Case report: A novel ACTA1 variant in a patient with nemaline rods and increased glycogen deposition

Background

Congenital myopathies are a group of heterogeneous inherited disorders, mainly characterized by early-onset hypotonia and muscle weakness. The spectrum of clinical phenotype can be highly variable, going from very mild to severe presentations. The course also varies broadly resulting in a fatal outcome in the most severe cases but can either be benign or lead to an amelioration even in severe presentations. Muscle biopsy analysis is crucial for the identification of pathognomonic morphological features, such as core areas, nemaline bodies or rods, nuclear centralizations and congenital type 1 fibers disproportion. However, multiple abnormalities in the same muscle can be observed, making more complex the myopathological scenario.

Case presentation

Here, we describe an Italian newborn presenting with severe hypotonia, respiratory insufficiency, inability to suck and swallow, requiring mechanical ventilation and gastrostomy feeding. Muscle biopsy analyzed by light microscopy showed the presence of vacuoles filled with glycogen, suggesting a metabolic myopathy, but also fuchsinophilic inclusions. Ultrastructural studies confirmed the presence of normally structured glycogen, and the presence of minirods, directing the diagnostic hypothesis toward a nemaline myopathy. An expanded Next Generation Sequencing analysis targeting congenital myopathies genes revealed the presence of a novel heterozygous c.965 T > A p. (Leu322Gln) variant in the ACTA1 gene, which encodes the skeletal muscle alpha-actin.

Conclusion

Our case expands the repertoire of molecular and pathological features observed in actinopathies. We highlight the value of ultrastructural examination to investigate the abnormalities detected at the histological level. We also emphasized the use of expanded gene panels in the molecular analysis of neuromuscular patients, especially for those ones presenting multiple bioptic alterations.

A biallelic variant in COX18 cause isolated Complex IV deficiency associated with neonatal encephalo-cardio-myopathy and axonal sensory neuropathy

Pathogenic variants impacting upon assembly of mitochondrial respiratory chain Complex IV (Cytochrome c Oxidase or COX) predominantly result in early onset mitochondrial disorders often leading to CNS, skeletal and cardiac muscle manifestations. The aim of this study is to describe a molecular defect in the COX assembly factor gene COX18 as the likely cause of a neonatal form of mitochondrial encephalo-cardio-myopathy and axonal sensory neuropathy. The proband is a 19-months old female displaying hypertrophic cardiomyopathy at birth and myopathy with axonal sensory neuropathy and failure to thrive developing in the first months of life. Serum lactate was consistently increased. Whole exome sequencing allowed the prioritization of the unreported homozygous substitution NM_001297732.2:c.667 G > C p.(Asp223His) in COX18. Patient's muscle biopsy revealed severe and diffuse COX deficiency and striking mitochondrial abnormalities. Biochemical and enzymatic studies in patient's myoblasts and in HEK293 cells after COX18 silencing showed a severe impairment of both COX activity and assembly. The biochemical defect was partially rescued by delivery of wild-type COX18 cDNA into patient's myoblasts. Our study identifies a novel defect of COX assembly and expands the number of nuclear genes involved in a mitochondrial disorder due to isolated COX deficiency.

Prominent muscle involvement in a familial form of mitochondrial disease due to a COA8 variant

