PMP22 Gene-Associated Neuropathies: Phenotypic Spectrum in a Cohort from India

An Elderly Woman with Complaints of Pain and Hearing Loss, Diagnosed with CMT1A with PMP22 Duplication

Charcot-Marie-Tooth (CMT) disease is a heterogeneous hereditary motor and sensory neuropathy of the peripheral nervous system, with CMT1A in particular being the most common form. We encountered a 76-year-old woman with CMT1A who had a history of pain attacks and hearing loss from a young age, with motor symptoms manifesting late in life. Her pain and hearing loss may have been related to CMT. Our case also raises the possibility that neuropathic pain and hearing loss may precede the classic motor symptoms of CMT1A.

Characterisation of Patients with SH3TC2 Associated Neuropathy in an Indian Cohort

Background

SH3TC2 variations lead to demyelinating recessive Charcot-Marie-Tooth (CMT) disease, which is commonly associated with early-onset scoliosis and cranial neuropathy. Data from Indian ethnicity is limited.

Objective

We aim to report the characteristics of patients with SH3TC2-associated neuropathy from an Indian cohort.

Patients and Methods

Data of five unrelated subjects with SH3TC2 variations were analyzed.

Results

Clinical features included female predominance (n = 4), early-onset neuropathy (n = 2), pes cavus and hammer toes (n = 4), kyphoscoliosis (n = 1), impaired vision and hearing (n = 1), facial muscle weakness (n = 1), impaired kinaesthetic sense (n = 3), tremor (n = 2), and ataxia (n = 1). Four patients had the "CMT" phenotype, while one patient had Roussy-Levy syndrome. All had demyelinating electrophysiology with conduction velocities being "very slow" in one, "slow" in one, "mildly slow" in two, and "intermediate" in one patient. Brain stem auditory evoked potentials were universally abnormal though only one patient had symptomatic deafness. Seven variants were identified in SH3TC2 [homozygous = 3 (c.1412del, c.69del, c.3152G>A), heterozygous = 4 (c.1105C>T, c.3511C>T, c.2028G>C, c.254A>T)]. Except for c.3511C>T variant, the rest were novel. Three patients had additional variations in genes having pathobiological relevance in other CMTs or amyotrophic lateral sclerosis.

Conclusion

We provide data on a cohort of patients of Indian origin with SH3TC2 variations and highlight differences from other cohorts. Though the majority were not symptomatic for hearing impairment, evoked potentials disclosed abnormalities in all. Further studies are required to establish the functional consequences of novel variants and their interacting molecular partners identified in the present study to strengthen their association with the phenotype.

Strategy for genetic analysis in hereditary neuropathy

Inherited neuropathies are a heterogeneous group of slowly progressive disorders affecting either motor, sensory, and/or autonomic nerves. Peripheral neuropathy may be the major component of a disease such as Charcot-Marie-Tooth disease or a feature of a more complex multisystemic disease involving the central nervous system and other organs. The goal of this review is to provide the clinical clues orientating the genetic diagnosis in a patient with inherited peripheral neuropathy. This review focuses on primary inherited neuropathies, amyloidosis, inherited metabolic diseases, while detailing clinical, neurophysiological and potential treatment of these diseases.

Genetic spectrum of inherited neuropathies in India

Background and Objectives:

Charcot-Marie-Tooth (CMT) disease is the commonest inherited neuromuscular disorder and has heterogeneous manifestations. Data regarding genetic basis of CMT from India is limited. This study aims to report the variations by using high throughput sequencing in Indian CMT cohort.

Methods:

Fifty-five probands (M:F 29:26) with suspected inherited neuropathy underwent genetic testing (whole exome: 31, clinical exome: 17 and targeted panel: 7). Their clinical and genetic data were analysed.

Results:

Age at onset ranged from infancy to 54 years. Clinical features included early-onset neuropathy (n=23), skeletal deformities (n=45), impaired vision (n=8), impaired hearing (n=6), facial palsy (n=8), thickened nerves (n=4), impaired cognition (n=5), seizures (n=5), pyramidal signs (n=7), ataxia (n=8) and vocal cord palsy, slow tongue movements and psychosis in one patient each. Twenty-eight patients had demyelinating electrophysiology. Abnormal visual and auditory evoked potentials were noted in 60.60% and 37.5% respectively. Sixty two variants were identified in 37 genes including variants of uncertain significance (n=34) and novel variants (n=45). Eleven patients had additional variations in genes implicated in CMTs/ other neurological disorders. Ten patients did not have variations in neuropathy associated genes, but had variations in genes implicated in other neurological disorders. In seven patients, no variations were detected.

Conclusion:

In this single centre cohort study from India, genetic diagnosis could be established in 87% of patients with inherited neuropathy. The identified spectrum of genetic variations adds to the pool of existing data and provides a platform for validation studies in cell culture or animal model systems.

Fibulin 5, a human Wharton's jelly-derived mesenchymal stem cells-secreted paracrine factor, attenuates peripheral nervous system myelination defects through the Integrin-RAC1 signaling axis

In the peripheral nervous system (PNS), proper development of Schwann cells (SCs) contributing to axonal myelination is critical for neuronal function. Impairments of SCs or neuronal axons give rise to several myelin-related disorders, including dysmyelinating and demyelinating diseases. Pathological mechanisms, however, have been understood at the elementary level and targeted therapeutics has remained undeveloped. Here, we identify Fibulin 5 (FBLN5), an extracellular matrix (ECM) protein, as a key paracrine factor of human Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) to control the development of SCs. We show that co-culture with WJ-MSCs or treatment of recombinant FBLN5 promotes the proliferation of SCs through ERK activation, whereas FBLN5-depleted WJ-MSCs do not. We further reveal that during myelination of SCs, FBLN5 binds to Integrin and modulates actin remodeling, such as the formation of lamellipodia and filopodia, through RAC1 activity. Finally, we show that FBLN5 effectively restores the myelination defects of SCs in the zebrafish model of Charcot-Marie-Tooth (CMT) type 1, a representative demyelinating disease. Overall, our data propose human WJ-MSCs or FBLN5 protein as a potential treatment for myelin-related diseases, including CMT.