Compound heterozygous variants in MYBPC1 lead to severe distal arthrogryposis type-1 manifestations

Dominant missense variants in MYBPC1 encoding slow Myosin Binding Protein-C (sMyBP-C) have been increasingly linked to arthrogryposis syndromes and congenital myopathy with tremor. Herein, we describe novel compound heterozygous variants - NM_002465.4:[c.2486_2492del];[c.2663A > G] - present in fibronectin-III (Fn-III) C7 and immunoglobulin (Ig) C8 domains, respectively, manifesting as severe, early-onset distal arthrogryposis type-1, with the carrier requiring intensive care and several surgical interventions at an early age. Computational modeling predicts that the c.2486_2492del p.(Lys829IlefsTer7) variant destabilizes the structure of the Fn-III C7 domain, while the c.2663A > G p.(Asp888Gly) variant causes minimal structural alterations in the Ig C8 domain. Although the parents of the proband are heterozygous carriers for a single variant, they exhibit no musculoskeletal defects, suggesting a complex interplay between the two mutant alleles underlying this disorder. As emerging novel variants in MYBPC1 are shown to be causatively associated with musculoskeletal disease, it becomes clear that MYBPC1 should be included in relevant genetic screenings.

Efficacy and Safety of Vamorolone Over 48 Weeks in Boys With Duchenne Muscular Dystrophy: A Randomized Controlled Trial

BACKGROUND AND OBJECTIVES

Vamorolone is a dissociative agonist of the glucocorticoid receptor that has shown similar efficacy and reduced safety concerns in comparison with prednisone in Duchenne muscular dystrophy (DMD). This study was conducted to determine the efficacy and safety of vamorolone over 48 weeks and to study crossover participants (prednisone to vamorolone; placebo to vamorolone).

METHODS

A randomized, double-blind, placebo-controlled and prednisone-controlled clinical trial of 2 doses of vamorolone was conducted in participants with DMD, in the ages from 4 years to younger than 7 years at baseline. The interventions were 2 mg/kg/d of vamorolone and 6 mg/kg/d of vamorolone for 48 weeks (period 1: 24 weeks + period 2: 24 weeks) and 0.75 mg/kg/d of prednisone and placebo for the first 24 weeks (before crossover). Efficacy was evaluated through gross motor outcomes and safety through adverse events, growth velocity, body mass index (BMI), and bone turnover biomarkers. This analysis focused on period 2.

RESULTS

A total of 121 participants with DMD were randomized. Vamorolone at a dose of 6 mg/kg/d showed maintenance of improvement for all motor outcomes to week 48 (e.g., for primary outcome, time to stand from supine [TTSTAND] velocity, week 24 least squares mean [LSM] [SE] 0.052 [0.0130] rises/s vs week 48 LSM [SE] 0.0446 [0.0138]). After 48 weeks, vamorolone at a dose of 2 mg/kg/d showed similar improvements as 6 mg/kg/d for North Star Ambulatory Assessment (NSAA) (vamorolone 6 mg/kg/d-vamorolone 2 mg/kg/d LSM [SE] 0.49 [1.14]; 95% CI -1.80 to 2.78, p = 0.67), but less improvement for other motor outcomes. The placebo to vamorolone 6 mg/kg/d group showed rapid improvements after 20 weeks of treatment approaching benefit seen with 48-week 6 mg/kg/d of vamorolone treatment for TTSTAND, time to run/walk 10 m, and NSAA. There was significant improvement in linear growth after crossover in the prednisone to vamorolone 6 mg/kg/d group, and rapid reversal of prednisone-induced decline in bone turnover biomarkers in both crossover groups. There was an increase in BMI after 24 weeks of treatment that then stabilized for both vamorolone groups.

DISCUSSION

Improvements of motor outcomes seen with 6 mg/kg/d of vamorolone at 24 weeks of treatment were maintained to 48 weeks of treatment. Vamorolone at a dose of 6 mg/kg/d showed better maintenance of effect compared with vamorolone at a dose of 2 mg/kg/d for most (3/5) motor outcomes. Bone morbidities of prednisone (stunting of growth and declines in serum bone biomarkers) were reversed when treatment transitioned to vamorolone.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov Identifier: NCT03439670.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that for boys with DMD, the efficacy of vamorolone at a dose of 6 mg/kg/d was maintained over 48 weeks.

