1339 J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.74.9.1339 on 21 August 2003. Downloaded from

SHORT REPORT Severe infantile hyperkalaemic and : broadening the clinical spectrum associated with the T704M mutation in SCN4A F Brancati, E M Valente, N P Davies, A Sarkozy, M G Sweeney, M LoMonaco, A Pizzuti, M G Hanna, B Dallapiccola ......

J Neurol Neurosurg Psychiatry 2003;74:1339–1341

the face and hand muscles, and paradoxical . Onset The authors describe an Italian kindred with nine individu- of paramyotonia is usually at birth.2 als affected by hyperkalaemic periodic paralysis associ- HyperPP/PMC shows characteristics of both hyperPP and ated with paramyotonia congenita (hyperPP/PMC). PMC with varying degrees of overlap and has been reported in Periodic paralysis was particularly severe, with several association with eight mutations in SCN4A gene (I693T, episodes a day lasting for hours. The onset of episodes T704M, A1156T, T1313M, M1360V, M1370V, R1448C, was unusually early, beginning in the first year of life and M1592V).3–9 While T704M is an important cause of isolated persisting into adult life. The paralytic episodes were hyperPP, this mutation has been only recently described in a refractory to treatment. Patients described minimal single hyperPP/PMC family. As with other SCN4A mutations, paramyotonia, mainly of the eyelids and hands. All there can be marked intrafamilial and interfamilial variability affected family members carried the threonine to in paralytic attack frequency and severity in patients harbour- methionine substitution at codon 704 (T704M) in exon 13 ing T704M.10–12 We report an Italian kindred, in which all of the voltage gated gene patients presented with an unusually severe and homogene- (SCN4A). The association between T704M and the ous hyperPP/PMC phenotype associated with the T704M. hyperPP/PMC phenotype has been only recently revealed. Nevertheless, such a severe phenotype has never been CASE REPORT reported so far in families with either hyperPP or hyperPP/ The VV family is a three generation kindred with nine mem- PMC. These data further broaden the clinical spectrum of bers affected by a remarkably severe, homogeneous hyperPP/ T704M and support the evidence that this mutation is a PMC phenotype (fig 1). Autosomal dominant inheritance was common cause of hyperPP/PMC. observed with no apparent lack of penetrance. A summary of the clinical data for each affected member is presented in table 1. The onset of paralytic episodes was around six to nine yperkalaemic periodic paralysis (hyperPP) and para- months of age in all patients. During infancy and childhood, (PMC) are autosomal dominant the episodes were frequent (up to two to three a week), lasting Hallelic diseases caused by mutations in the skeletal 10 minutes to two hours and were usually accompanied by http://jnnp.bmj.com/ muscle voltage gated sodium channel gene (SCN4A) on chro- muscle stiffness, mainly at the lower limbs. Nocturnal, poten- mosome 17q23.1 HyperPP is characterised by transient and tially life threatening episodes of complete paralysis with res- recurrent episodes of paralysis lasting minutes to hours, trig- piratory difficulties were experienced in the first years of life. gered by fasting or rest after exercise and accompanied by During adolescence, episodes were always related to a precipi- increased serum potassium concentrations. The episodes usu- tating factor (that is, rest after exercise, exposure to cold, alco- ally start in the first decade of life occurring on a weekly to hol intake, fasting), and carbohydrate intake sometimes alle- monthly basis and tend to decrease in severity and frequency viated the paralysis. The frequency and severity of episodes in adult life. A progressive proximal weakness may become insidiously worsened over the years. In adulthood, the attacks on October 1, 2021 by guest. Protected copyright. apparent in some people. The hallmarks of PMC are cold occurred with daily frequency and arose spontaneously or induced myotonic stiffness and weakness generally involving with minimal provocation (for example, sitting down for a

Table 1 Clinical characteristics of the affected individuals

Age at onset Frequency HyperK+ of paralytic of paralytic during Duration of Cardiac Response to Site of ID Sex (age) attacks attacks attacks episodes Precipitant factors arrhythmia drugs paramyotonia

