Genetic testing for mitochondrial disease: the United Kingdom best practice guidelines.

Primary mitochondrial disease describes a diverse group of neuro-metabolic disorders characterised by impaired oxidative phosphorylation. Diagnosis is challenging; >350 genes, both nuclear and mitochondrial DNA (mtDNA) encoded, are known to cause mitochondrial disease, leading to all possible inheritance patterns and further complicated by heteroplasmy of the multicopy mitochondrial genome. Technological advances, particularly next-generation sequencing, have driven a shift in diagnostic practice from 'biopsy first' to genome-wide analyses of blood and/or urine DNA. This has led to the need for a reference framework for laboratories involved in mitochondrial genetic testing to facilitate a consistent high-quality service. In the United Kingdom, consensus guidelines have been prepared by a working group of Clinical Scientists from the NHS Highly Specialised Service followed by national laboratory consultation. These guidelines summarise current recommended technologies and methodologies for the analysis of mtDNA and nuclear-encoded genes in patients with suspected mitochondrial disease. Genetic testing strategies for diagnosis, family testing and reproductive options including prenatal diagnosis are outlined. Importantly, recommendations for the minimum levels of mtDNA testing for the most common referral reasons are included, as well as guidance on appropriate referrals and information on the minimal appropriate gene content of panels when analysing nuclear mitochondrial genes. Finally, variant interpretation and recommendations for reporting of results are discussed, focussing particularly on the challenges of interpreting and reporting mtDNA variants.

Pathogenic SLC25A26 variants impair SAH transport activity causing mitochondrial disease.

The SLC25A26 gene encodes a mitochondrial inner membrane carrier that transports S-adenosylmethionine (SAM) into the mitochondrial matrix in exchange for S-adenosylhomocysteine (SAH). SAM is the predominant methyl-group donor for most cellular methylation processes, of which SAH is produced as a by-product. Pathogenic, biallelic SLC25A26 variants are a recognized cause of mitochondrial disease in children, with a severe neonatal onset caused by decreased SAM transport activity. Here, we describe two, unrelated adult cases, one of whom presented with recurrent episodes of severe abdominal pain and metabolic decompensation with lactic acidosis. Both patients had exercise intolerance and mitochondrial myopathy associated with biallelic variants in SLC25A26, which led to marked respiratory chain deficiencies and mitochondrial histopathological abnormalities in skeletal muscle that are comparable to those previously described in early-onset cases. We demonstrate using both mouse and fruit fly models that impairment of SAH, rather than SAM, transport across the mitochondrial membrane is likely the cause of this milder, late-onset phenotype. Our findings associate a novel pathomechanism with a known disease-causing protein and highlight the quests of precision medicine in optimizing diagnosis, therapeutic intervention and prognosis.

Outcomes in Multivessel Coronary Disease Stratified by The Society of Thoracic Surgeons Risk.

BACKGROUND: Surgical risk stratified outcomes after contemporary revascularization strategies have not been well described. We report these outcomes in patients undergoing percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) for multivessel coronary disease. METHODS: A total of 5836 patients with multivessel disease who underwent CABG (n = 4420) or PCI (n = 1416) were included in this retrospective observational analysis. Data were stratified based on The Society of Thoracic Surgeons risk score. A score less than 4% was considered low risk and a score greater than or equal to 4% was considered intermediate-high risk. Outcomes included mortality, inpatient readmissions, and repeat revascularizations. RESULTS: In the CABG population, 3863 (87.3%) were low risk and 557 (12.6%) were intermediate-high risk. The 5-year mortality for the low-risk cohort was 10.9% (95% confidence interval [CI], 9.83%-12.05%), and for the intermediate-high-risk cohort it was 40.1% (95% CI, 35.76%-44.54%). Among those undergoing PCI, 1163 (82.1%) were low risk, while 249 (17.6%) were intermediate-high risk. The 5-year mortality for the low-risk cohort was 21.6% (95% CI, 19.10%-24.26%), and for the intermediate-high-risk cohort it was 61.8% (95% CI, 54.72%-68.70%). CONCLUSIONS: This study reports outcomes stratified by surgical risk after PCI or CABG in patients with multivessel coronary disease. These data can help guide the revascularization strategy choice for individual patients.

Novel method for transaxillary Impella 5.0 implantation in patients with tortuous arterial anatomy.

A novel method of transaxillary Impella 5.0 implantation utilizing a vascular sheath can overcome difficult arterial anatomy and provide mechanical support for patients in critical cardiogenic shock.

