CLINICAL, ELECTROPHYSIOLOGICAL, AND MOLECULAR FINDINGS IN EARLY ONSET HEREDITARY NEUROPATHY WITH LIABILITY TO PRESSURE PALSY ANNA POTULSKA-CHROMIK, MD, PhD,1 ELENA SINKIEWICZ-DAROL, PhD,2 BARBARA RYNIEWICZ, MD, PhD,1 MARTA LIPOWSKA, MD, PhD,1 DAGMARA KABZINSKA, PhD,2 ANDRZEJ KOCHANSKI, MD, PhD,2 and ANNA KOSTERA-PRUSZCZYK, MD, PhD1 Department of Neurology, Medical University of Warsaw, Banacha 1a Street, 02–097 Warsaw, Poland 2 Neuromuscular Unit, Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland Accepted 21 March 2014 1
ABSTRACT: Introduction: The first episode of hereditary neuropathy with liability to pressure palsy (HNPP) in childhood is rare. Methods: We analyzed retrospectively the data of 7 patients with a deletion in PMP22 and onset of symptoms before age 18 years. Direct sequencing of the LITAF (lipopolysaccharide-induced tumor necrosis factor) gene was performed in patients and family members. Results: Clinical presentations varied from mononeuropathies to brachial plexopathy, with recurrent episodes in 4 patients. Electrophysiological abnormalities characteristic for HNNP were found in most subjects. Analysis of the LITAF gene revealed an Ile92Val polymorphism in 6 of 7 (86%) probands and 5 of 7 (83%) family members, over 4 times greater frequency than in the general population. Conclusions: Clinical suspicion of HNPP even when nerve conduction study results do not fulfill HNPP criteria should indicate genetic testing. In our patients, early-onset HNPP was associated frequently with isoleucine92valine LITAF polymorphism. Muscle Nerve 50: 914–918, 2014
Hereditary neuropathy with liability to pressure palsy (HNPP) is a rare autosomal dominant neuropathy characterized by recurrent mononeuropathies, often associated with compression or minor trauma. It is caused in most cases by deletion in the gene encoding peripheral myelin protein 22 (PMP22) or, less frequently, by PMP22 point mutations.1,3 Typically, the first mononeuropathy occurs during the second or third decade of life. Symptomatic early onset HNPP is very rare.4–10 Difficulty in diagnosing pediatric HNPP patients can be attributed to the fact that a typical pattern of abnormalities in nerve conduction studies is expected in patients older than 15 years.9,11,12 Abbreviations: CB, conduction block; CMAP, compound muscle action potential; CMT, Charcot-Marie-Tooth disease; Cx32, connexin32; DML, distal motor latency; EGR2, early growth response gene 2; EMG, electromyography; Gly118 Ser, glycine 118 serine; HNPP, hereditary neuropathy with liability to pressure palsy; Ile92Val, isoleucine92valine polymorphism; L, left; LITAF, lipopolysaccharide-induced tumor necrosis factor; MC, motor conduction velocity; MFN2, mitofusin 2; MPZ, myelin protein zero; MUW, Medical University of Warsaw; nd, not done NFL, light chain neurofilament protein; PMP22, peripheral myelin protein 22; R, right; RT-PCR, real-time polymerase chain reaction; SCV, sensory conduction velocity; SNAP, sensory nerve action potential amplitude Key words: Charcot-Marie-Tooth disease; childhood hereditary neuropathy; hereditary neuropathy with liability to pressure palsy; LITAF; PMP22 This study was financed by grant NN 402 27 63 36 to A.K. Correspondence to: A. Kostera-Pruszczyk; e-mail: [email protected] C 2014 Wiley Periodicals, Inc. V
Published online 26 March 2014 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24250
914
Early Onset HNPP
Guidelines for electrophysiological diagnosis of HNPP include the presence of diffuse electrophysiological abnormalities such as bilateral delayed median nerve distal motor latencies, bilateral reduced median sensory conduction velocity in the palm–wrist segment, and at least delayed distal motor latency or reduced motor nerve conduction velocity in 1 of the fibular nerves.9 The rarity of symptomatic HNPP in childhood raises the question if this early presentation is influenced by a modifier in addition to a deletion in PMP22. Previous reports suggested that phenotypic variations in Charcot-Marie-Tooth 1A (CMT1A) and CMT1D may be attributed to mutations in more than 1 gene.13 Mutations of the LITAF (lipopolysaccharide-induced tumor necrosis factor) gene described in patients with the PMP22 duplication were suggested as a cause of a severe phenotype of CMT1A.13 The aim of our study was to analyze retrospectively the clinical and electrophysiological findings and possible presence of a LITAF polymorphism in 7 patients with childhood onset HNPP. MATERIALS AND METHODS
This study was performed with Bioethical Committee approval no 120/2008 MUW. We analyzed retrospectively the data of 7 patients with a deletion of PMP22 who had onset of symptoms before age 18 years and were hospitalized between 2002 and 2011 in the Pediatric Ward of the Department of Neurology, Medical University of Warsaw. We also analyzed data from their 7 family members. On admission, all probands were considered to be sporadic cases. Detailed medical history disclosed that the parents from 3 families who were not previously aware of the disease had mild transient palsies in the past. In 3 further families, a diagnosis of HNPP was made in 3 asymptomatic members after nerve conduction studies and genetic testing. Their neurological examination was normal. To date, a 20-year-old sister of proband 3 had never experienced any symptoms of peripheral neuropathy. The mother of proband 4 was treated for sensory symptoms of bilateral MUSCLE & NERVE
