Sodium Channel Dysfunction inEpilepsy and Migraine

Sodium Channel Dysfunction inEpilepsy and Migraine

Edited by professor Yasser Metwally

www.yassermetwally.com

PhysiologyGeneration and propagation of action potentials

PharmacologyTargets for local anesthetics, anticonvulsants

GeneticsInherited disorders of muscle, heart, brain, nerve

PhysiologyGeneration and propagation of action potentials

PharmacologyTargets for local anesthetics, anticonvulsants

GeneticsInherited disorders of muscle, heart, brain, nerve

Voltage-Gated Sodium ChannelsVoltage-Gated Sodium Channels

Muscle Sodium Channelopathies (SCN4A)Hyperkalemia periodic paralysisParamyotonia congenitaPotassium-aggravated myotoniaHypokalemic periodic paralysis type 2Painful congenital myotoniaMyasthenic syndrome Malignant hyperthermia susceptibility Cardiac Sodium Channelopathies (SCN5A)Congenital long QT syndrome (Romano-Ward)Idiopathic ventricular fibrillation (Brugada syndrome)Isolated cardiac conduction system diseaseAtrial standstillCongenital sick sinus syndromeSudden infant death syndromeDilated cardiomyopathy, conduction disorder, supraventricular arrhythmiaBrain Sodium Channelopathies (SCN1A, SCN2A, SCN1B)Generalized epilepsy with febrile seizures plusSevere myoclonic epilepsy of infancy (Dravet syndrome)Intractable childhood epilepsy with frequent generalized tonic-clonic seizuresBenign familial neonatal-infantile seizuresFamilial hemiplegic migrainePeripheral Nerve Sodium Channelopathies (SCN9A)Familial primary erythermalgiaCongenital indifference to pain

Muscle Sodium Channelopathies (SCN4A)Hyperkalemia periodic paralysisParamyotonia congenitaPotassium-aggravated myotoniaHypokalemic periodic paralysis type 2Painful congenital myotoniaMyasthenic syndrome Malignant hyperthermia susceptibility Cardiac Sodium Channelopathies (SCN5A)Congenital long QT syndrome (Romano-Ward)Idiopathic ventricular fibrillation (Brugada syndrome)Isolated cardiac conduction system diseaseAtrial standstillCongenital sick sinus syndromeSudden infant death syndromeDilated cardiomyopathy, conduction disorder, supraventricular arrhythmiaBrain Sodium Channelopathies (SCN1A, SCN2A, SCN1B)Generalized epilepsy with febrile seizures plusSevere myoclonic epilepsy of infancy (Dravet syndrome)Intractable childhood epilepsy with frequent generalized tonic-clonic seizuresBenign familial neonatal-infantile seizuresFamilial hemiplegic migrainePeripheral Nerve Sodium Channelopathies (SCN9A)Familial primary erythermalgiaCongenital indifference to pain

Generalized epilepsy with febrile seizures plusSCN1B, SCN1A, SCN2A

Severe myoclonic epilepsy of infancySCN1A (NaV1.1)

Intractable childhood epilepsy with generalized tonic-clonic seizuresSCN1A (NaV1.1)

Benign familial neonatal-infantile seizuresSCN2A (NaV1.2)

Familial hemiplegic migraineSCN1A (NaV1.1)

Familial erythromelalgiaSCN9A (NaV1.7)

Congenital indifference to painSCN9A (NaV1.7)

Generalized epilepsy with febrile seizures plusSCN1B, SCN1A, SCN2A

Severe myoclonic epilepsy of infancySCN1A (NaV1.1)

Intractable childhood epilepsy with generalized tonic-clonic seizuresSCN1A (NaV1.1)

Benign familial neonatal-infantile seizuresSCN2A (NaV1.2)

Familial hemiplegic migraineSCN1A (NaV1.1)

Familial erythromelalgiaSCN9A (NaV1.7)

Congenital indifference to painSCN9A (NaV1.7)

Disorders of Neuronal Sodium ChannelsDisorders of Neuronal Sodium Channels

Generalized Epilepsy with Febrile Seizures Plus(GEFS+)

Generalized Epilepsy with Febrile Seizures Plus(GEFS+)

Phenotype

Familial epilepsy syndrome characterized by childhood onset of typical febrile seizures that often persist beyond age 6 years accompanied by afebrile generalized seizures exhibiting variablephenotypes (generalized tonic-clonic, absence, myoclonic, atonic, and myoclonic-astatic).

