Antoon Vandenberghe

Homozygous Defects in LMNA, Encoding Lamin A/C Nuclear-Envelope Proteins, Cause Autosomal Recessive Axonal Neuropathy in Human (Charcot-Marie-Tooth Disorder Type 2) and Mouse

The Charcot-Marie-Tooth (CMT) disorders comprise a group of clinically and genetically heterogeneous hereditary motor and sensory neuropathies, which are mainly characterized by muscle weakness and wasting, foot deformities, and electrophysiological, as well as histological, changes. A subtype, CMT2, is defined by a slight or absent reduction of nerve-conduction velocities together with the loss of large myelinated fibers and axonal degeneration. CMT2 phenotypes are also characterized by a large genetic heterogeneity, although only two genes---NF-L and KIF1Bbeta---have been identified to date. Homozygosity mapping in inbred Algerian families with autosomal recessive CMT2 (AR-CMT2) provided evidence of linkage to chromosome 1q21.2-q21.3 in two families (Zmax=4.14). All patients shared a common homozygous ancestral haplotype that was suggestive of a founder mutation as the cause of the phenotype. A unique homozygous mutation in LMNA (which encodes lamin A/C, a component of the nuclear envelope) was identified in all affected members and in additional patients with CMT2 from a third, unrelated family. Ultrastructural exploration of sciatic nerves of LMNA null (i.e., -/-) mice was performed and revealed a strong reduction of axon density, axonal enlargement, and the presence of nonmyelinated axons, all of which were highly similar to the phenotypes of human peripheral axonopathies. The finding of site-specific amino acid substitutions in limb-girdle muscular dystrophy type 1B, autosomal dominant Emery-Dreifuss muscular dystrophy, dilated cardiomyopathy type 1A, autosomal dominant partial lipodystrophy, and, now, AR-CMT2 suggests the existence of distinct functional domains in lamin A/C that are essential for the maintenance and integrity of different cell lineages. To our knowledge, this report constitutes the first evidence of the recessive inheritance of a mutation that causes CMT2; additionally, we suggest that mutations in LMNA may also be the cause of the genetically overlapping disorder CMT2B1.

Axonal phenotype of Charcot-Marie-Tooth disease associated with a mutation in the myelin protein zero gene

A French family had Charcot-Marie-Tooth disease type 2 (CMT2) which was characterised by late onset of peripheral neuropathy involvement, Argyll Robertson-like pupils, dysphagia, and deafness. Electrophysiological studies and nerve biopsy defined the neuropathy as axonal type. Genetic analysis of myelin protein zero (MPZ) found a mutation in codon 124 resulting in substitution of threonine by methionine. One of the patients, presently 30 years old, showed only Argyll Robertson-like pupils as an objective sign but no clinical or electrophysiological signs of peripheral neuropathy.

Rapid screening of myelin genes in CMT1 patients by SSCP analysis: identification of new mutations and polymorphisms in the P0 gene.

Charcot-Marie-Tooth type (CMT1) disease or hereditary motor and sensory neuropathy type I (HMSNI) is an autosomal dominant peripheral neuropathy. In most CMT1 families, the disease cosegregates with a 1.5-Mb duplication on chromosome 17p11.2 (CMT1A). A few patients have been found with mutations in the peripheral myelin protein 22 (PMP-22) gene located in the CMT1A region. In other families mutations have been identified in the major peripheral myelin protein po gene localized on chromosome Iq21-q23 (CMT1B). We performed a rapid mutation screening of the PMP-22 and P0 genes in non-duplicated CMT1 patients by single-strand conformation polymorphism analysis followed by direct polymerase chain reaction sequencing of genomic DNA. Six new single base changes in the P0 gene were observed: two missense mutations in, respectively, exons 2 and 3, two nonsense mutations in exon 4, and two silent mutations or polymorphisms in, respectively, exons 3 and 6.

A Locus for an Axonal Form of Autosomal Recessive Charcot-Marie-Tooth Disease Maps to Chromosome 1q21.2-q21.3

Charcot-Marie-Tooth disease (CMT) is a heterogeneous group of disorders that affect the peripheral nervous system. Three loci are known for the autosomal dominant forms of axonal CMT (CMT2), but none have yet been identified for autosomal recessive axonal CMT (ARCMT2). We have studied a large consanguineous Moroccan ARCMT2 family with nine affected sibs. The onset of CMT was in the 2d decade in all affected individuals who presented with a severe motor and sensory neuropathy, with proximal muscle involvement occurring in some patients. After exclusion of known loci for CMT2 and for demyelinating ARCMT2, a genomewide search was performed. Evidence for linkage was found with markers on chromosome 1q. The maximum pairwise LOD score was above the threshold value of 3.00, for markers D1S514, D1S2715, D1S2777, and D1S2721, and it reached 6.10 at the loci D1S2777, D1S2721, and D1S2624, according to multipoint LOD-score analysis. These markers defined a region of homozygosity that placed the gene in a 4.4-cM interval. Moreover, a recombination event detected in an unaffected 48-year-old individual excludes the D1S506 marker, thereby reducing the interval to 1.7 cM. In addition, the P0 gene, an attractive candidate because of both its location on chromosome 1q and its role in myelin structure, was excluded by physical mapping and direct sequencing.

Early‐onset Alzheimer's disease in 2 large Belgian families

Familial Alzheimers disease (FAD) is a dominantly inherited condition that may present with an early onset, and myoclonus occurs frequently in the course of the disease. We report clinical and neuropathologic data on 2 large Belgian families with FAD in which we obtained 17 autopsies of the CNS. In family A, each of 11 autopsies had the typical neuropathologic features of Alzheimers disease (AD), and there were a few cerebellar plaques in the molecular layer. In family B, in addition to the typical characteristics of AD in 6 autopsies, there were numerous amyloid plaques in the cortical cerebellar layers. In both families, we immunostained the amyloid deposits for the A4 protein, and they were negative for prion-associated protein immunoreactivity.

