Developing 3D SEM in a broad biological context

When electron microscopy (EM) was introduced in the 1930s it gave scientists their first look into the nanoworld of cells. Over the last 80 years EM has vastly increased our understanding of the complex cellular structures that underlie the diverse functions that cells need to maintain life. One drawback that has been difficult to overcome was the inherent lack of volume information, mainly due to the limit on the thickness of sections that could be viewed in a transmission electron microscope (TEM). For many years scientists struggled to achieve three-dimensional (3D) EM using serial section reconstructions, TEM tomography, and scanning EM (SEM) techniques such as freeze-fracture. Although each technique yielded some special information, they required a significant amount of time and specialist expertise to obtain even a very small 3D EM dataset. Almost 20 years ago scientists began to exploit SEMs to image blocks of embedded tissues and perform serial sectioning of these tissues inside the SEM chamber. Using first focused ion beams (FIB) and subsequently robotic ultramicrotomes (serial block-face, SBF-SEM) microscopists were able to collect large volumes of 3D EM information at resolutions that could address many important biological questions, and do so in an efficient manner. We present here some examples of 3D EM taken from the many diverse specimens that have been imaged in our core facility. We propose that the next major step forward will be to efficiently correlate functional information obtained using light microscopy (LM) with 3D EM datasets to more completely investigate the important links between cell structures and their functions.

Distal myopathy with upper limb predominance caused by filamin C haploinsufficiency

OBJECTIVE

In this study, we investigated the detailed clinical findings and underlying genetic defect in 3 presumably related Bulgarian families displaying dominantly transmitted adult onset distal myopathy with upper limb predominance.

METHODS

We performed neurologic, electrophysiologic, radiologic, and histopathologic analyses of 13 patients and 13 at-risk but asymptomatic individuals from 3 generations. Genome-wide parametric linkage analysis was followed by bidirectional sequencing of the filamin C (FLNC) gene. We characterized the identified nonsense mutation at cDNA and protein level.

RESULTS

Based on clinical findings, no known myopathy subtype was implicated in our distal myopathy patients. Light microscopic analysis of affected muscle tissue showed no specific hallmarks; however, the electron microscopy revealed changes compatible with myofibrillar myopathy. Linkage studies delineated a 9.76 Mb region on chromosome 7q22.1-q35 containing filamin C (FLNC), a gene previously associated with myofibrillar myopathy. Mutation analysis revealed a novel c.5160delC frameshift deletion in all patients of the 3 families. The mutation results in a premature stop codon (p.Phe1720LeufsX63) that triggers nonsense-mediated mRNA decay. FLNC transcript levels were reduced in muscle and lymphoblast cells from affected subjects and partial loss of FLNC in muscle tissue was confirmed by protein analysis.

CONCLUSIONS

The FLNC mutation that we identified is distinct in terms of the associated phenotype, muscle morphology, and underlying molecular mechanism, thus extending the currently recognized clinical and genetic spectrum of filaminopathies. We conclude that filamin C is a dosage-sensitive gene and that FLNC haploinsufficiency can cause a specific type of myopathy in humans.

Dominant GDAP1 mutations cause predominantly mild CMT phenotypes

OBJECTIVE

Ganglioside-induced differentiation associated-protein 1 (GDAP1) mutations are commonly associated with autosomal recessive Charcot-Marie-Tooth (ARCMT) neuropathy; however, in rare instances, they also lead to autosomal dominant Charcot-Marie-Tooth (ADCMT). We aimed to investigate the frequency of disease-causing heterozygous GDAP1 mutations in ADCMT and their associated phenotype.

METHODS

We performed mutation analysis in a large cohort of ADCMT patients by means of bidirectional sequencing of coding regions and exon-intron boundaries of GDAP1. Intragenic GDAP1 deletions were excluded using an allele quantification assay. We confirmed the pathogenic character of one sequence variant by in vitro experiments assaying mitochondrial morphology and function.

RESULTS

In 8 Charcot-Marie-Tooth disease (CMT) families we identified 4 pathogenic heterozygous GDAP1 mutations, 3 of which are novel. Three of the mutations displayed reduced disease penetrance. Disease onset in the affected individuals was variable, ranging from early childhood to adulthood. Disease progression was slow in most patients and overall severity milder than typically seen in autosomal recessive GDAP1 mutations. Electrophysiologic changes are heterogeneous but compatible with axonal neuropathy in the majority of patients.

