Hereditary Neuropathy With Liability To Pressure Palsies Research Articles

Mutations in the peripheral myelin genes and associated genes in inherited peripheral neuropathies

The peripheral myelin protein 22 gene (PMP22), the myelin protein zero gene (MPZ, P0), and the connexin 32 gene (Cx32, GJB1) code for membrane proteins expressed in Schwann cells of the peripheral nervous system (PNS). The early growth response 2 gene (EGR2) encodes a transcription factor that may control myelination in the PNS. Mutations in the respective genes, located on human chromosomes 17p11.2, 1q22-q23, Xq13.1, and 10q21.1-q22.1, are associated with several inherited peripheral neuropathies. To date, a genetic defect in one of these genes has been identified in over 1,000 unrelated patients manifesting a wide range of phenotypes, i.e., Charcot-Marie-Tooth disease type 1 (CMT1) and type 2 (CMT2), Dejerine-Sottas syndrome (DSS), hereditary neuropathy with liability to pressure palsies (HNPP), and congenital hypomyelination (CH). This large number of genetically defined patients provides an exceptional opportunity to examine the correlation between phenotype and genotype. Hum Mutat 13:11–28, 1999. © 1999 Wiley-Liss, Inc.

Mutations in the peripheral myelin genes and associated genes in inherited peripheral neuropathies.

The peripheral myelin protein 22 gene (PMP22), the myelin protein zero gene (MPZ, P0), and the connexin 32 gene (Cx32, GJB1) code for membrane proteins expressed in Schwann cells of the peripheral nervous system (PNS). The early growth response 2 gene (EGR2) encodes a transcription factor that may control myelination in the PNS. Mutations in the respective genes, located on human chromosomes 17p11.2, 1q22-q23, Xq13.1, and 10q21.1-q22.1, are associated with several inherited peripheral neuropathies. To date, a genetic defect in one of these genes has been identified in over 1,000 unrelated patients manifesting a wide range of phenotypes, i.e., Charcot-Marie-Tooth disease type 1 (CMT1) and type 2 (CMT2), Dejerine-Sottas syndrome (DSS), hereditary neuropathy with liability to pressure palsies (HNPP), and congenital hypomyelination (CH). This large number of genetically defined patients provides an exceptional opportunity to examine the correlation between phenotype and genotype.

3rd workshop of the European CMT consortium: 54th ENMC International Workshop on genotype/phenotype correlations in Charcot-Marie-Tooth type 1 and hereditary neuropathy with liability to pressure palsies 28-30 November 1997, Naarden, The Netherlands.

3rd workshop of the European CMT consortium: 54th ENMC International Workshop on genotype/phenotype correlations in Charcot-Marie-Tooth type 1 and hereditary neuropathy with liability to pressure palsies 28-30 November 1997, Naarden, The Netherlands.

Detection of hereditary neuropathy with liability to pressure palsies among patients with acute painless mononeuropathy or plexopathy.

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder characterized by recurrent mononeuropathies or brachial plexopathies, commonly associated with a chromosome 17p11.2-12 deletion encompassing the peripheral myelin protein-22 (PMP22) gene. We tried to identify criteria distinguishing HNPP among patients with acute painless mononeuropathy/plexopathy. We investigated by pulsed-field gel electrophoresis the presence of the deletion in 27 patients with isolated or recurrent acute painless mononeuropathy or brachial plexopathy, and no obvious cause of neuropathy. Eight patients carried the deletion, whereas 19 had neither the deletion nor mutations in the PMP22 gene. Age at onset, presenting modality, precipitating events, and rate of recovery did not significantly differ in the two groups. Family history was informative for HNPP diagnosis in 3 cases only. HNPP patients more often showed recurrent episodes, brachial plexopathy, and clinical or electrophysiologic involvement of other nerves. Non-HNPP patients more frequently had peroneal palsy, recent weight loss, and normal electrophysiologic examination in other nerves. Signs of generalized neuropathy and evidence of disease in other family member are often subtle in HNPP and must be thoroughly investigated in patients with acute painless mononeuropathy/plexopathy.