Isolated mitochondrial respiratory chain Complex IV (Cytochrome c Oxidase or COX) deficiency is the second most frequent isolated respiratory chain defect. Causative mutations are mainly identified in structural COX subunits or in proteins involved in the maturation and assembly of the COX holocomplex. We describe an Italian familial case of mitochondrial myopathy due to a variant in the COX assembly factor 8 gene (COA8). Patient 1 is a 52-year-old woman who presented generalized epilepsy and retinitis pigmentosa at 10 years of age. From her early adulthood she complained about cramps and myalgia after exercise, and bilateral hearing loss emerged. Last neurological examination (52 years of age) showed bilateral ptosis, muscle weakness, peripheral neuropathy, mild dysarthria and dysphonia, cognitive impairment. Muscle biopsy had shown the presence of ragged-red fibers. Patient 2 (Patient 1's sister) is a 53-year-old woman presenting fatigability, myalgia, and hearing loss. Neurological examination showed ptosis and muscle weakness. Muscle biopsy displayed a diffuse reduction of COX activity staining and ragged-red fibers. Both sisters presented secondary amenorrhea. After ruling out mtDNA mutations, Whole Exome Sequencing analysis identified the novel homozygous COA8 defect c.170_173dupGACC, p.(Pro59fs) in the probands. Loss-of-function COA8 mutations have been associated with cavitating leukoencephalopathy with COX deficiency in 9 reported individuals. Disease course shows an early-onset rapid clinical deterioration, affecting both cognitive and motor functions over months, followed by stabilization and slow improvement over several years. Our findings expand the clinical spectrum of COA8-related disease. We confirm the benign course of this rare disorder, highlighting its (intrafamilial) clinical variability.

Ischemic optic neuropathy as first presentation in patient with m.3243 A > G MELAS classic mutation

BACKGROUND

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a systemic disorder in which multi-organ dysfunction may occur from mitochondrial metabolism failure. Maternally inherited mutations in the MT-TL1 gene are the most frequent causes for this disorder. Clinical manifestations may include stroke-like episodes, epilepsy, dementia, headache and myopathy. Among these, acute visual failure, usually in association with cortical blindness, can occur because of stroke-like episodes affecting the occipital cortex or the visual pathways. Vision loss due to optic neuropathy is otherwise considered a typical manifestation of other mitochondrial diseases such as Leber hereditary optic neuropathy (LHON).

CASE PRESENTATION

Here we describe a 55-year-old woman, sister of a previously described patient with MELAS harbouring the m.3243A > G (p.0, MT-TL1) mutation, with otherwise unremarkable medical history, that presented with subacute, painful visual impairment of one eye, accompanied by proximal muscular pain and headache. Over the next weeks, she developed severe and progressive vision loss limited to one eye. Ocular examination confirmed unilateral swelling of the optic nerve head; fluorescein angiography showed segmental perfusion delay in the optic disc and papillary leakage. Neuroimaging, blood and CSF examination and temporal artery biopsy ruled out neuroinflammatory disorders and giant cell arteritis (GCA). Mitochondrial sequencing analysis confirmed the m.3243A > G transition, and excluded the three most common LHON mutations, as well as the m.3376G > A LHON/MELAS overlap syndrome mutation. Based on the constellation of clinical symptoms and signs presented in our patient, including the muscular involvement, and the results of the investigations, the diagnosis of optic neuropathy as a stroke-like event affecting the optic disc was performed. L-arginine and ubidecarenone therapies were started with the aim to improve stroke-like episode symptoms and prevention. The visual defect remained stable with no further progression or outbreak of new symptoms.

CONCLUSIONS

Atypical clinical presentations must be always considered in mitochondrial disorders, even in well-described phenotypes and when mutational load in peripheral tissue is low. Mitotic segregation of mitochondrial DNA (mtDNA) does not allow to know the exact degree of heteroplasmy existent within different tissue, such as retina and optic nerve. Important therapeutic implications arise from a correct diagnosis of atypical presentation of mitochondrial disorders.

Extracellular Matrix Disorganization and Sarcolemmal Alterations in COL6-Related Myopathy Patients with New Variants of COL6 Genes

