Novel Variants in MPV17, PRX, GJB1, and SACS Cause Charcot-Marie-Tooth and Spastic Ataxia of Charlevoix-Saguenay Type Diseases

Charcot-Marie-Tooth disease (CMT) and autosomal recessive spastic ataxia of Charlevoix-Saguenay type (ARSACS) are large heterogeneous groups of sensory, neurological genetic disorders characterized by sensory neuropathies, muscular atrophies, abnormal sensory conduction velocities, and ataxia. CMT2EE (OMIM: 618400) is caused by mutations in MPV17 (OMIM: 137960), CMT4F (OMIM: 614895) is caused by PRX (OMIM: 605725), CMTX1 (OMIM: 302800) is caused by mutations in GJB1 (OMIM: 304040), and ARSACS (OMIM: 270550) is caused by mutations in SACS (OMIM: 604490). In this study, we enrolled four families: DG-01, BD-06, MR-01, and ICP-RD11, with 16 affected individuals, for clinical and molecular diagnoses. One patient from each family was analyzed for whole exome sequencing and Sanger sequencing was done for the rest of the family members. Affected individuals of families BD-06 and MR-01 show complete CMT phenotypes and family ICP-RD11 shows ARSACS type. Family DG-01 shows complete phenotypes for both CMT and ARSACS types. The affected individuals have walking difficulties, ataxia, distal limb weakness, axonal sensorimotor neuropathies, delayed motor development, pes cavus, and speech articulations with minor variations. The WES analysis in an indexed patient of family DG-01 identified two novel variants: c.83G>T (p.Gly28Val) in MPV17 and c.4934G>C (p.Arg1645Pro) in SACS. In family ICP-RD11, a recurrent mutation that causes ARSACS, c.262C>T (p.Arg88Ter) in SACS, was identified. Another novel variant, c.231C>A (p.Arg77Ter) in PRX, which causes CMT4F, was identified in family BD-06. In family MR-01, a hemizygous missense variant c.61G>C (p.Gly21Arg) in GJB1 was identified in the indexed patient. To the best of our knowledge, there are very few reports on MPV17, SACS, PRX, and GJB1 causing CMT and ARSACS phenotypes in the Pakistani population. Our study cohort suggests that whole exome sequencing can be a useful tool in diagnosing complex multigenic and phenotypically overlapping genetic disorders such as Charcot-Marie-Tooth disease (CMT) and spastic ataxia of Charlevoix-Saguenay type.

Playing Disability Rugby League with Charcot-Marie-Tooth Disease: A Case Study

Charcot-Marie-Tooth (CMT) disease is a common inherited neurological disorder that causes damage to peripheral nerves. Reports of CMT patients participating in team-based sports such as disability rugby league are scarce. The objective of this case report was to evaluate the benefits of participation in disability rugby league in a 50-year-old male with CMT. Leg muscle mass and strength was worse for the case subject compared to two age-matched CMT participants with an exercise history; however, evidence of greater function in the case subject was observed through better 6-min walk test performance. Performance in a series of sport specific tests was noticeably worse for the case subject compared to a fellow rugby league player (age matched) with cerebral palsy. Inferior in-game performance was observed for the case subject compared to his fellow rugby league player in terms of distance covered, top running speed, and intensity. However, the case subject may have assumed a different role when playing as evident by the different behaviours he displayed during the games (i.e., less player contacts, tackles, or touches, but more passes of the ball). This case study provides information concerning disability rugby league as an adjunctive mode of treatment for CMT populations.

Characterising gait in paediatric neuromuscular disorders: an observational study of spatio-temporal gait in a clinical cohort

AIM

Few studies have characterised the relationship between disease and gait function in children and young people with rare neuromuscular disorders (NMDs). This study aimed to describe the relationship between disease and gait in a large paediatric cohort from a neuromuscular outpatient clinic.

METHODS

A prospective, cross-sectional study of gait in independently ambulant children and young people aged 4-21 years with a clinical or genetically confirmed NMD. Participants traversed an electronic walkway barefoot and in footwear at self-selected and fast pace. Analysis of disease included a typically developing (TD) reference group.

RESULTS

A sample of 113 participants with NMD, mean age 9.5 years (SD 3.1), 28% female, grouped into nine diagnostic subgroups. Eighty percent reported limitations to functional mobility. Children with NMD walked slower, with a shorter and wider step compared to a TD reference group, with moderate to large effect sizes for each of these gait parameters indicative of the clinical significance of these gait deviations. Children with Duchenne muscular dystrophy (DMD) walked slowest with a markedly wide gait pattern. Footwear had little overall effect on gait in children with NMDs. All children could accelerate over short distances.

