Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibodies: incidence using different testing criteria, and case series.

OBJECTIVES: To estimate the incidence of anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies utilising different testing criteria, and review the clinical details of a series of patients with associated autoimmune myopathy. METHODS: The incidence of anti-HMGCR antibodies in 2019 from 3 groups, South West London, Berkshire/Surrey and Southampton, were compared in the adult population. Anti-HMGCR antibodies were measured by commercial chemiluminescent and immunodot assays. The case notes of patients with anti-HMGCR antibodies were reviewed for the case series. RESULTS: The estimated incidence of anti-HMGCR antibodies in the first 2 groups was 1.94 per million adults per year, and in the third group 10.3 per million adults per year. In the first 2 groups the test criteria restricted analysis to specific clinician request for anti-HMGCR. In the third group test criteria included cases with less specific clinical features or a cytoplasmic indirect immunofluorescence anti-nuclear antibody pattern. The latter strategy had a positive predictive value of 66.1% for anti-HMGCR associated myopathy. A case series of 27 patients with anti-HMGCR antibodies revealed 19 with myopathy, oesophageal involvement in 26% and median peak CK 8000 IU/L. Response to treatment, including intravenous immunoglobulin, was good with CK normalising after median 5.5 months. In 8 cases there was no evidence of autoimmune muscle disease, 7 not statin exposed. CONCLUSIONS: Varying criteria result in a 5-fold difference in estimated incidence of anti-HMGCR antibodies, revealing positive cases without evidence of myopathy. Patients with anti-HMGCR myopathy respond well to immune suppression, supporting wider testing for these antibodies amongst patients with myopathy.

Genotype-phenotype correlation in primary carnitine deficiency.

Primary carnitine deficiency is caused by defective OCTN2 carnitine transporters encoded by the SLC22A5 gene. Lack of carnitine impairs fatty acid oxidation resulting in hypoketotic hypoglycemia, hepatic encephalopathy, skeletal and cardiac myopathy. Recently, asymptomatic mothers with primary carnitine deficiency were identified by low carnitine levels in their infant by newborn screening. Here, we evaluate mutations in the SLC22A5 gene and carnitine transport in fibroblasts from symptomatic patients and asymptomatic women. Carnitine transport was significantly reduced in fibroblasts obtained from all patients with primary carnitine deficiency, but was significantly higher in the asymptomatic women's than in the symptomatic patients' fibroblasts (P < 0.01). By contrast, ergothioneine transport (a selective substrate of the OCTN1 transporter, tested here as a control) was similar in cells from controls and patients with carnitine deficiency. DNA sequencing indicated an increased frequency of nonsense mutations in symptomatic patients (P < 0.001). Expression of the missense mutations in Chinese hamster ovary (CHO) cells indicated that many mutations retained residual carnitine transport activity, with no difference in the average activity of missense mutations identified in symptomatic versus asymptomatic patients. These results indicate that cells from asymptomatic women have on average higher levels of residual carnitine transport activity as compared to that of symptomatic patients due to the presence of at least one missense mutation.