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Table 1. Clinical characteristics of early-onset HNPP patients.* Gender
Age of onset, yrs
1 2
F M
4 13
3 4 5
M F M
6 7
Family
First symptom
Course
No of episodes
HNPP-affected family member
Provocative factors
Complete recovery Complete recovery
3 2
Father Father
Unknown Infection with fever
11 15 18
Fibular nerve palsy Proximal paresis of the left upper limb Fibular nerve palsy Bilateral fibular nerve palsy Radial nerve palsy
Improvement Complete recovery Complete recovery
1 1 2
On awakening Prolonged squatting Unknown
M
16
Fibular nerve palsy
1
Playing football
M
17
Musculocutaneous nerve palsy
Complete remission 22 months Improved - 4 months
Mother Mother 2 brothers 20y and 22y Unknown- adopted
2
Negative
Weight lifting
carpal tunnel syndrome with marked improvement after surgery at age 52 years. She reported no paresis. A brother of patient 5 was also asymptomatic until last follow-up at age 28 years. In 2 families, genetic testing of both biological parents was not possible. The probands were only children, so autosomal dominant transmission could not be demonstrated. Demographic data of patients and their family members are listed in Table 1. Genetic Testing. Genomic DNA was extracted from peripheral blood lymphocytes using the salting-out procedure. Deletion of the PMP22 gene was confirmed using the real-time polymerase chain reaction (RT-PCR) approach (as described by Aarskog and Vedeler14). A relative dosage (RQ) of the PMP22 gene ranged from 0.700 to 1.090 in normal individuals (2 copies of the PMP22 gene), from 0.359 to 0.595 in HNPP patients (1 copy) and from 1.176 to 2.324 in CMT1A patients (3 copies of PMP22 gene). The 3 coding exons 2–4 of the LITAF gene were amplified by PCR (primer sequences previously described by Street et al.).15 The PCR products were sequenced directly using BigDyeTM Terminator Version 1.1 Ready Reaction Cycle Sequencing kit on the ABI 3730/xl Genetic analyzer (Applied Biosystems). LITAF gene sequencing was performed in the patients and their family members. Nerve conduction studies were performed R EMG device. Motor and sensory using a KeypointV nerve conduction studies of the median, ulnar, fibular, tibial, and sural nerves were performed using surface electrodes in standard manner and compared with age-matched reference values. In the patients who tolerated EMG examination poorly, the number of nerves studied was limited, e.g., in the youngest (age 4 years), only median, tibial, both fibular, sural, and left facial nerves were investigated. The results of the nerve conduction studies were analyzed in all probands with respect to Early Onset HNPP
HNPP neurophysiological criteria.11 EMG study was also performed in the family members, if they consented. RESULTS
Detailed clinical characteristics are presented in Table 1. All probands had normal motor milestones. Patient 6, at age 7 years was diagnosed with epilepsy, for which he was treated for 3 years, with complete recovery. Six patients presented with mononeuropathies (4 with fibular, 1 with radial, or musculocutaneous nerve palsy). Four patients had recurrent episodes, including the patients with brachial plexus palsy. None of the patients or their family members suffered from neuropathic pain. Abnormalities were detected most frequently in median and fibular nerves. Conduction block was present in motor nerves of 3 of the 7 children. Detailed electrophysiological findings are listed in Table 2. A typical electrophysiological abnormality pattern was seen in all subjects older than 15 and in the patient who was age 4 years at diagnosis. Patients 3 and 4 did not meet electrophysiological criteria (ages 11 and 15) and presented with fibular nerve palsy. Proper clinical diagnosis was guided by the fact that patient 3 also had conduction block of the ulnar nerve, while in patient 4 fibular palsy was bilateral. Analysis of the LITAF gene revealed the presence of a c.274A>G (Ile92Val) sequence variant in 6 of the probands (all 7 were tested) and 5 of 6 tested family members (86% and 83%, respectively). This polymorphism was reported previously in 34/184 (18.5%) control chromosomes.16 Results are presented in Table 3. DISCUSSION
HNPP in children is rare, although the disease can start at any age. The youngest reported patient was a newborn with an Erb brachial plexus palsy.4 Our 7 patients included 1 patient who was symptomatic in the first decade of life. Similar single cases of early-onset HNPP were reported in the literature MUSCLE & NERVE
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915
Table 2. Nerve conduction study results in early onset HNPP patients.*
Patient/side
DML median (ms)
DML fibular (ms)
MCV fibular(m/s)
MCV ulnar across elbow(m/s)
SNAP ulnar(mV)
SNAP median(mV)
SNAP sural(mV)
SCV sural(m/s)
SCV median(m/s)
SCV ulnar(m/s)
1L/1R
6.8/nd
6.5/7.3
52.2/51.6
nd/nd
10/9.9
8.4/10
17/17
45.7/52.2
35.3/37.1
45.2/45.2
2L 3R/3L
4.5 4/4
7.5 5.2/5.2
43.4 42.5/44.3
52.2 22.7*/22.7
2.3 6.1/8.9
4.4 37/27
8.7 14/15
35.9 52.1/50
40.5 50/51.4
4R/4L
4/4.2
7.3/8.9
52.9/54
52.6/39.2
24/21
42/23
33/33
52.1/50
63.2/55.1
5L/5R
5.7/nd
9.8/8
37.8†/43.3
40.6/nd
1.5/nd
1.4/nd
1.4/1.6
29.8/27.4
42.3/nd
5.5 5 4 6.8 2
6.1 6.7 5.2 9.8 1
35.2 38 35.2 62.2 4
40 18.6* 18.6 52.6 1 of 6
4.3 3 1.5 24 2
8.7 4 1.4 10 4
7.3 14 1.4 33 5
42.6 45.2 29.8 52.2 5
35 32.4 32.4 63.2 2
35.9 59.9/ 54.3 57.8/ 52.1 45.6/ nd 32.9 38.6 32.9 59.9 2
6L 7L Min Max Patients with normal result
*Conduction block in ulnar nerve across elbow. †
Conduction block in fibular nerve at fibular head.