Decreased quality of life in Duchenne muscular disease patients related to functional neurological and cardiac impairment

In this prospective study involving 37 Duchenne muscular dystrophy (DMD) patients aged 8-18 years and older, we examined the impact of neurological and cardiac factors on quality of life (QoL). Our findings revealed a negative correlation between upper limb movement and overall mobility, self-service, and usual activities. Ambulatory and non-ambulatory DMD patients showed significant differences in mobility-related parameters. Cardiac evaluations demonstrated associations between mitral annular plane systolic excursion (MAPSE) and mobility-related aspects. The PEDSQL 3.0 neuromuscular model questionnaire further highlighted age-related and movement-related correlations with QoL. The loss of ambulatory status and reduced upper limb movement were negatively associated with QoL, while upper limb movement positively correlated with septal MAPSE. However, no significant associations were found between MAPSE and anxiety/depression. These findings underscore the multifaceted impact of DMD on QoL and emphasize the importance of considering both neurological and cardiac factors in comprehensive patient care.

Genetic findings in Czech patients with limb girdle muscular dystrophy

Limb girdle muscular dystrophies (LGMD) are a genetically heterogeneous group of muscular dystrophies. The study presents an overview of molecular characteristics of a large cohort of LGMD patients who are representative of the Czech LGMD population. We present 226 LGMD probands in which 433 mutant alleles carrying 157 different variants with a supposed pathogenic effect were identified. Fifty-four variants have been described only in the Czech LGMD population so far. LGMD R1 caplain3-related is the most frequent subtype of LGMD involving 53.1% of patients with genetically confirmed LGMD, followed by LGMD R9 FKRP-related (11.1%), and LGMD R12 anoctamin5-related (7.1%). If we consider identified variants, then all but five were small-scale variants. One large gene deletion was identified in the LAMA2 gene and two deletions in each of CAPN3 and SGCG. We performed comparison our result with other published studies. The results obtained in the Czech LGMD population clearly differ from the outcome of other LGMD populations in two aspects-we have a more significant proportion of patients with LGMD R1 calpain3-related and a smaller proportion of LGMD R2 dysferlin-related.

Telemedicine in Neuromuscular Diseases During Covid-19 Pandemic: ERN-NMD European Survey

BACKGROUND

Telemedicine (TM) contributes to bridge the gap between healthcare facilities and patients' homes with neuromuscular disease (NMD) because of mobility issues. However, its deployment is limited due to difficulties evaluating subtle neurological signs such as mild weakness or sensory deficits. The COVID-19 pandemic has disrupted healthcare delivery worldwide, necessitating rapid measures implementation by health care providers (HCPs) to protect patients from acquiring SARS-CoV-2 while maintaining the best care and treatment.

OBJECTIVES

Given the challenges faced by remote healthcare assistance of NMD patients, we aim to evaluate the use of TM in NMD during the COVID-19 pandemic.

METHODS

Based on the Model for Assessment-of-Telemedicine-Applications (MAST), we conducted a survey amongst clinicians of the ERN EURO NMD (European-Reference-Network-for-Rare-Neuromuscular-Diseases).

RESULTS

Based on 42 responses over 76 expected ones, our results show that the COVID-19 pandemic significantly increased the number of HCPs using TM (from 60% to 100%). The TM types most used during the COVID-19 period are teleconsultation and consultation by phone, particularly in the context of symptoms worsening in NMD patients with COVID-19 infection. Most European HCPs were satisfied when using TM but as a complementary option to physical consultations. Many responses addressed the issue of technical aspects needing improvement, particularly for elderly patients who need caregivers' assistance for accessing the TM platform.

CONCLUSIONS

TM has been essential during COVID-19, but its use still presents some limitations for NMD patients with cognitive deficits or for first-time diagnosis. Thus, TM should be used as complement to, rather than substitute, for face-to-face consultations.

Clinical practice guideline for the management of paediatric Charcot-Marie-Tooth disease

BACKGROUND AND OBJECTIVES

Charcot-Marie-Tooth disease (CMT) is the most common inherited neuropathy and often presents during childhood. Guidelines for the optimal management of common problems experienced by individuals with CMT do not exist, for either children or adults. We formed the Paediatric CMT Best Practice Guidelines Consortium to develop evidence and consensus-based recommendations for the clinical management of children and adolescents with CMT, with the primary objective of promoting optimal, standardised care globally.

METHODS

Development of this clinical practice guideline involved a series of systematic reviews covering 10 clinical questions, modified Delphi methodology involving an international panel of clinicians to generate consensus where evidence did not exist, and application of the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach to evaluate the body of literature and formulate recommendations.

RESULTS

The final guideline includes three evidence-based and 31 consensus-based recommendations. They encompass the management of muscle weakness, balance and mobility impairment, sensory symptoms, muscle cramps, impaired upper limb function, respiratory impairment, maintenance of joint range of motion and non-surgical management of joint deformity. Consensus was not achieved in some management areas, reflecting differences in practice between clinicians and healthcare settings, and highlighting the need for further research.

