S. Todorovic

Targeted next-generation sequencing of a 12.5 Mb homozygous region reveals ANO10 mutations in patients with autosomal-recessive cerebellar ataxia.

Autosomal-recessive cerebellar ataxias comprise a clinically and genetically heterogeneous group of neurodegenerative disorders. In contrast to their dominant counterparts, unraveling the molecular background of these ataxias has proven to be more complicated and the currently known mutations provide incomplete coverage for genotyping of patients. By combining SNP array-based linkage analysis and targeted resequencing of relevant sequences in the linkage interval with the use of next-generation sequencing technology, we identified a mutation in a gene and have shown its association with autosomal-recessive cerebellar ataxia. In a Dutch consanguineous family with three affected siblings a homozygous 12.5 Mb region on chromosome 3 was targeted by array-based sequence capture. Prioritization of all detected sequence variants led to four candidate genes, one of which contained a variant with a high base pair conservation score (phyloP score: 5.26). This variant was a leucine-to-arginine substitution in the DUF 590 domain of a 16K transmembrane protein, a putative calcium-activated chloride channel encoded by anoctamin 10 (ANO10). The analysis of ANO10 by Sanger sequencing revealed three additional mutations: a homozygous mutation (c.1150_1151del [p.Leu384fs]) in a Serbian family and a compound-heterozygous splice-site mutation (c.1476+1G>T) and a frameshift mutation (c.1604del [p.Leu535X]) in a French family. This illustrates the power of using initial homozygosity mapping with next-generation sequencing technology to identify genes involved in autosomal-recessive diseases. Moreover, identifying a putative calcium-dependent chloride channel involved in cerebellar ataxia adds another pathway to the list of pathophysiological mechanisms that may cause cerebellar ataxia.

Loss-of-function mutations in HINT1 cause axonal neuropathy with neuromyotonia.

Inherited peripheral neuropathies are frequent neuromuscular disorders known for their clinical and genetic heterogeneity. In 33 families, we identified 8 mutations in HINT1 (encoding histidine triad nucleotide–binding protein 1) by combining linkage analyses with next-generation sequencing and subsequent cohort screening of affected individuals. Our study provides evidence that loss of functional HINT1 protein results in a distinct phenotype of autosomal recessive axonal neuropathy with neuromyotonia.

Impaired receptor clustering in congenital myasthenic syndrome with novel RAPSN mutations

Objective: Congenital myasthenic syndromes (CMS) with underlying RAPSN mutations turned out to be of high clinical relevance due to their worldwide frequency. To date, all reported patients with CMS with sequence variations in the translated region of RAPSN carry the mutation N88K on at least one allele. The authors report two patients lacking the common N88K allele but harboring differing novel mutations of the RAPSN gene on both alleles: one patient is homozygous for a missense mutation (R164C); the second patient is compound heterozygous for a splice (IVS1-15C>A) and another missense mutation (L283P). Methods: The authors analyzed the RAPSN gene for sequence variations and carried out in vitro studies in order to delineate the potential pathogenicity of the three novel RAPSN mutations. Results: For the putative splice mutation (IVS1-15C>A), the authors constructed wild-type and mutated RAPSN minigenes for transfection and subsequent RNA analysis. The mutation generates a novel acceptor splice site leading to retention of 13 nucleotides of intron 1 in the mature mRNA and subsequently to a frameshift transcript. Cotransfection of wild-type AChR subunits with RAPSN-constructs carrying R164C and L283P indicate that both mutations diminish coclustering of AChR with rapsyn. Conclusions: Screening for the common mutation RAPSN N88K facilitates targeted genetic analysis in congenital myasthenic syndromes. However, absence of a N88K allele does not exclude underlying RAPSN mutations as cause of the congenital myasthenic syndromes. Sequencing of the entire gene may be considered in patients with joint contractures and respiratory problems even in the absence of the mutation N88K.

Survival and mortality of myotonic dystrophy type 1 (Steinert's disease) in the population of Belgrade

The purpose of this investigation was to determine survival and mortality in patients with myotonic dystrophy type 1 (DM1) in the Belgrade population within the period from 1983 to 2002. Data of a number of diagnosed DM1 patients with their demographic, clinical and genetic characteristics were gathered from hospital records in all neurologic institutions in Belgrade for the period 1983–2002. Death certificates were reviewed to determine the cause of death. Survival analysis by life table method and Cox proportional hazard model was performed. Within the observed period, in the population of Belgrade, 15 fatal outcomes among 101 patients with DM1 were registered. Average DM1 mortality rate was 0.5/1 000 000 (95% CI 0.3–0.8), and standardized mortality ratio (SMR) was 5.3. A significant inverse correlation was found between age at onset of DM1 and CTG repeats (P = 0.023). The cumulative probability of 15‐year survival for DM1 patients in Belgrade was 49 ± 5% (48 ± 2% for males and 50 ± 7% for females). Younger age at onset was a significant unfavorable prognostic factor (hazard ratio = 4.2; P = 0.012).

Eosinophilic myositis as presenting symptom in γ-sarcoglycanopathy

The patient reported here presented with first symptoms at the age of 10 showing an abnormal gait, calf hypertrophy and winged scapulae. She was diagnosed with eosinophilic myositis after muscle biopsy. A second muscle biopsy at the age of 20 and subsequent genetic testing, however, revealed the underlying condition of a primary gamma-sarcoglycanopathy, or LGMD2C. To our knowledge, this is the first LGMD2C patient reported who initially presented with eosinophilic myositis. Eosinophilia has been reported previously in patients with Calpainopathy and Becker Muscular Dystrophy and might be an early, but transient feature of a wider range of muscular dystrophies.

