Current profile of Charcot-Marie-Tooth disease in Africa: A systematic review

Whole genome sequencing increases the diagnostic rate in Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT) is one of the most common and genetically heterogeneous inherited neurological diseases, with more than 130 disease-causing genes. Whole genome sequencing (WGS) has improved diagnosis across genetic diseases, but the diagnostic impact in CMT is yet to be fully reported. We present the diagnostic results from a single specialist inherited neuropathy centre, including the impact of WGS diagnostic testing. Patients were assessed at our specialist inherited neuropathy centre from 2009 to 2023. Genetic testing was performed using single gene testing, next-generation sequencing targeted panels, research whole exome sequencing and WGS and, latterly, WGS through the UK National Health Service. Variants were assessed using the American College of Medical Genetics and Genomics and Association for Clinical Genomic Science criteria. Excluding patients with hereditary ATTR amyloidosis, 1515 patients with a clinical diagnosis of CMT and related disorders were recruited. In summary, 621 patients had CMT1 (41.0%), 294 CMT2 (19.4%), 205 intermediate CMT (CMTi, 13.5%), 139 hereditary motor neuropathy (HMN, 9.2%), 93 hereditary sensory neuropathy (HSN, 6.1%), 38 sensory ataxic neuropathy (2.5%), 72 hereditary neuropathy with liability to pressure palsies (HNPP, 4.8%) and 53 'complex' neuropathy (3.5%). Overall, a genetic diagnosis was reached in 76.9% (1165/1515). A diagnosis was most likely in CMT1 (96.8%, 601/621), followed by CMTi (81.0%, 166/205) and then HSN (69.9%, 65/93). Diagnostic rates remained less than 50% in CMT2, HMN and complex neuropathies. The most common genetic diagnosis was PMP22 duplication (CMT1A; 505/1165, 43.3%), then GJB1 (CMTX1; 151/1165, 13.0%), PMP22 deletion (HNPP; 72/1165, 6.2%) and MFN2 (CMT2A; 46/1165, 3.9%). We recruited 233 cases to the UK 100 000 Genomes Project (100KGP), of which 74 (31.8%) achieved a diagnosis; 28 had been otherwise diagnosed since recruitment, leaving a true diagnostic rate of WGS through the 100KGP of 19.7% (46/233). However, almost half of the solved cases (35/74) received a negative report from the study, and the diagnosis was made through our research access to the WGS data. The overall diagnostic uplift of WGS for the entire cohort was 3.5%. Our diagnostic rate is the highest reported from a single centre and has benefitted from the use of WGS, particularly access to the raw data. However, almost one-quarter of all cases remain unsolved, and a new reference genome and novel technologies will be important to narrow the 'diagnostic gap'.

AP2A2 mutation and defective endocytosis in a Malian family with hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) comprises a large group of neurogenetic disorders characterized by progressive lower extremity spasticity. Neurological evaluation and genetic testing were completed in a Malian family with early-onset HSP. Three children with unaffected consanguineous parents presented with symptoms consistent with childhood-onset complicated HSP. Neurological evaluation found lower limb weakness, spasticity, dysarthria, seizures, and intellectual disability. Brain MRI showed corpus callosum thinning with cortical and spinal cord atrophy, and an EEG detected slow background in the index patient. Whole exome sequencing identified a homozygous missense variant in the adaptor protein (AP) complex 2 alpha-2 subunit (AP2A2) gene. Western blot analysis showed reduced levels of AP2A2 in patient-iPSC derived neuronal cells. Endocytosis of transferrin receptor (TfR) was decreased in patient-derived neurons. In addition, we observed increased axon initial segment length in patient-derived neurons. Xenopus tropicalis tadpoles with ap2a2 knockout showed cerebral edema and progressive seizures. Immunoprecipitation of the mutant human AP-2-appendage alpha-C construct showed defective binding to accessory proteins. We report AP2A2 as a novel genetic entity associated with HSP and provide functional data in patient-derived neuron cells and a frog model. These findings expand our understanding of the mechanism of HSP and improve the genetic diagnosis of this condition.

Ethnicity-related differences in mitochondrial regulation by insulin stimulation in diabetes

Mitochondrial dysfunction has long been implicated in the development of insulin resistance, which is a hallmark of type 2 diabetes. However, recent studies reveal ethnicity-related differences in mitochondrial processes, underscoring the need for nuance in studying mitochondrial dysfunction and insulin sensitivity. Furthermore, the higher prevalence of type 2 diabetes among African Americans and individuals of African descent has brought attention to the role of ethnicity in disease susceptibility. In this review, which covers existing literature, genetic studies, and clinical data, we aim to elucidate the complex relationship between mitochondrial alterations and insulin stimulation by considering how mitochondrial dynamics, contact sites, pathways, and metabolomics may be differentially regulated across ethnicities, through mechanisms such as single nucleotide polymorphisms (SNPs). In addition to achieving a better understanding of insulin stimulation, future studies identifying novel regulators of mitochondrial structure and function could provide valuable insights into ethnicity-dependent insulin signaling and personalized care.

