Sodium channelopathy in neurological disorders

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Sodium channelopathy in neurological disorders
http://yassermetwally.com
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Sodium channelopathy in neurological disorders

  1. 1. Sodium Channel Dysfunction in Epilepsy and Migraine Edited by professor Yasser Metwally www.yassermetwally.com
  2. 2. Voltage-Gated Sodium Channels Physiology Generation and propagation of action potentials Pharmacology Targets for local anesthetics, anticonvulsants Genetics Inherited disorders of muscle, heart, brain, nerve
  3. 3. Muscle Sodium Channelopathies (SCN4A) Muscle Sodium Channelopathies (SCN4A) Hyperkalemia periodic paralysis Hyperkalemia periodic paralysis Paramyotonia congenita Paramyotonia congenita Potassium-aggravated myotonia Potassium-aggravated myotonia Hypokalemic periodic paralysis type 2 Hypokalemic periodic paralysis type 2 Painful congenital myotonia Painful congenital myotonia Myasthenic syndrome Myasthenic syndrome Malignant hyperthermia susceptibility Malignant hyperthermia susceptibility Cardiac Sodium Channelopathies (SCN5A) Cardiac Sodium Channelopathies (SCN5A) Congenital long QT syndrome (Romano-Ward) Congenital long QT syndrome (Romano-Ward) Idiopathic ventricular fibrillation (Brugada syndrome) Idiopathic ventricular fibrillation (Brugada syndrome) Isolated cardiac conduction system disease Isolated cardiac conduction system disease Atrial standstill Atrial standstill Congenital sick sinus syndrome Congenital sick sinus syndrome Sudden infant death syndrome Sudden infant death syndrome Dilated cardiomyopathy, conduction disorder, supraventricular arrhythmia Dilated cardiomyopathy, conduction disorder, supraventricular arrhythmia Brain Sodium Channelopathies (SCN1A, SCN2A, SCN1B) Brain Sodium Channelopathies (SCN1A, SCN2A, SCN1B) Generalized epilepsy with febrile seizures plus Generalized epilepsy with febrile seizures plus Severe myoclonic epilepsy of infancy (Dravet syndrome) Severe myoclonic epilepsy of infancy (Dravet syndrome) Intractable childhood epilepsy with frequent generalized tonic-clonic seizures Intractable childhood epilepsy with frequent generalized tonic-clonic seizures Benign familial neonatal-infantile seizures Benign familial neonatal-infantile seizures Familial hemiplegic migraine Familial hemiplegic migraine Peripheral Nerve Sodium Channelopathies (SCN9A) Peripheral Nerve Sodium Channelopathies (SCN9A) Familial primary erythermalgia Familial primary erythermalgia Congenital indifference to pain Congenital indifference to pain
  4. 4. Disorders of Neuronal Sodium Channels Generalized epilepsy with febrile seizures plus Generalized epilepsy with febrile seizures plus SCN1B, SCN1A, SCN2A SCN1B, SCN1A, SCN2A Severe myoclonic epilepsy of infancy Severe myoclonic epilepsy of infancy SCN1A (NaV1.1) SCN1A (NaV1.1) Intractable childhood epilepsy with generalized tonic-clonic seizures Intractable childhood epilepsy with generalized tonic-clonic seizures SCN1A (NaV1.1) SCN1A (NaV1.1) Benign familial neonatal-infantile seizures Benign familial neonatal-infantile seizures SCN2A (NaV1.2) SCN2A (NaV1.2) Familial hemiplegic migraine Familial hemiplegic migraine SCN1A (NaV1.1) SCN1A (NaV1.1) Familial erythromelalgia Familial erythromelalgia SCN9A (NaV1.7) SCN9A (NaV1.7) Congenital indifference to pain Congenital indifference to pain SCN9A (NaV1.7) SCN9A (NaV1.7)
  5. 5. 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 variable phenotypes (generalized tonic-clonic, absence, myoclonic, atonic, and myoclonic-astatic). Genetics GEFS+ Type I 19q13.1 SCN1B Voltage-gated Na channel ß1 subunit, SCN1B 19 GEFS+ Type II 2q22-24 SCN1A Voltage-gated Na channel α subunit, SCN1A, SCN2A SCN2A GEFS+ Type III 5q31.1-33.1 2 GABA receptor subunit γ2, GABRG2