II:2 F (81) <1 y 1/day no 1–15 min fasting, CTH no – – II:3 F (79) <1 y 1–3/day – 20 min RAE, CTH, stress – – – II:4 F (76) <1 y 1–3/day – 10 min fasting, CTH yes – – II:6 M (73) <1 y 1/day no 20 min RAE, fasting, carrots yes no (ACZ, CT) hand III:1 M (46) 6–7 months 1–2/day no 10 min–2 h RAE, fasting, CTH, alcohol no no (ACZ) eyes, hand III:3 M (45) 8 months 1–2/day no 1 h – no no (ACZ, SLB) eyes III:5 M (38) 9 months 2–3/day no 15 min RAE, CTH no no (ACZ) – IV:1 M (18) 6 months 1–2/week yes 20 min RAE, fasting, CTH – – eyes, hand IV:2 M (16) 8 months 1–2/week – 20 min RAE, CTH – –

RAE, rest after exercise; CTH, cold temperature and humidity; ACZ, acetazolamide; CT, chlorothiazide; SLB, salbutamol.

www.jnnp.com 1340 Brancati, Valente, Davies, et al J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.74.9.1339 on 21 August 2003. Downloaded from

Figure 1 Pedigree of the VV family. Black symbols represent clinically affected patients, a diagonal bar across symbols denotes deceased individuals. The black arrow indicates the proband of the family.

short time to have lunch or a short drive), becoming very patient was screened for the two common mutations resulting debilitating and interfering with most daily activities. The in hyperPP (M1592V,T704M), by means of PCR amplification main episodes lasted up to several hours, but focal weakness of the segment containing the mutation and digestion with in a muscle or group of muscles (for example, “floppy foot”) restriction enzymes TaiI and NsiI respectively. All tested could persist for days. Diffuse inter-episode weakness, mainly affected members were negative for the M1592V mutation but in the proximal muscles, invariably developed around the all harboured the T704M mutation in exon 13 as confirmed by fourth to fifth decade and was slowly progressive, with sequence analysis. None of the three unaffected individuals difficulty in climbing stairs and carrying shopping. Since the carried the T704M mutation. neonatal age, lid-lag phenomenon and profuse sweating were typical prodromal signs of an episode. Acetazolamide (up to DISCUSSION 1000 mg daily), chlorothiazide (500 mg daily), and salbutamol We have investigated an Italian family with hyperPP/PMC (either orally 2 mg thrice daily or inhaled 200 µg nasally) were carrying the T704M mutation in the SCN4A gene. This severe completely ineffective in preventing or aborting the episodes phenotype has never been reported in patients harbouring of paralysis. Two patients (II:4 and II:6) developed a cardiac T704M. In addition, differently from the commonly observed arrhythmia in their 60s, and one of them (II:6) required a wide intrafamilial variability, the nine affected individuals pacemaker implantation. showed a homogeneous phenotype. The association between Neurological examination showed calf hypertrophy in all T704M and hyperPP/PMC has been previously reported only in 4

affected individuals. Paradoxical myotonia was usually con- a Korean family by Kim and coworkers. Clinical comparison http://jnnp.bmj.com/ fined to eyelid closure and grip, and worsened with cooling; between the Korean family and the present family disclosed there was no percussion myotonia. Mild proximal muscle several common features, including similar precipitating fac- weakness was evident in adult family members without obvi- tors, mild paramyotonia, calf hypertrophy, and fixed proximal ous muscle wasting. Serum potassium concentrations weakness in affected adults. However, a number of important (measured during episodes in all but individuals II:3, II:4, and phenotypic differences between these two families can be IV:2) were either increased or at the upper limit of the normal distinguished. The onset of paralytic attacks in VV family was in range. (EMG), performed in patients III:3 the first months of life in all affected individuals. Conversely,