CONCLUSIONS

This clinical practice guideline provides practical and implementable guidance on the management of common clinical problems experienced by children with CMT and advocates for improved access to multidisciplinary care. Successful dissemination and implementation of these recommendations will be critical in ensuring their application across multiple healthcare settings.

New genotype-phenotype correlations in a large European cohort of patients with sarcoglycanopathy

Sarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. In 2016, several clinicians involved in the diagnosis, management and care of patients with LGMDR3-6 created a European Sarcoglycanopathy Consortium. The aim of the present study was to determine the clinical and genetic spectrum of a large cohort of patients with sarcoglycanopathy in Europe. This was an observational retrospective study. A total of 33 neuromuscular centres from 13 different European countries collected data of the genetically confirmed patients with sarcoglycanopathy followed-up at their centres. Demographic, genetic and clinical data were collected for this study. Data from 439 patients from 13 different countries were collected. Forty-three patients were not included in the analysis because of insufficient clinical information available. A total of 159 patients had a confirmed diagnosis of LGMDR3, 73 of LGMDR4, 157 of LGMDR5 and seven of LGMDR6. Patients with LGMDR3 had a later onset and slower progression of the disease. Cardiac involvement was most frequent in LGMDR4. Sixty per cent of LGMDR3 patients carried one of the following mutations, either in a homozygous or heterozygous state: c.229C>T, c.739G>A or c.850C>T. Similarly, the most common mutations in LMGDR5 patients were c.525delT or c.848G>A. In LGMDR4 patients the most frequent mutation was c.341C>T. We identified onset of symptoms before 10 years of age and residual protein expression lower than 30% as independent risk factors for losing ambulation before 18 years of age, in LGMDR3, LGMDR4 and LGMDR5 patients. This study reports clinical, genetic and protein data of a large European cohort of patients with sarcoglycanopathy. Improving our knowledge about these extremely rare autosomal recessive forms of LGMD was helped by a collaborative effort of neuromuscular centres across Europe. Our study provides important data on the genotype-phenotype correlation that is relevant for the design of natural history studies and upcoming interventional trials in sarcoglycanopathies.

Next generation sequencing and its application in the diagnostics of neuromuscular diseases

Neuromuscular diseases (NMDs) are a clinically and genetically heterogeneous group of diseases. Currently, 608 genes associated with different types of NMD have been identified. Most of these diseases are rare with a very low prevalence. Advance in the identification of genes associated with NMD can be attributed to technological development in an area of next generation sequencing (NGS) and the affordability of this methodical approach. NGS applications can be divided into analysis of (a) a selected set of genes, (b) an exom, and (c) a genome. The identification of pathogenic variants leads to a significant shift in the understanding of the etiopathogenesis of the disease, allows the prediction of the course of the disease, or its targeted treatment, which may be specific for individual types of NMD or even for particular pathogenic sequence variants.

Echocardiographic signs of subclinical cardiac function impairment in Duchenne dystrophy gene carriers

To assess subclinical cardiac function impairment in Duchenne dystrophy (DMD) female carriers. Forty-four female subjects proved as DMD carriers underwent echocardiographic examination including tissue Doppler imaging (TDI) of mitral and tricuspid annulus. Seventeen age-matched healthy female subjects served as controls. A significant differences in peak systolic annular velocity (Sa) between carriers and controls were found for lateral and septal part of the mitral annulus and for tricuspid annulus (0.09 vs. 0.11 m/s, p < 0.001, 0.08 vs. 0.09 m/s, p < 0.01 and 0.13 vs. 0.14 m/s, p = 0.02 respectively). There was also difference in early diastolic velocity (Ea) of the septal part of the mitral annulus (0.11 vs. 0.13 m/s, p = 0.03). The subclinical deterioration of systolic function is presented even in asymptomatic DMD female carriers.

UBTF Mutation Causes Complex Phenotype of Neurodegeneration and Severe Epilepsy in Childhood

INTRODUCTION

Neurodegenerative diseases of childhood present with progressive decline in cognitive, social, and motor function and are frequently associated with seizures in different stages of the disease. Here we report a patient with severe progressive neurodegeneration with drug-resistant epilepsy of unknown etiology from the age of 2 years.

METHODS AND RESULTS

Using whole exome sequencing, we found heterozygous missense de novo variant c.628G > A (p.Glu210Lys) in the UBTF gene. This variant was recently described as de novo in 11 patients with similar neurodegeneration characterized by developmental decline initially confined to motor development followed by language regression, appearance of an extrapyramidal movement disorder, and leading to severe intellectual disability. In 3 of the 11 patients described so far, seizures were also present.

