Alterations in the MYH7 gene can cause cardiac and skeletal myopathies. MYH7-related skeletal myopathies are extremely rare, and the vast majority of causal variants in the MYH7 gene are predicted to ...alter the rod domain of the of ss-cardiac myosin molecule, resulting in distal muscle weakness as the predominant manifestation. Here we describe two unrelated patients harboring an in-frame deletion in the MYH7 gene that is predicted to result in deletion of a single amino acid (p.Glu500del) in the head domain of ss-cardiac myosin. Both patients display an unusual skeletal myopathy phenotype with congenital axial stiffness and muscular hypertonus, but no cardiac involvement. Clinical data, MRI results and histopathological data were collected retrospectively in two unrelated boys (9 and 3.5 years old). Exome sequencing uncovered the same 3-bp in-frame deletion in exon 15 (c.1498_1500delGAG) of the MYH7 gene of both patients, a mutation which deletes a highly conserved glutamate residue (p.Glu500del) in the relay loop of the head domain of the ss-cardiac myosin heavy chain. The mutation occurred de novo in one patient, whereas mosaicism was detected in blood of the father of the second patient. Both boys presented with an unusual phenotype of prenatal polyhydramnios, congenital axial stiffness and muscular hypertonus. In one patient the phenotype evolved into an axial/proximal skeletal myopathy without distal involvement or cardiomyopathy, whereas the other patient exhibited predominantly stiffness and respiratory involvement. We review and compare all patients described in the literature who possess a variant predicted to alter the p.Glu500 residue in the ss-cardiac myosin head domain, and we provide in-silico analyses of potential effects on polypeptide function. The data presented here expand the phenotypic spectrum of mutations in the MYH7 gene and have implications for future diagnostics and therapeutic approaches.
Mitochondrial complex I is the largest multi-protein enzyme complex of the oxidative phosphorylation system. Seven subunits of this complex are encoded by the mitochondrial and the remainder by the ...nuclear genome. We review the natural disease course and signs and symptoms of 130 patients (four new cases and 126 from literature) with mutations in nuclear genes encoding structural complex I proteins or those involved in its assembly. Complex I deficiency caused by a nuclear gene defect is usually a non-dysmorphic syndrome, characterized by severe multi-system organ involvement and a poor prognosis. Age at presentation may vary, but is generally within the first year of life. The most prevalent symptoms include hypotonia, nystagmus, respiratory abnormalities, pyramidal signs, dystonia, psychomotor retardation or regression, failure to thrive, and feeding problems. Characteristic symptoms include brainstem involvement, optic atrophy and Leigh syndrome on MRI, either or not in combination with internal organ involvement and lactic acidemia. Virtually all children ultimately develop Leigh syndrome or leukoencephalopathy. Twenty-five percent of the patients died before the age of six months, more than half before the age of two and 75 % before the age of ten years. Some patients showed recovery of certain skills or are still alive in their thirties . No clinical, biochemical, or genetic parameters indicating longer survival were found. No clear genotype-phenotype correlations were observed, however defects in some genes seem to be associated with a better or poorer prognosis, cardiomyopathy, Leigh syndrome or brainstem lesions.
The goal of the study was to retrospectively evaluate a cohort of children and adults with mitochondrial diseases (MDs) in a single-center experience. Neurological clinical examination, brain ...magnetic resonance imaging (MRI) and spectroscopy, muscle biopsy, metabolic and molecular-genetic analysis were evaluated in 26 children and 36 adult patients with MD in Slovenia from 2004 to 2018. Nijmegen MD criteria (MDC) were applied to all patients and the need for a muscle biopsy was estimated. Exome-sequencing was used in half of the patients. Twenty children (77.0%) and 12 adults (35.0%) scored a total of ≥8 on MDC, a result that is compatible with the diagnosis of definite MD. Yield of exome-sequencing was 7/22 (31.0%), but the method was not applied systematically in all patients from the beginning of diagnostics. Brain MRI morphological changes, which can be an imaging clue for the diagnosis of MD, were found in 17/24 children (71.0%). In 7/26 (29.0%) children, and in 20/30 (67.0%) adults, abnormal mitochondria were found on electron microscopy (EM) and ragged-red fibers were found in 16/30 (53.0%) adults. Respiratory chain enzymes (RCEs) and/or pyruvate dehydrogenase complex (PDHc) activities were abnormal in all the children and six adult cases. First, our data revealed that MDC was useful in the clinical diagnosis of MD, and second, until the use of NGS methods, extensive, laborious and invasive diagnostic procedures were performed to reach a final diagnosis. In patients with suspected MD, there is a need to prioritize molecular diagnosis with the more modern next-generation sequencing (NGS) method.
