Clinical, genetic and electrophysiologic correlation in hereditary neuropathy with liability to pressure palsies with involvement of PMP22 gene at chromosome 17p11.2

Clinical and neurophysiological features of the hereditary neuropathy with liability to pressure palsy due to the 17p11.2 deletion

ABSTRACT The hereditary neuropathy with liability to pressure palsies (HNPP) is an autossomal dominant disorder manifesting recurrent mononeuropathies. Objective Evaluate its clinical and nerve conduction studies (NCS) characteristics, searching for diagnostic particularities. Method We reviewed the neurological manifestations of 39 and the NCS of 33 patients. Results Family history was absent in 16/39 (41%). The onset complaints were weakness in 24, pain in 6, sensory deficit in 5 and paresthesias in 4. Pain was seen in 3 other patients. The following neuropathy patterns were found: multiple mononeuropathy (26), mononeuropathy (7), chronic sensorimotor polyneuropathy (4), chronic sensory polyneuropathy (1) and unilateral brachial plexopathy (1). NCS showed a sensorimotor neuropathy with focal conduction slowing in 31, two had mononeuropathy and another brachial plexopathy. Conclusion HNPP presentation is variable and may include pain. The most frequent pattern is of an asymmetrical sensory and motor neuropathy with focal slowing at specific topographies on NCS.

Screening of the 17p11.2--p12 region in a large cohort of patients with Charcot-Marie-Tooth (CMT) disease or hereditary neuropathy with liability to pressure palsies (HNPP)

Within the last decade, numerous methods have been applied to detect the most common mutation in patients affected with Charcot-Marie-Tooth (CMT) disease, i.e. submicroscopic duplication in the 17p11.2--p12 region. In 1993, another neuropathy - known as hereditary neuropathy with liability to pressure palsies (HNPP) - has been shown to be caused by a 17p11.2--p12 deletion. Historically, Southern blot analysis was the first approach to identify CMT1A duplication or HNPP deletion. This time- and labor-consuming method requires prior selection of DNA samples. In fact, only CMT patients affected with the demyelinating form of CMT1 have been screened for CMT1A duplication. After the 17p11.2--p12 duplication was identified in the CMT1 families, subsequent studies revealed additional axonal features in the patients harboring the 17p11.2--p12 duplication. Thus it seems reasonable to test all patients affected with CMT for the presence of the 17p11.2--p12 duplication. To evaluate the utility of real-time polymerase chain reaction (Q-PCR) and restriction fragment length polymorphism PCR (RFLP-PCR), we screened a large group of 179 families with the diagnosis of CMT/HNPP for the presence of the 17p11.2--p12 duplication/deletion. Due to a high frequency of CMT1A duplication in familial cases of CMT, we propose (in contrast to the previous studies) to perform Q-PCR analysis in all patients diagnosed with CMT.

Clinical and electrophysiologic features of HNPP patients with 17p11.2 deletion

OBJECTIVES

Although the diagnosis of hereditary neuropathy with liability to pressure palsies (HNPP) is important for correct prognostic evaluation and genetic counseling, the diagnosis is frequently missed or delayed. Our main aim on undertaking this study was to characterize the electrodiagnostic features of HNPP.

MATERIAL AND METHODS

Clinical, electrophysiologic and molecular studies were performed on Korean HNPP patients with 17p11.2 deletion. The results of electrophysiologic studies were compared with those of Charcot-Marie-Tooth disease type 1 A (CMT1A) patients carrying 17p11.2 duplication.

RESULTS

Eight HNPP (50 motor, 39 sensory nerves) and six CMT1A (28 motor, 16 sensory nerves) patients were included. Sensory nerve conduction was slow in 97% of HNPP nerves. Motor nerve conduction at common entrapment sites was also abnormally slow in 87.5%, whereas at non-entrapment sites conduction slowing was infrequent. Distal motor latency (DML) was prolonged in 80% of HNPP nerves, and terminal latency index (TLI) was significantly lower in HNPP than in normal controls and in CMT1A patients (P < 0.01). In contrast to CMT1A, where severity of nerve conduction slowing was not different among nerve groups, HNPP sensory nerve conduction was more slowed in the median and ulnar nerves than in the sural nerve (P < 0.01), and DML was more prolonged in the median nerve than in the other motor nerves (P < 0.01). TLIs were significantly lower in HNPP than in the normal control and CMT1A patients for the median and ulnar nerves (P < 0.01), and were also significantly reduced for the peroneal nerve (P < 0.05) compared with those of the normal controls.