DML, distal motor latency; MCV, motor conduction velocity; SCV, sensory conduction velocity; SNAP, sensory nerve action potential amplitude; nd, not done; R, right; L, left; No, number.
and recently summarized.7,8 Although HNPP is a well-defined disease, in the setting of early-onset and no family history, the diagnosis can be challenging. Factors that trigger the symptoms can be identified in most HNPP patients. The onset of symptoms was painless and acute in all but 1 of our probands; in half of them a precipitating factor such as prolonged squatting, pressure on the nerve during sleep, or vigorous physical exercise could be identified. In the patient with brachial plexopathy who developed his symptoms on both occasions during febrile infection, an infection-related or inflammatory plexopathy was suspected at first. It is of interest that fever was reported previously as a trigger of recurrent fibular nerve palsy in a girl with HNPP.17 In the remaining 3 patients, a provocative factor was not identified, possibly related to the young age of the children who could not always report all details accompanying the onset of symptoms. Most of our patients had the typical disease course similar to what is observed in adults, including recurrent and transient nerve palsies with recovery. None of them reported pain, however decreased sensation was confirmed during clinical examination in 2 patients. Abnormalities in sensory nerves (decreased conduction velocity or amplitude) were recorded in most of the patients. Fibular nerve palsy was the most frequent presentation of HNPP in four of 7 children. Two of them (aged 11 and 15) did not have nerve conduction study results typical for HNPP. Yet in patient 916
Early Onset HNPP
4, the symptoms were bilateral after relatively mild pressure due to squatting, and in patient 3 axonal injury to the fibular nerve was accompanied by conduction block in the ulnar nerve indicating unusual sensitivity to pressure in both. Epilepsy in patient 6 seems to be coincidental. His brain MRI was normal. To date only a few cases of central nervous system involvement have been described in HNPP.18–20 Authors of guidelines for diagnosis of HNPP recognize that electrophysiological criteria are met
Table 3. LITAFIle92Val polymorphism results in all family members with confirmed PMP22 deletion.* Family no.
Family members
1
Proband Father Proband Father Proband
2 3
4
5
6 7
LITAF
Mother Sister Proband Mother
Ile92Val Ile92Val Ile92Val Ile92Val Ile92Val-585C> T (3’UTR Ile92Val Not found Ile92Val Ile92Val
Proband Brother1 Brother2 Proband Proband
Not found Not done* Ile92Val Ile92Val Ile92Val
HNPP symptoms – ever Yes Yes/in adolescence Yes Yes/in adolescence Yes Yes/ in adolescence Asymptomatic Yes No palsies /Carpal tunnel syndrome. with marked improvement after surgery Yes No Yes/in first decade of life Yes Yes
*Not available for genetic testing.
