ABSTRACT
BACKGROUND: In 2014 the incidence of anti-HMGCR myopathy in New Zealand was â¼1.7 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 â¼1/9000 in Polynesians and â¼1/48000 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.
ABSTRACT
BACKGROUND: Detecting antidrug antibodies (ADAs) against infliximab or adalimumab is useful for therapeutic drug monitoring. Various ADA detection methods exist, and antibody titer is an output in some algorithms. Homogenous mobility shift assay (HMSA) measures relative ADA concentration and determines drug-ADA complex size in vitro. However, the relevance of complex size determination in drug monitoring remains unclear. Hence, the association between complex size, ADA concentration, and sample detectable neutralizing activity was evaluated. METHODS: Sera from infliximab-treated and adalimumab-treated patients who tested positive for ADA in the National Screening Service were analyzed using 3 ADA assays. HMSA determined the relative ADA concentrations and complex sizes, competitive ligand-binding assay evaluated the sample neutralizing capacity, and enzyme-linked immunosorbent assay detected immunoglobulin (Ig)G4 ADA. RESULTS: Most ADA-positive samples (>80%) formed drug-ADA dimer complexes, whereas 17% had dimer and multimer complexes, and 3% had multimeric complexes. Multimer presence had 100% positive predictive value for detectable neutralizing activity. ADA concentration and detectable neutralizing activity were moderately correlated (r = 0.65) in adalimumab-treated patients and strongly correlated (r = 0.81) in infliximab-treated patients. In adalimumab-treated patients, multimer presence was a stronger predictor of neutralizing activity than ADA concentration was, but not in infliximab-treated patients. However, in infliximab-treated patient samples, multimer presence revealed a distinct subset with high ADA concentrations, neutralizing activity, and IgG4 ADA. CONCLUSIONS: Multimers detected using HMSA had a strong positive predictive value for competitive ligand-binding assay detectable neutralizing activity. Multimeric IgG4-containing ADA-drug complexes revealed a distinct subset of infliximab-treated patient samples, whose clinical relevance merits further investigation.
