No abstract

Oral supplementation with l-carnitine is a common therapeutic modality for mitochondrial disorders despite limited evidence of efficacy. Recently, a number of studies have demonstrated that a gut microbiota-dependent metabolite of l-carnitine, trimethylamine oxide (TMAO), is an independent and dose-dependent risk factor for cardiovascular disease (CVD). Given the limited data demonstrating efficacy with oral l-carnitine therapy and the newly raised questions of potential harm, we assessed plasma TMAO levels in patients with mitochondrial disease with and without oral l-carnitine supplementation. Nine subjects were recruited and completed the study. Eight out of 9 subjects at baseline had plasma TMAO concentrations <97.5th percentile (<15.5 μM). One subject with stage 3 renal disease, had marked elevation in plasma TMAO (pre 33.98 μm versus post 101.6 μm). Following at least 3 months of l-carnitine supplementation (1000 mg per day), plasma TMAO levels were markedly increased in 7out of 9 subjects; overall, plasma TMAO significantly increased 11.8-fold (p < 0.001) from a baseline median level of 3.54 μm (interquartile range (IQR) 2.55–8.72) to 43.26 (IQR 23.99–56.04) post supplementation. The results of this study demonstrate that chronic oral l-carnitine supplementation markedly increases plasma TMAO levels in subjects with mitochondrial disorders. Further studies to evaluate both the efficacy and long term safety of oral l-carnitine supplementation for the treatment of mitochondrial disorders are warranted.

Familial platelet disorder with propensity to myeloid malignancy (FPD/AML) is an autosomal dominant syndrome characterised by platelet abnormalities and a predisposition to myelodysplasia (MDS) and/or acute myeloid leukemia (AML). The disorder, caused by inherited mutations in RUNX1, is uncommon with only 14 pedigrees reported. We screened 10 families with a history of more than one first- degree relative with MDS/AML and detected inherited mutations in RUNX1 in 5 of these pedigrees. Several affected members had normal platelet counts or platelet function, features not previously reported in FPD/AML. The median incidence of MDS/AML among carriers of RUNX1 mutation was 35%. Individual treatments varied but included hematopoietic stem cell transplantation (HSCT) from siblings before recognition of the inherited leukemogenic mutation. Transplantation was associated with a high incidence of complications including early relapse, failure of engraftment and post-transplantation lymphoproliferative disorder. As acquired trisomy 13 and 21 and FLT3-ITD have all been associated with RUNX1 mutation in sporadic MDS/AML, a combination of single nucleotide polymorphism profiling and mutation analysis was performed to determine whether these secondary genetic events were implicated in the onset of overt malignancy in FPD/AML. Five disease (MDS and/or AML) samples from 4 of our pedigrees with FPD/AML were screened and in all cases, these abnormalities were excluded. Therefore, the secondary mutations that promote MDS/AML in individuals with germline RUNX1 mutations are distinct from those reported in sporadic cases and require further investigation. The small size of modern families and the clinical heterogeneity of the FPD/AML syndrome may have resulted in the diagnosis being previously overlooked. Based on our data, FPD/AML may be more prevalent than previously recognized and therefore, it would appear prudent to screen young patients with MDS/AML for RUNX1 mutation, particularly prior to consideration of sibling HSCT.