Gene for hereditary neuropathy with liability to pressure palsies (HNPP) maps to chromosome 17 at or close to the locus for HMSN type 1

Chronic Inflammatory Demyelinating Polyneuropathy Manifesting as Neuropathy With Liability to Pressure Palsies: A Case Report

INTRODUCTION

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a progressive demyelinating neuropathy, which typically presents with proximal and distal neuropathic symptoms and is typically responsive to immunomodulatory therapies. Many variants have been subsequently described in the literature and have similarly shown to be responsive to immunotherapy.

CASE PRESENTATION

We present a case of a 43-year-old Middle Eastern/Arabic man presenting with symptoms of mixed sensorimotor neuropathy most evident at entrapment sites mimicking hereditary neuropathy with liability to pressure palsies. His electrodiagnostic study revealed features of acquired demyelinating neuropathy and a negative genetic workup. Alternative diagnosis of CIDP was considered in the context of symptomatic disease progression, negative genetic workup, and electrodiagnosis leading to initiation of immunotherapy with intravenous immunoglobulins. His neuropathy responded confirming our diagnosis of an inflammatory demyelinating polyneuropathy.

CONCLUSIONS

We describe a previously unknown variant of CIDP with phenotypic characteristics of hereditary neuropathy with liability to pressure palsies and its potential for successful treatment with intravenous immunoglobulins. This case illustrates an unusual presentation of CIDP mimicking hereditary neuropathy with liability to pressure palsies.

Hereditary neuropathy with liability to pressure palsy presenting with hand drop in a young child

Hereditary neuropathy with liability to pressure palsy (HNPP) results from the deletion of the PMP22 gene in chromosome 17p11.2. Clinically, it presents with painless pressure palsies, typically in the 2nd and 3rd decades of life, being a rare entity in childhood. We present the case study of a six-year-old male child who presented with left hand drop that he kept for over four weeks. Electrophysiological studies suggested HNPP and genetic studies confirmed it. With this paper, we pretend to create awareness to this entity as a diagnosis to be considered in a child with painless monoparesis and to emphasize the importance of electrophysiological studies in the diagnosis.

Loss of heterozygosity on chromosome 17p predicts neoplastic progression in Barrett's esophagus

BACKGROUND AND AIM

Endoscopic surveillance for adenocarcinoma in patients with Barrett's esophagus is costly, with one cancer detected every 48-441 patient years of follow up. Genetic abnormalities, including loss of heterozygosity at sites of tumor suppressor genes, have been detected in malignant and premalignant Barrett's esophagus. The aim of this prospective study was to determine if loss of heterozygosity analysis could identify patients with Barrett's esophagus at greatest risk of adenocarcinoma, for whom endoscopic surveillance is most appropriate.

METHODS

Loss of heterozygosity analysis was performed on endoscopic biopsies from 48 patients as part of a Barrett's surveillance program using 14 microsatellite markers shown previously to detect loss of heterozygosity in more than 30% of esophageal adenocarcinomas. Patients were followed up endoscopically for a median of 5 years.

RESULTS

Loss of heterozygosity was detected in nine patients. Three patients with loss of heterozygosity on chromosome 5q or 9p did not progress beyond metaplasia. Loss of heterozygosity at 17p11.1-p13 was detected in six patients, all of whom demonstrated dysplasia and/or carcinoma during follow up (four low-grade dysplasia, one high-grade dysplasia and one adenocarcinoma).

CONCLUSION

Loss of heterozygosity at 17p11.1-p13 on chromosome 17p identifies patients with Barrett's esophagus at risk of neoplastic progression and can supplement histology in determining the frequency of endoscopy during surveillance.

Epidural analgesia in labour for a patient with hereditary neuropathy with liability to pressure palsy

Hereditary neuropathy with liability to pressure palsy (HNPP) is a rare but probably under-diagnosed disorder of peripheral nerves in which individuals suffer from repeated motor and sensory neuropathies (pressure palsies) following brief nerve compression or mild trauma. A seemingly trivial insult such as sitting or kneeling may result in a focal neurological deficit lasting for hours to months. Despite the growing recognition of this problem, information regarding the anaesthetic management of labour is sparse. We present a woman with HNPP who was provided with a modified epidural regimen (low concentration bupivacaine and fentanyl) for analgesia in labour and delivery. Labour progressed uneventfully and there were no neurological sequelae following delivery.

Study on the gene and phenotypic characterisation of autosomal recessive demyelinating motor and sensory neuropathy (Charcot-Marie-Tooth disease) with a gene locus on chromosome 5q23-q33

OBJECTIVES

To report the occurrence of the autosomal recessive form of demyelinating Charcot-Marie-Tooth disease (CMT) with a locus on chromosome 5q23-33 in six non-related European families, to refine gene mapping, and to define the disease phenotype.

METHODS

In an Algerian patient with autosomal recessive demyelinating CMT mapped to chromosome 5q23-q33 the same unique nerve pathology was established as previously described in families with a special form of autosomal recessive demyelinating CMT. Subsequently, the DNA of patients with this phenotype was tested from five Dutch families and one Turkish family for the 5q23-q33 locus.

RESULTS

These patients and the Algerian families showed a similar and highly typical combination of clinical and morphological features, suggesting a common genetic defect. A complete cosegregation for markers D5S413, D5S434, D5S636, and D5S410 was found in the families. Haplotype construction located the gene to a 7 cM region between D5S643 and D5S670. In the present Dutch families linkage disequilibrium could be shown for various risk alleles and haplotypes indicating that most of these families may have inherited the underlying genetic defect form a common distant ancestor.