Detection of hereditary neuropathy with liability to pressure palsies among patients with acute painless mononeuropathy or plexopathy

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder characterized by recurrent mononeuropathies or brachial plexopathies, commonly associated with a chromosome 17p11.2-12 deletion encompassing the peripheral myelin protein-22 (PMP22) gene. We tried to identify criteria distinguishing HNPP among patients with acute painless mononeuropathy/plexopathy. We investigated by pulsed-field gel electrophoresis the presence of the deletion in 27 patients with isolated or recurrent acute painless mononeuropathy or brachial plexopathy, and no obvious cause of neuropathy. Eight patients carried the deletion, whereas 19 had neither the deletion nor mutations in the PMP22 gene. Age at onset, presenting modality, precipitating events, and rate of recovery did not significantly differ in the two groups. Family history was informative for HNPP diagnosis in 3 cases only. HNPP patients more often showed recurrent episodes, brachial plexopathy, and clinical or electrophysiologic involvement of other nerves. Non-HNPP patients more frequently had peroneal palsy, recent weight loss, and normal electrophysiologic examination in other nerves. Signs of generalized neuropathy and evidence of disease in other family member are often subtle in HNPP and must be thoroughly investigated in patients with acute painless mononeuropathy/plexopathy. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1686–1691, 1998.

Major histocompatibility complex class II expression and macrophage responses in genetically proven Charcot-Marie-Tooth type 1 and hereditary neuropathy with liability to pressure palsies.

This study examined major histocompatibility complex (MHC) class II expression and macrophage infiltration in sural nerve biopsies from patients with genetically proven Charcot-Marie-Tooth (CMT) 1A and 1B and hereditary neuropathy with liability to pressure palsies (HNPP) by immunocytochemistry. In both young and older patients with duplication of the PMP22 gene, MHC class II expression was consistently up-regulated and not closely related to the extent of macrophage infiltration. On the other hand, MHC class II expression was more variable in CMT1A and CMT1B caused by point mutations and in HNPP. The extent of nerve pathology as assessed by teased fiber preparations or electron microscopy was not predictive for the degree of MHC class II expression in CMT1/HNPP. We conclude that MHC class II up-regulation is a common feature in hereditary neuropathies. As shown for the animal model of globoid cell dystrophy, it is conceivable that increased expression of MHC class II molecules in CMT1 and HNPP accelerates nerve pathology.

Carpal tunnel syndrome in childhood: study of 6 cases

Six children, 4 girls and two boys, aged 5–14 years, with carpal tunnel syndrome (CTS) are reported. Median nerve entrapment had different aetiologies in each case. One patient developed unilateral CTS symptoms after intensive basketball training. He improved upon terminating this sporting activity. In 3 patients bilateral CTS was associated with Schwartz-Jampel syndrome, trigger finger and mucopolysaccharidosis I (MPS IS=Scheie syndrome), respectively. The latter subject, a boy aged 11 years who had severe bilateral muscle thenar weakness and atrophy, made a good recovery after surgery. Two cases with bilateral CTS had autosomal dominant disease. One of them showed familial CTS with thickening of the transverse carpal ligament. The other child (5 years old) presented early bilateral CTS as first manifestation of hereditary neuropathy with liability to pressure palsies (HNPP). His relatives were asymptomatic, but they showed electrophysiological and nerve biopsy changes consistent with HNPP. Nerve conduction studies (NCS) are diagnostic in paediatric CTS. Moreover, NCS is an objective method to evaluate the evolution of the nerve lesions after surgery. NCS must be performed in nerves of the propositus other than the median, as well as in first degree symptomatic and asymptomatic relatives in order to identify possible familial neuropathies.

Hereditary neuropathy with liability to pressure palsies. Phenotypic differences between patients with the common deletion and a PMP22 frame shift mutation.

In six families with hereditary neuropathy with liability to pressure palsies (HNPP) the 17p11.2 deletion was absent, but single strand conformation-analysis and subsequent sequencing demonstrated a heterozygous G-insertion in a stretch of six Gs at nt 276281 of the PMP22 gene, resulting in a frame shift after Gly94. Haplotype comparison of the six families revealed common ancestry. We compared the phenotype of 23 patients from these six families with the phenotype of 63 patients of 17 families with the common deletion. The patients with the G-insertion showed the clinical, electrophysiological and morphological characteristics of common HNPP, but in addition they had significantly more neuropathic features, mimicking hereditary motor and sensory neuropathy type I (HMSN I) or Charcot-Marie-Tooth disease type 1 (CMT1). To explain this distinct phenotype we suggest that, by translation of the mutated gene, a markedly changed polypeptide is formed without the normal cytoplasmic C-terminal of the native protein, resulting in a loss of function similar to that with the common deletion, but exerting an extra disturbance of Schwann cell functions, probably by hampering normal myelin formation or maintenance.

Mutation analysis of the nerve specific promoter of the peripheral myelin protein 22 gene in CMT1 disease and HNPP.

