PNKP Mutations Identified by Whole-Exome Sequencing in a Norwegian Patient with Sporadic Ataxia and Edema.

We identified PNKP mutations in a Norwegian woman with AOA. This patient had the typical findings with cognitive dysfunction, peripheral neuropathy, cerebellar dysarthria, horizontal nystagmus, oculomotor apraxia, and severe truncal and appendicular ataxia. In addition, she had hypoalbuminemia and massive lower limb edema which showed some improvement with treatment. Exome sequencing identified two heterozygous mutations, one in exon 14 (c.1196T>C, p.Leu399Pro) and one in exon 16 (c.1393_1396del, p.Glu465*). This is the first non-Portuguese patient with AOA due to PNKP mutations and provides independent verification that PNKP mutations cause AOA.

ADCK3 mutations with epilepsy, stroke-like episodes and ataxia: a POLG mimic?

BACKGROUND AND PURPOSE: Defects of coenzyme Q10 (CoQ10) metabolism cause a variety of disorders ranging from isolated myopathy to multisystem involvement. ADCK3 is one of several genes associated with CoQ10 deficiency that presents with progressive cerebellar ataxia, epilepsy, migraine and psychiatric disorders. Diagnosis is challenging due to the wide clinical spectrum and overlap with other mitochondrial disorders. METHODS: A detailed description of three new patients and one previously reported patient from three Norwegian families with novel and known ADCK3 mutations is provided focusing on the epileptic semiology and response to treatment. Mutations were identified by whole exome sequencing and in two measurement of skeletal muscle CoQ10 was performed. RESULTS: All four patients presented with childhood-onset epilepsy and progressive cerebellar ataxia. Three patients had epilepsia partialis continua and stroke-like episodes affecting the posterior brain. Electroencephalography showed focal epileptic activity in the occipital and temporal lobes. Genetic investigation revealed ADCK3 mutations in all patients including a novel change in exon 15: c.T1732G, p.F578V. There was no apparent genotype-phenotype correlation. CONCLUSION: ADCK3 mutations can cause a combination of progressive ataxia and acute epileptic encephalopathy with stroke-like episodes. The clinical, radiological and electrophysiological features of this disorder mimic the phenotype of polymerase gamma (POLG) related encephalopathy and it is therefore suggested that ADCK3 mutations be considered in the differential diagnosis of mitochondrial encephalopathy with POLG-like features.

EFNS review on the role of muscle biopsy in the investigation of myalgia.

BACKGROUND: Myalgia, defined as any pain perceived in muscle, is very common in the general population and a frequent cause for referral to neurologists, rheumatologists and internists in general. It is however only rarely due to primary muscle disease and often referred from ligaments, joints, bones, the peripheral and central nervous system. A muscle biopsy should only be performed if this is likely to be diagnostically useful. At present no 'guidelines' exist. METHODS: An EFNS panel of muscle specialists was set to review relevant studies from PubMed dating as far back as 1/1/1990. Only Class IV studies were available and therefore the recommendations arrived at are 'best practice recommendations' based on information harvested from the literature search and expert opinion. RESULTS: Muscle cramps should be recognized while drugs, infections, metabolic/ endocrinological and rheumatological causes of myalgia should be identified from the history and examination and pertinent laboratory tests. A muscle biopsy is more likely to be diagnostically useful if myalgia is exertional and if one or more of the following apply: i) there is myoglobinuria, (ii) there is a second wind phenomenon, (iii) there is muscle weakness, (iv) there is muscle hypertrophy /atrophy, (v) there is hyperCKemia (>2-3× normal), and (vi) there is a myopathic EMG. CONCLUSIONS: Patients presenting with myalgia can be recommended to have a biopsy based on careful history and examination and on simple laboratory screening.

Multi-system neurological disease is common in patients with OPA1 mutations.

