De novo mtDNA point mutations are common and have a low recurrence risk.

BACKGROUND: Severe, disease-causing germline mitochondrial (mt)DNA mutations are maternally inherited or arise de novo. Strategies to prevent transmission are generally available, but depend on recurrence risks, ranging from high/unpredictable for many familial mtDNA point mutations to very low for sporadic, large-scale single mtDNA deletions. Comprehensive data are lacking for de novo mtDNA point mutations, often leading to misconceptions and incorrect counselling regarding recurrence risk and reproductive options. We aim to study the relevance and recurrence risk of apparently de novo mtDNA point mutations. METHODS: Systematic study of prenatal diagnosis (PND) and recurrence of mtDNA point mutations in families with de novo cases, including new and published data. 'De novo' based on the absence of the mutation in multiple (postmitotic) maternal tissues is preferred, but mutations absent in maternal blood only were also included. RESULTS: In our series of 105 index patients (33 children and 72 adults) with (likely) pathogenic mtDNA point mutations, the de novo frequency was 24.6%, the majority being paediatric. PND was performed in subsequent pregnancies of mothers of four de novo cases. A fifth mother opted for preimplantation genetic diagnosis because of a coexisting Mendelian genetic disorder. The mtDNA mutation was absent in all four prenatal samples and all 11 oocytes/embryos tested. A literature survey revealed 137 de novo cases, but PND was only performed for 9 (including 1 unpublished) mothers. In one, recurrence occurred in two subsequent pregnancies, presumably due to germline mosaicism. CONCLUSIONS: De novo mtDNA point mutations are a common cause of mtDNA disease. Recurrence risk is low. This is relevant for genetic counselling, particularly for reproductive options. PND can be offered for reassurance.

Rapid Resolution of Blended or Composite Multigenic Disease in Infants by Whole-Exome Sequencing.

Whole-exome sequencing identified multiple genetic causes in 2 infants with heterogeneous disease. Three gene defects in the first patient explained all symptoms, but manifestations were overlapping (blended phenotype). Two gene defects in the second patient explained nonoverlapping symptoms (composite phenotype). Whole-exome sequencing rapidly and comprehensively resolves heterogeneous genetic disease.

Impact of withholding early parenteral nutrition on 2-year mortality and functional outcome in critically ill adults.

PURPOSE: In critically ill adults, withholding parenteral nutrition until 1 week after intensive care admission (Late-PN) facilitated recovery as compared with early supplementation of insufficient enteral nutrition with parenteral nutrition (Early-PN). However, the impact on long-term mortality and functional outcome, in relation to the estimated nutritional risk, remains unclear. METHODS: In this prospective follow-up study of the multicenter EPaNIC randomized controlled trial, we investigated the impact of Late-PN on 2-year mortality (N = 4640) and physical functioning, assessed by the 36-Item Short Form Health Survey (SF-36; in 3292 survivors, responding 819 [738-1058] days post-randomization). To account for missing data, we repeated the analyses in two imputed models. To identify potential heterogeneity of treatment effects, we investigated the impact of Late-PN in different nutritional risk subgroups as defined by Nutritional Risk Screening-2002-score, modified NUTrition Risk in the Critically Ill-score, and age (above/below 70 years), and we evaluated whether there was statistically significant interaction between classification to a nutritional risk subgroup and the effect of the randomized intervention. Secondary outcomes were SF-36-derived physical and mental component scores (PCS & MCS). RESULTS: Two-year mortality (20.5% in Late-PN, 19.8% in Early-PN; P = 0.54) and physical functioning (70 [40-90] in both study-arms; P = 0.99) were similar in both groups, also after imputation of missing physical functioning data. Likewise, Late-PN had no impact on 2-year mortality and physical functioning in any nutritional risk subgroup. PCS and MCS were similar in both groups. CONCLUSION: Late-PN did not alter 2-year survival and physical functioning in adult critically ill patients, independent of anticipated nutritional risk.

Radiotherapy for lentigo maligna and lentigo maligna melanoma - a systematic review.