Collagen VI is a heterotrimeric protein expressed in several tissues and involved in the maintenance of cell integrity. It localizes at the cell surface, creating a microfilamentous network that links the cytoskeleton to the extracellular matrix. The heterotrimer consists of three chains encoded by COL6A1, COL6A2 and COL6A3 genes. Recessive and dominant molecular defects cause two main disorders, the severe Ullrich congenital muscular dystrophy and the relatively mild and slowly progressive Bethlem myopathy. We analyzed the clinical aspects, pathological features and mutational spectrum of 15 COL6-mutated patients belonging to our cohort of muscular dystrophy probands. Patients presented a heterogeneous phenotype ranging from severe forms to mild adult-onset presentations. Molecular analysis by NGS detected 14 different pathogenic variants, three of them so far unreported. Two changes, localized in the triple-helical domain of COL6A1, were associated with a more severe phenotype. Histological, immunological and ultrastructural techniques were employed for the validation of the genetic variants; they documented the high variability in COL6 distribution and the extracellular matrix disorganization, highlighting the clinical heterogeneity of our cohort. The combined use of these different technologies is pivotal in the diagnosis of COL6 patients.

Case Report: Rare Homozygous RNASEH1 Mutations Associated With Adult-Onset Mitochondrial Encephalomyopathy and Multiple Mitochondrial DNA Deletions

Mitochondrial DNA (mtDNA) maintenance disorders embrace a broad range of clinical syndromes distinguished by the evidence of mtDNA depletion and/or deletions in affected tissues. Among the nuclear genes associated with mtDNA maintenance disorders, RNASEH1 mutations produce a homogeneous phenotype, with progressive external ophthalmoplegia (PEO), ptosis, limb weakness, cerebellar ataxia, and dysphagia. The encoded enzyme, ribonuclease H1, is involved in mtDNA replication, whose impairment leads to an increase in replication intermediates resulting from mtDNA replication slowdown. Here, we describe two unrelated Italian probands (Patient 1 and Patient 2) affected by chronic PEO, ptosis, and muscle weakness. Cerebellar features and severe dysphagia requiring enteral feeding were observed in one patient. In both cases, muscle biopsy revealed diffuse mitochondrial abnormalities and multiple mtDNA deletions. A targeted next-generation sequencing analysis revealed the homozygous RNASEH1 mutations c.129-3C>G and c.424G>A in patients 1 and 2, respectively. The c.129-3C>G substitution has never been described as disease-related and resulted in the loss of exon 2 in Patient 1 muscle RNASEH1 transcript. Overall, we recommend implementing the use of high-throughput sequencing approaches in the clinical setting to reach genetic diagnosis in case of suspected presentations with impaired mtDNA homeostasis.

Early Findings in Neonatal Cases of RYR1-Related Congenital Myopathies

Ryanodine receptor type 1-related congenital myopathies are the most represented subgroup among congenital myopathies (CMs), typically presenting a central core or multiminicore muscle histopathology and high clinical heterogeneity. We evaluated a cohort of patients affected with Ryanodine receptor type 1-related congenital myopathy (RYR1-RCM), focusing on four patients who showed a severe congenital phenotype and underwent a comprehensive characterization at few months of life. To date there are few reports on precocious instrumental assessment. In two out of the four patients, a muscle biopsy was performed in the first days of life (day 5 and 37, respectively) and electron microscopy was carried out in two patients detecting typical features of congenital myopathy. Two patients underwent brain MRI in the first months of life (15 days and 2 months, respectively), one also a fetal brain MRI. In three children electromyography was performed in the first week of life and neurogenic signs were excluded. Muscle MRI obtained within the first years of life showed a typical pattern of RYR1-CM. The diagnosis was confirmed through genetic analysis in three out of four cases using Next Generation Sequencing (NGS) panels. The development of a correct and rapid diagnosis is a priority and may lead to prompt medical management and helps optimize inclusion in future clinical trials.

Assessing the impact of short term outdoor air pollution exposure on cardiac dyspnea: a case study of the south of France

 

There is a growing body of evidence that air pollution is a significant threat to health worldwide. The time exposure to air pollution leads diverse impact on the health. A short-term exposure increases hospital admission and mortality rate, causing mainly respiratory and cardiovascular diseases, including dyspnea; whereas a long-term exposure reduce life expectancy. Although the relationship between short term exposure to air pollution and several cardiovascular pathologies, such as coronaropathy, is widely established, the link regarding cardiac dyspnea is quite controversial. Nevertheless, previous studies are lead on few selected cities preventing a global overview on an entire territory.

