Truncating and missense mutations in IGHMBP2 cause Charcot-Marie Tooth disease type 2.

Using a combination of exome sequencing and linkage analysis, we investigated an English family with two affected siblings in their 40s with recessive Charcot-Marie Tooth disease type 2 (CMT2). Compound heterozygous mutations in the immunoglobulin-helicase-µ-binding protein 2 (IGHMBP2) gene were identified. Further sequencing revealed a total of 11 CMT2 families with recessively inherited IGHMBP2 gene mutations. IGHMBP2 mutations usually lead to spinal muscular atrophy with respiratory distress type 1 (SMARD1), where most infants die before 1 year of age. The individuals with CMT2 described here, have slowly progressive weakness, wasting and sensory loss, with an axonal neuropathy typical of CMT2, but no significant respiratory compromise. Segregating IGHMBP2 mutations in CMT2 were mainly loss-of-function nonsense in the 5' region of the gene in combination with a truncating frameshift, missense, or homozygous frameshift mutations in the last exon. Mutations in CMT2 were predicted to be less aggressive as compared to those in SMARD1, and fibroblast and lymphoblast studies indicate that the IGHMBP2 protein levels are significantly higher in CMT2 than SMARD1, but lower than controls, suggesting that the clinical phenotype differences are related to the IGHMBP2 protein levels.

The LITAF/SIMPLE I92V sequence variant results in an earlier age of onset of CMT1A/HNPP diseases.

Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP) represent the most common heritable neuromuscular disorders. Molecular diagnostics of CMT1A/HNPP diseases confirm clinical diagnosis, but their value is limited to the clinical course and prognosis. However, no biomarkers of CMT1A/HNPP have been identified. We decided to explore if the LITAF/SIMPLE gene shared a functional link to the PMP22 gene, whose duplication or deletion results in CMT1A and HNPP, respectively. By studying a large cohort of CMT1A/HNPP-affected patients, we found that the LITAF I92V sequence variant predisposes patients to an earlier age of onset of both the CMT1A and HNPP diseases. Using cell transfection experiments, we showed that the LITAF I92V sequence variant partially mislocalizes to the mitochondria in contrast to wild-type LITAF which localizes to the late endosome/lysosomes and is associated with a tendency for PMP22 to accumulate in the cells. Overall, this study shows that the I92V LITAF sequence variant would be a good candidate for a biomarker in the case of the CMT1A/HNPP disorders.

A late-onset and mild form of Charcot-Marie-Tooth disease type 2 caused by a novel splice-site mutation within the Mitofusin-2 gene.

Charcot-Marie-Tooth type 2A disease (CMT2A) caused by mutations in the Mitofusin 2 gene (Mfn2) has been shown to be an early-onset axonal neuropathy with severe clinical course in the majority of the patients. In this study we present a unique phenotype of CMT2A disease characterized by late-onset polyneuropathy with a very mild clinical course. This rare form of CMT2A disease is caused by a new splice-site (c.311+1G>T) mutation within the MFN2 gene. Due to disturbance of the MFN2 splicing process, this mutation generates a short transcript which encodes a very short fragment of MFN2 protein. The c.311+1G>T mutation within the MFN2 gene results in the late -onset CMT2 disease.

A new missense GDAP1 mutation disturbing targeting to the mitochondrial membrane causes a severe form of AR-CMT2C disease.

Charcot-Marie-Tooth disease (CMT) caused by mutations in the ganglioside-induced differentiation-associated protein 1 (GDAP1) gene is characterized by a spectrum of phenotypes. Recurrent nonsense mutations (Q163X and S194X) showing regional distribution segregate with an early onset, severe course of recessive CMT disease with early loss of ambulancy. Missense mutations in GDAP1 have been reported in sporadic CMT cases with variable course of disease, among them the recurrent L239F missense GDAP1 mutation occurring in the European population. Finally, some GDAP1 mutations are associated with a mild form of CMT inherited as an autosomal dominant trait. In this study, we characterize the CMT phenotype in one Polish family with recessive trait of inheritance at the clinical, electrophysiological, morphological, cellular, and genetic level associated with a new Gly327Asp mutation in the GDAP1 gene. In spite of the nature of Gly327Asp mutation (missense), the CMT phenotype associated with this variant may be characterized as an early onset, severe axonal neuropathy, with severe skeletal deformities. The mutation lies within the transmembrane domain of GDAP1 and interferes with the mitochondrial targeting of the protein, similar to the loss of the domain in the previously reported Q163X and S194X mutations. We conclude that the loss of mitochondrial targeting is associated with a severe course of disease. Our study shows that clinical outcome of CMT disease caused by mutations in the GDAP1 gene cannot be predicted solely on the basis of genetic results (missense/nonsense mutations).

L239F founder mutation in GDAP1 is associated with a mild Charcot-Marie-Tooth type 4C4 (CMT4C4) phenotype.

