Bertold Schrank

Mutation in TACO1, encoding a translational activator of COX I, results in cytochrome c oxidase deficiency and late-onset Leigh syndrome

Defects in mitochondrial translation are among the most common causes of mitochondrial disease, but the mechanisms that regulate mitochondrial translation remain largely unknown. In the yeast Saccharomyces cerevisiae, all mitochondrial mRNAs require specific translational activators, which recognize sequences in 5′ UTRs and mediate translation. As mammalian mitochondrial mRNAs do not have significant 5′ UTRs, alternate mechanisms must exist to promote translation. We identified a specific defect in the synthesis of the mitochondrial DNA (mtDNA)-encoded COX I subunit in a pedigree segregating late-onset Leigh syndrome and cytochrome c oxidase (COX) deficiency. We mapped the defect to chromosome 17q by functional complementation and identified a homozygous single-base-pair insertion in CCDC44, encoding a member of a large family of hypothetical proteins containing a conserved DUF28 domain. CCDC44, renamed TACO1 for translational activator of COX I, shares a notable degree of structural similarity with bacterial homologs, and our findings suggest that it is one of a family of specific mammalian mitochondrial translational activators.

Muscle MRI findings in limb girdle muscular dystrophy type 2L

Limb girdle muscular dystrophy type 2L (LGMD2L) is an adult-onset slowly progressive muscular dystrophy associated with recessive mutations in the ANO5 gene. We analysed the muscle MRI pattern in a cohort of 25 LGMD2L patients in order to understand the extent and progression of muscle pathology in LGM2L and assess if muscle MRI might help in the diagnostic work-up of these patients. Our results showed a homogeneous pattern of muscle pathology on muscle MRI, with a predominant involvement of the posterior compartment muscles in both the thighs and calves. The muscles of the anterior compartments in the leg together with the sartorius and gracilis muscles were best preserved, which partially overlaps with patterns observed for other recessive LGMDs. Muscle MRI therefore does not appear to be as useful in the diagnostic work up of LGMD2L as for other neuromuscular diseases, such as Bethlem myopathy or myofibrillar myopathy.

ANO5 gene analysis in a large cohort of patients with anoctaminopathy: confirmation of male prevalence and high occurrence of the common exon 5 gene mutation

Limb girdle muscular dystrophy type 2L or anoctaminopathy is a condition mainly characterized by adult onset proximal lower limb muscular weakness and raised CK values, due to recessive ANO5 gene mutations. An exon 5 founder mutation (c.191dupA) has been identified in most of the British and German LGMD2L patients so far reported. We aimed to further investigate the prevalence and spectrum of ANO5 gene mutations and related clinical phenotypes, by screening 205 undiagnosed patients referred to our molecular service with a clinical suspicion of anoctaminopathy. A total of 42 unrelated patients had two ANO5 mutations (21%), whereas 14 carried a single change. We identified 34 pathogenic changes, 15 of which are novel. The c.191dupA mutation represents 61% of mutated alleles and appears to be less prevalent in non‐Northern European populations. Retrospective clinical analysis corroborates the prevalently proximal lower limb phenotype, the male predominance and absence of major cardiac or respiratory involvement. Identification of cases with isolated hyperCKaemia and very late symptomatic male and female subjects confirms the extension of the phenotypic spectrum of the disease. Anoctaminopathy appears to be one of the most common adult muscular dystrophies in Northern Europe, with a prevalence of about 20%–25% in unselected undiagnosed cases.

Clinical and neuropathological findings in patients with TACO1 mutations

We have recently identified mutations in the translation activator of cytochrome c oxidase 1 (TACO1) gene, leading to cytochrome c oxidase (COX) deficiency. Here, we report the clinical and neuroimaging findings of five members of a big consanguinous family homozygous for c.472insC in TACO1. All 5 patients had an uneventful early childhood and a subtle onset, slowly progressive cognitive dysfunction, dystonia or visual impairment between ages 4 and 16years. Affected girls had a milder phenotype and preserved ambulation into the late twenties. Brain MRI revealed bilateral, symmetric lesions of the basal ganglia in all affected family members, but less prominent in girls. TACO1 analysis showed no mutations in 17 patients with juvenile-onset Leigh syndrome and isolated COX or combined respiratory chain deficiency, indicating that TACO1 mutations are a rare cause of Leigh syndrome.