Phenotype

Familial epilepsy syndrome characterized by childhood onset of typical febrile seizures that often persist beyond age 6 years accompanied by afebrile generalized seizures exhibiting variablephenotypes (generalized tonic-clonic, absence, myoclonic, atonic, and myoclonic-astatic). Genetics

GEFS+ Type I 19q13.1Voltage-gated Na channel ß1 subunit, SCN1B

GEFS+ Type II 2q22-24Voltage-gated Na channel α subunit, SCN1A, SCN2A

GEFS+ Type III 5q31.1-33.1GABA receptor subunit γ2, GABRG2

Genetics

GEFS+ Type I 19q13.1Voltage-gated Na channel ß1 subunit, SCN1B

GEFS+ Type II 2q22-24Voltage-gated Na channel α subunit, SCN1A, SCN2A

GEFS+ Type III 5q31.1-33.1GABA receptor subunit γ2, GABRG2

19

SCN1B

2

SCN1ASCN2A

D188V T875M V1353LR1657C

R1648HI1656M

K1270T

++++

++++

++++

W1204R

V1428AA1685V

N

C

SCN1A Mutations in GEFS+SCN1A Mutations in GEFS+

All GEFS+ mutations are missense

Heterologous Expression of SCN1AHeterologous Expression of SCN1A

tsA201 cells

pCMV-SCN1A

EGFP

hβ2

pGFP-IRES-hβ2

CD8

hβ1

pCD8-IRES-hβ1

+ CD8-antibody beads

2 days+ fluorescence

Principles of Na Channel GatingPrinciples of Na Channel Gating

resting

OutOut

InIn

Na+Na+

active

Na+Na+

fast-inactivated

Na+Na+

I Na1 μA

-10

-120 mV 1 msV

resting

OutOut

InIn

Na+Na+

active

Na+Na+

fast-inactivated

Na+Na+

Principles of Na Channel GatingPrinciples of Na Channel Gating

% persistent current vs. transient current

0.2 % (n = 4)0.9 % (n = 8, p < 0.01)1.5 % (n = 4, p < 0.001)4.2 % (n = 4, p < 0.0005)

Properties of SCN1A GEFS+ MutantsProperties of SCN1A GEFS+ MutantsR1648H, T875M, W1204RR1648H, T875M, W1204R

GEFS+ mutants exhibit increased persistent INa

Christoph Lossin, Dao Wang

Voltage (mV)

-120 -80 -40 0 40

Voltage ramp -120 to +40 mV (20 mV/sec)

WT-SCN1A + hβ1 + hβ2

R1648H + hβ1 + hβ21 Sec

50 p

A

Responses to Voltage Ramp

R1648H exhibits inappropriate activation

Properties of SCN1A GEFS+ MutantsProperties of SCN1A GEFS+ Mutants

WT-SCN1A single channel analysisWT-SCN1A single channel analysis

B

Amplitude, pA-3 -2 -1 0

Eve

nts

0

1000

2000

3000

4000

5000

6000A

2 pA5 ms

0 mV

• WT-SCN1A channels inactivate rapidly and completelyCarlos Vanoye

Properties of SCN1A GEFS+ MutantsProperties of SCN1A GEFS+ Mutants

R1648H single channel analysisR1648H single channel analysis

A B

C D2 pA

5 ms2 pA

5 ms

0 mV -10 mV

• Late re-opening of R1648H channels explains persistent current• Bursting behavior is rare

Properties of SCN1A GEFS+ MutantsProperties of SCN1A GEFS+ Mutants

R1648H single channel analysisR1648H single channel analysis

• Late re-opening of R1648H channels explains persistent current• Bursting behavior is rare

Severe Myoclonic Epilepsy of Infancy(SMEI, Dravet syndrome)

Severe Myoclonic Epilepsy of Infancy(SMEI, Dravet syndrome)

Phenotype

Rare, often sporadic convulsive syndrome characterized by febrile seizures during the first year of life, followed by intractable generalized epilepsy, impaired psychomotor development and ataxia. Classic anti-convulsant agents (dilantin, carbamazapine) may worsen seizures. “Borderline” SMEI (SMEB) associated with less severe seizures and less developmental impairments, absence of myoclonic seizures. Sometimes diagnosed in adulthood.

Genetics

Transmission is not evident in most cases; de novo SCN1A mutations.