Here, we aim to fill this gap and finally establish the impact of pollution on cardiac dyspnea, using the “Région Sud” in the south of France, as a model. We focused on the period from 2013 to 2018 for which we dispose of clinical data of people having attended one of the 47 emergency departmentss of the region with symptoms related to cardiac dyspnea, collected by the gip e-santé ORUPACA, for a total of 43,404 events. We collected pollutants (NO2, PM10 and O3) and climate (temperature and pressure) measurements on a daily basis supplied by the French agency AtmoSud. We set up a reproducible statistical framework based on a distributed lag non-linear model (DLNM) to show the relationship between short term exposure to outdoor air pollution and the incidence of cardiac dyspnoea event for each of the defined 366 areas of the region.

This study showed that each pollutant has a significant effect on triggering cardiac dyspnoea. Specifically, we found that the biggest cities of the region, with more than 300000 habitants, such as Marseille and Nice have a significant increase of 1,5 and 1,2 respectively, if the NO2 pass the threshold of 200 mg/m3, three days before the dyspnea event. In cities with habitants between 50000 and 100000, such as Avignon and Fréjus, we found that is the O3 to have the most significant effect on the cardiac dyspnea events. A peak of O3 over 180 mg/m3 in these cities, will increase of five times the number of dyspnea events after 6 days. We observed a milder effect of PM10 on dyspnea events and mainly on cities on the coast, such as Marseille, Nice and Toulon, for which the risk of dyspnea events significantly increase if the level of PM10 overcome 50 mg/m3.

Importantly, we established the impact of three different pollutants on hospital admission for cardiac dyspnea in each of the 366 areas in the South of France. Overall, we observed that each pollutant impacts the cardiac dyspnea events on different time frame between the pollution peak and the event, such as: few days for NO2, between 6 and 8 days for O3 and the same day or the day before for PM10. Finally, we developed a user-friendly web application called HEART (Health, Environment in PACA Region Tool) to easily show the results of this study.

Funding Acknowledgement

Type of funding source: Public grant(s) – EU funding. Main funding source(s): Idex UCAJEDI

TYMP Variants Result in Late-Onset Mitochondrial Myopathy With Altered Muscle Mitochondrial DNA Homeostasis

Biallelic TYMP variants result in the mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), a juvenile-onset disorder with progressive course and fatal outcome. Milder late-onset (>40 years) form has been rarely described. Gene panel sequencing in a cohort of 60 patients featuring muscle accumulation of mitochondrial DNA (mtDNA) deletions detected TYMP defects in three subjects (5%), two of them with symptom onset in the fifth decade. One of the patients only displayed ptosis and ophthalmoparesis. Biochemical and molecular studies supported the diagnosis. Screening of TYMP is recommended in adult patients with muscle mtDNA instability, even in the absence of cardinal MNGIE features.

Novel mutations in DNA2 associated with myopathy and mtDNA instability

The maintenance of mitochondrial DNA (mtDNA) relies on proteins encoded by nuclear genes. Mutations in their coding sequences result in heterogenous clinical presentations featuring mtDNA instability in affected tissues. DNA2 is a multi-catalytic protein involved in the removal of single strand DNA during mtDNA replication or Long Patch Base Excision Repair pathway. We have previously described DNA2 mutations in adult patients affected with familial and sporadic forms of mitochondrial myopathy. Here we describe four novel probands presenting with limb weakness associated with novel DNA2 molecular defects. Biochemical assays were established to investigate the functional effects of these variants.