CONCLUSION

HNPP is characterized electrophysiologically by a generalized neuropathy, superimposed by focal entrapment neuropathies. The slowing of sensory conduction in nearly all nerves and the distal accentuation of motor conduction abnormalities are the main features of background polyneuropathy in HNPP. The distribution and severity of the background electrophysiologic abnormalities are closely related to the topography of common entrapment or compression sites, which suggests the possible pathogenetic role of subclinical pressure injury at these sites in the development of the distinct background polyneuropathy in HNPP.

[Diagnostic value of classical neurophysiologic profile in various phenotypes of hereditary, pressure-sensitive neuropathies]

PURPOSE

We looked for electrodiagnostic features that raise suspicion of hereditary neuropathy with liability to pressure palsies (HNPP).

METHOD

A retrospective review of eight cases with confirmed histologic (one case) or chromosome 17 deletion (seven cases) analysis was performed.

RESULTS

Autosomal dominant disease was present in 63% of the patients, 75% being men. Mean age at examination and at first symptom was 27 and 22 years respectively. Five patients have one or more acute nerve palsies, without residual deficit, but one presented sensory symptoms in internal saphena territory. Three patients had others phenotypes: a man presented with four episodes of facial palsy and one woman was asymptomatic; another patient with diabetes mellitus presented an associated chronic sensorimotor polyneuropathy. In agreement with other studies of HNPP we found in most patients a diffuse increase in distal motor latence, contrasting with normal or moderately decreased motor nerve conduction velocity, multiple electrophysiologic entrapment and diffuse reduction in sensory nerve action potential and/or velocity. However, this electrophysiological pattern was incomplete or masked in HNPP with cranial nerves palsies, in asymptomatic form of HNPP or in HNPP associated with polyneuropathy.

CONCLUSION

These data confirm the clinical phenotypic heterogeneity of the 17p11.2 deletion and highlight the limits of the classic electrophysiological pattern in asymptomatic HNPP or associated with uncommon clinical features.

Diagnostic strategy for familial and sporadic cases of neuropathy associated with 17p11.2 deletion

Clinical, electrophysiologic and molecular studies were performed on at-risk members of 14 families with hereditary neuropathy with liability to pressure palsies (HNPP), in order to detect asymptomatic carriers of the 17p11.2 deletion. Sporadic cases due to de novo deletion accounted for 21% of the investigated HNPP families. Approximately one half of deletion carriers were asymptomatic and did not display significant signs on clinical examination. The electrophysiologic hallmark in both symptomatic and asymptomatic deletion carriers was the presence of a nonuniform sensorimotor demyelinating polyneuropathy with conduction abnormalities preferentially located at common entrapment sites and distal nerve segments. A perfect correlation was found between the molecular and electrophysiologic analyses. A reliable screening method to detect clinically unaffected carriers of the deletion in families with HNPP was the evaluation of motor conduction in at least two nerves across usual entrapment sites, especially the ulnar nerve at the elbow, and evaluation of sensory conduction in the sural nerve. In sporadic cases due to a de novo deletion, electrophysiologic studies were suggestive but not sufficient for the diagnosis, and molecular analysis represented the most sensitive diagnostic tool.

Peroneal neuropathy after weight loss

The objectives of this study were to evaluate the clinical and electrophysiological findings in peroneal mononeuropathies following a weight-reduction diet. Thirty patients with acute peroneal palsy and weight loss were studied. Complete nerve conduction studies (NCS) were performed in upper and lower limbs. NCS showed conduction block (CB) of the peroneal nerve at the fibular head that recovered in 29 patients within 3 weeks to 3 months. Severity of CB was correlated with clinical weakness. Three patients had abnormalities consistent with polyneuropathy (PNP). NCS in asymptomatic relatives confirmed familial neuropathy. Nerve biopsy and molecular study were consistent with hereditary neuropathy with liability to pressure palsies (HNPP). One of these peroneal palsies (6 months) recovered after neurolysis. Weight loss might be a risk factor in peroneal mononeuropathies. NCS is a tool in the diagnosis of the site and severity of the nerve injury. Testing should be considered for relatives of patients with PNP because peroneal mononeuropathies may be the first expression of HNPP.