CONCLUSIONS

Gait, notably speed, step length, and width are clinically significant biomarkers of disease in paediatric NMDs, affording objective functional measures in clinical settings and research.Implications for rehabilitationGait should be considered a functional biomarker of disease in children and young people with neuromuscular disorders (NMDs).Comparison of gait in a paediatric neuromuscular cohort indicates that children with Duchenne muscular dystrophy (DMD) walk slowest with a shorter step length and a wider step width which increases with age and disease progression.Measurement of gait speed is a simple, pragmatic tool to monitor disease progression in the outpatient clinical environment and relates to everyday function.In clinical research, gait can be measured as a functional outcome to demonstrate change from disease-modifying interventions and treatments in NMDs.

Foot Assessment Clinical Scales in Charcot-Marie-Tooth Patients: A Scoping Review

Introduction

Charcot-Marie-Tooth disease (CMT) is a slow and progressive peripheral motor sensory neuropathy frequently associated with the cavo-varus foot deformity. We conducted a scoping review on the clinical scales used to assess foot deviations in CMT patients and analyzed their metric properties.

Evidence Acquisition

A first search was conducted to retrieve all scales used to assess foot characteristics in CMT patients from the Medline, Web of Science, Google Scholar, Cochrane, and PEDro databases. A second search was conducted to include all studies that evaluated the metric properties of such identified scales from the same databases. We followed the methodologic guidelines specific for scoping reviews and used the PICO framework to set the eligibility criteria. Two independent investigators screened all papers.

Evidence Synthesis

The first search found 724 papers. Of these, 41 were included, using six different scales: "Foot Posture Index" (FPI), "Foot Function Index", "Maryland Foot Score", "American Orthopedic Foot & Ankle Society's Hindfoot Evaluation Scale", "Foot Health Status Questionnaire", Wicart-Seringe grade. The second search produced 259 papers. Of these, 49 regarding the metric properties of these scales were included. We presented and analyzed the properties of all identified scales in terms of developmental history, clinical characteristics (domains, items, scores), metric characteristics (uni-dimensionality, inter- and intra-rater reliability, concurrent validity, responsiveness), and operational characteristics (normative values, manual availability, learning time and assessors' characteristics).

Conclusions

Our results suggested the adoption of the six-item version of the FPI scale (FPI-6) for foot assessment in the CMT population, with scoring provided by Rasch Analysis. This scale has demonstrated high applicability in different cohorts after a short training period for clinicians, along with good psychometric properties. FPI-6 can help health professionals to assess foot deformity in CMT patients over the years.

Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies

The foot-sole cutaneous receptors (section 2), their function in stance control (sway minimisation, exploratory role) (2.1), and the modulation of their effects by gait pattern and intended behaviour (2.2) are reviewed. Experimental manipulations (anaesthesia, temperature) (2.3 and 2.4) have shown that information from foot sole has widespread influence on balance. Foot-sole stimulation (2.5) appears to be a promising approach for rehabilitation. Proprioceptive information (3) has a pre-eminent role in balance and gait. Reflex responses to balance perturbations are produced by both leg and foot muscle stretch (3.1) and show complex interactions with skin input at both spinal and supra-spinal levels (3.2), where sensory feedback is modulated by posture, locomotion and vision. Other muscles, notably of neck and trunk, contribute to kinaesthesia and sense of orientation in space (3.3). The effects of age-related decline of afferent input are variable under different foot-contact and visual conditions (3.4). Muscle force diminishes with age and sarcopenia, affecting intrinsic foot muscles relaying relevant feedback (3.5). In neuropathy (4), reduction in cutaneous sensation accompanies the diminished density of viable receptors (4.1). Loss of foot-sole input goes along with large-fibre dysfunction in intrinsic foot muscles. Diabetic patients have an elevated risk of falling, and vision and vestibular compensation strategies may be inadequate (4.2). From Charcot-Marie-Tooth 1A disease (4.3) we have become aware of the role of spindle group II fibres and of the anatomical feet conditions in balance control. Lastly (5) we touch on the effects of nerve stimulation onto cortical and spinal excitability, which may participate in plasticity processes, and on exercise interventions to reduce the impact of neuropathy.