Additional neurological features have recently been described in seven families transmitting pathogenic mutations in OPA1, the most common cause of autosomal dominant optic atrophy. However, the frequency of these syndromal 'dominant optic atrophy plus' variants and the extent of neurological involvement have not been established. In this large multi-centre study of 104 patients from 45 independent families, including 60 new cases, we show that extra-ocular neurological complications are common in OPA1 disease, and affect up to 20% of all mutational carriers. Bilateral sensorineural deafness beginning in late childhood and early adulthood was a prominent manifestation, followed by a combination of ataxia, myopathy, peripheral neuropathy and progressive external ophthalmoplegia from the third decade of life onwards. We also identified novel clinical presentations with spastic paraparesis mimicking hereditary spastic paraplegia, and a multiple sclerosis-like illness. In contrast to initial reports, multi-system neurological disease was associated with all mutational subtypes, although there was an increased risk with missense mutations [odds ratio = 3.06, 95% confidence interval = 1.44-6.49; P = 0.0027], and mutations located within the guanosine triphosphate-ase region (odds ratio = 2.29, 95% confidence interval = 1.08-4.82; P = 0.0271). Histochemical and molecular characterization of skeletal muscle biopsies revealed the presence of cytochrome c oxidase-deficient fibres and multiple mitochondrial DNA deletions in the majority of patients harbouring OPA1 mutations, even in those with isolated optic nerve involvement. However, the cytochrome c oxidase-deficient load was over four times higher in the dominant optic atrophy + group compared to the pure optic neuropathy group, implicating a causal role for these secondary mitochondrial DNA defects in disease pathophysiology. Individuals with dominant optic atrophy plus phenotypes also had significantly worse visual outcomes, and careful surveillance is therefore mandatory to optimize the detection and management of neurological disability in a group of patients who already have significant visual impairment.

A novel mutation in the mitochondrial tRNA for tryptophan causing a late-onset mitochondrial encephalomyopathy.

BACKGROUND: Mitochondrial DNA (mtDNA) mutations are increasingly being recognized as causes of late-onset disease. We report a patient with a late-onset mitochondrial encephalomyopathy caused by a novel G > C transition in mtDNA at position 5556 in the gene encoding the tRNA for tryptophan (MTTW). AIMS: To investigate the cause of disease and assess the pathogenicity of this new mutation. METHODS: Clinical, histopathological and gene sequencing studies. Quantification of the mutation was performed in different tissues from the patient and two relatives and in single muscle fibres. RESULTS: The mutation was heteroplasmic, segregated in biochemically affected muscle fibres and was absent in blood. The level of mutation in skeletal muscle was higher than in brain, although the brain was clinically the most affected tissue. DISCUSSION: The 5556G > C mutation appears sporadic. It was not found in any of the family members tested, although some of them manifested disorders that can be associated with mtDNA disease. In addition to reporting the eighth mutation in MTTW, our case illustrates the challenges posed when assigning pathogenicity to mtDNA mutations.

Mitochondrial DNA depletion in progressive external ophthalmoplegia caused by POLG1 mutations.

OBJECTIVES: To investigate two patients with late onset, progressive external ophthalmoplegia (PEO) and sensory peripheral neuropathy. MATERIALS & METHODS: The patients aged 86 and 50 years were investigated clinically including magnetic resonance imaging of the brain, electrophysiological studies and, in one, skeletal muscle biopsy. Molecular studies included sequencing of the whole coding region of the POLG1 gene and mitochondrial DNA (mtDNA) analysis for deletions and depletion. RESULTS: Both patients were compound heterozygous for gene encoding the catalytic subunit of the DNA-polymerase gamma (POLG1) mutations. One had the p.737R and p.W748S mutations while the other carried the p.T251I, p.P587L and p.W748S mutations. While these mutations have been previously described, these combinations are novel. mtDNA studies in skeletal muscle showed evidence of multiple deletions and approximately 64% depletion of the mitochondrial genome. CONCLUSION: Our findings broaden the genotypic spectrum of POLG-associated PEO and show that in addition to multiple deletions, mtDNA depletion occurs and may contribute to the pathogenesis of this disorder.

