SD Locus (Shedding)

Testing Summary

The SD Locus (Shedding) trait test reliably determines if a dog has one of the following genotypes at the SD locus:

Detailed Summary

The SD Locus (Shedding) has been identified as one gene that can impact the degree of shedding in certain breeds of dog. A DNA variant in the MC5R gene (SD) has been associated with higher shedding in various breeds. However, the overall degree of shedding for a dog is dependent on a combination genes and a better understanding of a dog's degree of shedding currently comes from knowledge of a dog's genotypes at both the SD locus and IC (Improper Coat/Furnishings) locus. The MC5R gene is expressed in the hair follicle glands that produce the oily, waxy substance called sebum that assists in lubrication, water repellency, and thermo-regulation of the skin and hair. The SD variant disrupts the structure of sebum and results in increased shedding for breeds that show variation at the SD locus. One copy of the SD variant increases shedding from relatively low to moderate and two copies of the variant results in an increase to relatively high shedding. Dogs that have an improper coat/no furnishings also have a propensity to higher shedding. The SD locus and IC locus have an additive effect on each other. Dogs that have two copies of the SD variant (SD/SD) and two copies of the IC variant (IC/IC) are the highest shedding dogs compared to dogs that have no copies of the SD variant (sd/sd) and no copies of the IC variant (F/F). Various combinations of genotypes at the SD locus and IC locus can produce intermediate shedding states as indicated on the chart below:

Testing Tips

Genetic testing of the MC5R gene will reliably determine whether or not a dog is a genetic Carrier of the variant that contributes to higher shedding in certain breeds of dog. Shedding caused by the SD Locus is inherited in an autosomal incomplete dominant fashion meaning that only one copy of the SD variant is required to produce increased shedding. Dogs with one copy of the SD variant (sd/SD) can have moderate shedding that is in the spectrum somewhere between dogs with high shedding (SD/SD) and low shedding (sd/sd). Breeding two dogs that are carriers of the high shedding SD variant (sd/SD) will result in about 25% of the puppies inheriting two copies of the SD variant (SD/SD), high shedding, about 50% of the puppies inheriting one copy of the SD variant (sd/SD), moderate shedding, and about 25% of the puppies inheriting two copies of the sd variant (sd/sd), low shedding. To provide a better understanding of the overall shedding status, a dog should also be tested for the IC (Improper Coat/Furnishings) locus because the IC variant has also been associated with higher shedding in dogs. Dogs with an improper coat do not need to be tested for the IC locus because they all have an IC/IC genotype and will pass on one copy of IC (high shedding) to all of their offspring.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.

References

• Hayward JJ, Castelhano MG, Oliveira KC, Corey E, Balkman C, Baxter TL, Casal ML, Center SA, Fang M, Garrison SJ, Kalla SE, Korniliev P, Kotlikoff MI, Moise NS, Shannon LM, Simpson KW, Sutter NB, Todhunter RJ, Boyko AR. Complex disease and phenotype mapping in the domestic dog. Nat Commun 2016 Jan; 7:10460. [PubMed: 26795439]