Translation and cross-cultural adaptation of the Charcot-Marie-Tooth disease Pediatric Scale to Brazilian Portuguese and determination of its measurement properties

BACKGROUND

The Charcot-Marie-Tooth disease Pediatric Scale (CMTPedS) has been used to measure aspects of disability in children with all types of Charcot-Marie-Tooth disease (CMT).

OBJECTIVE

To translate and cross-culturally adapt the CMTPedS into Brazilian-Portuguese and determine its reliability and validity.

METHODS

The translation and cross-cultural adaptation followed international guidelines recommendations. Twenty individuals with CMT were assessed. Two examiners assessed the participants for inter-rater reliability. Face validity was assessed by eight physical therapists that judged the relevance of each test item. The Bland-Altman analysis (bias) and standard error of measurement (SEM) complemented the analysis. Furthermore, intraclass correlation coefficients (ICC), weighted kappa (k), and internal consistency (Cronbach's alpha) was determined.

RESULTS

The CMTPedS was successfully translated and cross-culturally adapted. Twenty children/youth were enrolled in the study. Of these, the majority (55%) were girls with a mean age of 13.9 (range: from 6 to 18) years. Regarding face validity, the CMTPedS-Br showed relevant items for assessing children and youth with CMT. The ICC for the total score showed excellent reliability (ICC_2.1  = 0.93, 95% CI = 0.84, 0.97). The most reliable items were grip, dorsiflexion and plantar flexion strength while the least reliable items were pinprick, vibration, and gait. The internal consistency was excellent (α = 0.96, 95% CI = 0.91, 0.99) and the agreement showed small variability (bias = 0.15, 95% CI= -4.28, 4.60).

CONCLUSION

The CMTPedS-Br showed adequate reliability and face validity to measure disability in individuals with CMT. This tool will allow Brazil to be part of multicentered studies on such a rare but debilitating condition.

Effectiveness of therapeutic footwear for children: A systematic review

BACKGROUND

It is estimated that 2% of the global childhood population is living with some form of mobility impairment. Although footwear interventions are proposed to aid ambulation, there appears to be a paucity in the understanding of the effects of therapeutic footwear. This review aims to explore the effectiveness of footwear as an intervention for mobility impairment in children.

METHODS

A systematic search of MEDLINE, CINAHL, PubMed, SPORTdiscus and Scopus databases were performed. Studies which focused on children with some form of mobility impairment, age of 9 months to 18 years, therapeutic footwear that allowed walking, and outcome measures that had explored biomechanical or skeletal geometry or psychosocial aspects were included in this review. Modified Downs and Black quality assessment index of randomised and non-randomised studies were used to assess the methodologies of included papers.

RESULTS

Out of 5003 articles sourced, 13 met the inclusion criteria for this review. These were grouped into two titled "corrective and "functional" based on the types of footwear used for intervention. Studies within the corrective footwear group included participants aged 11 months to 5 years with moderate congenital talipes equino varus or mobile pes planus. While using skeletal geometry as an outcome, there was a limited fair quality (level II) evidence that corrective footwear has no significant effect on the development of pes planus but may assist in the reduction of deformity in congenital talipes equino varus. The functional footwear group included participants aged 3 to 17 years, predominantly with mobile pes planus or cerebral palsy. Based on biomechanical measures as an outcome, there was a limited fair quality (level III) evidence that functional footwear alters biomechanical parameters in mobile pes planus (spatiotemporal) and cerebral palsy (spatiotemporal, kinematic). Although psychosocial outcomes were considered within two studies, the analysis was limited.

CONCLUSION

Only a limited number of studies have explored the effects of therapeutic footwear and only in a narrow range of mobility impairments. Further high-quality research is required to improve the evidence base for the effectiveness of therapeutic footwear. This should include a wide range of mobility impairments and should focus both on physical and psychosocial outcomes.

Walking and weakness in children: a narrative review of gait and functional ambulation in paediatric neuromuscular disease

Background

Weakness is the primary impairment in paediatric neuromuscular diseases, impacting gait and gait-related functional activities in ambulant children affected by these rare and often degenerative diseases. Gait speed is an indicator of health and disability, yet gait is a complex, multi-faceted activity. Using the International Classification of Function, Health and Disability (ICF) model, assessment of gait and functional ambulation should consider the impairments, activity limitations and participation restrictions due to disease, and factors related to the environment and the individual person.

Methods

This narrative review involved a literature search of databases including Medline, Embase and Pubmed from 1946 to October 2019. Inclusion criteria included assessments of gait, endurance and ambulatory function in paediatric (0–18 years) neuromuscular diseases.