Genetic defects are often still regarded as a life-long fate, which one has to cope with. It is true that in many cases an inherited disposition may lead to a severe disease; however, it is also true ...that the number of genetic defects with a treatment option is continuously increasing and in some of them the onset of disease symptoms can even be totally prevented. Knowledge of the precise molecular pathomechanism is often the basis for a treatment concept. Genome-wide sequencing has tremendously increased the possibility to identify a genetic defect and its broad application has meanwhile made a decisive contribution in routine diagnostics. After identifying a genetic alteration, it is still necessary to investigate the pathobiochemical consequences on the cellular and systemic level. This can be a time-consuming process since not all functional consequences can be immediately recognized. In the case of metabolic defects the treatment strategy can either be a supplementation of missing products or a removal of toxic substrates. The residual function of affected pathways can also often be improved. Recently, the direct correction of the affected genetic defects has become a treatment option for a selected number of diseases. As the first symptoms of disease usually occur early in life, pediatrics has a pioneering role in developing treatment strategies.
Background
Whereas propionic acidemia (PA) is a target disease of newborn screening (NBS) in many countries, it is not in others. Data on the benefit of NBS for PA are sparse.
Study design
Twenty PA ...patients diagnosed through NBS were compared to 35 patients diagnosed by selective metabolic screening (SMS) prompted by clinical findings, family history, or routine laboratory test results. Clinical and biochemical data of patients from 16 metabolic centers in Germany, Austria, and Switzerland were evaluated retrospectively. Additionally, assessment of the intelligent quotient (IQ) was performed. In a second step, the number of PA patients who have died within the past 20 years was estimated based on information provided by the participating metabolic centers.
Results
Patients diagnosed through NBS had neither a milder clinical course regarding the number of metabolic crises nor a better neurological outcome. Among NBS patients, 63% were already symptomatic at the time of diagnosis, and <10% of all patients remained asymptomatic. Among all PA patients, 76% were found to be at least mildly mentally retarded, with an IQ <69. IQ was negatively correlated with the number of metabolic decompensations, but not simply with the patients’ age. Physical development was also impaired in the majority of patients. Mortality rates tended to be lower in NBS patients compared with patients diagnosed by SMS.
Conclusion
Early diagnosis of PA through NBS seems to be associated with a lower mortality rate. However, no significant benefit could be shown for surviving patients with regard to their clinical course, including the number of metabolic crises, physical and neurocognitive development, and long-term complications.
Oncocytic tumours are characterised by hyperproliferation of mitochondria. We immunohistochemically analysed all enzymes of the oxidative phosphorylation system in 19 oncocytic thyroid tumours. A ...specific lack of complex I was detected, which was expressed at <5% of the level determined in surrounding non-cancerous tissue.