CONCLUSIONS

With this study, we broaden the phenotypic and genetic spectrum of autosomal dominant GDAP1-associated neuropathies. We show that patients with dominant GDAP1 mutations may display clear axonal CMT, but may also have only minimal clinical and electrophysiologic abnormalities. We demonstrate that cell-based functional assays can be reliably used to test the pathogenicity of unknown variants. We discuss the implications of phenotypic variability and the reduced penetrance of autosomal dominant GDAP1 mutations for CMT diagnostic testing and counseling.

Effect on tuberculosis outcomes of educational outreach to South African clinics during two randomised trials

SETTING

Public sector primary care clinics in Free State Province, South Africa.

OBJECTIVES

To investigate the effects of on-site in-service clinical skills training for nurse practitioners on tuberculosis (TB) treatment outcomes in the same clinics.

DESIGN

Analysis of TB programme data from clinics taking part in two consecutive randomised trials of educational outreach aimed at improving respiratory and human immunodeficiency virus/acquired immune-deficiency syndrome care based on the Practical Approach to Lung Health. We compared treatment outcomes between control and intervention clinics among all patients diagnosed with TB during either trial.

RESULTS

During the two trials, participating clinics treated 4187 and 2333 TB patients, respectively. Neither intervention was associated with better outcomes overall. However, among retreatment patients, cure or completion rates in intervention clinics were significantly higher during the second trial (OR 1.78, 95%CI 1.13-2.76). Patients in clinics that had received both interventions had higher cure or completion rates (OR 1.99, 95%CI 1.53-2.58) and lower default rates (OR 0.25, 95%CI 0.097-0.63) than patients in clinics that had received neither intervention.

CONCLUSION

Although not primarily focused on TB treatment, the interventions appeared to improve successful treatment completion rates among TB retreatment cases. Integrated care programmes support attainment of important TB programme goals.

Further evidence that mutations in FGD4/frabin cause Charcot-Marie-Tooth disease type 4H

BACKGROUND

Autosomal recessive demyelinating Charcot-Marie-Tooth neuropathy type 4H (CMT4H) manifests early onset, severe functional impairment, deforming scoliosis, and myelin outfoldings in the nerve biopsy. Mutations in the FGD4 gene encoding the Rho-GTPase guanine-nucleotide-exchange-factor frabin were reported in five families.

OBJECTIVE

To characterize a novel mutation in FGD4 and describe the related phenotype.

METHODS

A 20-year-old woman born of healthy consanguineous parents and affected with early-onset peroneal muscular atrophy underwent standard clinical, electrophysiologic, and pathologic (sural nerve biopsy) investigations. Mutational analysis of FGD4 was performed by direct sequencing of genomic DNA. Transcriptional analysis was done by reverse transcriptase PCR on leukocyte RNA.

RESULTS

The proband disclosed a moderately severe, scarcely progressive CMT, markedly slowed nerve conduction velocities, and a demyelinating neuropathy characterized by prominent myelin outfoldings. Mutational analysis disclosed a c.1762-2a>g transition in the splice-acceptor site of intron 14, which was predicted to cause a truncated frabin (p.Tyr587fsX14).

CONCLUSIONS

The report confirms genetic heterogeneity of FGD4, demonstrates that CMT4H has variable functional impairment, and suggests that frabin plays a crucial role during myelin formation.

Autosomal dominant congenital spinal muscular atrophy--a possible developmental deficiency of motor neurones?

We describe a kindred with an unusual congenital lower motor neuron disorder with significant but static muscle weakness predominantly affecting the lower limbs. The proband had talipes equinovarus and congenital hip contractures and did not walk until 19 months of age. Lower-extremity predominant, primarily proximal weakness was identified on assessment at three years. Over a 20 year follow-up there has been no clinical progression. The proband has a four-year-old daughter with very similar clinical findings. Electromyography and muscle biopsy suggest reduced numbers of giant normal duration motor units with little evidence of denervation or reinnervation. Dominant congenital spinal muscular atrophy predominantly affecting the lower limbs is rarely described. It is possible that the disorder is due to a congenital deficiency of motor neurons.