Lentigo maligna (LM) is the most common subtype of in situ melanoma und occurs frequently in the sun-exposed head and neck region in elderly patients. The therapeutic "gold standard" is surgical excision, as there is the risk of progression to invasive (lentigo maligna) melanoma (LMM). However, surgery is not feasible in certain patients due to age, comorbidities or patient preference. Radiotherapy using Grenz rays or superficial X-rays has been established as non-invasive alternative for the treatment of LM and LMM. We performed a systematic literature search of MEDLINE and Embase databases in September 2019 and identified 14 patient series using radiotherapy for LM or LMM. No prospective trials were found. The 14 studies reported a total of 1243 lesions (1075 LM and 168 LMM) treated with radiotherapy. Local recurrence rates ranged from 0 to 31% and were comparable to surgical series in most of the reports on radiotherapy. Superficial radiotherapy was prescribed in 5-23 fractions with a total dose of 35-57 Gy. Grenz ray therapy was prescribed in 42-160 Gy in 3-13 fractions with single doses up to 20 Gy. Cosmetic results were reported as "good" to "excellent" for the majority of patients.In conclusion, the available low-level evidence suggests that radiotherapy may be a safe and effective treatment for LM and LMM. Data from prospective trials such as the phase 3 RADICAL trial are needed to confirm these promising findings and to compare radiotherapy to other non-surgical therapies and to surgery.

Identifying sequence variants in the human mitochondrial genome using high-resolution melt (HRM) profiling.

Identifying mitochondrial DNA (mtDNA) sequence variants in human diseases is complicated. Many pathological mutations are heteroplasmic, with the mutant allele represented at highly variable percentages. High-resolution melt (HRM or HRMA) profiling was applied to comprehensive assessment of the mitochondrial genome and targeted assessment of recognized pathological mutations. The assay panel providing comprehensive coverage of the mitochondrial genome utilizes 36 overlapping fragments (301-658 bp) that employ a common PCR protocol. The comprehensive assay identified heteroplasmic mutation in 33 out of 33 patient specimens tested. Allele fraction among the specimens ranged from 1 to 100%. The comprehensive assay panel was also used to assess 125 mtDNA specimens from healthy donors, which identified 431 unique sequence variants. Utilizing the comprehensive mtDNA panel, the mitochondrial genome of a patient specimen may be assessed in less than 1 day using a single 384-well plate or two 96-well plates. Specific assays were used to identify the myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) mutation m.3243A>G, myoclonus epilepsy, ragged red fibers (MERRF) mutation m.8344A>G, and m.1555A>G associated with aminoglycoside hearing loss. These assays employ a calibrated, amplicon-based strategy that is exceedingly simple in design, utilization, and interpretation, yet provides sensitivity to detect variants at and below 10% heteroplasmy. Turnaround time for the genotyping tests is about 1 hr.

A novel mitochondrial m.4414T>C MT-TM gene variant causing progressive external ophthalmoplegia and myopathy.

We report a novel mitochondrial m.4414T>C variant in the mt-tRNAMet (MT-TM) gene in an adult patient with chronic progressive external ophthalmoplegia and myopathy whose muscle biopsy revealed focal cytochrome c oxidase (COX)-deficient and ragged red fibres. The m.4414T>C variant occurs at a strongly evolutionary conserved sequence position, disturbing a canonical base pair and disrupting the secondary and tertiary structure of the mt-tRNAMet. Definitive evidence of pathogenicity is provided by clear segregation of m.4414T>C mutant levels with COX deficiency in single muscle fibres. Interestingly, the variant is present in skeletal muscle at relatively low levels (30%) and undetectable in accessible, non-muscle tissues from the patient and her asymptomatic brother, emphasizing the continuing requirement for a diagnostic muscle biopsy as the preferred tissue for mtDNA genetic investigations of mt-tRNA variants leading to mitochondrial myopathy.

Whole Exome Sequencing Is the Preferred Strategy to Identify the Genetic Defect in Patients With a Probable or Possible Mitochondrial Cause.

