Anti-HMGCR myopathy: estimated five-fold higher incidence in Polynesian compared with European populations in Aotearoa/New Zealand

Abstract

Abstract Objective In 2014 the incidence of anti-3-hydroxy-3-methylglutaryl-CoA-reductase (HMGCR) myopathy in New Zealand was ∼1.7 case/million persons/year. This study aimed to re-estimate the population incidence and assess ethnic variation in those aged >40 years old. Methods An incidence cohort was defined by seropositivity for immunoprecipitating anti-HMGCR autoantibodies tested at a national reference laboratory between 1 October 2019 and 30 September 2021. Separately, ethnicity standardized incidence in >40 year olds discharged from New Zealand public hospitals for idiopathic and unspecified myopathy [International Statistical Classification of Disease and Related Health Problems Tenth Revision Australian Modification (ICD-10 AM) codes M60.8/M60.9], was examined for concordance. Results The 40 patients identified in the incidence cohort were all >40 years old and all had a prior history of statin use. Annual incidence was 4 cases/million/year (95% CI 2.8–5.5). In those >40 years old the incidence in Polynesians (Māori and Pacific Peoples combined) was 25 cases/million/year (95% CI 15.9–40.1), in Asians 5.7 cases/million/year (95% CI 0.7–20.5) and in Europeans 7 cases/million/year (95% CI 3.1–8.4). The risk in statin users aged >40 years was ∼1/9000 in Polynesians and ∼1/48 000 in Europeans. Ethnic difference in incidence of idiopathic and unspecified myopathy (ICD AM codes M60.8/M60.9) was also found in hospital discharges. Conclusion In the past half decade the estimated incidence of anti-HMGCR myopathy in New Zealand has doubled. Polynesian peoples of New Zealand >40 years old have an estimated 5-fold higher risk compared with European and Asian peoples. The estimated absolute risk in statin users >40 years old was 108 cases/million/year in Polynesians vs 21 cases/million/year in Europeans.