Two novel mutations in the GDAP1 and PRX genes in early onset Charcot-Marie-Tooth syndrome

Autosomal recessive Charcot-Marie-Tooth syndrome (AR-CMT) is often characterised by an infantile disease onset and a severe phenotype. Mutations in the ganglioside-induced differentiation-associated protein 1 (GDAP1) gene are thought to be a common cause of AR-CMT. Mutations in the periaxin (PRX) gene are rare. They are associated with severe demyelination of the peripheral nerves and sometimes lead to prominent sensory disturbances. To evaluate the frequency of GDAP1 and PRX mutations in early onset CMT, we examined seven AR-CMT families and 12 sporadic CMT patients, all presenting with progressive distal muscle weakness and wasting. In one family also prominent sensory abnormalities and sensory ataxia were apparent from early childhood. In three families we detected four GDAP1 mutations (L58LfsX4, R191X, L239F and P153L), one of which is novel and is predicted to cause a loss of protein function. In one additional family with prominent sensory abnormalities a novel homozygous PRX mutation was found (A700PfsX17). No mutations were identified in 12 sporadic cases. This study suggests that mutations in the GDAP1 gene are a common cause of early-onset AR-CMT. In patients with early-onset demyelinating AR-CMT and severe sensory loss PRX is one of the genes to be tested.

Charcot-Marie-Tooth disease: a clinico-genetic confrontation

Charcot-Marie-Tooth disease (CMT) is the most common neuromuscular disorder. It represents a group of clinically and genetically heterogeneous inherited neuropathies. Here, we review the results of molecular genetic investigations and the clinical and neurophysiological features of the different CMT subtypes. The products of genes associated with CMT phenotypes are important for the neuronal structure maintenance, axonal transport, nerve signal transduction and functions related to the cellular integrity. Identifying the molecular basis of CMT and studying the relevant genes and their functions is important to understand the pathophysiological mechanisms of these neurodegenerative disorders, and the processes involved in the normal development and function of the peripheral nervous system. The results of molecular genetic investigations have impact on the appropriate diagnosis, genetic counselling and possible new therapeutic options for CMT patients.

Charcot-Marie-Tooth disease: a clinico-genetic confrontation

Charcot-Marie-Tooth disease (CMT) is the most common neuromuscular disorder. It represents a group of clinically and genetically heterogeneous inherited neuropathies. Here, we review the results of molecular genetic investigations and the clinical and neurophysiological features of the different CMT subtypes. The products of genes associated with CMT phenotypes are important for the neuronal structure maintenance, axonal transport, nerve signal transduction and functions related to the cellular integrity. Identifying the molecular basis of CMT and studying the relevant genes and their functions is important to understand the pathophysiological mechanisms of these neurodegenerative disorders, and the processes involved in the normal development and function of the peripheral nervous system. The results of molecular genetic investigations have impact on the appropriate diagnosis, genetic counselling and possible new therapeutic options for CMT patients.

Phenotype of Charcot-Marie-Tooth disease Type 2

OBJECTIVE

To investigate the clinical and electrophysiologic phenotype of Charcot-Marie-Tooth disease (CMT) Type 2 in a large number of affected families.

METHODS

We excluded CMT Type 1, hereditary neuropathy with liability to pressure palsies, and CMT due to Cx32 gene mutations by DNA analysis. We performed genetic analysis of the presently known CMT Type 2 genes.

RESULTS

Sixty-one persons from 18 families were affected. Ninety percent of patients were able to walk with or without the help of aids. Proximal leg muscle weakness was present in 13%. Asymmetrical features were present in 15%. Normal or brisk knee reflexes were present in 36%. Extensor plantar responses without associated spasticity occurred in 10 patients from eight families. Only three causative mutations were identified in the MFN2, BSCL2, and RAB7 genes. No mutations were found in the NEFL, HSPB1, HSPB8, GARS, DNM2, and GDAP1 genes.

CONCLUSIONS

At group level, the clinical phenotype of Charcot-Marie-Tooth disease (CMT) Type 2 is uniform, with symmetric, distal weakness, atrophy and sensory disturbances, more pronounced in the legs than in the arms, notwithstanding the genetic heterogeneity. Brisk reflexes, extensor plantar responses, and asymmetrical muscle involvement can be considered part of the CMT Type 2 phenotype. The causative gene mutation was found in only 17% of the families we studied.