Mitochondrial disorders, characterized by clinical symptoms and/or OXPHOS deficiencies, are caused by pathogenic variants in mitochondrial genes. However, pathogenic variants in some of these genes can lead to clinical manifestations which overlap with other neuromuscular diseases, which can be caused by pathogenic variants in non-mitochondrial genes as well. Mitochondrial pathogenic variants can be found in the mitochondrial DNA (mtDNA) or in any of the 1,500 nuclear genes with a mitochondrial function. We have performed a two-step next-generation sequencing approach in a cohort of 117 patients, mostly children, in whom a mitochondrial disease-cause could likely or possibly explain the phenotype. A total of 86 patients had a mitochondrial disorder, according to established clinical and biochemical criteria. The other 31 patients had neuromuscular symptoms, where in a minority a mitochondrial genetic cause is present, but a non-mitochondrial genetic cause is more likely. All patients were screened for pathogenic variants in the mtDNA and, if excluded, analyzed by whole exome sequencing (WES). Variants were filtered for being pathogenic and compatible with an autosomal or X-linked recessive mode of inheritance in families with multiple affected siblings and/or consanguineous parents. Non-consanguineous families with a single patient were additionally screened for autosomal and X-linked dominant mutations in a predefined gene-set. We identified causative pathogenic variants in the mtDNA in 20% of the patient-cohort, and in nuclear genes in 49%, implying an overall yield of 68%. We identified pathogenic variants in mitochondrial and non-mitochondrial genes in both groups with, obviously, a higher number of mitochondrial genes affected in mitochondrial disease patients. Furthermore, we show that 31% of the disease-causing genes in the mitochondrial patient group were not included in the MitoCarta database, and therefore would have been missed with MitoCarta based gene-panels. We conclude that WES is preferable to panel-based approaches for both groups of patients, as the mitochondrial gene-list is not complete and mitochondrial symptoms can be secondary. Also, clinically and genetically heterogeneous disorders would require sequential use of multiple different gene panels. We conclude that WES is a comprehensive and unbiased approach to establish a genetic diagnosis in these patients, able to resolve multi-genic disease-causes.

A MELAS-associated ND1 mutation causing leber hereditary optic neuropathy and spastic dystonia.

OBJECTIVE: To report a novel mutation that is associated with Leber hereditary optic neuropathy (LHON) within the same family affected by spastic dystonia. DESIGN: Leber hereditary optic neuropathy is a mitochondrial disorder characterized by isolated central visual loss. Of patients with LHON, 95% carry a mutation in 1 of 3 mitochondrial DNA-encoded complex I genes. The complete mitochondrial DNA was screened for mutations in a patient with LHON without 1 of these 3 primary mutations. The heteroplasmy level and biochemical consequence of the mutation were determined. RESULTS: A pathogenic 3697G>A/ND1 mutation was detected and seemed associated with an isolated complex I deficiency. This family has similar clinical characteristics as the previously described families with LHON and dystonia with an ND6 mutation. CONCLUSIONS: The 3697G>A/ND1 mitochondrial DNA mutation causes the LHON and spastic dystonia phenotype in the same family. This mutation can also cause MELAS syndrome (which encompasses mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke), and other genetic factors may contribute to the clinical expression.

Novel SLC25A32 mutation in a patient with a severe neuromuscular phenotype.

In a 51-year-old patient of consanguineous parents with a severe neuromuscular phenotype of early-onset ataxia, myoclonia, dysarthria, muscle weakness and exercise intolerance, exome sequencing revealed a novel homozygous variant (c.-264_31delinsCTCACAAATGCTCA) in the mitochondrial FAD-transporter gene SLC25A32. Flavin adenine dinucleotide (FAD) is an essential co-factor for many mitochondrial enzymes and impaired mitochondrial FAD-transport was supported by a reduced oxidative phosphorylation complex II activity in the patient's muscle, decreased ATP production in fibroblasts, and a deficiency of mitochondrial FAD-dependent enzymes. Clinically, the patient showed improvement upon riboflavin treatment, which is a precursor of FAD. Our results confirm the recently reported case of SLC25A32 as a cause of riboflavin-responsive disease. Our patient showed a more severe clinical phenotype compared with the reported patient, corresponding with the (most likely) complete absence of the SLC25A32-encoding MFT (Mitochondrial Folate Transporter) protein.

An Analysis of Reliability and Accuracy of Muscle Thickness Ultrasonography in Critically Ill Children and Adults.

