Clinical predominance of proximal upper limb weakness in CMT1A syndrome

New evidence for secondary axonal degeneration in demyelinating neuropathies

Development of peripheral nervous system (PNS) myelin involves a coordinated series of events between growing axons and the Schwann cell (SC) progenitors that will eventually ensheath them. Myelin sheaths have evolved out of necessity to maintain rapid impulse propagation while accounting for body space constraints. However, myelinating SCs perform additional critical functions that are required to preserve axonal integrity including mitigating energy consumption by establishing the nodal architecture, regulating axon caliber by organizing axonal cytoskeleton networks, providing trophic and potentially metabolic support, possibly supplying genetic translation materials and protecting axons from toxic insults. The intermediate steps between the loss of these functions and the initiation of axon degeneration are unknown but the importance of these processes provides insightful clues. Prevalent demyelinating diseases of the PNS include the inherited neuropathies Charcot-Marie-Tooth Disease, Type 1 (CMT1) and Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) and the inflammatory diseases Acute Inflammatory Demyelinating Polyneuropathy (AIDP) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Secondary axon degeneration is a common feature of demyelinating neuropathies and this process is often correlated with clinical deficits and long-lasting disability in patients. There is abundant electrophysiological and histological evidence for secondary axon degeneration in patients and rodent models of PNS demyelinating diseases. Fully understanding the involvement of secondary axon degeneration in these diseases is essential for expanding our knowledge of disease pathogenesis and prognosis, which will be essential for developing novel therapeutic strategies.

A "Triple Trouble" Case of Facioscapulohumeral Muscular Dystrophy Accompanied by Peripheral Neuropathy and Myoclonic Epilepsy

Background

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by asymmetric muscular deficit of facial, shoulder-girdle muscles, and descending to lower limb muscles, but it exists in several extramuscular manifestations or overlapping syndromes. Herein, we report a "complex disease plus" patient with FSHD1, accompanied by peripheral neuropathy and myoclonic epilepsy.

Methods

Standard clinical assessments, particular auxiliary examination, histological analysis, and molecular analysis were performed through the new Comprehensive Clinical Evaluation Form, pulsed-field gel electrophoresis-based Southern blot, Multiplex Ligation-dependent Probe Amplification (MLPA), whole exome sequencing (WES), and targeted methylation sequencing.

Results

The patient presented with mild facial weakness, humeral poly-hill sign, scapular winging, peroneal weakness, drop foot, pes cavus, and myoclonic epilepsy. Furthermore, electrophysiology revealed severely demyelinated and axonal injury. The muscle and nerve biopsy revealed broadly fiber Type II grouping atrophy and myelinated nerve fibers that significantly decreased with thin myelinated fibers and onion bulbs changes. Generalized sharp and sharp-slow wave complexes on electroencephalography support the diagnosis toward myoclonic epilepsy. In addition, molecular testing demonstrated a co-segregated 20-kb 4q35-EcoRI fragment and permissive allele A, which corresponded with D4Z4 hypomethylation status in the family. Both the patient's mother and brother only presented the typical FSHD but lacked overlapping syndromes. However, no mutations for hereditary peripheral neuropathy and myoclonic epilepsy were discovered by MLPA and WES.

Conclusions

The present study described a "tripe trouble" with FSHD, peripheral neuropathy, and myoclonic epilepsy, adding the spectrum of overlapping syndromes and contributing to the credible diagnosis of atypical phenotype. It would provide a direct clue on medical care and genetic counseling.

Ulnar Nerve Tendon Transfers for Pinch

Power and tip pinch are an integral part of intrinsic hand function that can be significantly compromised with dysfunction of the ulnar nerve. Loss of power pinch is one component that can significantly affect an individual's ability to perform simple daily tasks. Tip pinch is less affected, as this task has significant contributions from the median nerve. To restore power pinch, the primary focus must be on restoring the action of the adductor pollicis primarily, and if indicated the first dorsal interosseous muscle and flexor pollicis brevis.

Facioscapulohumeral muscular dystrophy and Charcot-Marie-Tooth neuropathy 1A - evidence for "double trouble" overlapping syndromes

BACKGROUND

We report on a patient with genetically confirmed overlapping diagnoses of CMT1A and FSHD. This case adds to the increasing number of unique patients presenting with atypical phenotypes, particularly in FSHD. Even if a mutation in one disease gene has been found, further genetic testing might be warranted in cases with unusual clinical presentation.