Der Einsatz der Magnetresonanztomographie der Muskulatur bei der Diagnose neuromuskulärer Erkrankungen

ZusammenfassungDie Magnetresonanztomographie (MRT) der Skelettmuskulatur ist eine wertvolle diagnostische Zusatzuntersuchung in der neuromuskulären Sprechstunde. Im Gegensatz zur ganz fokal eingeschränkten Aussage der Muskelbiopsie gibt vor allem die MRT der Oberschenkelregion Auskunft über ein größeres Muskelareal bzw. multiple Muskeln und hat daher einen geringeren Sampling Error. Die MRT detektiert mit hoher Sensitivität den bei dystrophen oder degenerativen Myopathien regelhaft auftretenden fettigen Umbau von Muskeln einerseits und die bei entzündlichen Veränderungen oder akuten Rhabdomyolysen vermehrte Flüssigkeitseinlagerung in das Muskelgewebe andererseits. Sie ermöglicht eine rasche Zuordnung unklarer Krankheitsbilder, gibt einen Überblick über Intensität und Ausbreitung pathologischer Veränderungen und kann in Verlaufsuntersuchungen vor allem bei den Myositiden therapeutische Entscheidungen mitbeeinflussen. Im Vorfeld einer geplanten Muskelbiopsie ermöglicht sie die Wahl des aussagekräftigsten Biopsiemuskels. Zwar gibt es morphologisch fassbare Unterschiede zwischen neurogenen und myogenen Veränderungen; deren sichere Abgrenzung erfordert jedoch eine Einbeziehung neurologischer und neurophysiologischer Untersuchungen, so dass erst die interdisziplinäre Kooperation den Informationsgewinn optimiert.AbstractMagnetic resonance imaging (MRI) of skeletal muscle complements the diagnostic repertoire of a neuromuscular clinic. Especially imaging of the thigh and pelvic region covers a significant area of muscle containing multiple different muscles. MRI thus can avoid potential sampling errors that accompany the diagnosis of myopathy using EMG (electromyography) or muscle biopsy. T1-weighted images detect fatty transformation of muscle characteristic of dystrophic or degenerative myopathies with high sensitivity; fat-saturated STIR (short tau inversion recovery) imaging detects increased fluid accumulation found typically in inflammatory myopathies or with rhabdomyolysis. MRI provides an overview of both severity and distribution of pathologic changes. Its rapidly obtained results substantially influence the process of making a diagnosis in patients with unexplained weakness. Repeated examinations in treated patients with inflammatory myopathies can guide therapeutic decisions. If it is performed prior to a muscle biopsy, it helps to choose the most informative muscle and biopsy site. Although there are characteristic morphological changes for both neurogenic and myogenic processes, respectively, there is no absolute specificity. The optimal diagnostic yield therefore requires close interdisciplinary cooperation between radiologist, neurophysiologist and clinician.

Lifetime exercise intolerance with lactic acidosis as key manifestation of novel compound heterozygous ACAD9 mutations causing complex I deficiency

We report a 36-year-old female having lifetime exercise intolerance and lactic acidosis with nausea associated with novel compound heterozygous Acyl-CoA dehydrogenase 9 gene (ACAD9) mutations (p.Ala390Thr and p.Arg518Cys). ACAD9 is an assembly factor for the mitochondrial respiratory chain complex I. ACAD9 mutations are recognized as frequent causes of complex I deficiency. Our patient presented with exercise intolerance, rapid fatigue, and nausea since early childhood. Mild physical workload provoked the occurrence of nausea and vomiting repeatedly. Her neurological examination, laboratory findings and muscle biopsy demonstrated no abnormalities. A bicycle spiroergometry provoked significant lactic acidosis during and following exercise pointing towards a mitochondrial disorder. Subsequently, the analysis of respiratory chain enzyme activities in muscle revealed severe isolated complex I deficiency. Candidate gene sequencing revealed two novel heterozygous ACAD9 mutations. This patient report expands the mutational and phenotypic spectrum of diseases associated with mutations in ACAD9.