SMEI 2q22-24 Voltage-gated Na channel α subunit, SCN1A

Phenotype

Rare, often sporadic convulsive syndrome characterized by febrile seizures during the first year of life, followed by intractable generalized epilepsy, impaired psychomotor development and ataxia. Classic anti-convulsant agents (dilantin, carbamazapine) may worsen seizures. “Borderline” SMEI (SMEB) associated with less severe seizures and less developmental impairments, absence of myoclonic seizures. Sometimes diagnosed in adulthood.

Genetics

Transmission is not evident in most cases; de novo SCN1A mutations.

SMEI 2q22-24 Voltage-gated Na channel α subunit, SCN1A

++++

++++

++++

L986F

F891C

R921CL1255P

V1380M

W1424R

Q1440R

R1648C

G1664R

T1899I

N

C

frameshift or nonsensemissense

SCN1A Mutations in SMEISCN1A Mutations in SMEI

F1661S

G1749E

M924IV934A

del F1289

Most SMEI mutations are nonsense or frameshift

Effect of SCN1A TruncationEffect of SCN1A Truncation

X

p.A1067T

c.3608delAPremature stop codon

1 2 3 4

Western Blot probed with anti-SCN1A antibody

Human cerebellum lysates normalized for protein content

1: SMEI patient (5yo female)2: Age-matched control (5yo female)3: 24yo male control4: 28yo male control

Erin McArdle

Severity Spectrum of Epilepsies Associated with Na Channel Mutations

Severity Spectrum of Epilepsies Associated with Na Channel Mutations

GEFS+GEFS+ SMEISMEI

LessLess MoreMoreClinical SeverityClinical Severity

Gain-of-FunctionGain-of-Function Loss-of-FunctionLoss-of-Function

Provisional genotype-phenotype correlationProvisional genotype-phenotype correlation

V1353LR1657C

I1656M

++++

++++

++++

A1685VN

C

SCN1A Mutations in GEFS+SCN1A Mutations in GEFS+

V1353L and A1685V are nonfunctional

Functional heterogeneity of GEFS+ mutations

Christoph Lossin, Tommy Rhodes

Properties of SCN1A GEFS+ MutantsProperties of SCN1A GEFS+ MutantsI1656M, R1657CI1656M, R1657C

Functional heterogeneity of GEFS+ mutations

I1656MR1657C

WT-SCN1A

Variable current density Shift in activation curve

I1656M and R1657C do NOT exhibit increased persistent INa

++++

++++

++++

L986F

R1648C

G1674RN

C

SCN1A Mutations in SMEISCN1A Mutations in SMEI

F1661S

G1749E

8 – non-functional

Characterization of 13 SMEI alleles

5 - dysfunctional

G177E

I227S R393HH939Q

C959R

delF1289

T1909I

Y426N

Properties of SCN1A SMEI MutantsProperties of SCN1A SMEI MutantsG1749E, R1648C, F1661SG1749E, R1648C, F1661S

2 ms

0.2 nA

F1661SG1749E

2 ms

0.2 nA

0.5 nA

2 ms

WT-SCN1A

2 ms

0.5 nA

R1648C

Tommy Rhodes, Iori Ohmori

Properties of SCN1A SMEI MutantsProperties of SCN1A SMEI MutantsG1749E, R1648C, F1661SG1749E, R1648C, F1661S

2 ms

WT-SCN1AG1749ER1648CF1661S

Variable impairment of inactivation

TTX-sensitive late current at 200 msec:WT 0.4 ± 0.1%G1749E 0.5 ± 0.1%R1648C 3.6 ± 0.3%F1661S 3.8 ± 0.3%

50 ms

0 50 100 150 200-10

-8

-6

-4

-2

0

Nor

mal

ized

Cur

rent

(%)

Pulse Duration (ms)

WT-SCN1AG1749E

F1661SR1648C

Properties of SCN1A SMEI MutantsProperties of SCN1A SMEI MutantsG1749E, R1648C, F1661SG1749E, R1648C, F1661S

R1648C and F1661S exhibit persistent INa

Familial Hemiplegic MigraineFamilial Hemiplegic Migraine

Phenotype

Familial hemiplegic migraine is an inherited subtype of migraine with aura. Attacks are characterized by the presence of hemiparesis or hemiplegia, either isolated or associated with other aura symptoms such as hemianopic blurring of vision, unilateral paresthesias or numbness, and dysphasia. These symptoms usually last 30 to 60 minutes and are followed by a severe pulsatile headache lasting a few hours.