Sensorineural deafness in X-linked Charcot-Marie-Tooth disease with connexin 32 mutation (R142Q)

Objective: To report a family with X-linked Charcot-Marie-Tooth disease (CMTX) with proven connexin 32 (Cx32) mutation associated with deafness. Methods: Twelve members of a CMTX family were examined clinically. Electromyography and sensory and motor conduction studies were performed in three men, two women, and a 7-year-old boy. Audiometric testing was carried out in the three men, one woman, and an 8-year-old girl. Molecular genetic analysis was performed in six men and five women. Results: The three men and the 7-year-old boy had the usual sensorimotor deficit and pronounced reduction of motor nerve conduction velocity. A 15-year-old boy was asymptomatic and had only areflexia. The women had impairment of vibratory sensation and slight slowing of nerve conduction velocities. Sensorineural deafness was observed in the three men and in an 8-year-old girl without any motor or sensory deficit. Molecular genetic analysis revealed a new missense mutation located in codon 142 of the Cx32 gene leading to the substitution of an arginine by a glutamine. Conclusion: CMTX due to Cx32 mutations often shows interfamilial and intrafamilial phenotypic variation, which is also the hallmark of this family. The sensorineural deafness observed in this family suggests that Cx32 could play an important role in the auditory pathway.

Demyelinating X‐linked Charcot–Marie–Tooth disease: Unusual electrophysiological findings

X‐linked Charcot–Marie–Tooth disease (CMT‐X) is caused by mutations of connexin‐32 (Cx‐32), which encodes a gap‐junction protein. Whether the neuropathy is primarily demyelinative or axonal remains to be established. We report findings of prominent demyelination in a 71‐year‐old woman with late‐onset disease. Electrophysiological studies revealed a nonuniform slowing of motor conduction velocities and dispersion of compound action potentials indicative of a demyelinating process which was confirmed by nerve biopsy. Such electrophysiological features are unusual in hereditary neuropathies and are more commonly found with acquired chronic demyelinating neuropathies. A systematic search confirmed the molecular genomic diagnosis of CMT‐X, illustrating the value of such tests in sporadic cases. Severity of clinical symptoms and signs may vary with age and sex of the patient. The pathology of CMT‐X in other reported cases has been variably interpreted as axonal, demyelinating, or showing both features. Our observations emphasize the demyelinative nature.

SIMPLE mutation analysis in dominant demyelinating Charcot‐Marie‐Tooth disease: three novel mutations

Abstractu2003 Charcot‐Marie‐Tooth disease type 1C (CMT1C) is caused by mutations in the small integral membrane protein of the lysosome/late endosome (SIMPLE). We analyzed the coding sequence of SIMPLE in DNA of 53 unrelated cases of dominant demyelinating CMT disease with no mutations in PMP22, GJB1, MPZ, EGR2, and NEFL genes. Four different missense mutations were observed in six families. The mutation Gly112Ser was found in two families confirming its frequent occurrence in SIMPLE mutations. Three novel mutations were also identified: Ala111Gly (two families), Pro135Ser, and Pro135Thr. Familial studies revealed that all carriers of mutations (nu2003=u200338), aged from 1 to 78 years, were symptomatic, notably children under 10 years (nu2003=u20038). Motor conduction velocities in the median nerve ranked from 16.4 to 32.8u2003m/s (nu2003=u200320). In our series of 968 unrelated dominant demyelinating CMT cases (1992–2005), the percentage of SIMPLE mutations was 0.6 (6/968).

Vocal cord and diaphragm paralysis, as clinical features of a French family with autosomal recessive Charot-Marie-Tooth disease, associated with a new mutation in the GDAP1 gene

Axonal forms of Charot-Marie-Tooth disease, either dominantly or recessively inherited, are clinically and genetically heterogeneous. We describe the clinical and electrophysiological characteristics of an axonal autosomal recessive form of Charot-Marie-Tooth disease in a French family, associated with a new mutation of the ganglioside-induced differentiation-associated protein-1 gene (GDAP1). Two sisters, born to non-consanguineous parents, presented severe proximal and distal sensorimotor deficit, areflexia, pes cavus, scoliosis and vocal cord and diaphragm paralysis. They lost ambulation in the third decade and since then they have been wheelchair bound. Nerve conduction studies were consistent with an axonal neuropathy. Clinical and electrophysiological examination of their parents and their brother was normal. Genetic analysis revealed a homozygous thymidine deletion at nucleotide position 558 resulting in a frameshift at codon 186 and a stop codon at position 205. This axonal form of Charot-Marie-Tooth disease associated with a new GDAP1 mutation is recessively inherited and is characterized by a severe phenotype, since patients become wheelchair bound in the third decade, and present vocal cord and diaphram paralysis, which may be missed as they had no respiratory symptoms until the third decade.

Myelin widenings and MGUS-IgA: An immunoelectron microscopic study

A few studies have reported a variety of nonspecific histological lesions in patients with IgA monoclonal gammopathies and polyneuropathy. In our case, using electron microscopy, we observed widenings of the myelin lamellae identical to those commonly described in IgM neuropathies with anti–myelin‐associated glycoprotein activity. Using immunoelectron microscopy, we demonstrated a direct involvement of IgA in myelin lesions. The search for a direct link between monoclonal dysglobulinemia, regardless of type, and polyneuropathy is important and may influence treatment. Ann Neurol 2000;47:808–811