CONCLUSIONS

Our report expands the complex phenotype of neurodegeneration associated with the c.628G > A variant in the UBTF gene and helps to clarify the relation between this one single recurrent pathogenic variant described in this gene to date and its phenotype. The UBTF gene should be considered a novel candidate gene in neurodegeneration with or without epilepsy.

Cardiac profile of the Czech population of Duchenne muscular dystrophy patients: a cardiovascular magnetic resonance study with T1 mapping

BACKGROUND

The progressive cardiomyopathy that develops in boys with Duchenne and Becker muscular dystrophy (DMD/BMD) is presumed to be a secondary consequence of the fibrosis within the myocardium. There are only limited data on using parametric imaging in these patients. The purpose of this study was to assess native T1 and extracellular volume (ECV) values in DMD patients.

METHODS

The Czech population of males with DMD/BMD was screened. All eligible patients fulfilling the inclusion criteria were included. Forty nine males underwent cardiac magnetic resonance (MR) examination including T1 native and post-contrast mapping measurements. One DMD patient and all BMD patients were excluded from statistical analysis. Three groups were compared - Group D1 - DMD patients without late gadolinium enhancement (LGE) (n = 23), Group D2 - DMD patients with LGE (n = 20), and Group C - gender matched controls (n = 13).

RESULTS

Compared to controls, both DMD groups had prolonged T1 native relaxation time. These results are concordant in all 6 segments as well as in global values (1041 ± 31 ms and 1043 ± 37 ms vs. 983 ± 15 ms, both p < 0.05). Group D2 had significantly increased global ECV (0.28 ± 0.044 vs. 0.243 ± 0.013, p < 0.05) and segmental ECV in inferolateral and anterolateral segments in comparison with controls. The results were also significant after adjustment for subjects' age.

CONCLUSION

DMD males had increased native T1 relaxation time independent of the presence or absence of myocardial fibrosis. Cardiac MR may provide clinically useful information even without contrast media administration.

MRI in sarcoglycanopathies: a large international cohort study

OBJECTIVES

To characterise the pattern and spectrum of involvement on muscle MRI in a large cohort of patients with sarcoglycanopathies, which are limb-girdle muscular dystrophies (LGMD2C-2F) caused by mutations in one of the four genes coding for muscle sarcoglycans.

METHODS

Lower limb MRI scans of patients with LGMD2C-2F, ranging from severe childhood variants to milder adult-onset forms, were collected in 17 neuromuscular referral centres in Europe and USA. Muscle involvement was evaluated semiquantitatively on T1-weighted images according to a visual score, and the global pattern was assessed as well.

RESULTS

Scans from 69 patients were examined (38 LGMD2D, 18 LGMD2C, 12 LGMD2E and 1 LGMD2F). A common pattern of involvement was found in all the analysed scans irrespective of the mutated gene. The most and earliest affected muscles were the thigh adductors, glutei and posterior thigh groups, while lower leg muscles were relatively spared even in advanced disease. A proximodistal gradient of involvement of vasti muscles was a consistent finding in these patients, including the most severe ones.

CONCLUSIONS

Muscle involvement on MRI is consistent in patients with LGMD2C-F and can be helpful in distinguishing sarcoglycanopathies from other LGMDs or dystrophinopathies, which represent the most common differential diagnoses. Our data provide evidence about selective susceptibility or resistance to degeneration of specific muscles when one of the sarcoglycans is deficient, as well as preliminary information about progressive involvement of the different muscles over time.

Biomarkers predict outcome in Charcot-Marie-Tooth disease 1A

BACKGROUND

Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common inherited neuropathy, a debilitating disease without known cure. Among patients with CMT1A, disease manifestation, progression and severity are strikingly variable, which poses major challenges for the development of new therapies. Hence, there is a strong need for sensitive outcome measures such as disease and progression biomarkers, which would add powerful tools to monitor therapeutic effects in CMT1A.

METHODS

We established a pan-European and American consortium comprising nine clinical centres including 311 patients with CMT1A in total. From all patients, the CMT neuropathy score and secondary outcome measures were obtained and a skin biopsy collected. In order to assess and validate disease severity and progression biomarkers, we performed qPCR on a set of 16 animal model-derived potential biomarkers in skin biopsy mRNA extracts.

RESULTS

In 266 patients with CMT1A, a cluster of eight cutaneous transcripts differentiates disease severity with a sensitivity and specificity of 90% and 76.1%, respectively. In an additional cohort of 45 patients with CMT1A, from whom a second skin biopsy was taken after 2-3 years, the cutaneous mRNA expression of GSTT2, CTSA, PPARG, CDA, ENPP1 and NRG1-Iis changing over time and correlates with disease progression.