A novel Refsum-like disorder that maps to chromosome 20.

OBJECTIVE: Clinical and genetic characterization of a neurologic disorder resembling Refsum disease in a Norwegian consanguineous family. METHODS: The affected individuals comprise a brother and sister and their third cousin. The family comes from a small island community and genealogic studies showed that both sets of parents are descendants of a man born in 1585. Based on the hypothesis that this is an autosomal recessive disease and that the patients were homozygous for the same mutation (identical by descent), we used homozygosity mapping to define the genetic locus of this disorder. RESULTS: This slowly progressive disorder starts in childhood with signs of peripheral neuropathy (pes cavus, tendoachilles contracture). Hearing loss and cataract become evident in the third decade. Subsequently, patients develop a disorder of gait due to the combination of ataxia and spasticity, and a pigment retinopathy. While the clinical picture is reminiscent of Refsum disease, affected individuals have normal phytanic and pristanic acid levels in plasma, as well as normal enzymatic activity for alpha-oxidation. We mapped the disease to a 15.96 Mb region on chromosome 20 (20p11.21-q12), containing approximately 200 genes (maximum lod score = 6.3). Sequencing of 23 candidate genes failed to demonstrate detrimental sequence variants. CONCLUSIONS: Our findings show that the clinical syndromes that include Refsum disease are more heterogeneous than previously recognized. We have chosen to report the clinical features and mapping of this novel disorder in the hope that this will permit identification of other families and thus proper genetic characterization.

Clinical evolution of Kearns-Sayre syndrome with polyendocrinopathy and respiratory failure.

BACKGROUND: The triad of progressive external ophthalmoplegia, atypical retinal pigmentation and cardiac conduction defects characterizes Kearns-Sayre syndrome (KSS), which is most often caused by a single, large deletion of mitochondrial DNA. Endocrine disease appears to be more common in KSS than in other mitochondrial diseases. MATERIALS, METHODS AND RESULTS: A patient presenting with KSS developed Addison's disease, hypothyroidism and glucose intolerance. Thyroid peroxidase antibodies and adrenal 21-hydroxylase antibodies were identified. She developed acute respiratory failure requiring invasive ventilatory support, but improved and currently requires only non-invasive, nocturnal BiPAP treatment. DISCUSSION AND CONCLUSION: This case confirms the association of KSS and endocrine dysfunction. Our finding of autoantibodies to thyroid and adrenal glands distinguishes this patient from most other published cases and suggests a potential synergy between the two disease mechanisms. In addition, we demonstrate that respiratory failure can be a treatable event in this disease.

Autosomal recessive mitochondrial ataxic syndrome due to mitochondrial polymerase gamma mutations.

OBJECTIVE: To investigate three families and one sporadic case with a recessively inherited ataxic syndrome. METHODS: Clinical and genetic studies were performed in six individuals. Southern blotting and real time PCR were used to detect deletions of mtDNA and mutations in the POLG gene were identified using a combination of DHPLC and direct DNA sequencing. RESULTS: The patients have a distinctive, progressive disorder that starts with episodic symptoms such as migraine-like headache or epilepsy. Ataxia, which is a combination of central and peripheral disease, develops later as does ophthalmoplegia. The commonest form of epilepsy was focal and involved the occipital lobes. Myoclonus was common and patients have a high risk of status epilepticus. MRI typically shows signal changes in the central cerebellum, olivary nuclei, occipital cortex, and thalami. COX negative muscle fibers were found in four of six; in one patient these were rare and in another absent. Multiple mtDNA deletions were identified in all patients, although in two these were not apparent on Southern blotting and real time PCR was required to demonstrate the defect. Two families were homozygous for a previously described POLG mutation, G1399A (A467T). One family and the sporadic case had the same two new mutations, a G to C at position 1491 (Q497H) and a G to C at 2243 (W748S). CONCLUSIONS: Mutations in POLG cause a recessively inherited syndrome with episodic features and progressive ataxia. Characteristic changes on MRI are seen and although skeletal muscle may appear morphologically normal, multiple mtDNA deletions can be detected using real-time PCR.