Over 40 mutations in the GDAP1 gene have been shown to segregate with Charcot-Marie-Tooth disease (CMT). Among these, only two mutations, i.e., S194X and Q163X have been reported in a sufficient number of CMT families to allow for the construction of reliable phenotype-genotype correlations. Both the S194X and Q163X mutations have been shown to segregate with an early-onset and severe neuropathy resulting in loss of ambulance at the beginning of the second decade of life. In this study, we identified the L239F mutation in the GDAP1 gene in one Bulgarian and five Polish families. We hypothesized that the L239F mutation may result from a founder effect in the European population since this mutation has previously been reported in Belgian, Czech, and Polish patients. In fact, we detected a common disease-associated haplotype within the 8q13-q21 region in the Polish, German, Italian, Czech, and Bulgarian CMT families. Like the previously detected "regional" S194X and Q163X mutations, respectively present in Maghreb countries and in patients of Spanish descent, the L239F mutation seems to be the most common GDAP1 pathogenic variant in the Central and Eastern European population. Given the likely presence of a common ancestor harboring the L239F mutation, we decided to compare the phenotypes of the CMT (L239F) patients collected in this study with those of previously reported cases. In contrast to CMT4A caused by the S194X and Q163X mutations, the CMT phenotype resulting from the L239F substitution represents a milder clinical entity with a long-preserved period of ambulance at least until the end of the second decade of life.

A patient with both Charcot-Marie-Tooth disease (CMT 1A) and mild spinal muscular atrophy (SMA 3).

In the present study, we report a single Polish SMA family in which the 17p11.2-p12 duplication causative for the Charcot-Marie-Tooth type 1A disease (CMT1A) was found in addition to a deletion of exons 7 and 8 of the SMN1 gene. A patient harboring both SMA and CMT1A mutations manifested with SMA3 phenotype and foot deformity. Her electrophysiological testing showed chronic neurogenic changes in proximal muscles that are typical for SMA, but also slowed conduction velocity in motor and sensory fibers that is typical for demyelinating neuropathy.

[Silver syndrome--case report]. / Zespól Silvera--opis przypadku.

Silver syndrome (Silver spastic paraplegia syndrome) is a rare disorder of the peripheral nervous system that combines features of spastic paraparesis and peripheral neuropathy. The underlying genetic defects are two mutations in the BSCL2 gene which have been described in several families. Silver syndrome--related to the N88S mutation in the BSCL2 gene--is characterized by a spectrum of clinical findings. The coexistence of sensory fiber damage and motor deficit leads to the diagnosis of Charcot-Marie-Tooth disease in some patients, while others are diagnosed with spastic paresis due to predominant pyramidal symptoms. If the symptoms are limited to the motor deficit, hereditary motor neuropathy is diagnosed in some cases. In this report, we describe a case of the Silver syndrome in a Polish family that has been verified by genetic testing. Due to the lack of pyramidal symptoms and slightly expressed sensory fiber damage (in neurographic studies), motor neuropathy type of the Silver syndrome with minor sensory component was diagnosed.

A novel Met116Thr mutation in the GDAP1 gene in a Polish family with the axonal recessive Charcot-Marie-Tooth type 4 disease.

Mutations in the gene coding for ganglioside-induced differentiation-associated protein-1 (GDAP1), which maps to chromosome 8q21, have been described in families with autosomal recessive Charcot-Marie-Tooth disease (CMT4A). Interestingly, some mutations in the GDAP1 gene have been reported in the demyelinating form of CMT1 disease, whereas others were found in patients with the axonal type of CMT disease. So far, 23 mutations in the GDAP1 gene have been reported in patients of different ethnic origins. In this study we report a novel mutation Met116Thr in the GDAP1 gene identified in a three generation Polish family with axonal CMT4.

SIMPLE mutations in Charcot-Marie-Tooth disease and the potential role of its protein product in protein degradation.

Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous group of inherited peripheral neuropathies characterized by progressive weakness and atrophy of distal limb muscles. Recently, SIMPLE/LITAF was shown to be responsible for an autosomal dominant demyelinating form of CMT linked to 16p (CMT1C). Although two transcripts encoding different proteins (SIMPLE and LITAF) have been reported from the same gene, we could not confirm the existence of LITAF. Here we show that the LITAF transcript appears to result from a DNA sequencing error. We screened the SIMPLE gene for mutations in a cohort of 192 patients with CMT or related neuropathies, each of whom tested negative for other known genetic causes of CMT. In 16 unrelated CMT families we identified nine different nucleotide variations in SIMPLE that were not detected in control chromosomes. SIMPLE mutations can occur de novo, associated with sporadic CMT1 and may convey both demyelinating and axonal forms. Bioinformatics analyses and other observations of SIMPLE suggest that 1) it could be a member of the RING finger motif-containing subfamily of E3 ubiquitin ligases that are associated with the ubiquitin-mediated proteasome processing pathway, 2) it could interact through its PPXY motifs with a WW domain containing protein, for instance with NEDD4, an E3 ubiquitin ligase, and 3) it could interact through the PSAP motif with TSG10, a protein associated with endosomal multivesicular protein sorting. Since both SIMPLE and Hrs are endosomal proteins and have both PPXY and P(S/T)AP motifs, we hypothesize that SIMPLE, like Hrs, is potentially a clathrin adaptor aiding in the retention of ubiquitinated proteins on to the endosomes. Thus the potential E3 ubiquitin ligase activity of SIMPLE, alteration in its interactions with NEDD4 or TSG101, or changes in its properties as a clathrin coat adaptor may underlie the pathogenesis of Charcot-Marie-Tooth disease.