Results

Fifty-two papers were identified reporting assessments of gait speed, timed function, endurance and ambulatory capacity, gait-related balance and qualitative descriptive assessments of gait function and effect of disease on gait and gait-related activities. Gait speed is an indicator of disability and children with neuromuscular disease walk slower than typically developing peers. Increasing disease severity and age were associated with slower walking in children with Duchenne muscular dystrophy and Charcot-Marie-Tooth disease. The six-minute walk test is used widely as a test of endurance and ambulatory capacity; six-minute walk distance was substantially reduced across all paediatric neuromuscular diseases. Endurance and ambulatory capacity was more limited in children with spinal muscular atrophy type 3, congenital muscular dystrophy and older boys with Duchenne muscular dystrophy. Only a few papers considered normalisation of gait parameters accounting for the effect on gait of height in heterogeneous groups of children and linear growth in longitudinal studies. Balance related to gait was considered in five papers, mainly in children with Charcot-Marie-Tooth disease. There was limited investigation of factors including distance requirements and terrain in children’s typical environments and personal factors related to self-perception of disease effect on gait and gait-related function.

Conclusion

Assessments of gait and functional ambulation are important considerations in documenting disease progression and treatment efficacy in the clinical setting; and in clinical trials of disease-modifying agents and physiotherapeutic interventions in paediatric neuromuscular diseases. There is a need for expert consensus on core gait and functional ambulation assessments for use in clinical and research settings.

Challenges in modelling the Charcot-Marie-Tooth neuropathies for therapy development

Much has been achieved in terms of understanding the complex clinical and genetic heterogeneity of Charcot-Marie-Tooth neuropathy (CMT). Since the identification of mutations in the first CMT associated gene, PMP22, the technological advancement in molecular genetics and gene technology has allowed scientists to generate diverse animal models expressing monogenetic mutations that closely resemble the CMT phenotype. Additionally, one can now culture patient-derived neurons in a dish using cellular reprogramming and differentiation techniques. Nevertheless, despite the fact that finding a disease-causing mutation offers a precise diagnosis, there is no cure for CMT at present. This review will shed light on the exciting advancement in CMT disease modelling, the breakthroughs, pitfalls, current challenges for scientists and key considerations to move the field forward towards successful therapies.

Gait and footwear in children and adolescents with Charcot-Marie-Tooth disease: A cross-sectional, case-controlled study

OBJECTIVE

Children with Charcot-Marie-Tooth disease (CMT) report problems with gait and footwear. We evaluated differences in spatio-temporal gait variables and gait variability between children with CMT and typically developing (TD) children, and investigated the effect of footwear upon gait.

METHOD

A cross-sectional study of 30 children with CMT and 30 age- and gender-matched TD children aged 4-18 years. Gait was assessed at self-selected speed on an electronic walkway while barefoot and in two types of the child's own footwear; optimal (e.g., athletic-type runners) and suboptimal (e.g., flip-flops).

RESULTS

Children with CMT walked more slowly (mean (SD) -13.81 (3.61) cm/s), with shorter steps (-6.28 (1.37) cm), wider base of support (+2.47 (0.66) cm; all p < 0.001) and greater base of support variability (0.48 (0.15) cm, p = 0.002) compared to TD children. Gait was faster in optimal footwear than suboptimal (-7.55 (1.31) cm/s) and barefoot (-7.42 (1.07) cm/sec; both p < 0.001) in the combined group of children. Gait in suboptimal footwear was more variable compared to barefoot and optimal footwear. Greater base of support variability and reduced balance was moderately correlated for both groups (CMT and TD).

CONCLUSION

Gait is slower with shorter, wider steps and greater base of support variability in children with CMT. Poor balance is associated with greater base of support gait variability. Suboptimal footwear negatively affects gait in all children (CMT and TD), which has clinical implications for children and adolescents with CMT who have weaker feet and ankles, and poor balance.

Electromyographic and biomechanical analysis of step negotiation in Charcot Marie Tooth subjects whose level walk is not impaired

BACKGROUND

Charcot-Marie-Tooth (CMT) is a slowly progressive disease characterized by muscular weakness and wasting with a length-dependent pattern. Mildly affected CMT subjects showed slight alteration of walking compared to healthy subjects (HS).

RESEARCH QUESTION

To investigate the biomechanics of step negotiation, a task that requires greater muscle strength and balance control compared to level walking, in CMT subjects without primary locomotor deficits (foot drop and push off deficit) during walking.