Anaesthetic complications associated with myotonia congenita: case study and comparison with other myotonic disorders.

Myotonia congenita (MC) is caused by a defect in the skeletal muscle chloride channel function, which may cause sustained membrane depolarisation. We describe a previously healthy 32-year-old woman who developed a life-threatening muscle spasm and secondary ventilation difficulties following a preoperative injection of suxamethonium. The muscle spasms disappeared spontaneously and the surgery proceeded without further problems. When subsequently questioned, she reported minor symptoms suggesting a myotonic condition. Myotonia was found on clinical examination and EMG. The diagnosis MC was confirmed genetically. Neither the patient nor the anaesthetist were aware of the diagnosis before this potentially lethal complication occurred. We give a brief overview of ion channel disorders including malignant hyperthermia and their anaesthetic considerations.

Mutation in the gene encoding ferritin light polypeptide causes dominant adult-onset basal ganglia disease.

We describe here a previously unknown, dominantly inherited, late-onset basal ganglia disease, variably presenting with extrapyramidal features similar to those of Huntington's disease (HD) or parkinsonism. We mapped the disorder, by linkage analysis, to 19q13.3, which contains the gene for ferritin light polypeptide (FTL). We found an adenine insertion at position 460-461 that is predicted to alter carboxy-terminal residues of the gene product. Brain histochemistry disclosed abnormal aggregates of ferritin and iron. Low serum ferritin levels also characterized patients. Ferritin, the main iron storage protein, is composed of 24 subunits of two types (heavy, H and light, L) which form a soluble, hollow sphere. Brain iron deposition increases normally with age, especially in the basal ganglia, and is a suspected causative factor in several neurodegenerative diseases in which it correlates with visible pathology, possibly by its involvement in toxic free-radical reactions. We found the same mutation in five apparently unrelated subjects with similar extrapyramidal symptoms. An abnormality in ferritin strongly indicates a primary function for iron in the pathogenesis of this new disease, for which we propose the name 'neuroferritinopathy'.

Mitochondrial enteropathy: the primary pathology may not be within the gastrointestinal tract.

BACKGROUND: Mitochondrial DNA (mtDNA) defects are an important cause of disease. Although gastrointestinal symptoms are common in these patients, their pathogenesis remains uncertain. AIM: To investigate the role of the mtDNA defect in the production of gastrointestinal dysfunction. PATIENT: A 20 year old woman who presented at 15 years of age with recurrent vomiting and pseudo-obstruction, who did not respond to conservative management and ultimately had subtotal gastrectomy and Roux-en-y reconstruction. She subsequently presented with status epilepticus and was found to have a mitochondrial respiratory chain disorder due to a pathogenic mtDNA point mutation (A3243G). METHODS: Resected bowel was studied using light and electron microscopy and mtDNA analysed from both mucosal and muscular layers using polymerase chain reaction generated RFLP analysis. RESULTS: Histological and electron microscopic studies revealed no morphological abnormalities in the resected stomach, and molecular genetic analysis failed to identify the genetic defect in either the mucosal or muscle layers. CONCLUSION: This study suggests that in some individuals with gastrointestinal symptoms associated with established mitochondrial DNA disease, the primary pathology of the mitochondrial enteropathy lies outside the gastrointestinal tract.

The epidemiology of pathogenic mitochondrial DNA mutations.

