Tinetti and Berg balance scales correlate with disability in hereditary peripheral neuropathies: a preliminary study

BACKGROUND

The combination of distal muscle weakness, sensory defects and feet deformities leads to disequilibrium in patients affected by Charcot-Marie-Tooth (CMT) neuropathy. Studies relating the outcome of balance scales and clinical severity of CMT are lacking.

AIM

To evaluate the accuracy of the Tinetti Balance scale (TBS) and Berg Balance scale (BBS) in identifying balance disorders and quantifying disease severity in CMT patients.

DESIGN

Observational study.

SETTING

University of Genoa-IRCCS AOU San Martino IST-Department of Neurology, Italy.

POPULATION

Nineteen individuals with a diagnosis of CMT (12 females, 7 males, age 41.26±12.42).

METHODS

All subjects underwent an evaluation with both TBS and BBS. Disability was quantified with CMT neuropathy score (CMTNS). Moreover, a complete neurophysiological study was performed. Distal lower limbs strength was evaluated with MRC scale. Pearson rank order correlation was used to determine the correlation between the scores on the two tests and to identify an eventual correlation between TBS or BBS and the CMTNS.

RESULTS

Both scales showed a highly significant negative correlation with the CMTNS (r=-0.78, P<0.0005 and r=-0.77, P<0.001, respectively) and distal weakness on the anterior tibial muscles (AT) (TBS: AT left: r=0.65, P<0.005 and AT right: 0.59, P<0.01; BBS: AT left r=+0.71, P<0.001 and AT right r=+0.66, P<0.005). We found also a highly significant, positive correlation between the two different balance scales (r=+0.9, P<0.0001).

CONCLUSION

TBS and BBS strongly correlate with disease disability and distal muscular weakness.

CLINICAL REHABILITATION IMPACT

Both TBS and BBS may play a relevant role in the assessment of disability in patients affected by CMT. Further studies are needed to validate our results in a larger population.

Contribution of copy number variations in CMT1X: a retrospective study

BACKGROUND AND PURPOSE

Charcot-Marie-Tooth disease type 1X (CMT1X) is an X-linked dominant hereditary motor-sensory peripheral neuropathy, which results from mutations in the Gap Junction B1 (GJB1) gene. In a few cases, gene deletions have been linked to the disease, but their relative contribution in the pathogenesis of CMT1X has not been assessed yet. Herein a retrospective study to establish the incidence of gene deletions is described.

METHODS

Copy number variation analysis was performed by multiplex ligation-dependent probe amplification, whilst the breakpoints were defined by Sanger sequencing.

RESULTS

A novel GJB1 deletion was identified in a family presenting with a classical CMT1X phenotype. The rearrangement includes the coding and the regulatory regions of GJB1.

CONCLUSIONS

GJB1 deletions appear to be a rare but not insignificant cause of CMT1X and are associated with a typical disease phenotype. Accordingly, patients negative for point mutations whose pedigree and clinical records strongly suggest the possibility of CMT1X should be tested for GJB1 copy number variations.

An abnormal mRNA produced by a novel PMP22 splice site mutation associated with HNPP

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant, demyelinating neuropathy. Point mutations in the PMP22 gene are a rare cause of HNPP. A novel PMP22 splice site mutation (c.179+1 G-->C) is reported in an HNPP family. By reverse transcriptase-polymerase chain reaction experiments, this mutation was shown to cause the synthesis of an abnormal mRNA in which a premature stop codon probably produces a truncated non-functional protein.

A novel mutation of GDAP1 associated with Charcot-Marie-Tooth disease in three Italian families: evidence for a founder effect

BACKGROUND

Mutations in a gene encoding a novel protein of unknown function-the ganglioside-induced differentiation-associated protein 1 gene (GDAP1)-are associated with the autosomal recessive Charcot-Marie-Tooth disease type 4A (CMT4A).

OBJECTIVE

To investigate the role of GDAP1 mutations in causing autosomal recessive neuropathies in an Italian population.

METHODS AND RESULTS

76 patients with severe early onset polyneuropathy and possible autosomal recessive inheritance were screened for mutations. A T>G transversion (c.347 T>G) at codon 116 (M116R) was detected in four affected subjects from three apparently unrelated families. All patients had early onset of disease with pronounced foot deformities and impaired walking. Neurophysiological studies showed an extremely variable expression. Sural nerve biopsies revealed signs of both de-remyelination and axonal impairment, the most prominent feature being a severe loss of larger fibres. Haplotype analysis of the GDAP1 locus demonstrated a common disease haplotype.