CONCLUSIONS

In summary, we provide evidence that cutaneous transcripts in patients with CMT1A serve as disease severity and progression biomarkers and, if implemented into clinical trials, they could markedly accelerate the development of a therapy for CMT1A.

Muscular dystrophies and myopathies: the spectrum of mutated genes in the Czech Republic

Inherited neuromuscular disorder (NMD) is a wide term covering different genetic disorders affecting muscles, nerves, and neuromuscular junctions. Genetic and clinical heterogeneity is the main drawback in a routine gene-by-gene diagnostics. We present Czech NMD patients with a genetic cause identified using targeted next-generation sequencing (NGS) and the spectrum of these causes. Overall 167 unrelated patients presenting NMD falling into categories of muscular dystrophies, congenital muscular dystrophies, congenital myopathies, distal myopathies, and other myopathies were tested by targeted NGS of 42 known NMD-related genes. Pathogenic or probably pathogenic sequence changes were identified in 79 patients (47.3%). In total, 37 novel and 51 known disease-causing variants were detected in 23 genes. In addition, variants of uncertain significance were suspected in 7 cases (4.2%), and in 81 cases (48.5%) sequence changes associated with NMD were not found. Our results strongly indicate that for molecular diagnostics of heterogeneous disorders such as NMDs, targeted panel testing has a high-clinical yield and should therefore be the preferred first-tier approach. Further, we show that in the genetic diagnostic practice of NMDs, it is necessary to take into account different types of inheritance including the occurrence of an autosomal recessive disorder in two generations of one family.

Improving diagnosis of inherited peripheral neuropathies through gene panel analysis

BACKGROUND

Inherited peripheral neuropathies (IPN) are the most common inherited neurological condition. It represents a highly heterogeneous group, both clinically and genetically. Targeted disease specific gene panel massively parallel sequencing (MPS) seems to be a useful tool in diagnosis of disorders with high genetic heterogeneity.

METHODS

In our study, we have designed, validated and updated our own custom gene panel of all known genes associated with IPN. One hundred and ninety-eight patients have been tested so far. Only patients in whom mutations in more common causes or relevant genes have already been excluded were enrolled. Five consecutive panel designs were prepared according to recent literature search, the last one covering ninety-three genes. Each patient was tested only once. All data were evaluated with at least two different pipelines.

RESULTS

In summary, causative mutation has been found in fifty-one patients (26 %). The results were inconclusive in thirty-one (16 %) patients. No variants of likely significance to IPN were found in one hundred and sixteen (58 %) patients.

CONCLUSION

MPS gene panel enables testing of all known IPN causes at once with high coverage and at an affordable cost making it truly a method of choice also in IPN. Gene panel testing results in several interesting results and findings.

HSMNR belongs to the most frequent types of hereditary neuropathy in the Czech Republic and is twice more frequent than HMSNL

Hereditary motor and sensory neuropathy type Russe (HMSNR), also called CMT4G, is an autosomal recessive inherited peripheral neuropathy (IPN) caused by a founder mutation in the HK1 gene. HMSNR affects only patients with Roma origin, similar to the better known HMSN type Lom clarified earlier. By testing IPN patients with Roma origin, we realized that HMSNR affects surprisingly many patients in the Czech Republic. HMSNR is one of the most frequent types of IPN in this country and appears to be twice more frequent than HMSNL. Pronounced lower limb atrophies and severe deformities often lead to walking inability in even young patients, but hands are usually only mildly affected even after many years of disease duration. The group of 20 patients with HMSNR presented here is the first report about the prevalence of HMSNR from central Europe.

Mutations in HINT1 are one of the most frequent causes of hereditary neuropathy among Czech patients and neuromyotonia is rather an underdiagnosed symptom

Mutations in the HINT1 gene were recently discovered as being the major cause of autosomal recessive axonal neuropathy with neuromyotonia. This combination was clinically recognized and described previously in a few reports but is generally unknown. We aimed to establish the importance of HINT1 mutations as the cause of hereditary neuropathy and particularly hereditary motor neuropathy/axonal Charcot-Marie-Tooth (HMN/CMT2) among Czech patients. Overall, mutations in the HINT1 gene seem to be a surprisingly frequent cause of inherited neuropathy in our group of patients. Biallelic pathogenic mutations were found in 21 patients from 19 families. The prevalent mutation in the Czech population is the p.R37P (95% of pathogenic alleles). Clinically, all patients with biallelic mutations presented with early onset of symptoms at the end of the first decade. Foot/toe extension weakness to plegia was present in almost all patients. Neuromyotonia was present in all but two patients. However, it had been properly recognized in only three patients prior to molecular genetic diagnosis. HINT1 mutations seem to be one of the most frequent causes of inherited neuropathy and are probably the most frequent cause of HMN in Czech patients. We suggest all HMN/CMT2 patients be tested for the presence of the prevalent mutation, the p.R37P.

