Molecular Genetics of Sodium Channel Myotonias Michael Hanna CINCH NDM Meeting Kansas 3 June 2007 MRC Centre for Neuromuscular Disease Institute of Neurology Queen Square London

Overview Sodium channel gene Known phenotype-genotype links Review recent UK study of SCN4A gene and myotonia

Complete Ion channel without accessory subunits I II III IV Nav1.4 Cav1.1 + I IV x1 III II COOH NH x4 Kir2.1 NH COOH C D B E F G H I J K L M N O P Q R A NH COOH + - CLC-1 x2

Skeletal muscle Sodium channel gene Chromosome 17q 24 exons 36 point mutations all missense Multiple founders Impaired inactivation +

Phenotype Common genotype Hypo PP R672H/G/S Hyper PP T704M K sensitive normoPP R675G/Q/W HyperPP/PC R1448C/H Cold induced HypoPP/myt P1158S Paramyotonia congenita T1313A/M Painful cong myotonia V445M PAM-MF MP G1306A/V/E

Queen Square PP Database Genetically defined June 2007: CACNA1S 26 R528H 34 R1239H 1 R1239G SCN4A 40 T704M 13 M1592V 4 R675G 1 R672S

SCN4A genotype-phenotype 40 T704M HyperPP+/- myt 13 M1592V HyperPP+/- myt 4 R675G K sens-Normo 1 R672S HypoK

UK study Sodium channel Myotonia Aim –identify a sodium channel myotonia cohort Source-UK NSCAG Clinical database muscle channelopathies Inclusion criteria- “relaxed” Paramyotonia Prominent history cold exacerbation +/-weakness EMG myotonia DM1 /DM2 excluded SCN4A automated DNA analysis and detailed clinical analysis of mutation positive vs negative cases

UK study Sodium channel Myotonia 39 cases identified 27 exon 22/exon 24 12 SCN4A neg 3/27 PAM mts 2/27 new mts 2/12 T704M 1/12 new mts

Mutation Reported Phenotypes Phenotypes in UK Cohort Frequency in UK cohort (patients/kindred) Q270K**** PMC 1/1 T704M HyperPP HyperPP/PMC 2/1 G1306A PAM (MF) PMC/PAM G1306E PAM (MP) T1313M 10/6 R1448C 4/2 R1448H 2/2 R1448L**** - G1456E 3/1 F1473S 1/1 [3/1] V1589M PAM L1436P****

PAM mutations PMC clinical phenotype G1306E Myotonia Permanens G1306A Myotonia Fluctuans Clinical impression vs EMG criteria

Mutation Frequency in our cohort (patients/kindred) ***Q270K 1/1*** D1-S5 T704M 2/1 G1306A G1306E 1/1 T1313M 10/6 R1448C 4/2 R1448H 2/2 ***R1448L 1/1*** D4-S4 G1456E 3/1 F1473S V1589M ***L1436P 1/1 **** D4-S4 {I693T 1/1}

R1448L Typical PMC Paramyotonia Cold exacerbation myotonia Cold induced weakness Additional features – sensorineural deafness, generalised chorea ?unrelated

L1436P I693T

L1436P PMC phenotype Newcastle Myositis-immunosuppression Coincidence?/ other cases

L1436P I693T

L1436P I693T

Q270K PMC Marked pain Domain I mutations and pain? Treatment resistant

L1436P I693T

Mutation “negative” cases Clear paramyotonia with cold exacerbation Older age at onset Prominent painful myotonia Upper and lower limbs equally affected Fixed weakness ? Additional SCN4A mutations, ?CLCN1 ? Non-genetic phenocopies

Summary Exon 22/24 hotspot for PMC mutations DNA screening strategy Extending SCN4A analysis 75% hit rate Clinical distinction between PAM-PMC not always easy ? Genetic overlap cf EMG ? Further heterogeneity associated with PMC phenotype

Ion Channel Group Queen Square Research NSCAG Service Doreen Fialho Veronica Tann Susie Tomlinson Martin Koltzenburg Dimitri Kullmann Emma Stanley Nick Wood Cath Woodward Mary Davis Sanj Rajakulendran Mary Sweeney Emma Matthews Dennis Stevens Stephanie Schorge Andrew Haworth Tracey Graves Hugh Bostock Funding Support MRC, Wellcome Trust, ERF, BRT, ULCH-NHS Trust Special Trustees DoH NSCAG. Action Research, CINCH

Inherited mutations alter ion channel function and structure and cause human disease Copyright ©2005 American Society for Clinical Investigation

Clinical Classification Periodic Paralysis Nondystrophic Myotonias Andersen Tawil Syndrome Hypo- kalaemic PP Hyper- kalaemic PP Paramyotonia congenita Myotonia congenita VG Ca2+ channel (Dihydropyridine receptor) Cav1.1 (CACNA1S) VG skeletal muscle Na+ channel Nav1.4 (SCN4A) Molecular Classification VG skeletal muscle Cl- channel CLC-1 (CLCN1) Inward rectifying K+ channel Kir 2.1 (KCNJ2)

Skeletal muscle Na+ channel NaV1.4