ObjectiveTo further delineate the clinical and genetic spectrum of epileptic and neurodevelopmental conditions associated with variants in STX1B.MethodsWe screened our diagnostic in-house database (comprising >20,000 exome sequencing datasets) for pathogenic and likely pathogenic variants inSTX1B. The detected cases were phenotyped in detail, and the findings were compared to previously published case reports.ResultsWe identified four unrelated individuals with pathogenic or likely pathogenic variants in STX1B (one missense and three loss-of-function variants). All patients displayed epileptic phenotypes, including epileptiform discharges on electroencephalography (without apparent seizures), developmental and epileptic encephalopathy and focal epilepsy. Three of the four patients had developmental delay. Febrile seizures occurred in two individuals. One patient with focal epilepsy underwent epilepsy surgery without lasting improvement. The neuropathological workup of brain tissue revealed a mild malformation of cortical development without alterations of cortical lamination or dysplastic neurons.ConclusionsOur findings confirm the wide clinical range ofSTX1B-related epileptic conditions and highlight the necessity of genetic testing prior to epilepsy surgery in cases with monogenic epilepsy. The identification of loss-of-function variants in very differently affected individuals suggests that no clear genotype-phenotype correlation can be established.

Leber's hereditary optic neuropathy (LHON) is the most frequent mitochondrial disease and was the first to be genetically defined by a point mutation in mitochondrial DNA (mtDNA). A molecular diagnosis is achieved in up to 95% of cases, the vast majority of which are accounted for by 3 mutations within mitochondrial complex I subunit-encoding genes in the mtDNA (mtLHON). Here, we resolve the enigma of LHON in the absence of pathogenic mtDNA mutations. We describe biallelic mutations in a nuclear encoded gene, DNAJC30, in 33 unsolved patients from 29 families and establish an autosomal recessive mode of inheritance for LHON (arLHON), which to date has been a prime example of a maternally inherited disorder. Remarkably, all hallmarks of mtLHON were recapitulated, including incomplete penetrance, male predominance, and significant idebenone responsivity. Moreover, by tracking protein turnover in patient-derived cell lines and a DNAJC30-knockout cellular model, we measured reduced turnover of specific complex I N-module subunits and a resultant impairment of complex I function. These results demonstrate that DNAJC30 is a chaperone protein needed for the efficient exchange of complex I subunits exposed to reactive oxygen species and integral to a mitochondrial complex I repair mechanism, thereby providing the first example to our knowledge of a disease resulting from impaired exchange of assembled respiratory chain subunits.

Inherited inborn errors of metabolism can cause premature severe dilated cardiomyopathy in infants and cause sudden unexpected death (SUDI). PPA2 gene encoding the mitochondrial pyrophosphatase is involved in many reactions for energy metabolism of the cell. Biallelic mutations induce a mitochondrial disease with a particularly serious cardiac phenotype. In an international consortium, we identified recently 11 new cases from 5 unrelated families, with homozygous or compound heterozygous hypomorphic PPA2 variations. We reviewed the clinical features and outcomes from both our patients and those previously described in the literature [1], [2]. All of the cases (n = 28) suffered from cardiac defects. MRI, when performed, showed dilated left ventricle while histology of cardiac muscle documented typical diffuse myocardial fibrosis or necrosis. Twenty-four patients (86%) died suddenly from cardiogenic shock at a median age of 11.5 months (range, 11 days to 20 years) even in case of active resuscitation attempt. Ventricular fibrillation was sometimes noted just before the cardiac arrest. Acute myocarditis was basically suspected. Interestingly, three times, very low alcohol consummation was reported as trigger before the death while 5 children had a proved viral disease. Alcohol metabolism and viral illness likely increase the stress of the cells already deprived of adequate ATP. The survivor cases underwent defibrillator implantation. Moreover, two of them expressed mild neurological features such as cerebellar syndrome. PPA2 gene plays a significant role in inherited infant dilated cardiomyopathies. According to the genotype, sudden death can happen very early in the childhood or might be triggered with alcohol absorption or common viral illness. PPA2 should be systematically added in the currently used cardiomyopathy genes panels but also in SUDI's since cardiac manifestations can be extremely acute especially in neonates.