Frequent genes in rare diseases: panel-based next generation sequencing to disclose causal mutations in hereditary neuropathies

Hereditary neuropathies comprise a wide variety of chronic diseases associated to more than 80 genes identified to date. We herein examined 612 index patients with either a Charcot‐Marie‐Tooth phenotype, hereditary sensory neuropathy, familial amyloid neuropathy, or small fiber neuropathy using a customized multigene panel based on the next generation sequencing technique. In 121 cases (19.8%), we identified at least one putative pathogenic mutation. Of these, 54.4% showed an autosomal dominant, 33.9% an autosomal recessive, and 11.6% an X‐linked inheritance. The most frequently affected genes were PMP22 (16.4%), GJB1 (10.7%), MPZ, and SH3TC2 (both 9.9%), and MFN2 (8.3%). We further detected likely or known pathogenic variants in HINT1, HSPB1, NEFL, PRX, IGHMBP2, NDRG1, TTR, EGR2, FIG4, GDAP1, LMNA, LRSAM1, POLG, TRPV4, AARS, BIC2, DHTKD1, FGD4, HK1, INF2, KIF5A, PDK3, REEP1, SBF1, SBF2, SCN9A, and SPTLC2 with a declining frequency. Thirty‐four novel variants were considered likely pathogenic not having previously been described in association with any disorder in the literature. In one patient, two homozygous mutations in HK1 were detected in the multigene panel, but not by whole exome sequencing. A novel missense mutation in KIF5A was considered pathogenic because of the highly compatible phenotype. In one patient, the plasma sphingolipid profile could functionally prove the pathogenicity of a mutation in SPTLC2. One pathogenic mutation in MPZ was identified after being previously missed by Sanger sequencing. We conclude that panel based next generation sequencing is a useful, time‐ and cost‐effective approach to assist clinicians in identifying the correct diagnosis and enable causative treatment considerations.

Targeted sequencing with expanded gene profile enables high diagnostic yield in non-5q-spinal muscular atrophies

Spinal muscular atrophies (SMAs) are a heterogeneous group of disorders characterized by muscular atrophy, weakness, and hypotonia due to suspected lower motor neuron degeneration (LMND). In a large cohort of 3,465 individuals suspected with SMA submitted for SMN1 testing to our routine diagnostic laboratory, 48.8% carried a homozygous SMN1 deletion, 2.8% a subtle mutation, and an SMN1 deletion, whereas 48.4% remained undiagnosed. Recently, several other genes implicated in SMA/LMND have been reported. Despite several efforts to establish a diagnostic algorithm for non‐5q‐SMA (SMA without deletion or point mutations in SMN1 [5q13.2]), data from large‐scale studies are not available. We tested the clinical utility of targeted sequencing in non‐5q‐SMA by developing two different gene panels. We first analyzed 30 individuals with a small panel including 62 genes associated with LMND using IonTorrent‐AmpliSeq target enrichment. Then, additional 65 individuals were tested with a broader panel encompassing up to 479 genes implicated in neuromuscular diseases (NMDs) with Agilent‐SureSelect target enrichment. The NMD panel provided a higher diagnostic yield (33%) than the restricted LMND panel (13%). Nondiagnosed cases were further subjected to exome or genome sequencing. Our experience supports the use of gene panels covering a broad disease spectrum for diseases that are highly heterogeneous and clinically difficult to differentiate.