Human induced pluripotent stem cell models for the study and treatment of Duchenne and Becker muscular dystrophies

Duchenne and Becker muscular dystrophies are the most common muscle diseases and are both currently incurable. They are caused by mutations in the dystrophin gene, which lead to the absence or reduction/truncation of the encoded protein, with progressive muscle degeneration that clinically manifests in muscle weakness, cardiac and respiratory involvement and early death. The limits of animal models to exactly reproduce human muscle disease and to predict clinically relevant treatment effects has prompted the development of more accurate in vitro skeletal muscle models. However, the challenge of effectively obtaining mature skeletal muscle cells or satellite stem cells as primary cultures has hampered the development of in vitro models. Here, we discuss the recently developed technologies that enable the differentiation of skeletal muscle from human induced pluripotent stem cells (iPSCs) of Duchenne and Becker patients. These systems recapitulate key disease features including inflammation and scarce regenerative myogenic capacity that are partially rescued by genetic and pharmacological therapies and can provide a useful platform to study and realize future therapeutic treatments. Implementation of this model also takes advantage of the developing genome editing field, which is a promising approach not only for correcting dystrophin, but also for modulating the underlying mechanisms of skeletal muscle development, regeneration and disease. These data prove the possibility of creating an accurate Duchenne and Becker in vitro model starting from iPSCs, to be used for pathogenetic studies and for drug screening to identify strategies capable of stopping or reversing muscular dystrophinopathies and other muscle diseases.

Can Intestinal Pseudo-Obstruction Drive Recurrent Stroke-Like Episodes in Late-Onset MELAS Syndrome? A Case Report and Review of the Literature

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a maternally inherited mitochondrial disorder that is most commonly caused by the m. 3243A>G mutation in the MT-TL1 mitochondrial DNA gene, resulting in impairment of mitochondrial energy metabolism. Although childhood is the typical age of onset, a small fraction (1–6%) of individuals manifest the disease after 40 years of age and usually have a less aggressive disease course. The clinical manifestations are variable and mainly depend on the degree of heteroplasmy in the patient's tissues and organs. They include muscle weakness, diabetes, lactic acidemia, gastrointestinal disturbances, and stroke-like episodes, which are the most commonly observed symptom. We describe the case of a 50-year-old male patient who presented with relapsing intestinal pseudo-obstruction (IPO) episodes, which led to a late diagnosis of MELAS. After diagnosis, he presented several stroke-like episodes in a short time period and developed a rapidly progressive cognitive decline, which unfortunately resulted in his death. We describe the variable clinical manifestations of MELAS syndrome in this atypical and relatively old patient, with a focus on paralytic ileus and stroke-like episodes; the first symptom may have driven the others, leading to a relentless decline. Moreover, we provide a brief revision of previous reports of IPO occurrence in MELAS patients with the m.3243A>G mutation, and we investigate its relationship with stroke-like episodes. Our findings underscore the importance of recognizing gastrointestinal disturbance to prevent neurological comorbidities.

Subclinical Leber's hereditary optic neuropathy with pediatric acute spinal cord onset: more than meets the eye

Background

Leber’s hereditary optic neuropathy (LHON) is a mitochondrial disease characterized by visual loss consequent to optic nerve atrophy. In some cases, LHON is associated with heterogeneous neurological extraocular manifestations and is referred to as “Leber plus disease”; rarely it is associated with a multiple sclerosis (MS)-like syndrome known as Harding disease, but no pediatric extraocular acute spinal onset is reported.

Case presentation

We describe the case of a 5-year-old girl carrying the G3460A mtDNA mutation who was referred to clinical examination for bilateral upper and lower limb weakness with no sign of optic neuropathy. Spinal cord MRI showed hyperintense signal alterations in T2-weighted and restricted diffusion in DWI sequences in the anterior portion of the cervical and dorsal spinal cord resembling a spinal cord vascular injury. No association between this mutation and pediatric spinal cord lesions has previously been reported. Alternative diagnostic hypotheses, including infective, ischemic and inflammatory disorders, were not substantiated by clinical and instrumental investigations.