CASE PRESENTATION

The reported 53 years old male patient suffered from walking difficulties and foot deformities first noticed at age 20. Later on, he developed scapuloperoneal and truncal muscle weakness, along with atrophy of the intrinsic hand and foot muscles, pes cavus, claw toes and a distal symmetric hypoesthesia. Motor nerve conduction velocities were reduced to 20 m/s in the upper extremities, and not educible in the lower extremities, sensory nerve conduction velocities were not attainable. Electromyography showed both, myopathic and neurogenic changes. A muscle biopsy taken from the tibialis anterior muscle showed a mild myopathy with some neurogenic findings and hypertrophic type 1 fibers. Whole-body muscle MRI revealed severe changes in the lower leg muscles, tibialis anterior and gastrocnemius muscles were highly replaced by fatty tissue. Additionally, fatty degeneration of shoulder girdle and straight back muscles, and atrophy of dorsal upper leg muscles were seen. Taken together, the presenting features suggested both, a neuropathy and a myopathy. Patient's family history suggested an autosomal dominant inheritance.Molecular testing revealed both, a hereditary motor and sensory neuropathy type 1A (HMSN1A, also called Charcot-Marie-Tooth neuropathy 1A, CMT1A) due to a PMP22 gene duplication and facioscapulohumeral muscular dystrophy (FSHD) due to a partial deletion of the D4Z4 locus (19 kb).

CONCLUSION

Molecular testing in hereditary neuromuscular disorders has led to the identification of an increasing number of atypical phenotypes. Nevertheless, finding the right diagnosis is crucial for the patient in order to obtain adequate medical care and appropriate genetic counseling, especially in the background of arising curative therapies.

Distinguishing the 4qA and 4qB variants is essential for the diagnosis of facioscapulohumeral muscular dystrophy in the Chinese population

Facioscapulohumeral muscular dystrophy (FSHD) is the third most common inherited muscular dystrophy with markedly clinical variability and complex genetic cause. Several reports pertaining to the Caucasian population have confirmed that there are 4qA and 4qB variants of the 4qter subtelomere, and FSHD is uniquely associated with the 4qA variant. However, few data relevant to the Chinese population have been published. In present paper, detailed clinical and genetic re-evaluations were performed in members of four special families who had been initially diagnosed as atypical or asymptomatic FSHD based only on the D4Z4 repeat length analysis. The FSHD-sized D4Z4 repeats in the probands from families 1, 2 and 3 were identified as 4qB variants. These patients were further confirmed as limb-girdle muscular dystrophy (LGMD2) or myotonic dystrophy (DM1) by molecular analyses. Specifically, we identified a 4qB variant on chromosome 10 in the healthy members of the fourth FSHD family with complex D4Z4 rearrangements of two exchanged repeat arrays. For the first time, we demonstrated in the Chinese population that D4Z4 contractions on the 4qB variant do not cause FSHD and 4qB variant on chromosome 10 might also represent intermediate structures in the transition from 4q to 10q. Furthermore, our results emphasize that D4Z4 repeat length analysis alone is not sufficient for the diagnosis of FSHD, especially when used as an exclusion criterion. This analysis should be accompanied by 4qA/4qB variant determination and integrated chromosome assignments, especially in patients with obscure and unclassified myopathies similar to atypical forms of FSHD.

Neurofibromatosis type 1 associated with Charcot-Marie-Tooth type 1A

Neurofibromatosis and Charcot-Marie-Tooth are genetic disorders of the nervous system affecting the development and growth of nerve cells and demyelination of peripheral neurons, respectively. We report a 22-year-old man who presented clinical manifestations of both neurofibromatosis type 1 (NF1) and Charcot-Marie-Tooth type 1A. The simultaneous occurrence of neurofibromatosis and Charcot-Marie-Tooth disease has rarely been reported. More extensive reports and further investigations of this combination will certainly provide a better understanding of this linkage in the near future.

A LARGE FAMILY WITH CHARCOT-MARIE-TOOTH TYPE 1A AND TYPE 2 DIABETES MELLITUS

Charcot-Marie-Tooth (CMT) disease is a hereditary demyelinating peripheral neuropathy, and CMT Type 1A is the most common form. In most cases, CMT1A is usually caused by duplication at chromosome 17p11.2-12. Type 2 diabetes mellitus (Type 2 DM) is a common metabolic disorder, characterized by chronic hyperglycemia that can be associated with micro- and/or macrovascular complications. Only a few studies reported CMT1A duplication in association with Type 2 DM. This article explores the characteristics of a large family of 69 members with respect to CMT1A and Type 2 DM. CMT1A was detected in 28 of them. Molecular genetic study was performed in 22, and duplication was detected in all of them. Six of the 22 members with CMT1A also had Type 2 DM based on the American Diabetes Association diagnostic criteria. Association of these two conditions may be coincidental; however, the occurrence of these two diseases in this large family may also suggest a genetic basis. More extensive reports and further investigations of such families having this combination will certainly provide a better understanding of this link.