Spastin gene mutations in Bulgarian patients with hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) is an extremely heterogeneous group of neurodegenerative disorders affecting the longest axons in the central nervous system. The most common genetic form accounting for about 40% of the autosomal-dominant HSP (ADHSP) cases is spastin gene, SPG4. We performed mutation screening of the spastin gene on 36 unrelated HSP patients from three different ethnic groups (Bulgarian, Turks and Gypsies) and found four new mutations and one already reported. The phenotype-genotype correlations in Bulgarian SPG4 patients showed a great difference in the age at disease onset between patients with missense mutations and those harboring deletions and splice-site mutations. Our study is the first to present corroborative clinical data in favor of the general hypothesis that the clinical course of the disease is related to the type of the spastin mutation. The clinical and genealogical findings in Bulgarian SPG4 patients suggest that a positive family history for inheritance as an autosomal-dominant trait is a strong indication for spastin mutation screening.

Novel mutations in the HSN2 gene causing hereditary sensory and autonomic neuropathy type II

Hereditary sensory and autonomic neuropathy type II (HSAN-II) is caused by recessive mutations in the HSN2 gene assigned to chromosome 12p13.33. The authors report three unrelated HSAN-II families with homozygous or compound heterozygous mutations resulting in the truncation of the HSN2 protein. Genotype-phenotype correlations indicated that HSN2 mutations are associated with an early childhood onset of a predominantly sensory neuropathy, complicated by acromutilations in both upper and lower limbs.

Charcot-Marie-Tooth neuropathy type 2 and P0 point mutations: two novel amino acid substitutions (Asp61Gly; Tyr119Cys) and a possible "hotspot" on Thr124Met

Mutations in the gene for the major protein component of peripheral nerve myelin, myelin protein zero (MPZ, P0), cause hereditary disorders of Schwann cell myelin such as Charcot-Marie-Tooth neuropathy type 1B (CMT1B), Dejerine-Sottas syndrome (DSS), and congenital hypomyelinating neuropathy (CHN). More recently, P0 mutations were identified in the axonal type of CMT neuropathy, CMT2, which is different from the demyelinating variants with respect to electroneurography and nerve pathology. We screened 49 patients with a clinical and histopathological diagnosis of CMT2 for mutations in the P0 gene. Three heterozygous single nucleotide changes were detected: two novel missense mutations, Asp61Gly and Tyr119Cys, and the known Thr124Met substitution, that has already been reported in several CMT patients from different European countries. Haplotype analysis for the P0 locus proved that our patients with the 124Met allele were not related to a cohort of patients with the same mutation, all of Belgian descent and all found to share a common ancestor. Our data suggest that P0 mutations account for a detectable proportion of CMT2 cases with virtually every patient harbouring a different mutation but recurrence of the Thr124Met amino acid substitution. The high frequency of this peculiar genotype in the European CMT population is presumably not only due to a founder effect but Thr124Met might constitute a mutation hotspot in the P0 gene as well.

Absence of KIF1B mutation in a large Turkish CMT2A family suggests involvement of a second gene

BACKGROUND

Charcot-Marie-Tooth disease type 2A (CMT2A) was assigned to a 19.3-cM region on chromosome 1p35-36. A missense mutation in the kinesin family member 1B gene (KIF1B) was reported in a single CMT2A family.

OBJECTIVE

To report the clinical and genetic data of a Turkish family with CMT2A.

METHODS

Linkage to CMT2 loci was investigated in the family. Haplotype analysis of the CMT2A region was completed using additional single-nucleotide polymorphism and short tandem repeat markers. The KIF1B gene was sequenced on genomic DNA and cDNA in two patients.

RESULTS

A recombination event narrowed the CMT2A locus to a 9.3-cM region flanked by D1S160 and D1S434. No mutation in KIF1B was found.

CONCLUSION

The exclusion of KIF1B gene mutations in this family suggests the involvement of another CMT2A gene in the linked region.

SPTLC1 mutation in twin sisters with hereditary sensory neuropathy type I

Hereditary sensory neuropathy type I (HSN I) is an autosomal dominant ulceromutilating disorder of the peripheral nervous system characterized by progressive sensory loss. HSN I locus maps to chromosome 9q22.1-22.3 and is caused by mutations in the gene coding for serine palmitoyltransferase long-chain base subunit 1 (SPTLC1). A novel missense mutation in exon 13 of the SPTLC1 gene (c.1160G-->C; p.G387A) in twin sisters with a severe HSN I phenotype is reported.