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by the patients, even those who are asymptomatic and are older than age 15.11 Our study stresses the role of electrophysiological testing of the parents of probands with clinical diagnosis of HNPP. This approach allowed us to demonstrate the hereditary nature of neuropathy in almost half of the patients before genetic testing. Our data also showed that most of the patients below age 15 had diffuse electrophysiological abnormalities. Prolonged distal motor latency in the median nerve and reduced median sensory conduction velocity accompanied by prolonged DML or reduced CMAP of the fibular nerve were the most frequent abnormalities, as expected.21 Conduction block at common entrapment sites was found in 3 of our patients, reflecting the pathogenic role of pressure injury in the development of the neuropathic changes in HNPP. In all of our patients, early-onset HNPP was caused by deletion of PMP22. Although we could not reliably confirm the age of onset in the parents of our index cases, some data suggest that early onset of HNPP may be a familial feature.8 No factors related to childhood onset of HNPP were identified. However, there are reports indicating that mutations of 2 genes that cause CMT may lead to early clinical presentation. Meggouh et al. described a 2-year-old boy with severe neuropathy. He was a heterozygote for PMP22 duplication and a Gly118 Ser mutation in the LITAF gene previously associated with CMT1C disease. He also had an Iso92Val polymorphism of LITAF13,22 His father carried a PMP22 duplication and was diagnosed with CMT1A. His mother had a Gly112Ser substitution in LITAF previously reported as associated with CMT1C disease, and both parents carried the Iso92Val polymorphism of LITAF. The authors suggested that LITAF Gly112Ser mutations can severely affect the CMT phenotype caused by a PMP22 duplication, but the role of Iso92Val as a possible modifier of the boy’s phenotype was not elucidated further.13 When we tested the LITAF gene, an Iso92Val substitution was demonstrated in all but 1 of our probands (86%). Of the family members who had the PMP22 deletion, 83% carried this polymorphism. The Iso92Val polymorphism in LITAF was also reported in the mother and son with familial multifocal, acquired, demyelinating sensory and motor polyneuropathy. This family was negative for known PMP22, connexin32 (Cx32), myelin protein zero (MPZ), early growth response gene 2 (EGR2), light-chain neurofilament protein (NFL), and mitofusin 2 (MFN2) mutations.23 LITAF protein is expressed in many tissues, but it is abundant in Schwann cells.24 It is involved in the process of regulation of endosome-to-lysosome trafficking and Early Onset HNPP
cell signaling. A recent study demonstrated that CMT1C linked mutants lead to loss-of-function mutations and impair endosome-to-lysosome trafficking.25 Conduction block is a rare phenomenon in hereditary neuropathies, and it is most commonly seen in HNPP patients, but some of the CMT1C patients with LITAF mutations present with demyelinating neuropathy with conduction blocks.26 Of interest, CMT4J caused by mutation of FIG4, another regulator of endosome-to-lysosome trafficking, can also be associated with conduction block. The mechanism leading to conduction block in HNPP has not been explained thoroughly. Studies of axonal excitability in HNPP have demonstrated alterations in threshold electrotonus most pronounced at wrist, but also detectable at the elbow. The authors indicated that structural abnormalities at the nodes of Ranvier may predispose to conduction block in response to pressure or stretch.28 Although Iso92Val substitution in LITAF alone does not cause clinically relevant changes, it may lead to an early-onset phenotype when superimposed on PMP22 deletion. In conclusion, although the clinical presentation of HNPP in children is similar to what is observed in adults, electrophysiological findings before age 15 years may lack typical nerve conduction abnormalities. Clinical suspicion of HNPP even when the nerve conduction study results do not fulfill HNPP criteria should indicate further genetic testing. Extending evaluation to the parents improves diagnostic yield. Early-onset of HNPP was associated frequently with LITAF isoleucine92valine polymorphism in our small group of patients.
REFERENCES 1. Chance PF, Alderson MK, Leppig KA, Lensch MW, Matsunami N, Smith B. DNA deletion associated with hereditary neuropathy with liability to pressure palsies. Cell 1993;72:143–151. 2. Nelis E, Van Broeckhoven C, De Jonghe P, Lofgren A, Vandenberghe A, Latour P, et al. Estimation of the mutation frequencies in Charcot-Marie-Tooth disease type 1 and hereditary neuropathy with liability to pressure palsies: a European collaborative study. Eur J Hum Genet 1996;4:25–33. 3. Sahenk Z, Chen L, Freimer M. A novel PMP22 point mutation causing HNPP phenotype: studies on nerve xenografts. Neurology 1998; 51:702–707. 4. Meretoja P, Silander K, Kalimo H, Aula P, Meretoja A, Savontaus ML. Epidemiology of hereditary neuropathy with liability to pressure palsies (HNPP) in south western Finland. Neuromuscul Disord 1997; 7:529–532. 5. Gabreels-Festen AA, Gabreels FJ, Joosten EM, Vingerhoets HM, Renier WO. Hereditary neuropathy with liability to pressure palsies in childhood. Neuropediatrics 1992;23:138–143. 6. Ichikawa K, Nezu A. Hereditary neuropathy with liability to pressure palsies in childhood: report of a case and a brief review. Brain Dev 2005;27:152–154. 7. Antonini G, Luchetti A, Mastrangelo M, Ciambra GL, Di Netta S, et al. Early-onset hereditary neuropathy with liability to pressure palsy. Neuropediatrics 2007;38:50–54. 8. Bayrak AO, Battaloglu E, Turker H, Baris I, Oztas G. Hereditary neuropathy with liability to pressure palsy (HNPP) in childhood: a case study emphasizing the relevance of detailed electrophysiological
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examination for suspected HNPP in the first decade. Brain Dev 2009; 31:445–448. Cruz-Martinez A, Arpa J. Pediatric bilateral carpal tunnel syndrome as first manifestation of hereditary neuropathy with liability to pressure palsies (HNPP). Eur J Neurol 1998;5:316–317. Gyorgy I, Biro A, Mechler F, Molnar MJ. Hereditary neuropathy with liability to pressure palsy in childhood. Ideggyogy Sz 2008;61:423– 425. Dubourg O, Mouton P, Brice A, LeGuern E, Bouche P . Guidelines for diagnosis of hereditary neuropathy with liability to pressure palsies. Neuromuscul Disord 2000;10:206–208. Reisecker F, Leblhuber F, Lexner R, Radner G, Rosenkranz W, Wagner K. A sporadic form of hereditary neuropathy with liability to pressure palsies: clinical, electrodiagnostic, and molecular genetic findings. Neurology 1994;44:753–755. Meggouh F, de Visser M, Arts WF, De Coo RI, van Schaik IN, Baas F. Early onset neuropathy in a compound form of Charcot-Marie-Tooth disease. Ann Neurol 2005;57:589–591. Aarskog NK, Vedeler CA. Real-time quantitative polymerase chain reaction. A new method that detects both the peripheral myelin protein 22 duplication in Charcot-Marie-Tooth type 1A disease and the peripheral myelin protein 22 deletion in hereditary neuropathy with liability to pressure palsy. Hum Genet 2000;107:494–498. Street VA, Bennett CL, Goldy JD, Shirk AJ, Kleopa KA, Tempel BL, et al. Mutation of a putative protein degradation gene LITAF/SIMPLE in Charcot-Marie-Tooth disease 1C. Neurology 2003;60:22–26. Saifi GM, Szigeti K, Wiszniewski W, Shy ME, Krajewski K, Hausmanowa-Petrusewicz I, et al. SIMPLE mutations in CharcotMarie-Tooth disease and the potential role of its protein product in protein degradation. Hum Mutat 2005;25:372–383. Pisciotta C, Manganelli F, Dubbioso R, Ruggiero L, Iodice R, Santoro L. Thermosensistive hereditary neuropathy with liability to pressure palsy. Muscle Nerve 2011;43:448–449.