and III:5, revealed profuse myotonic discharges and myo- only two of seven affected members of the Korean family had on October 1, 2021 by guest. Protected copyright. pathic changes, consisting of low amplitude, early recruitment onset in infancy, while the other five patients had a more typi- pattern with decreased mean duration of motor unit cal onset towards the end of the first decade. Most striking was potentials, and high percentage of polyphasic potentials. A the difference in frequency of the episodes. In fact, in family VV McManis long exercise test (performed in individual III:3) the episodes of paralysis could occur several times a day with revealed a decrement between 40% and 90% in compound frequency and severity increasing with age. In addition, a muscle (CMAP) amplitude, suggesting an number of family members reported spontaneous attacks (that underlying .13 Cold immersion EMG to 20 is, without triggering factors). In family VV acetazolamide, degrees (performed in patients III:3 and III:5) also showed hydrochlorothiazide, and salbutamol (inhaled or oral) were marked CMAP amplitude decrement, consistent with PMC.14 ineffective in preventing or aborting the episodes, in contrast A muscle biopsy (performed in patient II:6 at age 37) showed with patients harbouring T704M, which often respond favour- a vacuolar with single large or multiple smaller ably to these treatments.11 15 vacuoles with no histochemical staining. Fibres varied in size Muscle biopsy revealed a vacuolar myopathy in one with occasional degeneration and without tubular aggregates. individual of the VV family, in agreement with other studies in Fibrosis was also observed with no inflammatory cells. families with the T704M mutation.16 Five of six affected indi- viduals in VV family had normal serum potassium concentra- MOLECULAR ANALYSIS tions during episodes (see table 1). This confirms previous After informed consent, blood was obtained from three suggestions that normokalaemic periodic paralysis represents patients (II:6, III:3, and IV:1), three unaffected family a variant of hyperPP and is associated with mutations in members (II:7, III:4, and III:6) and one spouse (III:2). Each SCN4A.

www.jnnp.com Severe infantile hyperkalaemic periodic paralysis with paramyotonia congenita and T704M 1341 J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.74.9.1339 on 21 August 2003. Downloaded from

It is interesting to speculate whether mutations in SCN4A REFERENCES could give rise to cardiac conduction defects in view of the 1 Ptacek L. The familial periodic paralyses and nondystrophic myiotonias. arrhythmias observed in individuals II:4 and II:6 in family VV. Am J Med 1998;108:58–70. Although this could be related to a different disorder, 2 Davies NP, Hanna MG. The skeletal muscle ion : basic McClatchey et al reported cardiac arrhythmia requiring science, clinical genetics and treatment. Curr Opinion Neurol pacemaker insertion in a 30 year old patients with paramyoto- 2001;14:539–51. 5 3 Plassart E, Eymard B, Maurs L, et al. Paramyotonia congenita: genotype nia congenital harbouring an S804F mutation in SCN4A. This to phenotype correlations in two families and report of a new mutation in is further supported by the fact that mutations in a closely the sodium channel gene. J Neurol Sci 1996;142:126–33. related channel gene, SCN5A, cause long QT syndrome (LQT3) 4 Kim J, Hahn Y, Sohn EH, et al. Phenotypic variation of a Thr704Met and that recent murine studies have demonstrated SCN4A mutation in skeletal sodium channel gene in a family with paralysis 17 18 periodica paramyotonica. J Neurol Neurosurg Psychiatry expression in cardiac muscle. In contrast with original 2001,70:618–23. northern blot analysis, SCN4A expression in human cardiac 5 McClatchey AI, McKenna-Yasek D, Cros D, et al. Novel mutations in muscle has recently been confirmed.19 20 families with unusual and variable disorders of the skeletal muscle sodium channel. Nat Genet 1992;2:148–52. This report expands the phenotypic variability of the 6 Ptacek LJ, Gouw L, Kwiecinski H, et al. Sodium channel mutations in T704M, further confirming the lack of genotype-phenotype paramyotonia congenita and hyperkalaemic periodic paralysis. Ann correlation in SCN4A mutations. Functional analysis has not Neurol 1993;33:300–7. so far offered an explanation for the wide phenotypic variabil- 7 Wagner S, Lerche H, Mitrovic N, et al. A novel sodium channel mutation causing a hyperkalaemic paralytic and paramyotonic syndrome with ity observed in the sodium channel disorders. Although modi- variable clinical expressivity. 1997;49:1018–25. fying genetic factors are probable, it is not clear whether these 8 Okuda S, Kanda F, Nishimoto K, et al. Hyperkalaemic periodic may be in the form of SCN4A polymorphisms or even paralysis and paramyotonia - a novel sodium channel mutation. J Neurol mutations in other channel genes. A gene 2001;248:1003–4. 9 Kelly P, Yang WS, Costigan D, et al. Paramyotonia congenita and such as KCNE3, in which mutations are a rare cause of hyperkalaemic periodic paralysis associated with a Met1592Val hypokalaemic or hyperkalaemic periodic paralysis, is an substitution in the skeletal muscle sodium channel alpha subunit—a large example of a possible modifying gene.21 kindred with a novel phenotype. Neuromusc Disord 1997;7:105–11. 10 Rudel R, Ricker K, Lehmann-Horn F. Genotype-phenotype correlations in In conclusion, we have identified a family with hyperPP/ human skeletal muscle sodium channel diseases. Arch Neurol PMC caused by the T704M mutation in SCN4A. This mutation 1993;50:1241–8. has been previously described and has been confirmed as 11 Feero WG, Wang J, Barany F, et al. Hyperkalemic periodic paralysis: pathogenic in functional studies.22 The affected individuals rapid molecular diagnosis and relationship of genotype to phenotype in 12 families. Neurology 1993;43:668–73. had a remarkably severe phenotype of hyperPP that was 12 Plassart E,ReboulJ,RimeCS,et al. Mutations in the sodium channel refractory to treatment, in association with mild paramyoto- gene (SCN4A) in 13 French families with hyperkalemic periodic nia congenita. T704M can be considered a common cause of paralysis and paramyotonia congenita: phenotype to genotype correlations and demonstration of the predominance of two mutations. hyperPP/PMC and patients with this phenotype should be Eur J Hum Genet 1994;2:110–24. screened for this mutation in the first instance. 13 Streib EW. AAEE minimonograph 27: of myotonic syndromes. Muscle Nerve 1987;10:603–15. 14 McManis PG, Lambert EH, Daube JR. The exercise test in periodic ACKNOWLEDGEMENTS paralysis. Muscle Nerve 1986;9:704–10. The authors thank the family members for their participation and A 15 Hanna MG, Stewart J, Shapira AHV, et al. Salbutamol treatment in a Ciavarella for technical support. patient with hyperkalaemic periodic paralysis due to a mutation in the skeletal muscle sodium channel gene (SCN4A). J Neurol Neurosurg ...... Psychiatry 1998;65:248–50. 16 Rudel R, Hanna MG, Lehmann-Horn F. Muscle channelopathies: Authors’ affiliations , periodic paralyses, paramyotonia and F Brancati, A Pizzuti, Department of Experimental Medicine and myotonia. In: Schapira AHV, Griggs RC, eds. Muscle diseases. Woburn: Pathology, “La Sapienza” University, Rome, Italy Butterworth Heinemann, 1999:135–75. E M Valente, A Sarkozy, B Dallapiccola, CSS Mendel Institute, IRCCS 17 Wang Q, Shen J, Splawski I, et al. SCN5A mutations associated with an