Autosomal dominant striatal degeneration (ADSD): Clinical description and mapping to 5q13-5q14

OBJECTIVE

To describe the clinical and neuroradiologic features and chromosomal mapping of a novel autosomal dominant disease affecting the basal ganglia.

METHODS

The authors characterized a large family with autosomal dominant basal ganglia disease (ADSD) clinically and by MRI, MR spectroscopy (MRS), and SPECT. The authors performed a whole genome genetic linkage scan to map the underlying genetic defect.

RESULTS

The main clinical features of the disease are dysarthria and gait disturbance without any apparent reduction in life expectancy. MRI demonstrated a distinctive lesion pattern restricted mainly to the putamen and caudate nucleus. Genetic linkage analysis localized the causative genetic defect to a 3.25 megabase candidate region on chromosome 5q13.3-q14.1.

CONCLUSIONS

ADSD is an autosomal dominant basal ganglia disease mapping to chromosome 5q13.3-q14.1.

Charcot-Marie-Tooth disease with giant axons: a clinicopathological and genetic entity

The authors report an Italian family with autosomal-dominant Charcot-Marie-Tooth disease (CMT) in which there were giant axons in the sural nerve biopsy. Linkage to the known CMT2 loci (CMT2A, CMT2B, CMT2D, CMT2F) and mutations in the known CMT2 genes (Cx32, MPZ, NEFL), GAN, NEFM, and CMT1A duplication/HNPP deletion were excluded. This family with CMT and giant axons has a pathologic and genetic entity distinct from classic CMT.

Mutations in the neurofilament light chain gene (NEFL) cause early onset severe Charcot-Marie-Tooth disease

Neurofilament light chain polypeptide (NEFL) is one of the most abundant cytoskeletal components of the neuron. Mutations in the NEFL gene were recently reported as a cause for autosomal dominant Charcot-Marie-Tooth type 2E (CMT2E) linked to chromosome 8p21. In order to investigate the frequency and phenotypic consequences of NEFL mutations, we screened 323 patients with CMT or related peripheral neuropathies. We detected six disease associated missense mutations and one 3-bp in-frame deletion clustered in functionally defined domains of the NEFL protein. Patients have an early onset and often a severe clinical phenotype. Electrophysiological examination shows moderately to severely slowed nerve conduction velocities. We report the first nerve biopsy of a CMT patient with a de novo missense mutation in NEFL, and found an axonal pathology with axonal regeneration clusters and onion bulb formations. Our findings provide further evidence that the clinical variation observed in CMT depends on the gene mutated and the specific type of mutation, and we also suggest that NEFL mutations need to be considered in the molecular evaluation of patients with sporadic or dominantly inherited CMT.

Mutations in GDAP1: autosomal recessive CMT with demyelination and axonopathy

BACKGROUND

Mutations in the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) were recently shown to be responsible for autosomal recessive (AR) demyelinating Charcot-Marie-Tooth disease (CMT) type 4A (CMT4A) as well as AR axonal CMT with vocal cord paralysis.

METHODS

The coding region of GDAP1 was screened for the presence of mutations in seven families with AR CMT in which the patients were homozygous for markers of the CMT4A locus at chromosome 8q21.1.

RESULTS

A nonsense mutation was detected in exon 5 (c.581C>G, S194X), a 1-bp deletion in exon 6 (c.786delG, G262fsX284), and a missense mutation in exon 6 (c.844C>T, R282C).

CONCLUSIONS

Mutations in GDAP1 are a frequent cause of AR CMT. They result in an early-onset, severe clinical phenotype. The range of nerve conduction velocities (NCV) is variable. Some patients have normal or near normal NCV, suggesting an axonal neuropathy, whereas others have severely slowed NCV compatible with demyelination. The peripheral nerve biopsy findings are equally variable and show features of demyelination and axonal degeneration.