CONCLUSIONS

The association of the mutation with a common haplotype suggested a common ancestor.

A novel mutation of myelin protein zero associated with an axonal form of Charcot-Marie-Tooth disease

OBJECTIVE

To report a new mutation in the MPZ gene which encodes myelin protein zero (P0), associated with an axonal form of Charcot-Marie-Tooth disease (CMT).

METHODS

Three patients from an Italian family with a mild, late onset axonal peripheral neuropathy are described clinically and electrophysiologically. To detect point mutation in MPZ gene the whole coding sequence was examined. The structure of the mutated protein was investigated using the three dimensional model of P0.

RESULTS

All patients showed a relatively mild CMT phenotype characterised by late onset and heterogeneity of the clinical and electrophysiological features. Molecular analysis demonstrated a novel heterozygous T/A transversion in the exon 3 of MPZ gene that predicts an Asp109Glu amino acid substitution in the extracellular domain of the P0. Asp109 is found at the protein surface, on beta strand E, in the interior of the P0 tetramer.

CONCLUSIONS

The identification of Asp109Glu mutation confirms the pivotal role of P0 in axonal neuropathies and stresses the phenotypic heterogeneity associated with MPZ mutations. This study suggests the value of screening for MPZ mutations in CMT family members with minor clinical and electrophysiological signs of peripheral neuropathy.

No evidence of association between CAG expansions and essential tremor in a large cohort of Italian patients

Essential tremor (ET) is one of the most common movement disorders. However the pathogenesis is as yet unknown, although a genetic cause has long been recognised. Clinical and molecular evidences suggested that the ET gene might contain a CAG expanded region. In a cohort of Italian ET patients Repeat Expansion Detection (RED) approach did not demonstrate large CAG expansions. We extended the study towards specific targets: the channel proteins hSKCa3 and CACNL1A4. Direct assessment of CAG stretches within these two genes did not demonstrate any CAG expansion in affected subjects. Also a case-control analysis failed to reveal any evidence of association, thus excluding these genes as a cause of ET.

The D355V mutation decreases EGR2 binding to an element within the Cx32 promoter

Mutations in the early growth response 2 (EGR2) gene are associated with some forms of Charcot--Marie--Tooth disease (CMT) and other demyelinating neuropathies. These mutations modify the EGR2 binding to specific DNA sequences suggesting a role in the transcriptional control of myelination-specific genes. Here we show that the D355V mutation, associated with a CMT case combining axonal and demyelinating abnormalities, reduces three times the affinity of EGR2 to its consensus sequence and ten times its affinity to a sequence in the human Cx32 promoter. These findings could indicate that this EGR2 mutation leads to the development of CMT1 through the transcriptional deregulation of Cx32 gene.

Clinical and genetic study of essential tremor in the Italian population

Essential tremor (ET) is one of the most common movement disorders. The pathogenesis is as yet unknown, although a genetic cause has long been recognised. Clinical and molecular evidence suggested that the ET gene contains a CAG expanded region. We examined a cohort of 240 Italian ET patients, classified as familial (193 cases) and sporadic (47 cases). The clinical manifestations of ET patients confirmed that the disorder is characterised by a large phenotypic variability. Repeat expansion detection (RED) approach did not demonstrate large CAG expansions. Six families were genotyped with 12 microsatellites markers of 2p and 3q regions and analysed according to parametrical methods. Lod scores values obtained in these families excluded the association of ET with 2p and 3q loci. Our findings confirm the presence of genetic heterogeneity and suggest that at least a third locus is involved in the pathogenesis of familial essential tremor.

Family and molecular data for a fine analysis of age at onset in Huntington disease

We analyzed the data on age at onset and CAG size of 319 patients clinically diagnosed with Huntington disease (HD) and 86 presymptomatic subjects recorded by four Italian Centers over the last 14 years. To overcome the problem of different CAG numbers found in each subject, also in the same family, the data were analyzed in terms of deviations from the average exponential relationship between onset and CAG number. The subject's year of birth was also considered to quantify possible sampling biases. Observations between relatives were compared with those of the whole group. The deviations were equal, on average, in subjects who inherited their HD gene from their fathers or mothers. Overall, our data argue in favor of a greater similarity across the same generation than across successive generations. In particular, an excess of parents with later than expected age of onset was observed, paralleled by a CAG-independent anticipation of onset in parent-child transmissions. These results can be interpreted in terms of a shared environment determining similar departures from the average CAG-onset relationship but also of a systematic effect that differentiates the two generations here examined.