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18. Tackenberg B, Moller JC, Rindock H, Bien S, Sommer N, Oertel WH, et al. CNS involvement in hereditary neuropathy with pressure palsies (HNPP). Neurology 2006;7:2250–2252. 19. Panas M, Karadima G, Kalfakis N, Floroskufi P, Vassilopoulos D. Charcot-Marie-Tooth disease type 1A with central nervous system involvement in two generations. J Neurol 2004;251:484–485. 20. Amato AA, Barohn RJ .Hereditary neuropathy with liability to pressure palsies: association with central nervous system demyelination. Muscle Nerve 1996;19:770–773. 21. Hong Y-H, Kim M, Kim H-J, Sung J-J, Kim SH, Lee K-W. Clinical and electrophysiological features of HNPP patients with 17p11.2 deletion. Acta Neurol Scand 2003;108:352–358. 22. Bennet CL, Shirk AJ, Huynh HM, Street VA, Nelis E, Van Maldergem L, et al. SIMPLE mutation in demyelinating neuropathy and distribution in sciatic nerve. Ann Neurol 2004;55:713–720. 23. Scelsa SN. Familial, demyelinating sensory and motor polyneuropathy with conduction block. Muscle Nerve 2010;41:558–562. 24. Lee SM, Olzmann JA, Chin LS, Li L. Mutations associated with Charcot-Marie-Tooth disease cause SIMPLE protein mislocalization and degradation by the proteasome and aggresome-autophagy pathways. J Cell Sci 2011;124:3319–3331. 25. Lee SM, Chin LS, Li L. Charcot-Marie-Tooth disease-linked protein SIMPLE functions with the ESCRT machinery in endosomal trafficking.). J Cell Biol 2012;199:799–816. 26. Gerding WM, Koetting J, Epplen JT, Neusch C. Hereditary motor and sensory neuropathy caused by a novel mutation in LITAF. Neuromuscul Disord 2009;19:701–703. 27. Cottenie E, Menezes MP, Rossor AM, Morrow JM, Yousry TA, Dick DJ, et al. Rapidly progressive asymmetrical weakness in CharcotMarie-Tooth disease type 4J resembles chronic inflammatory demyelinating polyneuropathy. Neuromuscul Disord 2013;23:399–403. 28. Jankelowitz SK, Burke D. Pathophysiology of HNPP explored using axonal excitability. J Neurol Neurosurg Psychiatry 2013;84: 806–812.