Bilateral hearing impairment as an early symptom in a patient with Charcot-Marie-Tooth Type 1: the first case report from Syria

Introduction

Charcot-Marie-Tooth (CMT) is a group of inherited neuromuscular disorders that vary clinically and genetically. It is characterized by peripheral nerve damage, leading to muscle weakness and sensory loss.

Case presentation

A 13-year-old male presented to the rheumatology department with bilateral hearing impairment since the age of 3 years, pes cavus, and difficulties walking. Some family members had Achilles tendon lengthening surgery. During physical examination, the patient had a shortened Achilles tendon, there are high arches in the feet, curled toes, loss of touch sensation in the feet, ankles, and legs, atrophy in the foot muscles. An eye examination revealed a discrepancy that needed glasses. Neurological findings included horizontal and vertical nystagmus, proprioception disorder, and demyelinating sensorimotor disorder diagnosed as CMT type 1. The audiogram showed bilateral sensorineural hearing impairment. MRI revealed spinal disc bulges. The treatment plan includes Achilles tendon lengthening surgery and physical therapy.

Clinical discussion

CMT patients need to receive supportive treatment including physical therapy, hearing aids, and glasses, to help improve their quality of life.

Conclusion

CMT disease is a genetic disorder that causes difficulties in movement, coordination, and daily activities due to muscle weakness and sensory impairments. In a few cases, patients have been documented to have bilateral hearing impairment as their first symptoms. It affects individuals in Syria and around the world, and requires proper diagnosis and treatment.

A meta-analysis on the prevalence of Charcot-Marie-Tooth disease and related inherited peripheral neuropathies

BACKGROUND

Charcot-Marie-Tooth disease and related inherited peripheral neuropathies (CMT&RIPNs) brings great suffering and heavy burden to patients, but its global prevalence rates have not been well described.

METHODS

We searched major English and Chinese databases for studies reporting the prevalence of CMT&RIPNs from the establishment of the databases to September 26, 2022. Based on the age, gender, study design, study region, and disease subtype, the included studies were correspondingly synthesized for meta-analyses on the overall prevalence and/or the subgroup analyses by using pool arcsine transformed proportions in the random-effects model.

RESULTS

Of the finally included 31 studies, 21 studied the whole age population and various types of CMT&RIPNs, and the others reported specific disease subtype(s) or adult or non-adult populations. The pooled prevalence was 17.69/100,000 (95% CI 12.32-24.33) for the whole age population and significantly higher for CMT1 [10.61/100,000 (95% CI 7.06-14.64)] than for other subtypes (P' < 0.001). Without statistical significance, the prevalence seemed higher in those aged ≥ 16 or 18 years (21.02/100,000) than in those aged < 16 years (16.13/100,000), in males (22.50/100,000) than in females (17.95/100,000), and in Northern Europe (30.97/100,000) than in other regions.

CONCLUSION

CMT&RIPNs are relatively more prevalent as CMT1 in the disease subtypes, and probably prevalent in older ages, males, and Northern Europe. More studies on the epidemiological characteristics of CMT&RIPNs with well-defined diagnosis criteria are needed to improve the prevalence evaluation and to arouse more attention to health care support.

A case for genomic medicine in South African paediatric patients with neuromuscular disease

Paediatric neuromuscular diseases are under-recognised and under-diagnosed in Africa, especially those of genetic origin. This may be attributable to various factors, inclusive of socioeconomic barriers, high burden of communicable and non-communicable diseases, resource constraints, lack of expertise in specialised fields and paucity of genetic testing facilities and biobanks in the African population, making access to and interpretation of results more challenging. As new treatments become available that are effective for specific sub-phenotypes, it is even more important to confirm a genetic diagnosis for affected children to be eligible for drug trials and potential treatments. This perspective article aims to create awareness of the major neuromuscular diseases clinically diagnosed in the South African paediatric populations, as well as the current challenges and possible solutions. With this in mind, we introduce a multi-centred research platform (ICGNMD), which aims to address the limited knowledge on NMD aetiology and to improve genetic diagnostic capacities in South African and other African populations.