We analysed the nerve specific promoter of the peripheral myelin protein 22 gene (PMP22) in a set of 15 unrelated patients with Charcot-Marie-Tooth type 1 disease (CMT1) and 16 unrelated...

Many facets of the peripheral myelin protein PMP22 in myelination and disease.

Peripheral myelin protein 22 (PMP22) is a small, hydrophobic glycoprotein, which is most prominently expressed by Schwann cells as a component of compact myelin of the peripheral nervous system (PNS). Recent progress in molecular genetics revealed that mutations affecting the PMP22 gene including duplications, deletions, and point mutations are responsible for the most common forms of hereditary peripheral neuropathies including Charcot-Marie-Tooth disease type 1A (CMT1A), hereditary neuropathy with liability to pressure palsies (HNPP), and a subtype of Dejerine-Sottas Syndrome (DSS). Functionally, PMP22 is involved in correct myelination during development of peripheral nerves, the stability of myelin, and the maintenance of axons. While most of these functions relate to a role of PMP22 as a structural component of myelin, PMP22 has also been proposed as a regulator of Schwann cell proliferation and differentiation. In this review, we will discuss our current knowledge of PMP22 and its related proteins in the normal organism as well as in disease. In particular, we will focus on how the function of PMP22 and its regulation may be relevant to particular disease mechanisms.

Human Meiotic Recombination Products Revealed by Sequencing a Hotspot for Homologous Strand Exchange in Multiple HNPP Deletion Patients

The HNPP (hereditary neuropathy with liability to pressure palsies) deletion and CMT1A (Charcot-Marie-Tooth disease type 1A) duplication are the reciprocal products of homologous recombination events between misaligned flanking CMT1A-REP repeats on chromosome 17p11. 2-p12. A 1.7-kb hotspot for homologous recombination was previously identified wherein the relative risk of an exchange event is 50 times higher than in the surrounding 98.7% identical sequence shared by the CMT1A-REPs. To refine the region of exchange further, we designed a PCR strategy to amplify the recombinant CMT1A-REP from HNPP patients as well as the proximal and distal CMT1A-REPs from control individuals. By comparing the sequences across recombinant CMT1A-REPs to that of the proximal and distal CMT1A-REPs, the exchange was mapped to a 557-bp region within the previously identified 1.7-kb hotspot in 21 of 23 unrelated HNPP deletion patients. Two patients had recombined sequences suggesting an exchange event closer to the mariner-like element previously identified near the hotspot. Five individuals also had interspersed patches of proximal or distal repeat specific DNA sequence indicating potential gene conversion during the exchange of genetic material. Our studies provide a direct observation of human meiotic recombination products. These results are consistent with the hypothesis that minimum efficient processing segments, which have been characterized in Escherichia coli, yeast, and cultured mammalian cells, may be required for efficient homologous meiotic recombination in humans.

Pediatric bilateral carpal tunnel syndrome as first manifestation of hereditary neuropathy with liability to pressure palsies (HNPP).

Pediatric bilateral carpal tunnel syndrome as first manifestation of hereditary neuropathy with liability to pressure palsies (HNPP).

Determination of gene dosage at the PMP22 and androgen receptor loci by quantitative PCR

Although many genetic diseases are caused by the presence of point mutations in respective genes, an increasing number of diseases are known to be caused by gene copy number changes. We report the development of a rapid and reliable PCR-based method for quantitation of gene copy number with sufficient sensitivity to detect single copy changes without the use of radioactive or fluorescent labeling. The sensitivity of this technique has been demonstrated by the detection of the DNA duplication or deletion occurring in two inherited peripheral neuropathies, Charcot-Marie-Tooth type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), that are caused by a reciprocal duplication or deletion event on chromosome 17p11.2-12. This method relies on the comparison of the amount of PCR product generated from a potentially duplicated or deleted target sequence with the amount of product generated from a disomic reference gene. The value of this ratio (target PCR product:reference PCR product) indicates whether the target sequence is duplicated, deleted, or unchanged. Using primers from within a duplicated or deleted region (PMP22 gene and EW401) and from within a reference region (NF1 gene), we tested 50 CMT1A, 30 HNPP, and 50 unaffected individuals for the presence of a DNA duplication or deletion. reference ratios of 1.58, 1.02, and 0.56 were detected for the CMT1A, unaffected, and HNPP groups, respectively. Thus, differentiation of the three groups of individuals was on the basis of gene copy number. This technique was successfully used to detect the difference in the X chromosome copy number between males and females (target:reference ratios of 1.1 and 2.3, respectively). This approach to the detection of DNA duplications and deletions is sensitive, accurate, and has potential applications in the quantitation of changes in gene copy number associated with diseases characterized by such chromosomal alterations.