Corticobasal degeneration shares a common genetic background with progressive supranuclear palsy

Corticobasal degeneration is a sporadic form of tauopathy, involving the cerebral cortex and extrapyramidal motor system. A series of affected subjects was genotyped for a set of genetic markers along the tau protein gene. A specific haplotype is significantly overrepresented in patients versus controls. This haplotype is the same already reported in association with progressive supranuclear palsy. These data show that corticobasal degeneration and progressive supranuclear palsy, in addition to several clinical, pathological, and molecular features, may have the same genetic background.

A novel mutation (D305V) in the early growth response 2 gene is associated with severe Charcot-Marie-Tooth type 1 disease

Hereditary motor and sensory neuropathies (HMSN) comprises a wide clinical spectrum of related disorders with defects in peripheral nerve myelination. Charcot-Marie-Tooth type 1 (CMT1) is the most common form and is usually a mild disease with onset in the first or second decade; however there is a interfamilial and intrafamilial clinical variation, ranging from asymptomatic expression to severe muscular weakness and atrophy. Recently point mutations in the early growth response 2 gene (EGR2/Krox-20) have been associated with hereditary myelinopathies. We investigated for mutations at the EGR2 gene a patient with severe CMT1 phenotype. Direct sequencing of EGR2 gene showed a heterozygous A T transversion at nucleotide 1064 that predicts an Asp305Val substitution within the first zinc-finger domain. The finding of a novel EGR2 mutation associated with a different phenotype confirms that peripheral neuropathies represent a continuum spectrum of related disorders due to an underlying defect in myelination.

Isolation and characterization of a novel transcript embedded within HIRA, a gene deleted in DiGeorge syndrome

We have isolated a few cDNAs from different human tissues, transcribed from the first intron of HIRA, a gene deleted in the DiGeorge syndrome. These cDNAs are produced by an intronic gene (22k48) which is transcribed by the HIRA opposite strand and is itself arranged in exons and subjected to alternative splicing. The longest continuum cDNA sequence we obtained is 3.6 kb long and contains 3 different exons and 2 introns. 22k48 cDNA is composed of several tandemly arranged repeated elements (Alu, LINEs, CAn) surrounding a unique sequence. In situ hybridization showed the presence of 22k48 RNA in the cytoplasm of CNS and PNS neurons. 22k48 RNA is able to bind cytoplasmic proteins in the range of 45 to 60 kDa. 22k48 is a new member of the small group of genes that are transcribed but not translated, and its haploinsufficiency could contribute to the pathogenesis of the DiGeorge syndrome.

Congenital hypomyelination due to myelin protein zero Q215X mutation

Congenital hypomyelination (CH) is a hereditary demyelinating peripheral neuropathy characterized by early infancy onset, distal muscle weakness, hypotonia, areflexia, and severe slowing of nerve conduction velocities. In the present report, the clinical, morphological, and immunohistochemical features of a CH case and the identification of a mutation in the gene (MPZ) for protein zero (P0) associated with this phenotype are described. This "de novo" mutation in a patient presenting with clinical features quite distinct from those of the more frequent Charcot-Marie-Tooth type 1B disease (CMT1B) or Dejerine-Sottas syndrome (DSS) confirms that CH is allelic with other disorders characterized by a less severe phenotype and a different clinical and neuropathological profile.

Exclusion of the ninjurin gene as a candidate for hereditary sensory neuropathies type I and type II

Ninjurin is a protein that is up-regulated in Schwann cells and neurons after peripheral nerve injury. Its role in promoting nerve regeneration and its expression in sensory neurons of dorsal root ganglia, as well as the chromosomal localization of the ninjurin gene, makes this gene a candidate for hereditary sensory neuropathies (HSN). In the present report, the human ninjurin gene was analyzed in 17 unrelated patients with HSN type I, two patients with HSN type II, and 10 normal controls, by single strand conformation polymorphism and by direct sequencing. All three exons and splice junctions of the gene were investigated and no mutations were found in our sample of patients. Our results rule out a mutation in the translated region of the ninjurin gene as a cause of HSN type I and type II.