CONCLUSIONS

This study refines the gene localisation of autosomal recessive demyelinating CMT, mapping to chromosome 5q23-33 and defines the phenotype characterised by a precocious and rapidly progressive scoliosis in combination with a relatively mild neuropathy and a unique pathology. Morphological alterations in Schwann cells of the myelinated and unmyelinated type suggest the involvement of a protein present in both Schwann cell types or an extracellular matrix protein rather than a myelin protein. The combination of pathological features possibly discerns autosomal recessive demyelinating CMT with a gene locus on chromosome 5q23-33 from other demyelinating forms of CMT disease.

Inherited neuropathies: from gene to disease

Inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B) and to another unknown autosome (CMT1C). CMT1A is most often associated with a tandem 1.5-megabase (Mb) duplication in chromosome 17p11.2-12, or in rare patients may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (P0 or MPZ) gene. The molecular defect in CMT1C is unknown. X-linked Charcot-Marie-Tooth neuropathy (CMTX), which has clinical features similar to CMT1, is associated with mutations in the connexin32 gene. Charcot-Marie-Tooth neuropathy type 2 (CMT2) is an axonal neuropathy, also of undetermined cause. One form of CMT2 maps to chromosome 1p36 (CMT2A), another to chromosome 3p (CMT2B) and another to 7p (CMT2D). Dejerine-Sottas disease (DSD), also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile-onset demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene or the P0 gene and shares considerable clinical and pathological features with CMT1. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5-Mb deletion in chromosome 17p11.2-12 and results from reduced expression of the PMP22 gene. CMT1A and HNPP are reciprocal duplication/deletion syndromes originating from unequal crossover during germ cell meiosis. Other rare forms of demyelinating peripheral neuropathies map to chromosome 8q, 10q and 11q. Hereditary neuralgic amyotrophy (familial brachial plexus neuropathy) is an autosomal dominant disorder causing painful, recurrent brachial plexopathies and maps to chromosome 17q25.

Atypical hereditary neuropathy with liability to pressure palsies (HNPP): the value of direct DNA diagnosis

We report two patients with suspected hereditary liability to pressure palsies. Neurophysiological studies showed a mixed axonal-demyelinating sensory-motor polyneuropathy with focal slowing of conduction velocities at the common sites of entrapment. Morphological studies on sural nerve biopsy from the proband showed active axonal regeneration without typical tomacula. Molecular analysis confirmed the presence of a deletion of chromosome 17p11.2 in both patients. Our observation confirms the heterogeneity of hereditary liability to pressure palsies and the relevance of DNA testing for the diagnosis of this hereditary neuropathy.

Molecular genetic analysis of the 17p11.2 region in patients with hereditary neuropathy with liability to pressure palsies (HNPP)

Hereditary neuropathy with liability to pressure palsies (HNPP) is in most cases associated with an interstitial deletion of the same 1.5-Mb region at 17p11.2 that is duplicated in Charcot-Marie-Tooth type 1A (CMT1A) patients. Unequal crossing-over following misalignment at flanking repeat sequences (CMT1A-REP), either leads to tandem duplication in CMT1A patients or deletion in HNPP patients. With the use of polymorphic DNA markers located within the CMT1A/HNPP duplication/deletion region we detected the HNPP deletion in 16 unrelated HNPP patients, 11 of Belgian and 5 of French origin. In all cases, the 1.5-Mb size of the HNPP deletion was confirmed by EcoRI dosage analysis using a CMT1A-REP probe. In the 16 HNPP patients, the same 370/320-kb EagI deletion-junction fragments were detected with pulsed field gel electrophoresis (PFGE), while in CMT1A patients, a 150-kb EagI duplication-junction fragment was seen. Thus, PFGE analysis of EagI-digested DNA with a CMT1A-REP probe allows direct detection of the HNPP deletion or the CMT1A duplication for DNA diagnostic purposes.

DNA analysis in Finnish patients with hereditary neuropathy with liability to pressure palsies (HNPP)

Hereditary neuropathy with liability to pressure palsies (HNPP) is a dominantly inherited disorder that presents as recurrent mononeuropathies precipitated by apparently trivial traumas. The presence of a deletion in 17p11.2 was analysed in 13 Finnish families with HNPP. The deletion was found in all patients who were neurologically and neurophysiologically confirmed to have HNPP. In the problematic cases the detection of the gene defect is the method of choice in the diagnosis of HNPP. Analysis of DNA can also be used to detect clinically unaffected family members.

Prevalence of the 1.5-Mb 17p deletion in families with hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder of the peripheral nerves leading to increased susceptibility to mechanical traction or compression. Some patients have been shown to be carriers of a 1.5-Mb deletion in chromosome 17p11.2, which corresponds to the duplicated region present in most patients with Charcot-Marie-Tooth disease type 1A. Recently, evidence has been presented that the deletion is not the only cause of HNPP. To determine the prevalence of the 1.5-Mb deletion, we have examined 22 unrelated families with HNPP in the following two ways: by polymerase chain reaction analysis of marker loci D17S122 and D17S261, and by gene dosage measurements with DNA probes for D17S122 (VAW409R3a) and D17S125 (VAW412R3a) and for the PMP-22 gene. The efficiency and sensitivity of these methods is discussed. Our results show that the prevalence of the 17p deletion in our families with HNPP is 68%. One patient, presenting as a sporadic case, was found to be affected by a de novo deletion in the paternal chromosome. Single-strand conformation analysis of the protein-coding region of the PMP-22 gene did not reveal any mutation in patients from the 7 families lacking the 17p deletion. As a group, these families could not be distinguished by clinical, electrophysiological, or morphological features from the families with the deletion.