Duplication analysis in Turkish Charcot-Marie-Tooth type 1A patients using short tandem repeat markers

Charcot-Marie-Tooth (CMT) is a common inherited peripheral neuropathy with a prevalence of 1 in 2,500. CMT has two distinct forms (CMT1 and CMT2) that can be identified electrophysiologically. A 1.5 Mb tandem microduplication including peripheral myelin protein 22 gene (PMP22) on chromosome 17p11.2-12 causes CMT1A. The increased gene dosage effect of PMP22 is thought to be responsible for the pathogenesis of CMT1A. In this study, 39 Turkish CMT1A patients and 60 unrelated control samples had been examined for the duplication using polymorphic short tandem repeat (STR) markers. Seven STR marker sites (AC005838-4A-, AC0013248-9A-, AC0013248-9B-, D17S2218, D17S2220, D17S2227, and D17S2229) on the duplicated region were amplified via polymerase chain reaction, electrophoresed through 8% polyacrilamide gel and evaluated for the duplication. The rate of duplication was 92.3' (36/39) in the patients whereas it was zero in the control samples. Allele distributions, number of alleles and heterozygosity values of more informative markers (D17S2218, D17S2220, D17S2227, and D17S2229) were assessed. It is found that approximately 85% of duplications in Turkish CMT1A patients were depicted by using D17S2220 and D17S2229 markers together.

17p duplicated Charcot-Marie-Tooth 1A: characteristics of a new population

The most frequent type of Charcot-Marie-Tooth (CMT) neuropathy is that associated with the 17p11.2-p12 chromosome duplication, whose characteristics have been well described in European and North American populations. In this study, we analyzed a Brazilian population exhibiting the mutation, found in 57 patients from 42 families (79%) of a cohort of 53 families with demyelinating CMT. Almost 20% of the duplicated cases were sporadic. In 77% of the duplicated families the mutation event occurred in the hot spot area of the CMT1A-Rep region. Forty-five percent of patients were females, 84% were Caucasians and 13% of African descent. Distal limb weakness was the most frequent abnormality, appearing in 84% of patients, although uncommon manifestations such as severe proximal weakness, floppy baby syndrome, diaphragmatic weakness and severe scoliosis were also observed. One patient was wheelchair-bound, and three suffered severe hand weakness. Sensory abnormalities were detected in 84% of the cases, but 80% were unaware of this impairment. Twelve patients complained of positive sensory manifestations such as pain and paresthesias. Progression was reported by 40%. Motor conduction velocities in the upper limbs were always less than 35 m/s, and less than 30.4 m/s in the peroneal nerve. The findings of this study expand the clinical spectrum of the disease.

Contractions of D4Z4 on 4qB subtelomeres do not cause facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is associated with contractions of the D4Z4 repeat in the subtelomere of chromosome 4q. Two allelic variants of chromosome 4q (4qA and 4qB) exist in the region distal to D4Z4. Although both variants are almost equally frequent in the population, FSHD is associated exclusively with the 4qA allele. We identified three families with FSHD in which each proband carries two FSHD-sized alleles and is heterozygous for the 4qA/4qB polymorphism. Segregation analysis demonstrated that FSHD-sized 4qB alleles are not associated with disease, since these were present in unaffected family members. Thus, in addition to a contraction of D4Z4, additional cis-acting elements on 4qA may be required for the development of FSHD. Alternatively, 4qB subtelomeres may contain elements that prevent FSHD pathogenesis.

Molecular Mechanisms, Diagnosis, and Rational Approaches to Management of and Therapy for Charcot-Marie-Tooth Disease and Related Peripheral Neuropathies

During the last decade, 18 genes and 11 additional loci harboring candidate genes have been associated with Charcot-Marie-Tooth disease (CMT) and related peripheral neuropathies. Ten of these 18 genes have been identified in the last 2 years. This phenomenal pace of CMT gene discovery has fomented an unprecedented explosion of information regarding peripheral nerve biology and its pathologic manifestations in CMT. This review integrates molecular genetics with the clinical phenotypes and provides a flowchart for molecular-based diagnostics. In addition, we discuss rational approaches to molecular therapeutics, including novel biologic molecules (eg, small interfering ribonucleic acid [siRNA], antisense RNA, and ribozymes) that potentially could be used as drugs in the future. These may be applicable in attempts to normalize gene expression in cases of CMT type 1A, wherein a 1.5 Mb genomic duplication causes an increase in gene dosage that is associated with the majority of CMT cases. Aggresome formation by the PMP22 gene product, the disease-associated gene in the duplication cases, could thus be avoided. We also discuss alternative therapeutics, in light of other neurodegenerative disorders, to disrupt such aggresomes. Finally, we review rational therapeutic approaches, including the use of antioxidants such as vitamin E, coenzyme Q10, or lipoic acid to relax potential oxidative stress in peripheral nerves, for CMT management.