During the past decade, there have been many descriptions of patients with neurological disorders due to mitochondrial DNA (mtDNA) mutations, but the extent and spectrum of mtDNA disease in the general population have not yet been defined. Adults with suspected mtDNA disease in the North East of England were referred to a single neurology center for investigation over the 10-year period from 1990 to 1999 inclusive. We defined the genetic defect in these individuals. For the midyear period of 1997, we calculated the minimum point prevalence of mtDNA disease in the adults of working age (> 16-<60 years old for female subjects and <65 years old for male subjects) and the minimum prevalence of adults and children (<60 years for female subjects, <65 years for male subjects) at risk of developing mtDNA disease. mtDNA defects caused disease in 6.57 per 100,000 individuals in the adult population of working age, and 7.59 per 100,000 unaffected adults and children were at risk of developing mtDNA disease. Overall, 12.48 per 100,000 individuals in the adult and child population either had mtDNA disease or were at risk of developing mtDNA disease. These results reflect the minimum prevalence of mtDNA disease and pathogenic mtDNA mutations and demonstrate that pathogenic mtDNA mutations are a common cause of chronic morbidity. These findings have resource implications, particularly for supportive care and genetic counseling.

Longitudinal analysis of the segregation of mtDNA mutations in heteroplasmic individuals.

The mutation load of the pathogenic LHON (Leber hereditary optic neuropathy) mtDNA mutation at nucleotide 3460 has been followed over time in the WBC/platelet fraction from members of a matrilineal pedigree. Longitudinal analysis over a sampling period of five to six years indicates that, in all five heteroplasmic family members, the mutation load decreases at a mean overall rate of approximately 1% per year. There was no change in mutation load in homoplasmic wildtype or in homoplasmic mutant individuals. For the purposes of comparison, a longitudinal analysis of a silent mtDNA polymorphism at nucleotide 14560 was also carried out for members of a second matrilineal pedigree. In contrast to the results for the pathogenic mtDNA mutation, there was no change in the proportion of the silent polymorphism in the WBC/platelet fraction of four family members over a period of seven years. These results indicate that the pathogenic 3460 LHON mutation segregates under negative selection in these cell populations. One possible mechanism through which selection may operate is that, in heteroplasmic individuals, the hematopoietic stem cells are generally homoplasmic, either for the wildtype or for the mutant allele. The homoplasmic mutant stem cells, because of their mitochondrial respiratory chain defect, produce fewer mature WBCs and platelets over time than do the wildtype stem cells. Alternatively, the stem cells may be heteroplasmic and selection may act to favor proliferation of mitochondria with lower levels of the pathogenic mutation in the WBC/platelet cell populations.

Conversion of a reporter gene for mitochondrial gene expression using iterative mega-prime PCR.

Mammalian mitochondria possess their own multicopy genome, mtDNA. Although much is known about mtDNA replication and transcription, our knowledge of the mechanisms governing mt-RNA processing, stability and translation remains rudimentary. We have taken a step towards addressing these issues by altering the luciferase reporter gene to accommodate the variation in mitochondrial codon recognition. 19 essential substitutions have been generated by an iterative mega-primer PCR technique. To mimic mt-mRNA species and to optimise intramitochondrial translation, further engineering has produced a template which, when transcribed in vitro, generates an RNA species with only two nucleotides upstream from the initiation codon, an absence of a 3' untranslated region and a polyadenylated tail of 40 residues. It is intended that mt-luciferase (mt-luc) RNA will be an excellent reporter for revealing cis-acting elements essential for in organello RNA processing, maturation and expression. Additionally, the mt-luc gene can be readily incorporated into any novel mitochondrial transducing vectors to assess intra-organellar transcription and translation.

Spontaneous intracranial hypotension: clinical and magnetic resonance imaging characteristics.

The syndrome of spontaneous intracranial hypotension (SIH) is an uncommon cause of postural headache. We describe three patients with classical low pressure headache associated with low CSF pressure, one of whom presented with sudden deafness and another with a unilateral VIth nerve palsy. Initial magnetic resonance imaging (MRI) scans revealed bilateral diffuse subdural fluid collections in all three cases. Follow up MRI scans performed on two patients at 6 months demonstrated partial resolution of the subdural collections but persistent striking meningeal enhancement despite clinical recovery. These findings differ from previous reported cases wherein clinical resolution of postural symptoms was preceded or closely followed by resolution of the MRI changes.