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ABSTRACT: Introduction: The first episode of hereditary neuropathy with liability to pressure palsy (HNPP) in childhood is rare. Methods: We analyzed retrospectively the data of 7 patients with a deletion in PMP22 and onset of symptoms before age 18 years. Direct sequencing of the LITAF (lipopolysaccharide-induced tumor necrosis factor) gene was performed in patients and family members. Results: Clinical presentations varied from mononeuropathies to brachial plexopathy, with recurrent episodes in 4 patients. Electrophysiological abnormalities characteristic for HNNP were found in most subjects. Analysis of the LITAF gene revealed an Ile92Val polymorphism in 6 of 7 (86%) probands and 5 of 7 (83%) family members, over 4 times greater frequency than in the general population. Conclusions: Clinical suspicion of HNPP even when nerve conduction study results do not fulfill HNPP criteria should indicate genetic testing. In our patients, early-onset HNPP was associated frequently with isoleucine92valine LITAF polymorphism. Muscle Nerve 50: 914–918, 2014
Hereditary neuropathy with liability to pressure palsy (HNPP) is a rare autosomal dominant neuropathy characterized by recurrent mononeuropathies, often associated with compression or minor trauma. It is caused in most cases by deletion in the gene encoding peripheral myelin protein 22 (PMP22) or, less frequently, by PMP22 point mutations.1,3 Typically, the first mononeuropathy occurs during the second or third decade of life. Symptomatic early onset HNPP is very rare.4–10 Difficulty in diagnosing pediatric HNPP patients can be attributed to the fact that a typical pattern of abnormalities in nerve conduction studies is expected in patients older than 15 years.9,11,12 Abbreviations: CB, conduction block; CMAP, compound muscle action potential; CMT, Charcot-Marie-Tooth disease; Cx32, connexin32; DML, distal motor latency; EGR2, early growth response gene 2; EMG, electromyography; Gly118 Ser, glycine 118 serine; HNPP, hereditary neuropathy with liability to pressure palsy; Ile92Val, isoleucine92valine polymorphism; L, left; LITAF, lipopolysaccharide-induced tumor necrosis factor; MC, motor conduction velocity; MFN2, mitofusin 2; MPZ, myelin protein zero; MUW, Medical University of Warsaw; nd, not done NFL, light chain neurofilament protein; PMP22, peripheral myelin protein 22; R, right; RT-PCR, real-time polymerase chain reaction; SCV, sensory conduction velocity; SNAP, sensory nerve action potential amplitude Key words: Charcot-Marie-Tooth disease; childhood hereditary neuropathy; hereditary neuropathy with liability to pressure palsy; LITAF; PMP22 This study was financed by grant NN 402 27 63 36 to A.K. Correspondence to: A. Kostera-Pruszczyk; e-mail: [email protected] C 2014 Wiley Periodicals, Inc. V
Published online 26 March 2014 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.24250
914
Early Onset HNPP
Guidelines for electrophysiological diagnosis of HNPP include the presence of diffuse electrophysiological abnormalities such as bilateral delayed median nerve distal motor latencies, bilateral reduced median sensory conduction velocity in the palm–wrist segment, and at least delayed distal motor latency or reduced motor nerve conduction velocity in 1 of the fibular nerves.9 The rarity of symptomatic HNPP in childhood raises the question if this early presentation is influenced by a modifier in addition to a deletion in PMP22. Previous reports suggested that phenotypic variations in Charcot-Marie-Tooth 1A (CMT1A) and CMT1D may be attributed to mutations in more than 1 gene.13 Mutations of the LITAF (lipopolysaccharide-induced tumor necrosis factor) gene described in patients with the PMP22 duplication were suggested as a cause of a severe phenotype of CMT1A.13 The aim of our study was to analyze retrospectively the clinical and electrophysiological findings and possible presence of a LITAF polymorphism in 7 patients with childhood onset HNPP. MATERIALS AND METHODS
This study was performed with Bioethical Committee approval no 120/2008 MUW. We analyzed retrospectively the data of 7 patients with a deletion of PMP22 who had onset of symptoms before age 18 years and were hospitalized between 2002 and 2011 in the Pediatric Ward of the Department of Neurology, Medical University of Warsaw. We also analyzed data from their 7 family members. On admission, all probands were considered to be sporadic cases. Detailed medical history disclosed that the parents from 3 families who were not previously aware of the disease had mild transient palsies in the past. In 3 further families, a diagnosis of HNPP was made in 3 asymptomatic members after nerve conduction studies and genetic testing. Their neurological examination was normal. To date, a 20-year-old sister of proband 3 had never experienced any symptoms of peripheral neuropathy. The mother of proband 4 was treated for sensory symptoms of bilateral MUSCLE & NERVE
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Table 1. Clinical characteristics of early-onset HNPP patients.* Gender
Age of onset, yrs
1 2
F M
4 13
3 4 5
M F M
6 7
Family
First symptom
Course
No of episodes
HNPP-affected family member
Provocative factors
Complete recovery Complete recovery
3 2
Father Father
Unknown Infection with fever
11 15 18
Fibular nerve palsy Proximal paresis of the left upper limb Fibular nerve palsy Bilateral fibular nerve palsy Radial nerve palsy
Improvement Complete recovery Complete recovery
1 1 2
On awakening Prolonged squatting Unknown
M
16
Fibular nerve palsy
1
Playing football
M
17
Musculocutaneous nerve palsy
Complete remission 22 months Improved - 4 months
Mother Mother 2 brothers 20y and 22y Unknown- adopted
2
Negative
Weight lifting
