1. 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

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

3. 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

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

5. 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

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

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

8. 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

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

10. 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/ [3/1]
V1589M
PAM
L1436P****

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

12. 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}

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

15. L1436P
I693T

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

17. L1436P
I693T

18. L1436P
I693T

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

21. L1436P
I693T

22. 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

23. 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

24. 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

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

28. 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)

29. Skeletal muscle Na+ channel NaV1.4