Snowdrop (SNO): A Dilution Mutation in the SLC45A2 Gene in Horses

In 2020, our team discovered the Snowdrop (SNO) gene, a rare coat color dilution found in a specific line of Gypsy horses. This newly identified mutation expands our understanding of horse coat color genetics and adds to the list of known dilution genes.

What is the Snowdrop (SNO)?

The Snowdrop (SNO) variant is a new dilution mutation in the SLC45A2 gene. This is the same gene responsible for other coat dilutions in horses, such as; Cream (CR), Pearl (PRL), and Sunshine (SUN). Mutations in this gene affect how pigment is produced and deposited in the hair and skin, leading to unique coat colors.

How was Snowdrop (SNO) discovered?

Snowdrop (SNO) was first identified in a Gypsy mare that appeared to be smokey cream, but did not carry any of the known dilution or white-spotting genes! After extensive testing and careful sequencing, along with further research with comparison to her relatives, our team found a unique genetic change in the SLC45A2 gene that explained her unusual appearance. This newly identified mutation was officially named Snowdrop (SNO).

Inheritance and Expression

Snowdrop (SNO) is an autosomal recessive mutation. It is unclear whether the Snowdrop (SNO) mutation affects eumelanin or pheomelanin, but it is suspected to dilute eumelanin in the homozygous (sno/sno) form.

Homozygous (sno/sno): Horses with two copies of the gene show a strong dilution of black pigment in the mane and tail, often appearing pale with pink skin around the muzzle and white eyelashes.

Heterozygous (sno/n): Horses with just one copy appear to have no effect on phenotype, unless paired with another dilution gene such as Cream (CR), Pearl (PRL), or Sunshine (SUN).

Health and Viability

No adverse health effects have been associated with the Snowdrop mutation. Snowdrop is not lethal.

Research Status

While its full effects are still being studied, so far, Snowdrop (SNO) has only been found in Gypsy horses and it is linked to a particular line of Gypsy horses, making it a unique part of the breed’s genetic history. The origin and allele frequency is unknown at this time, research is ongoing.

If you have a horse who you suspect may carry this gene we encourage you to test and join the research!

Conclusion

The Snowdrop (SNO) variant is a rare and fascinating discovery that highlights just how much there still is to learn about horse genetics! Snowdrop (SNO) can mimic other dilutions, genetic testing is the only way to confirm if a horse carries the Snowdrop (SNO) variant. If you own a Gypsy horse or suspect your horse may carry this mutation, genetic testing will help you know for sure.

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Read The Snowdrop (SNO) Paper Here