Hereditary neuropathy with liability to pressure palsies with a small deletion interrupting the PMP22 gene

Hereditary neuropathy with liability to pressure palsies is associated with a deficiency in the Peripheral Myelin Protein 22 (PMP22). Most hereditary neuropathy with liability to pressure palsies cases are caused by a deletion of a 1.5 Mb region on chromosome 17p11.2-12 encompassing the PMP22 gene. We describe a hereditary neuropathy with liability to pressure palsies family that lacks the common deletion, but carries a small deletion spanning the 3' region of the PMP22 gene, causing only a partial deletion of one copy of the gene.

Autosomal dominant juvenile amyotrophic lateral sclerosis and distal hereditary motor neuronopathy with pyramidal tract signs: synonyms for the same disorder?

Autosomal dominant juvenile amyotrophic lateral sclerosis (ALS) is a rare disorder and so far only one family has been reported. Genetic linkage studies mapped the disease locus to chromosome 9q34 (ALS4). The diagnosis of ALS in this family is based on the clinical signs with almost exclusively lower motor neurone pathology in combination with less prominent pyramidal tract signs. Atypical features include normal life expectancy, the absence of bulbar involvement and the symmetrical distal distribution of atrophy and weakness. We performed a molecular genetic study in three families that we had diagnosed as having distal hereditary motor neuronopathy, i.e. distal spinal muscular atrophy or spinal Charcot-Marie-Tooth syndrome, and found linkage to the ALS4 locus. The clinical phenotype in these three families, of different geographic origin (Austria, Belgium and England), is strikingly similar to the autosomal dominant juvenile ALS family except for a younger onset age in two of the distal hereditary motor neuronopathy families. These data suggest that ALS4 and distal hereditary motor neuronopathy with pyramidal tract signs may be one and the same disorder.

[Hereditary neuropathy with liability to pressure palsies: study of six Spanish families]

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant inherited demyelinating neuropathy typically characterized by recurrent episodes of acute painless peripheral nerve palsies often preceded by minor trauma or compression at entrapment sites. However, less classical phenotypes have been reported. A 1.5 Mb deletion in chromosome 17 p11.2 has been shown to be the genetic basis of the disease in the majority of HNPP patients. The few families without this deletion harbored a mutation in the PMP22 gene. We performed a clinical, neurophysiological and molecular genetic study of 6 Spanish HNPP families. Five families (22 individuals) showed the classical chromosome 17 p11.2 deletion and one family (3 individuals) had a novel 3'splice-site mutation in PMP22. Neurophysiological abnormalities were detected in all symptomatic (n=21) and asymptomatic (n=4) deletion or mutation carriers, even in childhood. In addition to the typical presentation we observed other phenotypes: recurrent focal short-term sensory symptoms, a progressive mononeuropathy, a Charcot-Marie-Tooth (CMT) disease-like chronic progressive polyneuropathy, a chronic sensory polyneuropathy and a chronic inflammatory demyelinating polyneuropathy. We report new or very rare phenotypesThese atypical clinical aspects and intrafamilial heterogeneity are present in families with the HNPP deletion as well as in the family with the PMP22 mutation. However, the CMT disease-like chronic polyneuropathy was more common in the PMP22 mutation family. Intrafamilial heterogeneity also seemed to be more pronounced in this kinship. Patients in this family had a mild chronic motor and sensory polyneuropathy neurophysiologically characterized by delayed distal latencies, reduced nerve conduction velocities (NCV) within the demyelinating range, mildly decreased amplitudes of motor and sensory evoked potentials and absence of conduction blocks. In contrast, patients with the common HNPP deletion, regardless of their phenotype, had a diffuse increase in distal motor latencies contrasting with moderately reduced motor NCVs, preserved sensory nerve action potentials, slowing of NCVs at the common entrapment sites and occasionally conduction blocks. In this study we confirm the clinical and molecular heterogeneity of HNPP, emphasizing the need for a mutation analysis of the PMP22 gene when the common 17p11.2 deletion is not found in clinically suspected HNPP patients. We conclude that the 3'splice-site mutation in PMP22 and the common HNPP deletion have largely the same functional consequences although some clinical and neurophysiological differences were observed.