carpal tunnel syndrome with marked improvement after surgery at age 52 years. She reported no paresis. A brother of patient 5 was also asymptomatic until last follow-up at age 28 years. In 2 families, genetic testing of both biological parents was not possible. The probands were only children, so autosomal dominant transmission could not be demonstrated. Demographic data of patients and their family members are listed in Table 1. Genetic Testing. Genomic DNA was extracted from peripheral blood lymphocytes using the salting-out procedure. Deletion of the PMP22 gene was confirmed using the real-time polymerase chain reaction (RT-PCR) approach (as described by Aarskog and Vedeler14). A relative dosage (RQ) of the PMP22 gene ranged from 0.700 to 1.090 in normal individuals (2 copies of the PMP22 gene), from 0.359 to 0.595 in HNPP patients (1 copy) and from 1.176 to 2.324 in CMT1A patients (3 copies of PMP22 gene). The 3 coding exons 2–4 of the LITAF gene were amplified by PCR (primer sequences previously described by Street et al.).15 The PCR products were sequenced directly using BigDyeTM Terminator Version 1.1 Ready Reaction Cycle Sequencing kit on the ABI 3730/xl Genetic analyzer (Applied Biosystems). LITAF gene sequencing was performed in the patients and their family members. Nerve conduction studies were performed R EMG device. Motor and sensory using a KeypointV nerve conduction studies of the median, ulnar, fibular, tibial, and sural nerves were performed using surface electrodes in standard manner and compared with age-matched reference values. In the patients who tolerated EMG examination poorly, the number of nerves studied was limited, e.g., in the youngest (age 4 years), only median, tibial, both fibular, sural, and left facial nerves were investigated. The results of the nerve conduction studies were analyzed in all probands with respect to Early Onset HNPP
HNPP neurophysiological criteria.11 EMG study was also performed in the family members, if they consented. RESULTS
Detailed clinical characteristics are presented in Table 1. All probands had normal motor milestones. Patient 6, at age 7 years was diagnosed with epilepsy, for which he was treated for 3 years, with complete recovery. Six patients presented with mononeuropathies (4 with fibular, 1 with radial, or musculocutaneous nerve palsy). Four patients had recurrent episodes, including the patients with brachial plexus palsy. None of the patients or their family members suffered from neuropathic pain. Abnormalities were detected most frequently in median and fibular nerves. Conduction block was present in motor nerves of 3 of the 7 children. Detailed electrophysiological findings are listed in Table 2. A typical electrophysiological abnormality pattern was seen in all subjects older than 15 and in the patient who was age 4 years at diagnosis. Patients 3 and 4 did not meet electrophysiological criteria (ages 11 and 15) and presented with fibular nerve palsy. Proper clinical diagnosis was guided by the fact that patient 3 also had conduction block of the ulnar nerve, while in patient 4 fibular palsy was bilateral. Analysis of the LITAF gene revealed the presence of a c.274A>G (Ile92Val) sequence variant in 6 of the probands (all 7 were tested) and 5 of 6 tested family members (86% and 83%, respectively). This polymorphism was reported previously in 34/184 (18.5%) control chromosomes.16 Results are presented in Table 3. DISCUSSION
HNPP in children is rare, although the disease can start at any age. The youngest reported patient was a newborn with an Erb brachial plexus palsy.4 Our 7 patients included 1 patient who was symptomatic in the first decade of life. Similar single cases of early-onset HNPP were reported in the literature MUSCLE & NERVE
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Table 2. Nerve conduction study results in early onset HNPP patients.*
Patient/side
DML median (ms)
DML fibular (ms)
MCV fibular(m/s)
MCV ulnar across elbow(m/s)
SNAP ulnar(mV)
SNAP median(mV)
SNAP sural(mV)
SCV sural(m/s)
SCV median(m/s)
SCV ulnar(m/s)
1L/1R
6.8/nd
6.5/7.3
52.2/51.6
nd/nd
10/9.9
8.4/10
17/17
45.7/52.2
35.3/37.1
45.2/45.2
2L 3R/3L
4.5 4/4
7.5 5.2/5.2
43.4 42.5/44.3
52.2 22.7*/22.7
2.3 6.1/8.9
4.4 37/27
8.7 14/15
35.9 52.1/50
40.5 50/51.4
4R/4L
4/4.2
7.3/8.9
52.9/54
52.6/39.2
24/21
42/23
33/33
52.1/50
63.2/55.1
5L/5R
5.7/nd
9.8/8
37.8†/43.3
40.6/nd
1.5/nd
1.4/nd
1.4/1.6
29.8/27.4
42.3/nd
5.5 5 4 6.8 2
6.1 6.7 5.2 9.8 1
35.2 38 35.2 62.2 4
40 18.6* 18.6 52.6 1 of 6
4.3 3 1.5 24 2
8.7 4 1.4 10 4
7.3 14 1.4 33 5
42.6 45.2 29.8 52.2 5
35 32.4 32.4 63.2 2
35.9 59.9/ 54.3 57.8/ 52.1 45.6/ nd 32.9 38.6 32.9 59.9 2
6L 7L Min Max Patients with normal result
*Conduction block in ulnar nerve across elbow. †
Conduction block in fibular nerve at fibular head.
DML, distal motor latency; MCV, motor conduction velocity; SCV, sensory conduction velocity; SNAP, sensory nerve action potential amplitude; nd, not done; R, right; L, left; No, number.
and recently summarized.7,8 Although HNPP is a well-defined disease, in the setting of early-onset and no family history, the diagnosis can be challenging. Factors that trigger the symptoms can be identified in most HNPP patients. The onset of symptoms was painless and acute in all but 1 of our probands; in half of them a precipitating factor such as prolonged squatting, pressure on the nerve during sleep, or vigorous physical exercise could be identified. In the patient with brachial plexopathy who developed his symptoms on both occasions during febrile infection, an infection-related or inflammatory plexopathy was suspected at first. It is of interest that fever was reported previously as a trigger of recurrent fibular nerve palsy in a girl with HNPP.17 In the remaining 3 patients, a provocative factor was not identified, possibly related to the young age of the children who could not always report all details accompanying the onset of symptoms. Most of our patients had the typical disease course similar to what is observed in adults, including recurrent and transient nerve palsies with recovery. None of them reported pain, however decreased sensation was confirmed during clinical examination in 2 patients. Abnormalities in sensory nerves (decreased conduction velocity or amplitude) were recorded in most of the patients. Fibular nerve palsy was the most frequent presentation of HNPP in four of 7 children. Two of them (aged 11 and 15) did not have nerve conduction study results typical for HNPP. Yet in patient 916
Early Onset HNPP
4, the symptoms were bilateral after relatively mild pressure due to squatting, and in patient 3 axonal injury to the fibular nerve was accompanied by conduction block in the ulnar nerve indicating unusual sensitivity to pressure in both. Epilepsy in patient 6 seems to be coincidental. His brain MRI was normal. To date only a few cases of central nervous system involvement have been described in HNPP.18–20 Authors of guidelines for diagnosis of HNPP recognize that electrophysiological criteria are met
Table 3. LITAFIle92Val polymorphism results in all family members with confirmed PMP22 deletion.* Family no.