Determining Gene Dosage

Numerous investigations (both clinical and basic) in today’s molecular biology laboratory require accurate quantification of DNA by the polymerase chain reaction (PCR). To name a few important examples, quantitative PCR has been used to quantify viral copy number, to perform gene expression studies, and to diagnose genetic diseases. In this issue of Clinical Chemistry , Poropat and Nicholson describe a quantitative PCR assay for the determination of gene dosage (i.e., the number of copies of a gene per somatic cell) of the PMP22 gene, a myelin gene involved in inherited neuropathies (1). The PMP22 gene is extremely sensitive to copy number; for example, it is duplicated in the autosomal dominant Charcot-Marie Tooth type I (CMT1A) disease and is deleted in the autosomal dominant hereditary neuropathy with liability to pressure palsies (HNPP). Because the expression of the disorders can be quite variable and CMT1A shows genetic heterogeneity, the DNA testing for these diseases establishes a secure diagnosis; it also permits genetic counseling and testing for high-risk family members. For molecular laboratories involved in genetic disorders, gene dosage determinations are clinically important and frequently performed. In addition to CMT1A and HNPP, there are many genetic disorders where the primary defect is due either to allelic deletions (e.g., Duchenne muscular dystrophy, spinal muscular atrophy, α-thalassemia, growth hormone deficiency, and familial hypercholesterolemia) or to duplications (e.g., Klinefelter syndrome and Down syndrome). Furthermore, for the determination of the carrier state of disorders such as Duchenne muscular dystrophy and spinal muscular atrophy, the accurate determination of heterozygous deletions is essential. Originally, gene dosage determinations were made from Southern blots. The protocol was laborious and required large amounts of DNA. Furthermore, optimal conditions were required; very high-quality blots were necessary, with consistent transfer and hybridization and low background. We have found that Southern autoradiographic bands >10 kb …

PCR-based strategy for the diagnosis of hereditary neuropathy with liability to pressure palsies and Charcot-Marie-Tooth disease type 1A.

Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP) are inherited peripheral neuropathies. In most cases these disorders are caused by either the duplication (in CMT1A) or the deletion (in HNPP) of a 1.5-megabase DNA fragment on chromosome 17p11.2, which contains the peripheral myelin protein 22 gene (PMP22). We developed a rapid and simple quantitative PCR assay for the detection of the CMT1A duplication or the HNPP deletion. The assay is based on the quantitative determination of the copy number of a 240-base pair DNA fragment from exon 4 of the PMP22 gene. Quantification was done on an automated fluorescence sequencer. Using this method we analyzed four families with the HNPP phenotype. In these families we identified the deletion in all affected individuals. To test the validity of the method, we compared the quantitative PCR results from 50 DNA samples, including 15 samples from individuals with HNPP, 15 samples from CMT1A patients, and 20 from normal controls, with the results obtained by Southern blot analysis. Concordant results were obtained in 49 of the 50 cases.

Autosomal dominant Charcot-Marie-Tooth disease type 1A and hereditary neuropathy with liability to pressure palsies: detection of the recombination in Slovene patients and exclusion of the potentially recessive Thr118Met PMP22 point mutation.

Charcot-Marie-Tooth disease type 1 (CMT1) and hereditary neuropathy with liability to pressure palsies (HNPP) are the most frequent autosomal dominantly inherited disorders of the peripheral nervous system. The recessive inheritance is observed only exceptionally. Unequal crossing-over of misaligned flanking CMT1A-REP elements on chromosome 17p11.2 is the most frequent cause of the CMT1A duplication and of the reciprocal deletion in HNPP patients. Recently a recombination was noted. In our study 71 Slovene CMT1 patients from 36 families, 12 HNPP patients from 6 families and their 31 healthy relatives were analysed for the presence of these recombination mutations. In 29 of 36 unrelated CMT1 (81%) and in all 6 unrelated HNPP patients the duplication or the deletion, on chromosome 17p11.2-12 was detected. In 26 out of 29 duplication patients (CMT1A) (90%) a 3.2 kb EcoRI/SacI duplication junction fragment was observed. The analogous 7.8 kb EcoRI/EcoRI deletion junction fragment was found in 4 out of 6 unrelated HNPP deletion patients (67%). Overall we found a recombination mutation inside the in 86% of unrelated Slovene CMT1A and HNPP patients. One hundred and thirty-six DNA samples of the CMT1 and HNPP patients and of the healthy controls were negative for the potentially recessive Thr118Met PMP22 amino acid substitution. Dominantly inherited CMT1A duplications and HNPP deletions on chromosome 17p11.2 are thus, as in most other European countries, the most common mutations in Slovene CMT1 and HNPP patients. No signs of polymorphism or of potentially recessive mutation were found at the specific Thr118Met PMP22 site.