METHODS

We collected data (kinematic, kinetic, and surface electromyographic) during walking on level ground and step negotiation, from 98 CMT subjects with mild-to-moderate impairment. Twenty-one CMT subjects (CMT-NLW, normal-like-walkers) were selected for analysis, as they showed values of normalized ROM during swing and produced work at push-off at ankle joint comparable to those of 31 HS. Step negotiation tasks consisted in climbing and descending a two-step stair. Only the first step provided the ground reaction force data. To assess muscle activity, each EMG profile was integrated over 100% of task duration and the activation percentage was computed in four phases that constitute the step negotiation tasks.

RESULTS

In both tasks, CMT-NLW showed distal muscle hypoactivation. In addition, during step-ascending CMT-NLW subjects had relevant lower activities of vastus medialis and rectus femoris than HS in weight-acceptance, and, on the opposite, a greater activation as compared to HS in forward-continuance. During step-descending, CMT-NLW showed a reduced activity of tibialis anterior during controlled-lowering phase.

SIGNIFICANCE

Step negotiation revealed adaptive motor strategies related to muscle weakness due to disease in CMT subjects without any clinically apparent locomotor deficit during level walking. In addition, this study provided results useful for tailored rehabilitation of CMT patients.

Gait phenotypes in paediatric hereditary spastic paraplegia revealed by dynamic time warping analysis and random forests

The Hereditary Spastic Paraplegias (HSP) are a group of heterogeneous disorders with a wide spectrum of underlying neural pathology, and hence HSP patients express a variety of gait abnormalities. Classification of these phenotypes may help in monitoring disease progression and personalizing therapies. This is currently managed by measuring values of some kinematic and spatio-temporal parameters at certain moments during the gait cycle, either in the doctor´s surgery room or after very precise measurements produced by instrumental gait analysis (IGA). These methods, however, do not provide information about the whole structure of the gait cycle. Classification of the similarities among time series of IGA measured values of sagittal joint positions throughout the whole gait cycle can be achieved by hierarchical clustering analysis based on multivariate dynamic time warping (DTW). Random forests can estimate which are the most important isolated parameters to predict the classification revealed by DTW, since clinicians need to refer to them in their daily practice. We acquired time series of pelvic, hip, knee, ankle and forefoot sagittal angular positions from 26 HSP and 33 healthy children with an optokinetic IGA system. DTW revealed six gait patterns with different degrees of impairment of walking speed, cadence and gait cycle distribution and related with patient's age, sex, GMFCS stage, concurrence of polyneuropathy and abnormal visual evoked potentials or corpus callosum. The most important parameters to differentiate patterns were mean pelvic tilt and hip flexion at initial contact. Longer time of support, decreased values of hip extension and increased knee flexion at initial contact can differentiate the mildest, near to normal HSP gait phenotype and the normal healthy one. Increased values of knee flexion at initial contact and delayed peak of knee flexion are important factors to distinguish GMFCS stages I from II-III and concurrence of polyneuropathy.

Responsiveness of gait analysis parameters in a cohort of 71 CMT subjects

Detection of worsening in the slowly progressive Charcot-Marie-Tooth disease (CMT) is difficult. As previous clinical scales showed low responsiveness, novel outcome measures are under study, including innovative approaches such as quantitative muscle MRI and instrumented movement analysis. Since gait analysis proved able to reliably quantify CMT locomotor deficits, we aimed to explore whether it can be a sensitive-to-change outcome measure in CMT studies. Clinical and biomechanical evaluations were performed in 71 CMT subjects at baseline and after a mean (±sd) of 28.9 ± 9.5 months. Locomotor tasks included natural walking, ascending and descending steps. Instrumented analysis of such tasks provided indexes related to muscle strength (kinetic parameters) and joint movement (kinematic parameters). Parameter responsiveness was expressed as Standardized Response Mean (SRM). Considering the whole CMT group, several parameters showed moderate responsiveness; subgrouping subjects according to disease severity allowed reaching high responsiveness (SRM >0.80). CMT Examination Score showed moderate responsiveness (SRM 0.53) in the minimally affected group; kinematic parameters were more responsive in this group, whereas kinetic parameters in the most severely affected one. Biomechanical parameters can represent suitable outcome measures for CMT by showing moderate-to-high responsiveness. These data suggest that appropriate selection of patient population and outcome measures is crucial for clinical trials' design.