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

ABSTRACT

BACKGROUND: In 2014 the incidence of anti-HMGCR myopathy in New Zealand was ∼1.7 case/million persons/year. OBJECTIVE: Re-estimate the population incidence and assess ethnic variation in those >40-year -olds. SETTING: An incidence cohort was defined by seropositivity for immunoprecipitating anti-HMGCR autoantibodies tested at a national reference laboratory between 1 October 2019-30 September 2021.Separately, ethnicity standardized incidence in > 40-year-olds discharged from New Zealand public hospitals for idiopathic and unspecified myopathy (ICD AM codes M60.8/60.9), was examined for concordance. RESULTS: The forty 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 the incidence in Polynesians (Maori and Pacific peoples combined) was 25cases/million/year (95% CI 15.9 -40.1), in Asians 5.7cases/million/year (95% CI 0.7 -20.5) and in Europeans 7cases/million/year (95% CI 3.1 -8.4). The risk in statin users aged > 40 years was ∼1/9000 in Polynesians and ∼1/48000 in Europeans.Ethnic difference in incidence of idiopathic and unspecified myopathy (ICD AM codes M60.8/60.9) 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-year-olds was 108 cases/million/year in Polynesians vs 21 cases/million/year in Europeans.