Casa Sollievo della Sofferenza, San Giovanni Rotondo and Rome, Italy inherited cardiac arrhythmia, long QT syndrome. Cell 1995;80:805–11. http://jnnp.bmj.com/ N P Davies, M G Sweeney, M G Hanna, Muscle and Neurogenetics 18 Zimmer T, Bollensdorff C, Houfe V, et al. Mouse heart Na+ channels: Section, Institute of Neurology, London, UK primary structure and function of two isoforms and alternatively spliced M LoMonaco, Department of Neurology, Catholic University, Rome, Italy variants. Am J Physiol Heart Circ Physiol 2002;282:H1007–17. 19 George AL, Komisarof J, Kallen RG, et al. Primary structure of the adult Funding: We gratefully acknowledge the financial support of the Italian human skeletal muscle voltage-dependent sodium channel. Ann Neurol Ministry of Health, the Wellcome Trust and the National Specialist 1992;31:131–7. Commissioning Advisory Group (NSCAG), UK. 20 Pereon Y, Lande G, Memolombe S, et al. Paramyotonia congenita with an SCN4A mutation affecting cardiac repolarisation. Neurology Competing interests: none declared. 2003;60:340–2. 21 Abbott GW, Butler MH, Bendahhou S, et al. MiRP2 forms potassium Correspondence to: Dr F Brancati, CSS Mendel Institute, Viale Regina channels in skeletal muscle with Kv3.4 and is associated with periodic on October 1, 2021 by guest. Protected copyright. Margherita, 261, 00198 Rome, Italy; [email protected] paralysis. Cell 2001;104:217–31. 22 Hayward LJ, Sandoval GM, Cannon SC. Defective slow inactivation of Received 13 December 2002 sodium channels contributes to familial periodic paralysis. Neurology Accepted in revised form 4 March 2003 1999;52:1447–53.

www.jnnp.com