Conclusions

Our case reports a novel pediatric clinical manifestation associated with the m.3460G > A mtDNA mutation, broadening the clinical spectrum of this disease. Early identification of new cases and monitoring of carriers beginning in childhood is important to prevent neurological deterioration and preserve long-term function.

Stormorken Syndrome Caused by a p.R304W STIM1 Mutation: The First Italian Patient and a Review of the Literature

Stormorken syndrome is a rare autosomal dominant disease that is characterized by a complex phenotype that includes tubular aggregate myopathy (TAM), bleeding diathesis, hyposplenism, mild hypocalcemia and additional features, such as miosis and a mild intellectual disability (dyslexia). Stormorken syndrome is caused by autosomal dominant mutations in the STIM1 gene, which encodes an endoplasmic reticulum Ca²⁺ sensor. Here, we describe the clinical and molecular aspects of a 21-year-old Italian female with Stormorken syndrome. The STIM1 gene sequence identified a c.910C > T transition in a STIM1 allele (p.R304W). The p.R304W mutation is a common mutation that is responsible for Stormorken syndrome and is hypothesized to cause a gain of function action associated with a rise in Ca²⁺ levels. A review of published STIM1 mutations (n = 50) and reported Stormorken patients (n = 11) indicated a genotype-phenotype correlation with mutations in a coiled coil cytoplasmic domain associated with complete Stormorken syndrome, and other pathological variants outside this region were more often linked to an incomplete phenotype. Our study describes the first Italian patient with Stormorken syndrome, contributes to the genotype/phenotype correlation and highlights the possibility of directly investigating the p.R304W mutation in the presence of a typical phenotype.

Highlights

- Stormorken syndrome is a rare autosomal dominant disease.

- Stormoken syndrome is caused by autosomal dominant mutations in the STIM1 gene.

- We present the features of a 21-year-old Italian female with Stormorken syndrome.

- Our review of published STIM1 mutations suggests a genotype-phenotype correlation.

- The p.R304W mutation should be investigated in the presence of a typical phenotype.

Expandable porous organic frameworks with built-in amino and hydroxyl functions for CO2and CH4capture

Organic functions built on the node of a porous covalent architecture exhibit excellent affinity for CO₂(54 kJ mol⁻¹) and CH₄(25 kJ mol⁻¹): the interaction of CO₂favorably with amine groups was observed by 2D NMR.

Linezolid-induced lactic acidosis: the thin line between bacterial and mitochondrial ribosomes

INTRODUCTION

Linezolid inhibits bacterial growth by targeting bacterial ribosomes and by interfering with bacterial protein synthesis. Lactic acidosis is a rare, but potentially lethal, side effect of linezolid. Areas covered: The pathogenesis of linezolid-induced lactic acidosis is reviewed with special emphasis on aspects relevant to the recognition, prevention and treatment of the syndrome. Expert opinion: Linezolid-induced lactic acidosis reflects the untoward interaction between the drug and mitochondrial ribosomes. The inhibition of mitochondrial protein synthesis diminishes the respiratory chain enzyme content and thus limits aerobic energy production. As a result, anaerobic glycolysis and lactate generation accelerate independently from tissue hypoxia. In the absence of any confirmatory test, linezolid-induced lactic acidosis should be suspected only after exclusion of other, more common, causes of lactic acidosis such as hypoxemia, anemia or low cardiac output. Normal-to-high whole-body oxygen delivery, high venous oxygen saturation and lack of response to interventions that effectively increase tissue oxygen provision all suggest a primary defect in oxygen use at the mitochondrial level. During prolonged therapy with linezolid, blood drug and lactate levels should be regularly monitored. The current standard-of-care treatment of linezolid-induced lactic acidosis consists of drug withdrawal to reverse mitochondrial intoxication and intercurrent life support.