Surgical versus percutaneous multivessel coronary revascularization in patients with chronic kidney disease.

OBJECTIVES: This study compared contemporary outcomes following surgical versus percutaneous coronary revascularization for multivessel coronary artery disease (MVCAD) in patients with chronic kidney disease. METHODS: Patients with MVCAD and a reduced glomerular filtration rate (<60 ml/min) undergoing coronary bypass surgery (CABG) or percutaneous coronary intervention (PCI) at a single institution between 2010 and 2017 were included. The primary outcome was major adverse cardiac and cerebrovascular events (MACCE) defined as a composite outcome of death, stroke, myocardial infarction or repeat revascularization. Multivariable Cox regression models were used for risk-adjustment and propensity matching was also performed. RESULTS: A total of 1853 patients were included in the study (1269 CABG, 584 PCI). CABG was associated with greater 5-year freedom from MACCE (70.1% vs 47.3%, P < 0.0001), a finding that persisted after risk-adjustment. The rates of early and late mortality and readmission were also lower with CABG as were individual rates of myocardial infarction and repeat revascularization. A propensity-matched analysis generated 704 well-matched patients (352 in each arm) with similar results, including greater 5-year freedom from MACCE (72.8% vs 45.8%, P < 0.0001), improved 5-year survival (73.9% vs 52.3%, P < 0.0001), lower readmission (cause-specific hazard ratio 0.68, 95% confidence interval 0.58-0.80; P < 0.0001), lower individual rates of myocardial infarction (2.6% vs 9.7%, P < 0.0001) and repeat revascularization (1.1% vs 7.4%, P < 0.0001). CONCLUSIONS: CABG is associated with a lower MACCE rate than that of PCI in patients with MVCAD and chronic kidney disease. Multidisciplinary discussions regarding the optimal revascularization strategy are important in MVCAD, particularly in more complex scenarios such as chronic kidney disease.

Coronary Bypass Versus Percutaneous Revascularization in Multivessel Coronary Artery Disease.

BACKGROUND: This study focused on contemporary outcomes after coronary artery bypass graft (CABG) surgery versus percutaneous coronary intervention (PCI) in patients with multivessel coronary artery disease (MVCAD). METHODS: This was a propensity-matched retrospective, observational analysis. Patients with MVCAD who underwent CABG or PCI between 2010 and 2018 and for whom data were available through the National Cardiovascular Data Registry or The Society of Thoracic Surgeons Adult Cardiac Surgery Database were included. The primary outcome was overall survival. Secondary outcomes included freedom from inpatient readmission and freedom from repeat revascularization. RESULTS: Of the initial 6,163 patients with MVCAD, the propensity-matched cohort included 844 in each group. The estimated 1-year mortality was 11.5% and 7.2% (p < 0.001) in the PCI and CABG groups, respectively, with an overall hazard ratio for mortality of PCI versus CABG of 1.64 (95% confidence interval [CI], 1.29 to 2.10; p < 0.001). The overall hazard ratio for readmission for PCI versus CABG was 1.42 (95% CI, 1.23 to 1.64; p < 0.001). The overall hazard ratio for repeat revascularization for PCI versus CABG was 4.06 (95% CI, 2.39 to 6.91; p < 0.001). Overall major adverse cardiovascular events and individual outcomes of mortality, readmission, and repeat revascularization all favored CABG across virtually all major clinical subgroups. CONCLUSIONS: This contemporary propensity-matched analysis of patients undergoing coronary revascularization for MVCAD demonstrates a significant mortality benefit with CABG over PCI, and this benefit is consistent across virtually all major patient subgroups. Futures studies are needed reflecting routine practice to assess how best to approach shared decision making and informed consent when it comes to revascularization decisions in any patient with MVCAD.

Distal myopathy with cachexia: an unrecognised phenotype caused by dominantly-inherited mitochondrial polymerase γ mutations.

BACKGROUND: The myopathy associated with mutations in the nuclear-encoded mitochondrial DNA maintenance gene POLG, coding for the catalytic subunit of DNA polymerase, is typically proximal with early ophthalmoplegia. RESULTS: We report two unrelated patients in whom a distal, mainly upper limb, myopathy was the predominant and early clinical feature. One patient also suffered with marked cachexia. DNA genomic sequence analysis identified novel dominant heterozygous missense POLG mutations (Leu896Arg and Tyr951His) located within the conserved catalytic polymerase domain of the protein in both cases. CONCLUSIONS: Distal upper limb myopathy/cachexia is not previously described with dominant POLG mutations and our observations further highlight the diverse clinical spectrum of POLG-related mitochondrial disorders. These data indicate that dominant POLG mutations should be considered in the differential diagnosis of distal upper limb predominant myopathy.