Autosomal recessive limb-girdle muscular dystrophies in the Czech Republic

Background

Autosomal recessive limb-girdle muscular dystrophies (LGMD2) include a number of disorders with heterogeneous etiology that cause predominantly weakness and wasting of the shoulder and pelvic girdle muscles. In this study, we determined the frequency of LGMD subtypes within a cohort of Czech LGMD2 patients using mutational analysis of the CAPN3, FKRP, SGCA, and ANO5 genes.

Methods

PCR-sequencing analysis; sequence capture and targeted resequencing.

Results

Mutations of the CAPN3 gene are the most common cause of LGMD2, and mutations in this gene were identified in 71 patients in a set of 218 Czech probands with a suspicion of LGMD2. Totally, we detected 37 different mutations of which 12 have been described only in Czech LGMD2A patients. The mutation c.550delA is the most frequent among our LGMD2A probands and was detected in 47.1% of CAPN3 mutant alleles. The frequency of particular forms of LGMD2 was 32.6% for LGMD2A (71 probands), 4.1% for LGMD2I (9 probands), 2.8% for LGMD2D (6 probands), and 1.4% for LGMD2L (3 probands).

Further, we present the first results of a new approach established in the Czech Republic for diagnosis of neuromuscular diseases: sequence capture and targeted resequencing. Using this approach, we identified patients with mutations in the DYSF and SGCB genes.

Conclusions

We characterised a cohort of Czech LGMD2 patients on the basis of mutation analysis of genes associated with the most common forms of LGMD2 in the European population and subsequently compared the occurrence of particular forms of LGMD2 among countries on the basis of our results and published studies.

Three new PLP1 splicing mutations demonstrate pathogenic and phenotypic diversity of Pelizaeus-Merzbacher disease

Pelizaeus-Merzbacher disease is a severe X-linked disorder of central myelination caused by mutations affecting the proteolipid protein gene. We describe 3 new PLP1 splicing mutations, their effect on splicing and associated phenotypes. Mutation c.453_453+6del7insA affects the exon 3B donor splice site and disrupts the PLP1-transcript without affecting the DM20, was found in a patient with severe Pelizaeus-Merzbacher disease and in his female cousin with early-onset spastic paraparesis. Mutation c.191+1G>A causes exon 2 skipping with a frame shift, is expected to result in a functionally null allele, and was found in a patient with mild Pelizaeus-Merzbacher disease and in his aunt with late-onset spastic paraparesis. Mutation c.696+1G>A utilizes a cryptic splice site in exon 5, causes partial exon 5 skipping and in-frame deletion, and was found in an isolated patient with a severe classical Pelizaeus-Merzbacher. PLP1 splice-site mutations express a variety of disease phenotypes mediated by different molecular pathogenic mechanisms.

Congenital cataract, facial dysmorphism and demyelinating neuropathy (CCFDN) in 10 Czech Gypsy children--frequent and underestimated cause of disability among Czech Gypsies

BACKGROUND

Congenital Cataract Facial Dysmorphism and demyelinating Neuropathy (CCFDN, OMIM 604468) is an autosomal recessive multi-system disorder which was first described in Bulgarian Gypsies in 1999. It is caused by the homozygous founder mutation c.863 + 389C > T in the CTDP1 gene. The syndrome has been described exclusively in patients of Gypsy ancestry. The prevalence of this disorder in the Gypsy population in the Czech Republic and Central Europe is not known and is probably underestimated and under-diagnosed.

METHODS

We clinically diagnosed and assessed 10 CCFDN children living in the Czech Republic. All patients are children of different ages, all of Gypsy origin born in the Czech Republic. Molecular genetic testing for the founder CTDP1 gene mutation was performed.

RESULTS

All patients are homozygous for the c.863 + 389C > T mutation in the CTDP1 gene. All patients presented a bilateral congenital cataract and microphthalmos and had early cataract surgery. Correct diagnosis was not made until the age of two. All patients had variably delayed motor milestones. Gait is characteristically paleocerebellar in all the patients. Mental retardation was variable and usually mild.

CONCLUSIONS

Clinical diagnosis of CCFDN should be easy for an informed pediatrician or neurologist by the obligate signalling trias of congenital bilateral cataract, developmental delay and later demyelinating neuropathy. Our data indicate a probably high prevalence of CCFDN in the Czech Gypsy ethnic subpopulation.