Early onset Charcot-Marie-Tooth type 1B disease caused by a novel Leu190fs mutation in the myelin protein zero gene.

The spectrum of Charcot-Marie-Tooth (CMT) phenotypes segregating with mutations in the Myelin Protein Zero (MPZ) gene is wide and ranges from congenital hypomyelinating neuropathy (CHN) through demyelinating form of CMT to the axonal type of CMT disease. Within 94 MPZ gene mutations reported up to now, only a few were identified in the exon 4 of the MPZ gene. In this study we have identified a novel Leu190fs mutation in the MPZ gene. The Leu190fs mutation was found in a 14-year-old girl suffering from Charcot-Marie-Tooth type 1 disease (CMT1) with onset in early infancy. Similarly to the other MPZ gene frame-shift mutations reported as far the Leu190fs seems to have a dominant negative effect.

A severe recessive and a mild dominant form of Charcot-Marie-Tooth disease associated with a newly identified Glu222Lys GDAP1 gene mutation.

Charcot-Marie-Tooth (CMT) disease caused by mutations in the GDAP1 gene has been shown to be inherited via traits that may be either autosomal recessive (in the majority of cases) [CMT4A] or autosomal dominant [CMT2K]. CMT4A disease is characterized by an early onset, and a severe clinical course often leading to a loss of ambulation, whereas CMT2K is characterized by a mild clinical course of benign axonal neuropathy beginning even in the 6th decade of life. Clinical data from a GDAP1 mutated patient suggests that the presence of a particular mutation is associated with a certain trait of inheritance. The association of a particular GDAP1 gene mutation and a dominant or recessive trait of inheritance is of special importance for genetic counseling and the prenatal diagnostics as regards severe forms of CMT. In the present study we report on two CMT families in which a newly identified Glu222Lys mutation within the GDAP1 gene segregates both in autosomal dominant and recessive traits. Our study shows that at least some GDAP1 gene mutations may segregate with the CMT phenotype as both dominant and recessive traits. Thus, genetic counseling for CMT4A/CMT2K families requires more extensive data on GDAP1 phenotype-genotype correlations.

Dysmyelinating and demyelinating Charcot-Marie-Tooth disease associated with two myelin protein zero gene mutations.

Mutations in the myelin protein zero (MPZ) gene are the third most frequent cause of hereditary motor and sensory neuropathies (HMSN), also called Charcot-Marie-Tooth disorders (CMT). Only in case of recurrent mutations occurring in the MPZ gene is it possible to draw phenotype-genotype correlations essential for establishing the prognosis and outcomes of CMT1. We have surveyed a cohort of 67 Polish patients from CMT families with demyelinating neuropathy for mutations in the MPZ gene. In this study, we report two CMT families in which the Ile135Thr and Pro132Leu mutations have been identified for the MPZ gene. These MPZ gene mutations had not been identified hitherto in the Polish population. The Pro132Leu mutation segregates with a severe early-onset dysmyelinating-hypomyelinating neuropathy, whereas the Ile135Thr substitution is associated with the classical phenotype of CMT1. To the best of our knowledge, we present here, for the first time, morphological data obtained in two sural nerve biopsies pointing to a hypomyelination-dysmyelination process in a family harboring the Pro132Leu mutation in the MPZ gene.

Is a novel I214M substitution in the NEFL gene a cause of Charcot-Marie-Tooth disease? Functional analysis using cell culture models.

Recent studies have shown that mutations in neurofilament light subunit gene (NEFL) cause Charcot-Marie-Tooth (CMT) disease. Since the first description of the Gln333Pro mutation in the NEFL gene, 10 pathogenic mutations in the NEFL gene have been reported in patients affected with CMT disease. We report a novel I214M amino acid substitution in the NEFL gene in two unrelated patients affected with CMT. Because the I214M amino acid substitution in the NEFL protein was not detected in a CMT affected brother of the proband, its pathogenic effect became unclear. In order to determine whether this amino acid substitution is a benign polymorphism or causative of the disease, we performed a functional analysis of the mutant I214M neurofilament protein (NFL). Transfections of the mutant protein in cultured cells revealed an increased tendency to form highly compacted filamentous structures but no other alterations of neurofilament assembly or transport were observed. Furthermore, the sibling of one of the patients was also affected with CMT but did not have the I214M substitution. These data suggest that this I214M substitution in the NEFL gene was not a direct cause of the disease but could be a polymorphism or possibly a modifier of the CMT phenotype.