New phenotypic diversity associated with the mitochondrial tRNA(SerUCN) gene mutation

We performed detailed clinical, histopathological, biochemical, in vitro translation and molecular genetic analysis in patients from two unrelated families harbouring the tRNA(SerUCN) 7472C-insertion mutation. Proband 1 developed a progressive neurodegenerative phenotype characterised by myoclonus, epilepsy, cerebellar ataxia and progressive hearing loss. Proband 2 had a comparatively benign phenotype characterised by isolated myopathy with exercise intolerance. Both patients had the 7472C-insertion mutation in identical proportions and they exhibited a similar muscle biochemical and histopathological phenotype. However, proband 2 also had a previously unreported homoplasmic A to C transition at nucleotide position 7472 in the tRNA(SerUCN) gene. This change lengthens further the homopolymeric C run already expanded by the 7472C-insertion. These data extend the phenotypic range associated with the 7472C-insertion to include isolated skeletal myopathy, as well as a MERRF-like phenotype.     

Increased risk of stroke in patients with the A12308G polymorphism in mitochondria

Factors which increase the risk of stroke in patients with the A3243G (mitochondrial encephalomyopathy, lactic acidosis, and stroke [MELAS]) mutation in human mitochondrial DNA are unclear. Previous work on lung-cancer cells with an A3243G mutation showed that a mutation in the mitochondrial transfer gene for leucine tRNA(Leu(CUN)) was able to ameliorate the A3243G-induced biochemical phenotype. We analysed the tRNA(Leu(CUN)) gene in 48 unrelated A3243G cases. We showed that a polymorphism, A12308G, in tRNA(Leu(CUN)) increases the risk of developing stroke in patients with the A3243G mutation (relative risk=2.17). This may have implications for genetic counselling.     

The mitochondrial DNA G13513A transition in ND5 is associated with a LHON/MELAS overlap syndrome and may be a frequent cause of MELAS

We report on 4 male patients with clinical, radiological, and muscle biopsy findings typical of the mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) phenotype. Skeletal muscle mitochondrial DNA (mtDNA) analysis showed that all patients harbored a heteroplasmic G13513A mutation in the ND5 subunit gene. One of these cases (Patient 1) presented with symptoms characteristic of Leber's hereditary optic neuropathy (LHON) 2 years before the first stroke-like episode. Quantitative analysis in several postmortem tissue sections showed that the relative proportions of mutant mtDNA were generally lower than those reported with other pathogenic mtDNA mutations. Single-fiber polymerase chain reaction studies demonstrated significantly higher amounts of mutant mtDNA in ragged red fibers (RRFs) compared with non-RRFs. This study indicates that the G13513A transition is likely to be pathogenic, that it can cause an LHON/MELAS overlap syndrome, and that it may be a more frequent cause of MELAS than previously recognized.     

Phenotypic heterogeneity in a large Thai slow-channel congenital myasthenic syndrome kinship

The slow-channel congenital myasthenic syndrome (SCCMS) is an autosomal dominant neuromuscular disorder caused by mutations in different subunits of the acetylcholine receptor (AChR). We here report our clinical findings in three generations of a large Thai kinship suffering from SCCMS and trace the disease to the p.Gly153Ser mutation in the AChR α subunit. The same mutation had previously been reported only in Caucasian but not in Asian patients. The clinical features include ptosis, ophthalmoparesis, and weakness of the cervical and finger extensor muscles as well as marked phenotypic heterogeneity.     

Long-term effectiveness of acetazolamide on permanent weakness in hyperkalemic periodic paralysis

Acetazolamide is commonly used as an empirical treatment for inherited periodic paralyses although some patients may develop deleterious effects. We report a 65 year-old man with hyperkalemic periodic paralysis and late-onset permanent weakness in association with the common T704M mutation in α-subunit, skeletal muscle voltage-gated sodium channel gene. He rapidly recovered from weakness after acetazolamide treatment. Magnetic resonance imaging of thighs comparing pre- and post-treatment revealed a significant increase in muscle bulk. The patient has been without any type of weakness for over 6 years. This data show the remarkable benefit of acetazolamide on permanent weakness of hyperkalemic periodic paralysis in association with the T704M mutation.     

Idiopathic hypertrophic cranial pachymeningitis.

Idiopathic hypertrophic cranial pachymeningitis is a rare chronic inflammatory process of unknown origin that can cause neurological deficits owing to thickening of the dura. Patients with this condition commonly present with cranial neuropathy accompanied by localized headache. The clinical features, neuroimaging findings, histopathological features and treatment outcomes for three patients with this condition are reported here. The first patient presented with subacute dull headache in the left temporal area followed by left abducens nerve palsy. The second patient suffered from a cranial nerve IX-XII lesion accompanied by an occipital headache and the third patient presented with left optic neuropathy and mild headache in the frontal area. In all patients, MRI of the brain revealed prominent dural thickening, and histopathological study of the dura revealed chronic inflammatory cell infiltration. Combined therapy with corticosteroid and immunosuppressive drugs was effective, resulting in almost complete resolution of the symptoms and signs, except for visual impairment in one patient.     

Paroxysmal neuromyotonia: a new sporadic channelopathy

Neuromyotonia is a heterogeneous group of genetic and autoimmune channelopathies resulting in hyperexcitability of peripheral nerves. We report an unusual case of neuromyotonia, which to our knowledge has not been previously described. The patient developed intermittent attacks of severe painful muscle stiffness accompanied by sweating, myokymia and raised serum creatine kinase. Genetic analysis of KCNA1, KCNQ2 and SCN4A genes did not identify pathogenic mutation. Serum voltage-gated potassium channel antibody was also negative. He was successfully treated with acetazolamide and carbamazepine. This appears to be a new neuromuscular disease, "paroxysmal neuromyotonia", the etiology of which is still unknown.     

Prevalence,clinical features and treatment outcomes of patients with myasthenia gravis positive for antibodies to muscle-specific kinase in Thailand

A small but variable subgroup of patients with myasthenia gravis (MG) who have antibodies to muscle-specific kinase (MuSKAb-MG) can present with distinct phenotypes and are often treatment-resistant. The prevalence, clinical phenotypes and outcomes of treatment of patients with MuSKAb-MG in Thailand were determined. Eight (16.3%) of the 49 patients with generalized MG who were negative for acetylcholine receptor antibodies (AChRAb) were positive for muscle-specific kinase antibodies. Most patients had predominant oculobulbar features and respiratory failure occurred in three. At follow up, three out of the seven patients who underwent thymectomy were in complete stable remission and four had improved and were on reduced immunosuppression medication, suggesting a possible benefit of thymectomy.