Predictive testing for Huntington's disease: ten years' experience in two Italian centres

Pre-symptomatic testing for Huntington's disease (HD) has been available as a clinical service in the medical centres of Rome and Genoa since December 1987, initially by DNA-linkage and since mid-1993 by direct mutation analysis. A multidisciplinary approach and a protocol which follows the Ethical Issue Policy Statement on Huntington's Disease Molecular Genetics Predictive Test has been used. In the period under study, 332 subjects requested the test, 288 were enrolled in the protocol and nearly half of these completed it. One hundred and forty-eight people withdrew from the testing procedure for various reasons but most frequently due to a more realistic evaluation of all possible consequences of test results, induced by psychological counselling. Therefore, 140 people completed the test. The overall gene-carrier/non-carrier ratio was 0.46:1. None of the identified gene carriers had catastrophic reactions such as suicide, suicide attempts or major psychiatric disorders. All appear to have had a similar pattern of reactions to an adverse result and none expressed regret for undergoing the test. In conclusion, presymptomatic testing for HD can be considered a safe procedure without adverse consequences when framed in an integrated protocol at qualified genetic centres.

mRNA distribution in adult human brain of GRIN2B, a N-methyl-D-aspartate (NMDA) receptor subunit

The expression of the N-methyl-D-aspartate (NMDA) receptor subunit NR2B/epsilon2 (GRIN2B) in the human adult brain was assayed by in situ hybridisation, by using a specific cRNA probe. The full length GRIN2B cDNA was cloned and sequenced. It showed a 90% nucleotide conservation when compared to the rodent homologue. GRIN2B gene is expressed at high levels in the fronto-parieto-temporal cortex and hippocampus pyramidal cells and, at a lower extent, in the basal ganglia (amygdala and striatum). The cerebellar granule cells does not show any mRNA expression. The non-ubiquitous anatomical distribution of the GRIN2B mRNA in the central nervous system suggests that the gene could be involved in specific functions pertaining to the expressing cell groups.

Correlation between PMP-22 messenger RNA expression and phenotype in hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is associated with a deletion in chromosome 17p11.2, which includes the gene for the peripheral myelin protein 22 (PMP-22). A "gene dosage" effect is probably the mechanism underlying HNPP, but the amount of PMP-22 mRNA in sural nerves of HNPP patients is highly variable and the role of PMP-22 underexpression in impairing myelination has yet to be clarified. We have studied 6 genetically proven HNPP patients, to evaluate the relationship between PMP-22 mRNA levels, and clinical, neurophysiological, and neuropathological findings. Underexpression of PMP-22 mRNA correlates with disease severity and with mean axon diameter and g ratio, but not with myelin thickness, number of "tomacula," or nerve conduction parameters. Our findings further confirm that underexpression of PMP-22 is the main pathogenetic mechanism underlying the severity of clinical symptoms and signs in HNPP. Smaller axons in sural nerves of HNPP patients with lower PMP-22 levels suggests that underexpression of PMP-22 may also affect axon development.

Underexpression of messenger RNA for peripheral myelin protein 22 in hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is associated with a deletion in chromosome 17p11.2, including the gene for the peripheral myelin protein 22 (PMP-22). Because of the proposal that a decreased dosage of the PMP-22 gene was the cause of HNPP, we evaluated sural nerves from eight patients with the 17p11.2 deletion and from five normal controls. The relative amount of PMP-22 mRNA was significantly lower in HNPP patients compared with normal controls (p < 0.02) using a semiquantitative reverse transcriptase-polymerase chain reaction. There was no significant decrease of Pzero mRNA. Sural nerves from HNPP patients showed normal immunostaining with monoclonal antibodies against PMP-22, Pzero, and myelin basic protein, and only rare myelinated fibers, classified as "tomacula," showed a patchy staining of the compact myelin with monoclonal antibody against PMP-22. The significant underexpression of PMP-22 mRNA in HNPP patients compared with normal controls demonstrates that a decreased dosage of the PMP-22 gene is the most likely pathogenetic mechanism in HNPP.