Exclusion of 5 functional candidate genes for distal hereditary motor neuropathy type II (distal HMN II) linked to 12q24.3

Distal hereditary motor neuropathies (distal HMNs) are characterised by degeneration of anterior horn cells of the spinal cord resulting in muscle weakness and atrophy. Distal HMN type II is genetically linked to chromosome 12q24.3 and located within a 13 cM region flanked by markers D12S86 and D12S340. We previously excluded the human phospholipase A2 group 1B gene (PLA2G1B) as the disease causing gene. Here, we report the mutation analysis of five other candidate genes localised within the distal HMN II region: the cytoskeletal proteins paxillin (PXN) and restin (RSN); the acidic ribosomal phosphoprotein, large P0 subunit (RPLP0); a nucleoside diphosphate kinase (NME2B); and the beta 3 subunit of the voltage-gated calcium channel (CACNB3). DNA sequencing of the coding regions was performed but no disease causing mutations could be identified, hence excluding these five genes for distal HMN type II.

Hereditary Neuralgic Amyotrophy (HNA) is genetically heterogeneous

Hereditary Neuralgic Amyotrophy (HNA) is an autosomal dominantly inherited recurrent focal neuropathy affecting mainly the brachial plexus. Linkage to markers on chromosome 17q25 was found in 1996 and subsequent reports confirmed linkage of HNA to this locus. Recently a family with a chronic undulating rather than remitting-relapsing clinical course of HNA was described by a Dutch group. This family did not have linkage to the 17q25 locus. Here we describe for the first time clinically and genetically two families with classic remitting-relapsing HNA that are not linked to the previously described HNA locus on chromosome 17q25. These results demonstrate that clinically homogeneous classical HNA is genetically heterogeneous.

Infantile demyelinating neuropathy associated with a de novo point mutation on Ser72 in PMP22 and basal lamina onion bulbs in skin biopsy

Codon 72 has been designated as a hot spot for distinct missense mutations in the peripheral myelin protein 22 (PMP22) gene. Ser72Leu substitution was associated with Dejerine-Sottas syndrome (DSS) in four patients and with congenital hypomyelination neuropathy (CHN) in one patient. Our objective was to report one other DSS patient with Ser72Leu substitution in PMP22 and to concurrently illustrate how less invasive procedures such as skin biopsy could provide a rapid and reliable alternative to conventional sural nerve biopsy for the characterization of histophenotypic features. A skin biopsy was carried out in a 2 4/12-year-old girl with muscle atrophy, hypotonia and weakness, as well as generalized areflexia and absent sensory and motor nerve responses. Standard electron microscope techniques were used. PMP22 was screened by automated direct nucleotide sequencing analysis. Morphological examination revealed basal lamina onion bulbs surrounding a de- or hypomyelinated axon in all nerve bundles. Mutation analysis demonstrated a missense point mutation in codon 72 of the PMP22 gene leading to a Ser72Leu substitution. Further genotype-phenotype correlations will have to determine whether morphologically distinct phenotypes can be correlated with specific mutations. For this purpose, cutaneous nerve bundles could serve as an alternative tool to help identify and classify subtypes in this heterogeneous syndrome.

Caspr1/Paranodin/Neurexin IV is most likely not a common disease-causing gene for inherited peripheral neuropathies

Contactin associated protein 1 (Caspr1/Paranodin/Neurexin IV) is an axonal transmembrane molecule mainly localised at the paranodal junction. Since molecular alterations in septate-like junctions at the paranodes might have important consequences for the function of the nerve fiber, we considered that Caspr1 could be involved in the pathogenesis of inherited peripheral neuropathies. In this study, we physically mapped the Caspr1 gene on chromosome 17q21.1 and determined its genomic structure. We performed a mutation analysis of the Caspr1 gene in a cohort of 64 unrelated patients afflicted with distinct inherited peripheral neuropathies. Since no disease causing mutations were found, we suggest that Caspr1 is probably not a common cause of inherited peripheral neuropathies.

A new locus for autosomal dominant Charcot-Marie-Tooth disease type 2 (CMT2F) maps to chromosome 7q11-q21

Charcot-Marie-Tooth disease (CMT) constitutes a genetically heterogeneous group of inherited motor and sensory peripheral neuropathies. The axonal type of CMT is designated CMT type 2 (CMT2). Four loci for autosomal dominant CMT2 have been reported so far. Only in CMT2E, linked to chromosome 8p21, disease-causing mutations in the gene for neurofilament light chain (NEFL) were identified. In this study we report a multigenerational Russian family with autosomal dominant CMT2 and assign the locus to chromosome 7q11-q21. The CMT2 neuropathy in this family represents a novel genetic entity designated CMT2F.