The Recurrence Risk of Ischemic Stroke in Childhood

Objective: To determine the risk of recurrence of ischemic stroke in children and to evaluate the influence of etiological factors and underlying mechanisms on recurrence rate. Subjects and Methods: Thirty-six children (21 boys and 15 girls) with clinically and radiographically proven ischemic cerebral infarction were prospectively followed up over a period of 1–9 years (median 5 years 5 months). The median age of onset of stroke was 8.4 years (1–16 years). Patients with hemorrhagic stroke, neonatal infarction and sinovenous thrombosis were not included. The patients were analyzed according to the mechanisms and etiology of the initial and recurrent stroke event. Results: For the initial stroke, cardioembolic (33.3%) and arteriopathic processes (36.1%) were identified as the most probable mechanisms of arterial ischemic stroke. Prothrombotic abnormalities were found in 4 children (11.1%). Underlying pathology in the remaining 7 (19.4%) was not known. Recurrent ischemic infarction was diagnosed in 5 children (13.9%) within 5 days to 18 months (median 6 months) after the first stroke manifestation. In 3 of them stroke recurrence was due to cardiac or transcardiac embolism. Cardiac abnormality prior to the first stroke was detected in 1 child. Clinically silent multiple cerebral infarcts disclosed by MRI preceded the overt stroke episode in 2 patients. Conclusion: Congenital and acquired heart diseases were the most common cause of repeated stroke in our study. The risk of recurrence appeared to be fivefold higher in children with cardiac disease irrespective of the coexistence of other risk factors. The risk factors of stroke in children were multiple and overlapping. Consequently, recognition of the major one and its underlying mechanism is crucial for both effective therapeutic approach and the prevention of recurrence.

Proximal dystrophin gene deletions and protein alterations in becker muscular dystrophy.

Abstract: Alterations in production of cytoskeletal protein dystrophin caused by in‐frame gene mutations lead to the Becker muscular dystrophy. In this study we analyzed genotype‐phenotype correlation in a group of Becker muscular dystrophy patients with deletions affecting the proximal part of dystrophin gene, encompassing exons 3–13. Four patients with deletions affecting N terminal dystrophin domain had early onset and faster progression of the disease, while three patients with deletions in the proximal part of dystrophins rod domain had a more benign disease course. Our study suggests that proximal gene deletions in Becker muscular dystrophy have various phenotypic effects depending on the affected domain of protein dystrophin.

Epidemiology of myotonic dystrophy type 1 (Steinert disease) in Belgrade (Serbia)

The aim of this study was to estimate the incidence and prevalence of myotonic dystrophy type 1 (DM1) in Belgrade during the period 1983-2002. The patients who had DM1 were ascertained through hospital records from all neurological departments in Belgrade during 1983-2002. The molecular genetic analysis was performed in all patents included in the study. We identified 101 DM1 patients (52 males and 49 females). The average annual incidence rate of DM1 in Belgrade for the period observed was 2.0/1,000,000 (95% confidence interval (CI), 0.3-8.3), 2.1/1,000,000 (95% CI, 0.3-8.3) for males and 2.0/1,000,000 (95% CI, 0.3-8.3) for females. The highest age-specific DM1 incidence was registered in the age group 20-49: 3.4/1,000,000 (95% CI, 0.5-7.6), 4.0/1,000,000 (95% CI, 1.1-10.2) in males and 2.5/1,000,000 (95% CI, 0.5-7.6) in females. In the population of Belgrade, a cumulative probability of acquiring DM1 was 1 per 8621 for men and 1 per 9259 for women (1 per 8940 of the population for both sexes). The prevalence of DM1 in Belgrade on 31 December 2002 was 5.3/100,000 (95% CI, 4.2-6.6).

Association of Krabbe leukodystrophy and congenital fiber type disproportion

Hypotonia and weakness developed in a 12-month-old boy whose psychomotor development had previously been normal. The muscle biopsy demonstrated a disparity in the mean diameters of type 1 and type 2 fibers and satisfied major histologic criteria for diagnosis of congenital fiber type disproportion (CFTD). However, deterioration of motor and mental function, which developed subsequently, strongly suggested progressive encephalopathy. Examination of leukocyte cerebral enzymes at 15 months of age revealed a complete lack of galactosylceramide-beta-galactosidase. Selective type 1 fiber atrophy with type 1 fiber predominance has been observed in various conditions, including Krabbe disease. We report an additional case of Krabbe leukodystrophy associated with CFTD. The finding on the molecular level will resolve the dilemma of whether CFTD is a congenital myopathy or whether these patterns of disproportion may result from a number of different processes that interfere with the maturation of the developing motor unit.

Association of progressive myoclonic epilepsy and spinal muscular atrophy

It is well known that certain hereditary diseases of the nervous system sometimes occur concurrently within particular families. This report presents a Yugoslav family of Hungarian origin in whom 2 brothers had progressive myoclonic epilepsy and proximal weakness and atrophy of muscles. Electromyography and muscle biopsy confirmed neurogenic atrophy. Electroencephalography disclosed paroxysmal spike-and-wave and polyspike-and-wave complexes with photic-induced myoclonic jerking. The combination of these clinical features is extremely rare and probably constitutes a clinical syndrome that has not been reported previously.