Background: Acute necrotizing encephalopathy of childhood (ANEC) is a rare, febrile encephalopathy due to neurotropic viral infection causing rapid alteration of consciousness and seizures. In cranial magnetic resonance imaging (cMRI), symmetrical involvement of the thalami is characteristic, as is absence of pleocytosis and increased protein level in cerebrospinal fluid (CSF).

Pyruvate dehydrogenase complex (PDHc) defect is a well-known cause of mitochondrial disorders (MD) with at least six responsible genes (PDHA1, PDHB, DLAT, DLD, PDHX, PDP1). The aim of this work was to assess the diagnostic value of biochemical methods in recognition of PDHc defect in Polish patients with suspicion of MD. In the first step, Western blot of the E1α subunit was performed on 86 archive muscle bioptates with suspicion of MD. In the second step, Sanger PDHA1 sequencing was performed in 21 cases with low E1α expression. In the third step, 7 patients with negative results of PDHA1 sequencing were subjected to whole-exome sequencing (WES). This protocol revealed 4 patients with PDHA1 and one with DLD mutations. Four additional probands were diagnosed outside the protocol (WES or Sanger sequencing). The molecular characterization of PDHc defect was conducted in a total of 9 probands: 5 according to and 4 off the protocol. Additionally, two affected relatives were recognized by a family study. Altogether we identified seven different PDHA1 changes, including two novel variants [c.464T > C (p.Met155Thr) and c.856_859dupACTT (p.Arg288Leufs*10)] and one DLD variant. The lactate response to glucose load in the PDHA1 subset was compared to a subset of non PDHc-related MD. Opposite responses were observed, with an increase of 23% and decrease of 27%, respectively. The results show that determining lactate response to glucose load and muscle E1α expression may contribute to distinguishing PDHc-related and other MD, however, WES is becoming the method of choice for MD diagnostics.

ECHS1 encodes the short chain enoyl coenzyme A (CoA) hydratase an enzyme located in the inner mitochondrial Matrix, which catalyzes the second step of fatty acid oxidation and is involved in the metabolism of valine and isoleucine. Recently two siblings with mutations in ECHS1 have been described presenting a clinical picture with symmetrical basal ganglia alterations and encephalopathy suggesting a mitochondrial disease. This disorder can be diagnosed by increased excretion of S-(2-carboxypropyl) cysteine and methacrylyl-CoA and acryloyl-CoA in urine (Peters et al. Brain 2014 Nov;137:2903–8).

A non-classical clinical course of Barth Syndrome (BTHS) A six year-old boy, born to non-consanguineous, healthy parents was primarily referred because of growth retardation. Auxological parameters were below the 3rd percentile after having been normal at birth. Especially the extent of microcephaly (<3 SD) was impressive. Additionally, mild generalized muscular hypotonia was present. Psychomotor development was regular. Gastrointestinal, endocrinological and nutritional workup revealed no explanatory pathological findings. Metabolic workup including lactate profile, pyruvate and lactate/pyruvate ratio was normal. MRI of the brain and MR-spectroscopy showed no pathologies. Eighteen months later the patient presented with episodes of painless muscular weakness and severe exercise intolerance triggered by a febrile infection. Clinical findings included muscular weakness, hypotonia and positive Gower's sign in the absence of muscular atrophy. Diagnostic workup again was unremarkable. The combination of unclear muscular symptoms and persistent growth retardation prompted mitochondrial workup. Activity of complex I, III and IV in oxidative phosphorylation was reduced. Whole exome sequencing revealed a mutation in the tafazzine gene described as associated with early onset, severe BTHS. The diagnosis of BTHS was supported by a specific pattern of fatty acid profile of cardiolipin. Nevertheless, characteristic signs and symptoms for BTHS such as cardiomyopathy, neutropenia or 3-methylglutaconic aciduria have never been observed in the patient.