Benefit of long-term dual anti-platelet therapy in patients treated with drug-eluting stents: from the NHLBI dynamic registry.

The optimal duration of dual-antiplatelet therapy (DAPT) after drug-eluting stent (DES) implantation is an important, unanswered question. This study was designed to evaluate the association of varying durations of DAPT on clinical outcomes after DES implantation for the treatment of coronary artery disease. Using the National Heart, Lung, and Blood Institute Dynamic Registry, patients enrolled in the last 2 waves after index percutaneous coronary intervention with DES and who were event free at the time of landmark analysis were included. Landmark analysis was performed 12 and 24 months after percutaneous coronary intervention, and patients were stratified according to continued use of DAPT or not. Subjects were evaluated for rates of death, myocardial infarction, and stent thrombosis at 4 years from their index procedures. The numbers of evaluable patients were 2,157 and 1,918 for the 12- and 24-month landmarks, respectively. In both landmark analyses, there was a significantly lower 4-year rate of death or myocardial infarction in the group that continued DAPT compared to the group that did not (12 months: 10.5% vs 14.5%, p = 0.01; 24 months: 5.7% vs 8.6%, p = 0.02). Beneficial differences in the group that continued on DAPT were preserved after multivariate and propensity adjustment. There were no significant differences in definite stent thrombosis in either landmark analysis. In conclusion, at 12 and 24 months after DES implantation, continued use of DAPT was associated with lower 4-year risk for death and myocardial infarction.

Adults with RRM2B-related mitochondrial disease have distinct clinical and molecular characteristics.

Mutations in the nuclear-encoded mitochondrial maintenance gene RRM2B are an important cause of familial mitochondrial disease in both adults and children and represent the third most common cause of multiple mitochondrial DNA deletions in adults, following POLG [polymerase (DNA directed), gamma] and PEO1 (now called C10ORF2, encoding the Twinkle helicase) mutations. However, the clinico-pathological and molecular features of adults with RRM2B-related disease have not been clearly defined. In this multicentre study of 26 adult patients from 22 independent families, including five additional cases published in the literature, we show that extra-ocular neurological complications are common in adults with genetically confirmed RRM2B mutations. We also demonstrate a clear correlation between the clinical phenotype and the underlying genetic defect. Myopathy was a prominent manifestation, followed by bulbar dysfunction and fatigue. Sensorineural hearing loss and gastrointestinal disturbance were also important findings. Severe multisystem neurological disease was associated with recessively inherited compound heterozygous mutations with a mean age of disease onset at 7 years. Dominantly inherited heterozygous mutations were associated with a milder predominantly myopathic phenotype with a later mean age of disease onset at 46 years. Skeletal muscle biopsies revealed subsarcolemmal accumulation of mitochondria and/or cytochrome c oxidase-deficient fibres. Multiple mitochondrial DNA deletions were universally present in patients who underwent a muscle biopsy. We identified 18 different heterozygous RRM2B mutations within our cohort of patients, including five novel mutations that have not previously been reported. Despite marked clinical overlap between the mitochondrial maintenance genes, key clinical features such as bulbar dysfunction, hearing loss and gastrointestinal disturbance should help prioritize genetic testing towards RRM2B analysis, and sequencing of the gene may preclude performance of a muscle biopsy.

Anterior laxity, slippage, and recovery of function in the first year after tibialis allograft anterior cruciate ligament reconstruction.