The peripheral myelin protein 22 and epithelial membrane protein family

The peripheral myelin protein 22 (PMP22) and the epithelial membrane proteins (EMP-1, -2, and -3) comprise a subfamily of small hydrophobic membrane proteins. The putative four-transmembrane domain structure as well as the genomic structure are highly conserved among family members. PMP22 and EMPs are expressed in many tissues, and functions in cell growth, differentiation, and apoptosis have been reported. EMP-1 is highly up-regulated during squamous differentiation and in certain tumors, and a role in tumorigenesis has been proposed. PMP22 is most highly expressed in peripheral nerves, where it is localized in the compact portion of myelin. It plays a crucial role in normal physiological and pathological processes in the peripheral nervous system. Progress in molecular genetics has revealed that genetic alterations in the PMP22 gene, including duplications, deletions, and point mutations, are responsible for several forms of hereditary peripheral neuropathies, including Charcot-Marie-Tooth disease type 1A (CMT1A), Dejerine-Sottas syndrome (DDS), and hereditary neuropathy with liability to pressure palsies (HNPP). The natural mouse mutants Trembler and Trembler-J contain a missense mutation in different hydrophobic domains of PMP22, resulting in demyelination and Schwann cell proliferation. Transgenic mice carrying many copies of the PMP22 gene and PMP22-null mice display a variety of defects in the initial steps of myelination and/or maintenance of myelination, whereas no pathological alterations are detected in other tissues normally expressing PMP22. Further characterization of the interactions of PMP22 and EMPs with other proteins as well as their regulation will provide additional insight into their normal physiological function and their roles in disease and possibly will result in the development of therapeutic tools.

Chronic demyelinating hypertrophic brachial plexus neuropathy

A patient with unilateral, painless, chronic progressive upper limb sensorimotor deficit showed electrophysiological evidence of a focal demyelinating neuropathy with almost complete conduction block across the brachial plexus. Magnetic resonance imaging disclosed marked brachial plexus hypertrophy. Intravenous immunoglobulin led to fast and complete recovery, maintained by intermittent perfusions. Hypertrophic brachial plexus neuropathy can be a presentation of focal chronic inflammatory demyelinating polyradiculoneuropathy. Objective and quantitative assessment of hand function is useful to evaluate treatment results and to optimize treatment regimens.

Hereditary neuropathy with liability to pressure palsies in children

The clinical and neurophysiologic findings of two children presenting with focal weakness and atrophy in unusual nerve distributions and no apparent antecedent injuries are reported. Patient 1 presented with a droopy left shoulder that was initially attributed to scoliosis. Patient 2 presented with right biceps brachii atrophy that was first brought to his parent's attention during a routine physical examination. In addition to documenting focal spinal accessory and musculocutaneous mononeuropathies as the cause of weakness in Patients 1 and 2, respectively, nerve conduction studies also revealed evidence of superimposed diffuse demyelinating polyneuropathy in both children. The latter findings suggested the diagnosis of hereditary neuropathy with liability to pressure palsies and led to definitive DNA diagnoses.

Spectrum of clinical and electrophysiologic features in HNPP patients with the 17p11.2 deletion

OBJECTIVE

To study the clinical and electrophysiologic features of a large series of carriers of the 17p11.2 deletion.

BACKGROUND

The 17p11.2 deletion is associated in most patients with recurrent acute nerve palsies, which is the typical presentation of hereditary neuropathy with liability to pressure palsies (HNPP). Nevertheless, a few other phenotypes have been reported.

METHODS

On the basis of clinical and electrophysiologic data, the authors conducted a retrospective study of 99 individuals with the 17p11.2 deletion referred to their neurogenetic department between 1993 and 1997.

RESULTS

In addition to the typical presentation of HNPP, they describe five other phenotypes in 15 patients: recurrent positional short-term sensory symptoms, progressive mononeuropathy, Charcot-Marie-Tooth disease-like polyneuropathy, chronic sensory polyneuropathy, and chronic inflammatory demyelinating polyneuropathy-like, recurrent subacute polyneuropathy; and 14 asymptomatic patients. In all the deletion carriers, regardless of their phenotype and by the second decade, the authors found a characteristic, multifocal electrophysiologic neuropathy consisting of a diffuse increase in distal motor latencies contrasting with normal or moderately reduced motor nerve conduction velocities, a diffuse reduction in sensory nerve action potential, and multiple focal slowing of nerve conduction at the usual sites of entrapment. The key diagnostic criterion is a bilateral slowing of sensory and motor nerve conduction at the carpal tunnel with at least one abnormal parameter for motor conduction in one peroneal nerve.

CONCLUSION

The authors confirm the clinical phenotypic heterogeneity of the 17p11.2 deletion and suggest that electrophysiologic examination is a reliable tool for screening suspected HNPP patients in its various clinical presentations.

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.

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.