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.