Fine mapping of de novo CMT1A and HNPP rearrangements within CMT1A-REPs evidences two distinct sex-dependent mechanisms and candidate sequences involved in recombination.

The molecular mechanism resulting in the duplication or deletion of a 1.5 Mb region of 17p11.2-p12, associated, respectively, with Charcot-Marie-Tooth type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), has been proposed to be an unequal crossing-over during meiosis between the two chromosome 17 homologues generated by misalignment of the proximal and distal CMT1A-REP repeats, two homologous sequences flanking the 1.5 Mb CMT1A/HNPP monomer unit. In a recent study of a large series of de novo cases of CMT1A and HNPP, two distinct sex-dependent mechanisms were identified. Rearrangements of paternal origin, essentially duplications, were indeed generated by unequal meiotic crossing-over between the two chromosome 17 homologues, but duplications and deletions of maternal origin resulted from an intrachromosomal process, either unequal sister chromatid exchange or, in the case of deletion, excision of an intrachromatidal loop. In order to determine how these recombinations occur, 24 de novo crossover breakpoints were localized within the 1.7 kb rearrangement hot spot by comparing the sequences of the parental CMT1A-REPs with the chimeric copy in affected offspring. Nineteen out of 21 paternal crossovers were found in a 741 bp hot spot. All the breakpoints of maternal origin (n = 3), however, were located outside this interval, but in closely flanking sequences, supporting the hypothesis that two distinct sex-dependent mechanisms are involved. Several putative recombination promoting sequences in the hot spot, which are rare or absent in the surrounding 7.8 kb, were identified.

Spectrum of mutations in Finnish patients with Charcot-Marie-Tooth disease and related neuropathies.

Our patient material included families and sporadic patients of Finnish origin with the diagnosis of Charcot-Marie-Tooth (CMT) disease types 1 and 2, Dejerine-Sottas syndrome (DSS), and hereditary neuropathy with liability to pressure palsies (HNPP). We screened for mutations in the peripheral myelin protein genes connexin 32 (Cx32), myelin protein zero (P0) and peripheral myelin protein 22 (PMP22) by direct sequencing. All patients chosen for mutation screening were negative for the 1.5 Mb duplication/deletion at 17p11.2-p12. Eleven Cx32 mutations were found in 12 families, six with a CMT2 diagnosis, three with a CMT1 diagnosis and three with unclassified CMT. The total number of patients in these 12 CMTX families was 61, giving a minimum prevalence of 1.2/100,000 for CMTX in Finland. Four of the mutations, Pro58Arg, Pro172Leu, Asn175Asp and Leu204Phe, have not been previously reported. One male patient with an early onset CMT had a double Cx32 mutation, Arg22Gln and Val63Ile. The double de novo mutation was found to be of maternal grandpaternal origin. In the P0 gene a Ser78Leu mutation was found in one family with severe CMT1 and a de novo Tyr82Cys mutation was found in one DSS patient. Both mutations have been previously reported in other CMT1 families. A novel PMP22 mutation, deletion of Phe84, was found in one sporadic DSS patient. Our mutation screening results show the necessity of molecular diagnosis, in addition to clinical and electrophysiological evaluation, for proper subtyping of the disease and for accurate genetic counseling.

Epidemiology of hereditary neuropathy with liability to pressure palsies (HNPP) in south western Finland

An epidemiological study of hereditary neuropathy with liability to pressure palsies (HNPP) was carried out in south western Finland, with a population of 435 000. The diagnosis was established in 69 patients from 23 unrelated families through family and medical history, clinical neurological and neurophysiological examinations and with documentation of the deletion at gene locus 17p11.2 in at least one member of each family. This gave a prevalence of at least 16/100 000, which is remarkably high. However, due to the insidious nature of HNPP, most probably it is still an underestimation. This is the first population-based prevalence figure reported for HNPP. The prevalence is somewhat lower than that obtained for CMT in the same population, which agrees with the proposal that HNPP and CMT 1A are reciprocal products of the same unequal crossing-over. The clinical pictures of our patients were, in general, similar to those previously described in HNPP.

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.