Developmental transcription factor NFIB is a putative target of oncofetal miRNAs and is associated with tumour aggressiveness in lung adenocarcinoma

Genes involved in fetal lung development are thought to play crucial roles in the malignant transformation of adult lung cells. Consequently, the study of lung tumour biology in the context of lung development has the potential to reveal key developmentally relevant genes that play critical roles in lung cancer initiation/progression. Here, we describe for the first time a comprehensive characterization of miRNA expression in human fetal lung tissue, with subsequent identification of 37 miRNAs in non-small cell lung cancer (NSCLC) that recapitulate their fetal expression patterns. Nuclear factor I/B (NFIB), a transcription factor essential for lung development, was identified as a potential frequent target for these 'oncofetal' miRNAs. Concordantly, analysis of NFIB expression in multiple NSCLC independent cohorts revealed its recurrent underexpression (in ∼40-70% of tumours). Interrogation of NFIB copy number, methylation, and mutation status revealed that DNA level disruption of this gene is rare, and further supports the notion that oncofetal miRNAs are likely the primary mechanism responsible for NFIB underexpression in NSCLC. Reflecting its functional role in regulating lung differentiation, low expression of NFIB was significantly associated with biologically more aggressive subtypes and, ultimately, poorer survival in lung adenocarcinoma patients. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Selective mitochondrial depletion, apoptosis resistance, and increased mitophagy in human Charcot-Marie-Tooth 2A motor neurons

Charcot-Marie-Tooth 2A (CMT2A) is an inherited peripheral neuropathy caused by mutations in MFN2, which encodes a mitochondrial membrane protein involved in mitochondrial network homeostasis. Because MFN2 is expressed ubiquitously, the reason for selective motor neuron (MN) involvement in CMT2A is unclear. To address this question, we generated MNs from induced pluripotent stem cells (iPSCs) obtained from the patients with CMT2A as an in vitro disease model. CMT2A iPSC-derived MNs (CMT2A-MNs) exhibited a global reduction in mitochondrial content and altered mitochondrial positioning without significant differences in survival and axon elongation. RNA sequencing profiles and protein studies of key components of the apoptotic executioner program (i.e. p53, BAX, caspase 8, cleaved caspase 3, and the anti-apoptotic marker Bcl2) demonstrated that CMT2A-MNs are more resistant to apoptosis than wild-type MNs. Exploring the balance between mitochondrial biogenesis and the regulation of autophagy-lysosome transcription, we observed an increased autophagic flux in CMT2A-MNs that was associated with increased expression of PINK1, PARK2, BNIP3, and a splice variant of BECN1 that was recently demonstrated to be a trigger for mitochondrial autophagic removal. Taken together, these data suggest that the striking reduction in mitochondria in MNs expressing mutant MFN2 is not the result of impaired biogenesis, but more likely the consequence of enhanced mitophagy. Thus, these pathways represent possible novel molecular therapeutic targets for the development of an effective cure for this disease.

Identification of novel mutations in five patients with mitochondrial encephalomyopathy

MELAS, MERRF, LHON and NARP, are well-established mitochondrial syndromes associated with specific point mutations of mitochondrial DNA (mtDNA). However, these recurrent mtDNA mutations account for only a minority of mitochondrial disease cases. To evaluate the impact of novel mtDNA mutations, we performed mtDNA sequence analysis in muscle and other tissues of 240 patients with different mitochondrial neuromuscular syndromes. We identified a total of 33 subjects with novel, private or uncommon mutations. Among these, five novel mutations were found in both paediatric and adult cases. We here report on the clinical description of these patients, as well as the biochemical and molecular genetic characterization of the corresponding mutations. Patients 1 and 2 showed changes in ND genes, patient 3 carried a heteroplasmic deletion in the COI gene, patients 4 and 5 carried heteroplasmic mutations in tRNA(Trp) and tRNA(Phe), respectively. Altogether, these data indicate that mtDNA analysis must become part of the routine screening for mitochondrial disorders.