A 6-year-old boy of Roma decent, born to nonconsanguineous, healthy parents was primarily referred because of growth retardation. Auxological parameters were below the 3rd percentile after having been normal at birth. The 3rd percentile had been crossed at age 12 months, without any catch-up growth afterward. Especially, the extent of microcephaly (< 3 standard deviation) was impressive. In addition, mild generalized muscular hypotonia was present. Psychomotor development was regular. Gastrointestinal, endocrinological, and nutritional work-up revealed no explanatory pathological findings. Metabolic work-up including lactate profile, pyruvate and lactate/pyruvate ratio, urinary organic acids, plasma amino acid profile, ammonia, creatine kinase, total and free carnitine, and acylcarnitine profile was normal. Magnetic resonance imaging (MRI) of the brain and MR spectroscopy showed no pathologies. Overall, 18 months later, the patient presented with episodes of painless muscular weakness and severe exercise intolerance triggered by a febrile infection. Clinical findings included muscular weakness, hypotonia, and positive Gower’s sign in the absence of muscular atrophy.

Case Report: Mitochondrial DNA mutations of ATP6 affect a subunit of ATP synthase (complex V of the oxidative phosphorylation) and present mostly as severe neurologic diseases with neuropathy, ataxia, retinitis pigmentosa [NARP] or as maternal inherited Leigh syndrome (MILS). Only recently, patients with hypertrophic CMP and ATP6 mutations have been described.

Aims: Kearns-Sayre syndrome (KSS) is a mitochondrial deoxyribonucleic acid (mtDNA) syndrome defined by ophthalmoplegia, pigmentary retinopathy, onset less than age 20 years plus: cardiac conduction defects, cerebellar syndrome or cerebrospinal fluid protein > 100 mg/dL. KSS may affect many organ systems causing encephalomyopathy, endocrinopathies, sensorineural hearing loss, and renal involvement. De novo single large-scale mtDNA deletions are detectable at high heteroplasmic levels in muscle of almost all patients.

A mitochondrial matrix-specific p53 construct (termed p53-290) in HepG2 cells was utilized to determine the impact of p53 in the mitochondrial matrix following oxidative stress. H2O2 exposure reduced cellular proliferation similarly in both p53-290 and vector cells, and p53-290 cells demonstrating decreased cell viability at 1 mM H2O2 (~ 85% viable). Mitochondrial DNA (mtDNA) abundance was decreased in a dose-dependent manner in p53-290 cells while no change was observed in vector cells. Oximetric analysis revealed reduced maximal respiration and reserve capacity in p53-290 cells. Our results demonstrate that mitochondrial matrix p53 sensitizes cells to oxidative stress by reducing mtDNA abundance and mitochondrial function.

Aims: Inherited mitochondrial diseases comprise a group of highly heterogeneous disorders that result in defective oxidative phosphorylation, which present with a wide spectrum of phenotypic features ranging from neonatal fatalities to late onset neurodegenerative disorders. Because of its genetic heterogeneity, identifying the cause for mitochondrial disorders remains a challenge and most patients lack a molecular diagnosis.

Case 1: 12 year old girl, 2nd of 4 children of consanguineous Iraqi parents with bilateral, dyskinetic, spastic paresis. Until 4 years of age normal development, than increasing tremor and dystonia, rigor and spasticity of the lower, later of the upper extremities. Progressively scoliosis, loss of gait, loss of speech, hypertrophic cardiomyopathy and symptomatic epilepsy developed. Therapy with intrathecal Baclofen slightly stabilized the situation.

Complex I (C I) deficiency is a frequent cause (30%) of pediatric mitochondrial disease, presenting with a phenotypic spectrum from lethal multisystem disorder to mild myopathy. More than 80% of the patients present neurologic symptoms. The diagnosis is based on biochemical analysis of C I-activity in muscle or fibroblasts. The molecular diagnosis is difficult to establish due to a large number of candidate genes (>80). Therefore prognostic evaluation, genetic counseling, prenatal diagnosis and also therapeutic approaches are difficult.

The mitochondrial phosphate carrier is an essential enzyme of mitochondrial ATP synthesis. The enzyme is expressed in two tissue-specific isoforms by mutually exclusive alternative splicing of the SLC25A3 gene transcript. A first phosphate carrier defect was described recently as a novel defect of oxidative phosphorylation.