Redundant contribution of a Transient Receptor Potential cation channel Member 1 exon 11 single nucleotide polymorphism to equine congenital stationary night blindness.
Authors: Scott Michelle L, John Emily E, Bellone Rebecca R, Ching John C H, Loewen Matthew E, Sandmeyer Lynne S, Grahn Bruce H, Forsyth George W
Journal: BMC veterinary research
Summary
# Editorial Summary: TRPM1 and Equine Congenital Stationary Night Blindness Congenital stationary night blindness (CSNB) in Appaloosas and related breeds stems from impaired retinal function, specifically affecting ON-bipolar cells that normally express the TRPM1 ion channel—a protein critical for low-light vision. Scott *et al.* used molecular and genetic techniques to investigate whether a specific SNP (C>T at position ECA1 108,249,293) contributed meaningfully to disease pathology alongside the previously identified transposon insertion in intron 1 that was known to suppress TRPM1 transcript levels. The researchers found that whilst this SNP does create a binding site for Nova-1 protein, which subsequently disrupts mRNA splicing and produces non-functional transcripts, its contribution to overall CSNB pathogenesis proved redundant—the primary intron 1 transposon insertion accounts for the substantial reduction in functional TRPM1 expression. For equine professionals involved in breeding decisions, genetic screening, or understanding disease mechanisms, this work clarifies that the intron 1 insertion mutation remains the primary driver of CSNB and should be the focus of testing programmes, whilst the SNP identified here appears to play at most a minor additive role. This distinction streamlines diagnostic priorities and emphasises that single-gene defects often involve complex regulatory interactions rather than simple loss-of-function mutations.
Read the full abstract on PubMed
Practical Takeaways
- •CSNB in Appaloosa and other breeds involves multiple genetic mechanisms at the TRPM1 locus, complicating genetic screening and breeding decisions
- •Night blindness in affected horses results from impaired retinal function at the cellular level and cannot be managed through training or environmental modification
- •Breeders should implement genetic testing for both known TRPM1 mutations to identify carriers and affected individuals before breeding
Key Findings
- •A second TRPM1 SNP (ECA1 108,249,293 C>T) contributes to CSNB by introducing a Nova-1 protein binding site that disrupts normal splicing
- •Nova-1 binding to the SNP-induced consensus site produces unstable, non-functional mRNA transcripts in affected horses
- •The SNP acts redundantly with a known transposon-like insertion in intron 1 to reduce TRPM1 expression in ON-bipolar retinal cells