A study of the phenotypic variability and disease progression in Laing myopathy through the evaluation of muscle imaging

Expanding the Clinical Spectrum of DRP2-Associated Charcot-Marie-Tooth Disease

BACKGROUND AND OBJECTIVES

Germline truncating variants in the DRP2 gene (encoding dystrophin-related protein 2) cause the disruption of the periaxin-DRP2-dystroglycan complex and have been linked to Charcot-Marie-Tooth disease. However, the causality and the underlying phenotype of the genetic alterations are not clearly defined.

METHODS

This cross-sectional retrospective observational study includes 9 patients with Charcot-Marie-Tooth disease (CMT) with DRP2 germline variants evaluated at 6 centers throughout Spain.

RESULTS

We identified 7 Spanish families with 4 different DRP2 likely pathogenic germline variants. In agreement with an X-linked inheritance, men harboring hemizygous DRP2 variants presented with an intermediate form of CMT, whereas heterozygous women were asymptomatic. Symptom onset was variable (36.6 ± 16 years), with lower limb weakness and multimodal sensory loss producing a mild-to-moderate functional impairment. Nerve echography revealed an increase in the cross-sectional area of nerve roots and proximal nerves. Lower limb muscle magnetic resonance imaging confirmed the presence of a length-dependent fatty infiltration. Immunostaining in intradermal nerve fibers demonstrated the absence of DRP2 and electron microscopy revealed abnormal myelin thickness that was also detectable in the sural nerve sections.

DISCUSSION

Our findings support the causality of DRP2 pathogenic germline variants in CMT and further define the phenotype as a late-onset sensory and motor length-dependent neuropathy, with intermediate velocities and thickening of proximal nerve segments.

Distal myopathy

Distal myopathies are a group of genetic, primary muscle diseases. Patients develop progressive weakness and atrophy of the muscles of forearm, hands, lower leg, or feet. Currently, over 20 different forms, presenting a variable age of onset, clinical presentation, disease progression, muscle involvement, and histological findings, are known. Some of them are dominant and some recessive. Different variants in the same gene are often associated with either dominant or recessive forms, although there is a lack of a comprehensive understanding of the genotype-phenotype correlations. This chapter provides a description of the clinicopathologic and genetic aspects of distal myopathies emphasizing known etiologic and pathophysiologic mechanisms.

Charcot-Marie-Tooth neuropathy score and ambulation index are both predictors of orthotic need for patients with CMT

Charcot-Marie-Tooth (CMT) disease is the most common hereditary neuropathy with an estimated prevalence of 1 person affected on 2500. Frequent symptoms include distal weakness and muscle wasting, sensory loss, reduced deep tendon reflexes, and skeletal deformities, such as hammer toes and pes cavus. CMT is a progressive disease and patients' needs change over their lifetime. In particular, ambulation aids are increasingly needed to maintain ambulation and reduce the risk of falls. We performed a retrospective analysis of medical records from 149 patients with confirmed CMT to evaluate patients ambulation needs related to the severity of their CMT as measured by the CMT Neuropathy Score (CMTNS) and Ambulation Index (AI). Most patients required some form of orthotics (86.6%). The CMTNS and AI scores both differed significantly between patients with no orthotics compared to those who wore insoles/inserts. The CMTNS and AI also differed significantly between patients wearing insoles and those with ankle foot orthotics (AFOs). CMTNS and the AI were valid predictors of the type and choice of the orthotics. Both the CMTNS and AI can be effective tools to aid in the correct choice of orthotics in patients affected by CMT.

Two decades of advances in muscle imaging in children: from pattern recognition of muscle diseases to quantification and machine learning approaches

Muscle imaging has progressively gained popularity in the neuromuscular field. Together with detailed clinical examination and muscle biopsy, it has become one of the main tools for deep phenotyping and orientation of etiological diagnosis. Even in the current era of powerful new generation sequencing, muscle MRI has arisen as a tool for prioritization of certain genetic entities, supporting the pathogenicity of variants of unknown significance and facilitating diagnosis in cases with an initially inconclusive genetic study. Although the utility of muscle imaging is increasingly clear, it has not reached its full potential in clinical practice. Pattern recognition is known for a number of diseases and will certainly be enhanced by the use of machine learning approaches. For instance, MRI heatmap representations might be confronted with molecular results by obtaining a probabilistic diagnosis based in each disease "MRI fingerprints". Muscle ultrasound as a screening tool and quantified techniques such as Dixon MRI seem still underdeveloped. In this paper, we aim to appraise the advances in recent years in pediatric muscle imaging and try to define areas of uncertainty and potential advances that might become standardized to be widely used in the future.