De novo duplication in Charcot-Marie-Tooth type 1A

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Use of cosH1 probe in hereditary neuropathy with liability to pressure palsies: a reliable genetic test for demonstration of identical size of 17p11.2 deletion in unrelated patients

We describe pulsed-field gel electrophoresis (PFGE) analysis of 10 unrelated Italian families and seven isolated cases with hereditary neuropathy with liability to pressure palsies (HNPP). Our sample includes patients with different clinical features, varying from classical liability to pressure palsies to ingravescent polyneuropathy. The frequency and the uniformity in size of the 17p11.2 deletion was evaluated by using cosH1 probe from the Charcot-Marie-Tooth neuropathy type 1A (CMT1A)-REP region. The presence of the deletion was demonstrated in all our patients; furthermore, the deletion was of identical size, although our patients had different clinical features. Molecular analysis of the 17p11.2 region by PFGE method proved to be a reliable and non-invasive method of diagnosis in HNPP cases both familial and isolated.

Molecular analysis of the IT15 gene in patients with apparently 'sporadic' Huntington's disease

The diagnosis of Huntington's disease (HD) may be uncertain in patients without a positive family history, particularly when atypical clinical features are present. We examined the expanded trinucleotide (CAG) repeat sequence in the IT15 gene of 27 'sporadic' cases, classified as having clinically probable or clinically doubtful HD. An abnormal number of CAG repeats (42-85) were found in 14 patients. Mutation analysis confirmed the diagnosis in 63.6% of patients with clinically probable HD and in 43.7% of patients with clinically doubtful HD. DNA analysis allows an accurate diagnosis of apparently 'sporadic' HD patients and has important implications for genetic counselling.

Estimation of the mutation frequencies in Charcot-Marie-Tooth disease type 1 and hereditary neuropathy with liability to pressure palsies: a European collaborative study

A European collaboration on Charcot-Marie-Tooth type 1 (CMT1) disease and hereditary neuropathy with liability to pressure palsies (HNPP) was established to estimate the duplication and deletion frequency, respectively, on chromosome 17p11.2 and to make an inventory of mutations in the myelin genes, peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ) and connexin 32 (Cx32) located on chromosomes 17p11.2, 1q21-q23 and Xq13.1, respectively. In 70.7% of 819 unrelated CMT1 patients, the 17p11.2 duplication was present. In 84.0% of 156 unrelated HNPP patients, the 17p11.2 deletion was present. In the nonduplicated CMT1 patients, several different mutations were identified in the myelin genes PMP22, MPZ and Cx32.

Molecular analysis of three cases with hereditary motor and sensory neuropathy with myelin outfolding

We describe three patients affected by a congenital motor and sensory neuropathy with excessive myelin outfoldings (MOs) [15]. Clinical and electrophysiological features supported the diagnosis of hereditary motor and sensory neuropathy. We previously reported a genetic study on these three patients, which failed to demonstrate either the duplication in chromosome 17p11.2 or the mutations at exons 1 and 2 of the peripheral myelin protein gene (PMP-22) and suggested an autosomal recessive (AR) inheritance. In this study we described the absence of the most common mutations, which characterized other forms of hereditary motor and sensory neuropathy (HMSN). In particular the absence of molecular changes in the PMP-22 gene definitively sets HMSN with MOs apart from the more common CMT1A, hereditary neuropathy with liability to pressure palsies (HNPP) and progressive sensory-motor polyneuropathy with tomaculous changes at sural nerve biopsy.

Progressive sensory-motor polyneuropathy with tomaculous changes is associated to 17p11.2 deletion

We examined for the presence of 17p11.2 deletion, by Southern blotting and fluorescent in situ hybridization, 3 cases with progressive sensory-motor polyneuropathy and diffuse tomaculous changes at sural nerve biopsy. We demonstrated in all the cases the 17p11.2 deletion, previously reported in hereditary neuropathy with pressure palsy, an inherited disorder of the peripheral nervous system with similar pathologic changes but a different clinical phenotype. The molecular study of the 17p11.2 region should be considered as a non invasive method for differential diagnosis in selected cases of progressive polyneuropathy.

Molecular diagnosis of hereditary neuropathy with liability to pressure palsies (HNPP) by detection of 17p11.2 deletion in Italian patients

Hereditary neuropathy with a liability to pressure palsies (HNPP) is an autosomal dominant disorder characterized by recurrent pressure palsies generally precipitated by minor trauma; weakness and paraesthesia usually improve and recover completely in a few months. By Southern blotting and fluorescent in situ hybridization analysis we confirm the presence of a 17p11.2 deletion in familial and in isolated cases of HNPP, suggesting that molecular analysis of the 17p11.2 region could also be a reliable and non-invasive method of diagnosis in sporadic cases, where a correct diagnosis usually requires a nerve biopsy. Although HNPP is a mild disease and not all patients seek medical attention, a presymptomatic diagnosis is useful for assessing the risk during genetic counselling, due to the inheritance of the mutation.