Phenotypic variability in a large Czech family with a dynamin 2-associated Charcot-Marie-Tooth neuropathy

Mutations in the Dynamin 2 gene (DNM2) cause autosomal dominant centronuclear myopathy or autosomal dominant (AD) Charcot-Marie-Tooth (CMT) disease. Here the authors report one large Czech family with 15 members affected with an AD CMT phenotype of extraordinary variability. Genetic linkage analysis using SNP arrays revealed a locus of about 9.6 Mb on chromosome 19p13.1-13.2. In this critical interval, 373 genes were located. The only gene herein known to be associated with an intermediate type of CMT was Dynamin 2 (DNM2). Subsequent sequence analysis of the DNM2 gene in the index patient revealed a novel missense mutation p.Met580Thr. This missense mutation segregated with the neuropathy, indicating the causal character of this mutation. The phenotype of CMT in this family shows mild to moderate impairment with relatively preserved upper limbs and a very broad range of the onset of clinical symptoms from an early onset around the age of 12 to the late onset during the fifth decade. Electrophysiology showed an intermediate type of peripheral neuropathy. The motor median nerve conduction velocity varied from 36 m/s to normal values with signs of asymmetrical affection of peripheral nerves. No additional symptoms such as cranial nerve involvement, cataract, and signs of neutropenia or myopathy syndrome were observed in any member of the family yet. The progression was slow with no loss of ambulation. The authors suggest that the characterization of clinical variability in a single family may help to direct the genetic analysis directly to the rarely observed DNM2 mutations.

Four novel point mutations in the PMP22 gene with phenotypes of HNPP and Dejerine-Sottas neuropathy

We report four novel point mutations in the PMP22 gene with two different phenotypes: mutation p.Ser79Thr arose de novo in a patient with the Dejerine-Sottas neuropathy (DSN) phenotype; and mutations c.78+5 G>A, c.320-1 G>C, and p.Trp140Stop segregated with HNPP in 5 families.Our findings show that point mutations in PMP22 may be more likely in HNPP patients than in CMT1 patients after exclusion of CMT1A/HNPP.

High frequency of SH3TC2 mutations in Czech HMSN I patients

Charcot-Marie-Tooth (CMT) neuropathy type 4C (CMT4C) is an autosomal recessive (AR), demyelinating neuropathy with early spine deformities caused by mutations in the SH3TC2 gene. To determine the spectrum of SH3TC2 mutations in the Czech population, the entire coding region of SH3TC2 was sequenced in 60 unrelated Czech patients. The prevalent mutation was shown to be the p.Arg954Stop. Therefore, 412 additional patients referred for CMT testing were tested for the presence of p.Arg954Stop only. Of 60 patients in whom the SH3TC2 gene was sequenced, at least one mutation was detected in 13 (21.7%) patients and biallelic pathogenic mutations were detected in 7 (11.6%) patients. Of the 412 patients tested for p.Arg954Stop, the mutation was found in 8 patients (1.94%), 6 were homozygous and 2 were heterozygous. The second causative mutation was detected by sequencing in one of the patients but not in the other. Nine novel sequence variants were detected. Their pathogenicity was further tested in silico and in control samples. Mutations in the SH3TC2 gene are a frequent cause of demyelinating hereditary neuropathy among Czech patients. In total, at least one mutation was found in 21 unrelated patients. CMT4C seems to be the most frequent type of AR CMT and one of the most frequent of all CMT types. Mutation p.Arg954Stop is highly prevalent in the Czech population. Patients with demyelinating neuropathy along with non-dominant mode of inheritance and negative for CMT1A/hereditary neuropathy with liability to pressure palsy should be tested for the presence of the p.Arg954Stop mutation or other mutations in the SH3TC2 gene.

Utility of Charcot-Marie-Tooth Neuropathy Score in children with type 1A disease

The aim of this study was to evaluate the utility of the Charcot-Marie-Tooth Neuropathy Score (CMTNS) for evaluation of disease severity in young children with Charcot-Marie-Tooth type 1A. Current validated scoring scales for Charcot-Marie-Tooth are the CMTNS and the Neuropathy Impairment Score (NIS). Both work well for adult patients, and usually also for children over 10 years of age. There is no validation of scales for young children. Children with genetically proven Charcot-Marie-Tooth type 1A disease (n = 20, aged 3 to 10 years) were examined clinically, followed by electrophysiologic examination, and were scored under the CMTNS scale. The clinical symptoms were mild; the two most frequent symptoms were difficulty in heel walking and lower limb areflexia. The score was maximally abnormal in four of the nine categories. Categories for sensation, sensory symptoms, and motor symptoms of the arms were normal in all cases. The score was below 8 for all tested children. To conclude, the CMTNS in children aged 10 years and younger has limited sensitivity; out of nine categories, only four are useful. Thus, evaluation of disease severity and progression in young children with Charcot-Marie-Tooth disease remains limited, and there is need for other, effective scoring systems.