BACKGROUND: Muscle wasting starts already within the first week in critically patients and is strongly related to poor outcome. Nevertheless, the early detection of muscle wasting is difficult. Therefore, we investigated the reliability and accuracy of ultrasonography to evaluate skeletal muscle wasting in critically ill children and adults. METHODS: This prospective observational study enrolled 30 sedated critically ill children and 14 critically ill adults. Two independent investigators made 210 ultrasonographical assessments of muscle thigh thickness. Inter- and intraobserver reliability and cutoff levels were calculated as a function of muscle thickness and the expected reduction in muscle size (predefined at 20% and 30%). RESULTS: Mean ± SD muscle thickness was 1.67 ± 0.55 cm in the pediatric and 2.10 ± 0.85 cm in the adult population. The median absolute interobserver variability was 0.07 cm (interquartile range [IQR], 0.04-0.20 cm) in the pediatric population and 0.05 cm (IQR, 0.03-0.09 cm) in the adult population. However, the absolute intraobserver accuracy had a 95% confidence interval of 0.43 cm in children and 0.22 cm in adults. Only a 30% decrease (0.50 cm) in muscle thickness can be detected in critically ill children. CONCLUSION: Although the interobserver variability is acceptable in the pediatric population, the intraobserver variability is too large with respect to the expected reduction in muscle thickness. In adults, ultrasonography may be a reliable tool for early detection of muscle mass wasting.

Polyhydramnios and cerebellar atrophy: a prenatal presentation of mitochondrial encephalomyopathy caused by mutations in the FBXL4 gene.

Severe recessive mitochondrial myopathy caused by FBXL4 gene mutations may present prenatally with polyhydramnios and cerebellar hypoplasia. Characteristic dysmorphic features are: high and arched eyebrows, triangular face, a slight upslant of palpebral fissures, and a prominent pointed chin. Metabolic investigations invariably show increased serum lactate and pyruvate levels.

Mitochondrial DNA damage analysis in bronchoalveolar lavage cells of preterm infants.

In mechanically ventilated preterm infants, the combination of immaturity, volutrauma, oxidative stress, and inflammatory processes can lead to chronic lung injury. Mitochondrial DNA (mtDNA) is more susceptible to oxidative damage than nuclear DNA. We aimed to investigate the level of mtDNA damage (deletions, mutations and changes in copy number) in bronchoalveolar lavage (BAL) cells from 10 preterm infants (27-30 weeks). A first BAL (BAL1) was done within 24 h of endotracheal intubation and BAL2 was performed 30-103 h thereafter. Deletions were analyzed by long range PCR, point mutations by heteroduplex analysis of the D-loop region, and copy number changes by real-time PCR. Using these methods, no deletions were found in any of the BAL samples. When BAL1 and BAL2 samples were compared no new mutations were found. In contrast, a marked decrease in mtDNA copy number was observed in 5 patients. In conclusion, we found that exposure of preterm infants to short term mechanical ventilation did not lead to detrimental consequences for the mtDNA in the form of mutations or deletions.

Chip-based mtDNA mutation screening enables fast and reliable genetic diagnosis of OXPHOS patients.

PURPOSE: Oxidative phosphorylation is under dual genetic control of the nuclear and the mitochondrial DNA (mtDNA). Oxidative phosphorylation disorders are clinically and genetically heterogeneous, which makes it difficult to determine the genetic defect, and symptom-based protocols which link clinical symptoms directly to a specific gene or mtDNA mutation are falling short. Moreover, approximately 25% of the pediatric patients with oxidative phosphorylation disorders is estimated to have mutations in the mtDNA and a standard screening approach for common mutations and deletions will only explain part of these cases. Therefore, we tested a new CHIP-based screening method for the mtDNA. METHODS: MitoChip (Affymetrix) resequencing was performed on three test samples and on 28 patient samples. RESULTS: Call rates were 94% on average and heteroplasmy detection levels varied from 5-50%. A genetic diagnosis can be made in almost one-quarter of the patients at a potential output of 8 complete mtDNA sequences every 4 days. Moreover, a number of potentially pathogenic unclassified variants (UV) were detected. CONCLUSIONS: The availability of long-range PCR protocols and the predominance of single nucleotide substitutions in the mtDNA make the resequencing CHIP a very fast and reliable method to screen the complete mtDNA for mutations.