Mapping of the human NMDAR2B receptor subunit gene (GRIN2B) to chromosome 12p12

The N-methyl-D-aspartate (NMDA) receptor channel is essential for synaptic transmission and synaptic plasticity underlying memory, learning, and development. Three subunits of the NMDA receptor channel, NMDAR2A, NMDAR2B, and NMDAR2C (NR2A, NR2B, and NR2C), previously identified in mouse by cDNA cloning and expression, share a high level of homology, although their patterns of expression within the brain may differ. In the present work we report the localization of the gene encoding the human NMDAR2B receptor subunit (called GRIN2B for glutamate receptor, ionotropic, N-methyl-D-aspartate 2B) to chromosome 12p12 by in situ hybridization and somatic cell hybrids.

Polymorphism analysis of the huntingtin gene in Italian families affected with Huntington disease

Two sources of variation in the huntingtin gene, the length of the CCG-rich segment downstream to the (CAG)n stretch undergoing expansion in Huntington disease (HD) and the deletion of 3 bp at codon positions 2642-2645 (delta 2642), were analysed on the normal and HD chromosomes of 80 Italian families affected with HD. No instances of meiotic instability of the CCG-rich segment were detected. A strong linkage disequilibrium was found between the HD mutation and alleles at both polymorphic regions: CCG-rich length alleles different from 176 bp are underrepresented while delta 2642 is overrepresented on HD chromosomes. The presence of such alleles on HD chromosomes does not affect age at onset of the disease. Normal chromosomes displayed a non-random association, shorter (CAG)n segments being preferentially followed by longer CCG-rich segments. Finally, the finding, among normal subjects, of carriers of variants on both chromosomes denotes that variation at either of the two polymorphisms does not impair the function of the huntingtin gene product.

Hereditary motor and sensory neuropathy with myelin outfolding: clinical, genetic and neuropathological study of three cases

We describe 3 patients affected by a congenital motor and sensory neuropathy with excessive myelin outfoldings (MOs). Clinical and electrophysiological features supported the diagnosis of hereditary motor and sensory neuropathy (HMSN). The genetic study failed to demonstrate either the duplication in chromosome 17p11.2 or the mutations at exons 1 and 2 of the myelin protein gene, PMP-22, recently observed in HMSN type Ia, and suggested an autosomal recessive (AR) inheritance. Sural nerve biopsy revealed a demyelinating process with prominent hypertrophic changes and excessive MOs formation. The percentage of MOs was significantly higher than in 3 age-matched HMSN Ia patients. MOs were morphologically and morphometrically different from tomacular-like thickenings of myelin. Myelin thickness was significantly lower than in the three HMSN Ia controls and linear regression showed a thinner myelin related to axon diameter. The reported cases demonstrate that HMSN with MOs is a well defined variant of HMSN and that a primary defect in the myelination process may be proposed as a possible pathogenic mechanism.

Homozygous hypertrophic hereditary motor and sensory neuropathies

We compared 25 autosomal dominant hereditary motor and sensory neuropathy (HMSN) type I patients with 7 subjects affected by hypertrophic HMSN with non-dominant inheritance. All the autosomal dominant HMSN I cases carried the chromosome 17p11.2 duplication, providing evidence that it is widely represented in HMSN I families. The second group included: two siblings born to unrelated, unaffected parents and suffering from hypertrophic HMSN of strikingly different severity; two sisters with HMSN I phenotype, born to first-cousin unaffected parents; two brothers with HMSN III phenotype born to unrelated parents both showing HMSN II phenotype; a child with classic HMSN III phenotype, born to unrelated, unaffected parents. The 17p11.2 duplication was not found in any of the patients of the second series or in their parents. Our data provide further evidence that: HMSN III is heterogeneous and encompasses the homozygous expressions of different neuropathic genes; it is advisable to separate autosomal recessive hypertrophic HMSN from dominant HMSN Ia, because they appear to be due to different DNA mutations.