Abstract Joubert syndrome (JS) is a clinically and genetically heterogeneous ciliopathy characterized by episodic hyperpnea and apnea, hypotonia, ataxia, cognitive impairment and ocular motor ...apraxia. The “molar tooth sign” is pathognomonic of this condition. Mutations in the MKS1 gene are a major cause of Meckel-Gruber syndrome (MKS), the most common form of syndromic neural tube defects, frequently resulting in perinatal lethality. We present the phenotype and genotype of a child with severe JS and agenesis of the corpus callosum (ACC). In our patient, a next generation sequencing (NGS) approach revealed the following two variants of the MKS1 gene: first, a novel missense variant c.240G > T (p.Trp80Cys), which affects a residue that is evolutionarily highly conserved in mammals and ciliates; second, a 29 bp deletion in intron 15 c.1408-35_1408-7del29, a founder mutation, which in a homozygous state constitutes the major cause of MKS in Finland. We review the MKS1 -variants in all of the eleven JS patients reported to date and compare these patients to our case. To our knowledge, this is the first patient with Joubert syndrome and agenesis of the corpus callosum where a potentially causal genotype is provided.
Kearns-Sayre syndrome (KSS) is a mitochondrial DNA (mtDNA) disorder characterized by ophthalmoplegia, ptosis, retinopathy, onset before age 20 years plus one: cardiac conduction defects, cerebellar ...syndrome, elevated CSF protein. KSS may affect many organs causing encephalomyopathy, sensorineural hearing loss, endocrinopathy and/or heart and renal involvement. De novo single large-scale mtDNA rearrangements are the genetic hallmark, detectable at high heteroplasmic levels. We present the first child with KSS described so far with a nuclear gene defect of RRM2B, encoding the small subunit of p53-inducible ribonucleotide reductase. In the 15 year-old girl, sensorineural hearing loss was noticed at the age of 11/2 year leading to cochlear implants at ages 2 and 6 years. Her psychomotor development was slightly retarded until the age of 10 years when muscle weakness and an atactic gait became increasingly evident. At the age of 8 years, the girl developed edema caused by a protein-loosing nephropathy. She now presents with ptosis, external ophthalmoplegia and retinitis pigmentosa. Muscle biopsy showed COX-positive and -negative ragged-red fibers, but no biochemical abnormalities of the respiratory chain complexes. Muscle mtDNA analysis revealed no single large-scale rearrangements, but multiple low-level mtDNA deletions. Nuclear gene analysis identified compound heterozygous mutations in the nuclear RRM2B gene: c.328C > T, p.Arg110Cys; c.846G > C, p.Met282Ile. Ribonucleotide reductase has a crucial role in the de novo conversion of ribonucleoside diphosphates into the corresponding deoxyribonucleoside diphosphates, and thus is essential for proper mtDNA synthesis. RRM2B mutations have been described so far only in a single adult patient with KSS. This second case, the first pediatric patient, underlines that KSS is not exclusively a sporadic mtDNA deletion/duplication disorder but rarely an autosomal recessive disease caused by nuclear encoded mtDNA transcription alteration.
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.
Previously, renal cell carcinoma tissues were reported to display a marked reduction of components of the respiratory chain. To elucidate a possible relationship between tumourigenesis and ...alterations of oxidative phosphorylation, we screened for mutations of the mitochondrial DNA (mtDNA) in renal carcinoma tissues and patient-matched normal kidney cortex. Seven of the 15 samples investigated revealed at least one somatic heteroplasmic mutation as determined by denaturating HPLC analysis (DHPLC). No homoplasmic somatic mutations were observed. Actually, half of the mutations presented a level of heteroplasmy below 25%, which could be easily overlooked by automated sequence analysis. The somatic mutations included four known D-loop mutations, four so far unreported mutations in ribosomal genes, one synonymous change in the ND4 gene and four nonsynonymous base changes in the ND2, COI, ND5 and ND4L genes. One renal cell carcinoma tissue showed a somatic A3243G mutation, which is a known frequent cause of MELAS syndrome (mitochondrial encephalomyopathy, lactic acidosis, stroke-like episode) and specific compensatory alterations of enzyme activities of the respiratory chain in the tumour tissue. No difference between histopathology and clinical progression compared to the other tumour tissues was observed. In conclusion, the low abundance as well as the frequently observed low level of heteroplasmy of somatic mtDNA mutations indicates that the decreased aerobic energy capacity in tumour tissue seems to be mediated by a general nuclear regulated mechanism.