Prevalence of the E321G MYH1 variant in Brazilian Quarter Horses.
Authors: de Albuquerque Ana L, Zanzarini Delfiol Diego J, Andrade Danilo G A, Albertino Lukas G, Sonne Luciana, Borges Alexandre S, Valberg Stephanie J, Finno Carrie J, Oliveira-Filho Jose P
Journal: Equine veterinary journal
Summary
# Editorial Summary: E321G MYH1 Variant in Brazilian Quarter Horses The E321G mutation in the MYH1 gene causes myosin heavy chain myopathy (MYHM) in Quarter Horses, a condition presenting as nonexertional rhabdomyolysis or immune-mediated myositis with acute muscular atrophy. De Albuquerque and colleagues investigated the prevalence of this mutation in the Brazilian Quarter Horse population by screening 299 registered animals across multiple disciplines (reining, barrel racing, halter, cutting and racing) using PCR-based genomic sequencing. Forty-four horses (14.7%) carried the heterozygous variant whilst 255 (85.3%) were homozygous wild-type, yielding an allele frequency of 0.074; notably, reining horses showed significantly higher heterozygosity prevalence than other disciplines (P = 0.008). Given that clinical cases of MYHM have been documented in Brazil and the mutation frequency appears concentrated in reining bloodlines, these findings warrant inclusion of E321G screening in breeding programmes and genetic counselling protocols, particularly for disciplines selecting for the athleticism traits associated with carrier lineages. Practitioners should heighten clinical awareness of MYHM presentation in Quarter Horses with acute onset myositis or rhabdomyolysis, especially in reining stock, whilst breeders implementing control measures may help prevent further mutation spread within the Brazilian population.
Read the full abstract on PubMed
Practical Takeaways
- •Genetic screening for the E321G MYH1 variant should be implemented in Brazilian Quarter Horse breeding programs, particularly for reining horses, to prevent further spread of this myopathy
- •Veterinarians evaluating Quarter Horses with unexplained muscle atrophy, rhabdomyolysis, or immune-mediated myositis should consider MYHM and recommend genetic testing for the E321G mutation
- •Breeders should be educated about the 14.7% carrier frequency in Brazilian QHs and implement selective breeding strategies to reduce the incidence of affected animals
Key Findings
- •14.7% of 299 Brazilian Quarter Horses were heterozygous (My/N) for the E321G MYH1 variant, with an allele frequency of 0.074
- •Reining horses had significantly higher prevalence of the E321G MYH1 variant heterozygosity compared to horses in other disciplines (P = 0.008)
- •Case report documented two related Quarter Horse foals with E321G MYH1 mutation presenting with clinical signs of MYHM and histological confirmation of immune-mediated myositis in one foal
- •The high prevalence of the MYH1 mutation in Brazilian QHs suggests MYHM should be included in genetic screening programs