eels are described. Ophthalmologic examinations, haematology and plasma biochemistry analyses were performed on an initial population of captive moray eels (n=10): green moray, Gymnothorax funebris Ranzani; spotted moray, Gymnothorax morninga (Cuvier) and reticulated moray, Muraena retifera Goode and Bean. Recently captured green moray eels comprised the control group (n=9). Clinical signs compatible with ocular lipid deposition were identified in six of ten captive eels (60%) vs. none of the controls. Green moray eels in the initial captive population (n=5) had significantly higher total protein, triglyceride, cholesterol and aspartate amino transferase values than the control eels. Dietary management was attempted in all captive eels, and surgical intervention was performed in three eels, including two from a separate population, with improved ocular clarity within 1month post-operatively. Histopathological evaluation of surgical specimens and two eyes from an additional affected eel that died suggested ocular lipid deposition. Eels in captivity have an apparent predisposition for hyperlipidaemia and ocular lipid deposition. Although limited in this study and complicated by exhibit restraints, dietary management was minimally effective, while surgery improved ocular clarity.