300 HEMIZYGOUS PRION PROTEIN GENE (PRNP) KNOCKOUT IN CATTLE FIBROBLASTS

Bovine spongiform encephalopathy (BSE) represents a real threat for human health, as has been demonstrated by the causal link with the variant form of Creutzfeldt-Jakob disease. The aim of our project is to create a bovine strain knockout for the prion protein gene (PRNP) that should be resistant to BSE infection. We combined the use of homologous recombination by PRNP targeting vectors in bovine fibroblasts with the subsequent use of nuclear transfer (NT). We transfected fetal (male) and adult (female) bovine fibroblasts by nucleofection, using targeting vectors disrupting the PRNP by means of loxP flanked cassettes. They expressed resistance to different drugs driven by a PGK or TK promoter and the thymidine kinase gene as a negative selection marker. We screened, by PCR, 907 drug-resistant colonies, from which we identified 8 Neo-resistant colonies with a recombined PRNP allele (overall efficiency 3.2%; 7/108 from fetal, 1/145 from adult; P < 0.5). Fibroblasts PRNP+/– Neo were used to produce NT blastocysts from which neural precursors cell lines were established (Lazzari et al. 2006 Stem Cells 24, 2514–2521). These lines were capable of extensive proliferation (over 120 doublings during 4 months of culture) and provided unlimited material for Southern blot analysis to confirm PCR findings. Three clones (2 from fetal and 1 from adult) were further analyzed and confirmed PRNP+/– by Southern blot and were subsequently used for NT to generate blastocysts for transfer to recipient heifers. On Day +40 of gestation, the pregnancy rate was 33.3% (9/30) for the fetal line and 50% (2/4) for the adult line. One of the fetuses originating from fetal fibroblasts was removed on Day +45 to establish a rejuvenated fibroblast cell line used for a second round of gene targeting to obtain a PRNP –/– clone. We nucleofected these fibroblasts with Puro, Hygro, and promoterless Hygro cassette-carrying targeting vectors. We screened 625 drug-resistant colonies by PCR but none tested positive for the second targeting. In conclusion, we have obtained heterozygous PRNP+/– fibroblasts with the Neo vector both in fetal and adult fibroblasts, but failed with other vectors. In the first targeting, the efficiency was 10 times greater in fetal v. adult fibroblasts. The derivation of neural precursor cell lines from cloned blastocysts is a useful procedure to have sufficient material for molecular analysis without the need of rejuvenating the cell through the production of a fetus. None of the vectors used for the targeting of the second allele was successful.

LAMA2 gene analysis in congenital muscular dystrophy: new mutations, prenatal diagnosis, and founder effect

OBJECTIVE

To determine if laminin-alpha2 deficiency is due to mutations in the LAMA2 gene or secondary to mutations in other congenital muscular dystrophy genes.

METHODS

We performed molecular analysis of LAMA2, by single-strand conformation polymorphism and sequencing, in 15 patients with undetectable or greatly reduced laminin-alpha2 expression. We also performed 4 prenatal diagnoses and investigated a founder effect.

RESULTS

We found 1 known and 9 previously undescribed LAMA2 mutations spanning all protein domains. These were nonsense or frameshifts causing laminin-alpha2 absence or, in 1 case, a homozygous missense mutation producing partial protein expression and milder phenotype. LAMA2 mutations were undetected in 5 patients, in 2 of whom FKRP mutations explained the phenotype. In 3 prenatal cases, the fetus was heterozygous for the mutation of interest and pregnancy continued; in 1 case, the fetus was affected and aborted. In 2 patients, the Cys967Stop mutation and identical haplotypes flanking the LAMA2 gene indicated a founder effect.

CONCLUSIONS

The clinical phenotype was severe in most patients with LAMA2 mutations and associated with undetectable protein expression. One case with no protein and another with partial expression had milder phenotypes. Typical white matter alterations on magnetic resonance imaging were found in all patients with LAMA2 mutations, supporting the utility of magnetic resonance imaging in differential diagnosis. The founder mutation (Cys967Stop) probably originated in Albania. Genetic characterization of affected families is mainly of use for prenatal diagnosis.