Genetics

Autosomal dominant

FHM1 19p13 Calcium channel α subunit, CACNA1AFHM2 1q21-q23 Na-K ATPase α2 subunit, ATP1A2FHM3 2q22-24 Voltage-gated Na channel α subunit, SCN1A

Phenotype

Familial hemiplegic migraine is an inherited subtype of migraine with aura. Attacks are characterized by the presence of hemiparesis or hemiplegia, either isolated or associated with other aura symptoms such as hemianopic blurring of vision, unilateral paresthesias or numbness, and dysphasia. These symptoms usually last 30 to 60 minutes and are followed by a severe pulsatile headache lasting a few hours.

Genetics

Autosomal dominant

FHM1 19p13 Calcium channel α subunit, CACNA1AFHM2 1q21-q23 Na-K ATPase α2 subunit, ATP1A2FHM3 2q22-24 Voltage-gated Na channel α subunit, SCN1A

SCN1A – a novel locus for familial hemiplegic migraineSCN1A – a novel locus for familial hemiplegic migraine

Dichgans, et al., Lancet 2005

Recovery at –100 mV

Voltage-dependence ofrecovery from inactivation

Expression in SCN5A

Properties of SCN1A Mutant in FHMProperties of SCN1A Mutant in FHM

Functional properties of Q1489K

Abnormal voltage-dependence of activation-4 mV shift in conductance vs voltage

Abnormal fast inactivation*increased persistent currentimpaired recovery from inactivation

Enhanced slow inactivation*Enhanced use-dependence

* Novel features

Kris Kahlig, Tommy Rhodes

1 10 100 10000.2

0.4

0.6

0.8

1.0

WT Q1489K

Nor

mal

ized

Cur

rent

Recovery period [ms]

Impaired recovery from inactivation

– 120 mV

-10 mV

∆t

WT Q1489Kτ1 (ms) 2.0 ± 0.1 1.5 ± 0.1 (P< 0.02)τ2 (ms) 54 ± 9.6 76 ± 5.0 (P < 0.05)A2 (%) 20 ± 1.0 32 ± 1.0 (P < 0.001)

50 ms

WT

Q1489K

WT 0.4%Q1489K 1.48 %

Increased persistent sodium current

Properties of SCN1A Mutant in FHMProperties of SCN1A Mutant in FHM

Kris Kahlig, Tommy Rhodes

Properties of SCN1A Mutant in FHMProperties of SCN1A Mutant in FHM

Abnormal use-dependence

0 20 40 60 80 100 120 140

0.25

0.5

0.75

1

Nor

mal

ized

cur

rent

Frequency (Pulses/Second)

WT Q1489K

Properties of SCN1A Mutant in FHMProperties of SCN1A Mutant in FHM

0 20 40 60 80 100 120 140

0.25

0.5

0.75

1

R1648H R1648C WT Q1489KN

orm

aliz

ed c

urre

nt

Frequency (Pulses/Second)

Epilepsy

Migraine

Abnormal use-dependence

Cortical Spreading Depression (CSD) of LeãoCortical Spreading Depression (CSD) of Leão

Cortical spreading depression, a transient depolarization wave that moves across the cortex, explains migraine aura.

Cortical spreading depression, a transient depolarization wave that moves across the cortex, explains migraine aura.

Leão, J Neurophysiol 1944

Role of CSD in Migraine PathogenesisRole of CSD in Migraine Pathogenesis

Summary and ConclusionsSummary and Conclusions

• Mutations in brain voltage-gated Na channels are associatedwith a diverse group of human epilepsy syndromes and rarecases of familial migraine.

• Functional defects range from loss- to gain-of-function

• Relationship between clinical syndrome and biophysicalphenotypes is complex

• Other genetic, developmental and environmental factorsmay influence the clinical expression channel mutations

• Computational modeling offers opportunities to define themechanistic basis for Na channel dysfunction and may helpwith the design of targeted therapies.

• Mutations in brain voltage-gated Na channels are associatedwith a diverse group of human epilepsy syndromes and rarecases of familial migraine.

• Functional defects range from loss- to gain-of-function

• Relationship between clinical syndrome and biophysicalphenotypes is complex

• Other genetic, developmental and environmental factorsmay influence the clinical expression channel mutations

• Computational modeling offers opportunities to define themechanistic basis for Na channel dysfunction and may helpwith the design of targeted therapies.