Clinical and in silico evidence for and against pathogenicity of 11 new mutations in the MPZ gene

Mutations in the myelin protein zero (MPZ) gene are one of the frequent causes of Charcot-Marie-Tooth (CMT) hereditary neuropathies. Because the mutation rate of MPZ gene is rather high and some mutations are reported as polymorphisms, the proper clinical, electrophysiological examination and the segregation of the new mutation in larger families are crucial for the correct interpretation of the pathogenic or non-pathogenic character of each novel mutation. We examined 11 families with novel MPZ mutations. Eight of the mutations (L48Q, T65N, E97fs, G103W, P132T, T143R, V146G, c.645+1G>T) seem to be pathogenic on the basis of perfect segregation with the CMT phenotype and two (G213R and D246N), on the contrary, seem to be non-pathogenic/rare polymorphisms because they are present in healthy relatives. The character of the V46M mutation is difficult to interpret definitely; it may cause a sensory neuropathy or may also be a rare polymorphism. Phenotypes associated with each of the new mutations include severe hereditary motor and sensory neuropathy type III (HMSN III), and mild phenotype CMT1B presented mostly with only decreased or absent reflexes, foot deformities and mild or even absent atrophies in the lower limbs. Our report and careful family investigations with genotype-phenotype correlations should help to improve genetic counselling and correct interpretation of DNA testing results in further isolated patients or smaller families worldwide where these novel mutations might be found.

Six new gap junction beta 1 gene mutations and their phenotypic expression in Czech patients with Charcot-Marie-Tooth disease

X-linked Charcot-Marie-Tooth (CMTX) disease is a hereditary motor and sensory neuropathy caused by mutations in the gap junction beta 1 gene (GJB1 codes for connexin 32). In this study we report six novel mutations p.Met1Arg, p.Leu9Phe, p.Ser17Tyr, p.Val63Phe, p.Val170Ile, and p.Leu212Phe in GJB1 and their phenotypic expression. These mutations affect both intracellular and extracellular parts of the GJB1 protein. The screened patients had previously excluded the duplication/deletion on 17p11.2 and the male-to-male transfer in the pedigree. Except p.Val170Ile, all reported mutations segregated with the CMT phenotype in the families and caused CMTX1 neuropathy. Mutations were not found in 200 control DNA samples. Additionally, we performed in silico analysis of the novel mutations with the program PANTHER. The PANTHER scored five mutations, all but p.Val170Ile, as likely deleterious and supported the pathogenicity of the found mutations. These results provided evidence that these five mutations are causative for CMTX1.

Point mutations in Czech DMD/BMD patients and their phenotypic outcome

Duchenne and Becker muscular dystrophies (DMD/BMD) are associated with mutations in the DMD gene. We determined the mutation status of 47 patients with dystrophinopathy without deletion or duplication in the DMD gene by screening performed by reverse transcription-PCR, protein truncation test, and DNA sequencing. We describe three patients with a mutation creating a premature termination codon (p.E55X, p.E1110X, and p.S3497PfsX2) but with a mild phenotype, which present three different ways of rescuing the DMD phenotype. In one patient we detected the insertion of a repetitive sequence AluYa5 in intron 56, which led to skipping of exon 57. Further, using quantitative analysis of DMD mRNA carrying various mutated alleles, we examine levels of mRNA degradation due to nonsense mediated mRNA decay. The quantity of dystrophin mRNA is different depending on the presence of a mutation leading to a premature termination codon, and position of the analysed mRNA region with respect to its 5' end or 3' end. Average relative amounts of DMD mRNAs carrying a premature termination codon is 48% and 17%, when using primers amplifying the 5' and 3' cDNA regions, respectively.

Cranial nerves palsy as an initial feature of an early onset distal hereditary motor neuropathy--a new distal hereditary motor neuropathy phenotype

Distal hereditary motor neuropathy is a heterogeneous group of disorders characterised by a pure motor axonal neuropathy. It is occasionally associated with additional signs such as facial weakness, vocal cord paralysis, weakness of the diaphragm, and pyramidal signs. Although predominantly the inheritance is autosomal dominant, all types of inheritance have been described. Here we report a Czech family with cranial nerves palsy as an initial feature of a non progressive infantile onset dominant distal hereditary motor neuropathy. This family may represent a new subtype of distal hereditary motor neuropathy.