Family members
1
Proband Father Proband Father Proband
2 3
4
5
6 7
LITAF
Mother Sister Proband Mother
Ile92Val Ile92Val Ile92Val Ile92Val Ile92Val-585C> T (3’UTR Ile92Val Not found Ile92Val Ile92Val
Proband Brother1 Brother2 Proband Proband
Not found Not done* Ile92Val Ile92Val Ile92Val
HNPP symptoms – ever Yes Yes/in adolescence Yes Yes/in adolescence Yes Yes/ in adolescence Asymptomatic Yes No palsies /Carpal tunnel syndrome. with marked improvement after surgery Yes No Yes/in first decade of life Yes Yes
*Not available for genetic testing.
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by the patients, even those who are asymptomatic and are older than age 15.11 Our study stresses the role of electrophysiological testing of the parents of probands with clinical diagnosis of HNPP. This approach allowed us to demonstrate the hereditary nature of neuropathy in almost half of the patients before genetic testing. Our data also showed that most of the patients below age 15 had diffuse electrophysiological abnormalities. Prolonged distal motor latency in the median nerve and reduced median sensory conduction velocity accompanied by prolonged DML or reduced CMAP of the fibular nerve were the most frequent abnormalities, as expected.21 Conduction block at common entrapment sites was found in 3 of our patients, reflecting the pathogenic role of pressure injury in the development of the neuropathic changes in HNPP. In all of our patients, early-onset HNPP was caused by deletion of PMP22. Although we could not reliably confirm the age of onset in the parents of our index cases, some data suggest that early onset of HNPP may be a familial feature.8 No factors related to childhood onset of HNPP were identified. However, there are reports indicating that mutations of 2 genes that cause CMT may lead to early clinical presentation. Meggouh et al. described a 2-year-old boy with severe neuropathy. He was a heterozygote for PMP22 duplication and a Gly118 Ser mutation in the LITAF gene previously associated with CMT1C disease. He also had an Iso92Val polymorphism of LITAF13,22 His father carried a PMP22 duplication and was diagnosed with CMT1A. His mother had a Gly112Ser substitution in LITAF previously reported as associated with CMT1C disease, and both parents carried the Iso92Val polymorphism of LITAF. The authors suggested that LITAF Gly112Ser mutations can severely affect the CMT phenotype caused by a PMP22 duplication, but the role of Iso92Val as a possible modifier of the boy’s phenotype was not elucidated further.13 When we tested the LITAF gene, an Iso92Val substitution was demonstrated in all but 1 of our probands (86%). Of the family members who had the PMP22 deletion, 83% carried this polymorphism. The Iso92Val polymorphism in LITAF was also reported in the mother and son with familial multifocal, acquired, demyelinating sensory and motor polyneuropathy. This family was negative for known PMP22, connexin32 (Cx32), myelin protein zero (MPZ), early growth response gene 2 (EGR2), light-chain neurofilament protein (NFL), and mitofusin 2 (MFN2) mutations.23 LITAF protein is expressed in many tissues, but it is abundant in Schwann cells.24 It is involved in the process of regulation of endosome-to-lysosome trafficking and Early Onset HNPP
cell signaling. A recent study demonstrated that CMT1C linked mutants lead to loss-of-function mutations and impair endosome-to-lysosome trafficking.25 Conduction block is a rare phenomenon in hereditary neuropathies, and it is most commonly seen in HNPP patients, but some of the CMT1C patients with LITAF mutations present with demyelinating neuropathy with conduction blocks.26 Of interest, CMT4J caused by mutation of FIG4, another regulator of endosome-to-lysosome trafficking, can also be associated with conduction block. The mechanism leading to conduction block in HNPP has not been explained thoroughly. Studies of axonal excitability in HNPP have demonstrated alterations in threshold electrotonus most pronounced at wrist, but also detectable at the elbow. The authors indicated that structural abnormalities at the nodes of Ranvier may predispose to conduction block in response to pressure or stretch.28 Although Iso92Val substitution in LITAF alone does not cause clinically relevant changes, it may lead to an early-onset phenotype when superimposed on PMP22 deletion. In conclusion, although the clinical presentation of HNPP in children is similar to what is observed in adults, electrophysiological findings before age 15 years may lack typical nerve conduction abnormalities. Clinical suspicion of HNPP even when the nerve conduction study results do not fulfill HNPP criteria should indicate further genetic testing. Extending evaluation to the parents improves diagnostic yield. Early-onset of HNPP was associated frequently with LITAF isoleucine92valine polymorphism in our small group of patients.
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