BACKGROUND: The increase in anterior laxity and slippage is greater with metal interference screw fixation of a hamstring anterior cruciate ligament (ACL) graft than a bone-patellar tendon-bone graft. HYPOTHESIS: When slippage-resistant fixation is used with a soft tissue graft, early recovery of function does not result in a clinically important increase in anterior laxity and slippage STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Nineteen subjects were treated with a single-tunnel, single-looped, tibialis allograft with slippage-resistant, cortical fixation. An examiner, different from the treating surgeon, used stereophotogrammetric analysis to compute the increase in anterior laxity at a 150 N anterior force and slippage between the day of surgery and each monthly follow-up interval, and determined recovery of function and motion. RESULTS: Anterior laxity did not increase between the day of surgery and 1 year (P = .23). Total slippage plateaued after 1 month, but increased 1.5 mm between the day of surgery and 1 month (P < .05). Extension and flexion plateaued after 2 months (P < .0001 and P < .02, respectively); activity level (Tegner score) plateaued after 3 months (P < .05), function (Lysholm score) plateaued after 4 months (P < .002), and subjective satisfaction (International Knee Documentation Committee score) plateaued after 6 months (P < .02). CONCLUSION: Early recovery of function after ACL reconstruction with a soft tissue allograft did not result in a clinically important increase in anterior laxity and slippage at 1 year. We believe the avoidance of an increase in anterior laxity was related to the use of a transtibial technique designed to place the femoral and tibial tunnels without roof and posterior cruciate ligament impingement, the use of cortical fixation devices designed to resist slippage, the use of an aseptically harvested fresh-frozen tibialis allograft that was not irradiated or chemically processed, and the use of a self-administered rehabilitation program designed to encourage an early return of motion and function.

Does graft construct lengthening at the fixations cause an increase in anterior laxity following anterior cruciate ligament reconstruction in vivo?

A millimeter-for-millimeter relation between an increase in length of an anterior cruciate ligament graft construct and an increase in anterior laxity has been demonstrated in multiple in vitro studies. Based on this relation, a 3 mm increase in length of the graft construct following surgery could manifest as a 3 mm increase in anterior laxity in vivo, which is considered clinically unstable. Hence, the two primary objectives were to determine whether the millimeter-for-millimeter relation exists in vivo for slippage-resistant fixation of a soft-tissue graft and, if it does not exist, then to what extent the increase in stiffness caused by biologic healing of the graft to the bone tunnel offsets the potential increase in anterior laxity resulting from lengthening at the sites of fixation. Sixteen subjects were treated with a fresh-frozen, nonirradiated, nonchemically processed tibialis allograft. Tantalum markers were injected into the graft, fixation devices, and bones. On the day of surgery and at 1, 2, 3, and 4 months, Roentgen stereophotogrammetric analysis was used to compute anterior laxity at 150 N of anterior force and the total slippage from both sites of fixation. A simple linear regression was performed to determine whether the millimeter-for-millimeter relation existed and a springs-in-series model of the graft construct was used to determine the extent to which the increase in stiffness caused by biological healing of the graft to the bone tunnel offset the increase in anterior laxity resulting from lengthening at the sites of fixation. There was no correlation between lengthening at the sites of fixation and the increase in anterior laxity at 1 month (R(2)=0.0, slope=0.2). Also, the increase in stiffness of the graft construct caused by biologic healing of the graft to the bone tunnel offset 0.7 mm of the 1.5 mm potential increase in anterior laxity resulting from lengthening at the sites of fixation. This relatively large offset of nearly 50% occurred because lengthening at the sites of fixation was small.

Migration of radio-opaque markers injected into tendon grafts: a study using roentgen stereophotogrammetric analysis (RSA).

An increase in anterior laxity following reconstruction of the anterior cruciate ligament (ACL) can result from lengthening of the graft construct either at the sites of fixation and/or between the sites of fixation (i.e., graft substance). Roentgen stereophotogrammetric analysis (RSA), which requires that radio-opaque markers be attached to the graft, has been shown to be a useful technique in determining lengthening in these regions. Previous methods have been used for attaching radio-opaque markers to the graft, but they all have limitations particularly for single-loop grafts. Therefore, the objective of this study was to evaluate injecting markers directly into the substance of a tendon as a viable method for measuring lengthening of single-loop graft constructs by determining the maximum amount of migration after cyclic loading. Tantalum spheres of 0.8 mm diameter were used as tendon markers. Ten single-loop tendon grafts were passed through tibial tunnels drilled in calf tibias and fixed with a tibial fixation device. Two tendon markers were inserted in one tendon bundle of each graft and the grafts were cyclically loaded for 225,000 cycles from 20 N to 170 N. At specified intervals, simultaneous radiographs were obtained of the tendon markers. Marker migration was computed as the change in distance between the two tendon markers parallel to the axis of the tibial tunnel. Marker migration had a root mean square (RMS) value of less than 0.1 mm. Because the RMS value indicates the error introduced into measurements of lengthening and because this error is negligible, the method described for attaching markers to single-loop ACL grafts has the potential to be useful for determining lengthening of single-loop ACL graft constructs in in vivo studies in humans.