  6. 6. SCN1A Mutations in GEFS+ R1648H I1656M K1270T + + + + + + + + + + + + N V1428A A1685V V1353L D188V T875M R1657C W1204R C All GEFS+ mutations are missense
  7. 7. Heterologous Expression of SCN1A CD8 EGFP hβ1 hβ2 pCMV-SCN1A pCD8-IRES-hβ1 pGFP-IRES-hβ2 2 days + fluorescence tsA201 cells + CD8-antibody beads
  8. 8. Principles of Na Channel Gating Na+ + Na+ + Out Out resting active In In Na+ + fast-inactivated
  9. 9. Principles of Na Channel Gating Na+ + Na+ + Out Out resting active In In Na+ + 1 μA I Na -10 fast-inactivated V -120 mV 1 ms
  10. 10. Properties of SCN1A GEFS+ Mutants R1648H, T875M, W1204R R1648H, T875M, W1204R GEFS+ mutants exhibit increased persistent INa % 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) Christoph Lossin, Dao Wang
  11. 11. Responses to Voltage Ramp R1648H exhibits inappropriate activation 50 pA WT-SCN1A + hβ1 + hβ2 R1648H + hβ1 + hβ2 1 Sec V/sec) mV (20 m 0 to +40 ramp -12 Voltage -120 -80 -40 0 40 Voltage (mV)
  12. 12. Properties of SCN1A GEFS+ Mutants WT-SCN1A single channel analysis 0 mV A B 6000 5000 4000 Events 3000 2000 1000 0 2 pA -3 -2 -1 0 5 ms Amplitude, pA • WT-SCN1A channels inactivate rapidly and completely Carlos Vanoye
  13. 13. Properties of SCN1A GEFS+ Mutants R1648H single channel analysis 0 mV -10 mV A B 2 pA 2 pA C 5 ms D 5 ms • Late re-opening of R1648H channels explains persistent current • Bursting behavior is rare
  14. 14. Properties of SCN1A GEFS+ Mutants R1648H single channel analysis • Late re-opening of R1648H channels explains persistent current • Bursting behavior is rare
  15. 15. 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
  16. 16. SCN1A Mutations in SMEI Most SMEI mutations are nonsense or frameshift L1255P R921C M924I R1648C V934A V1380M G1749E Q1440R + + + + + + + + + + + + F891C N G1664R F1661S W1424R T1899I del F1289 C L986F frameshift or nonsense missense
  17. 17. Effect of SCN1A Truncation X Premature stop codon c.3608delA p.A1067T 1 2 3 4 Human cerebellum lysates normalized for protein content 1: SMEI patient (5yo female) 2: Age-matched control (5yo female) 3: 24yo male control Western Blot probed 4: 28yo male control with anti-SCN1A antibody Erin McArdle
  18. 18. Severity Spectrum of Epilepsies Associated with Na Channel Mutations Clinical Severity Less More GEFS+ SMEI Provisional genotype-phenotype correlation Gain-of-Function Loss-of-Function
  19. 19. SCN1A Mutations in GEFS+ Functional heterogeneity of GEFS+ mutations I1656M + + + + + + + + + + + + N V1353L A1685V R1657C C V1353L and A1685V are nonfunctional Christoph Lossin, Tommy Rhodes
  20. 20. Properties of SCN1A GEFS+ Mutants I1656M, R1657C I1656M, R1657C Functional heterogeneity of GEFS+ mutations WT-SCN1A I1656M R1657C Variable current density Shift in activation curve I1656M and R1657C do NOT exhibit increased persistent INa
  21. 21. SCN1A Mutations in SMEI Characterization of 13 SMEI alleles H939Q R1648C G1749E I227S R393H C959R + + + + + + + + + + + + G177E N delF1289 F1661S G1674R Y426N C L986F T1909I 8 – non-functional 5 - dysfunctional
  22. 22. Properties of SCN1A SMEI Mutants G1749E, R1648C, F1661S G1749E, R1648C, F1661S WT-SCN1A R1648C 0.5 nA 0.5 nA 2 ms 2 ms G1749E F1661S 0.2 nA 0.2 nA 2 ms 2 ms Tommy Rhodes, Iori Ohmori
  23. 23. Properties of SCN1A SMEI Mutants G1749E, R1648C, F1661S G1749E, R1648C, F1661S WT-SCN1A G1749E R1648C F1661S 2 ms Variable impairment of inactivation
  24. 24. Properties of SCN1A SMEI Mutants G1749E, R1648C, F1661S G1749E, R1648C, F1661S R1648C and F1661S exhibit persistent INa 0 WT-SCN1A Normalized Current (%) -2 G1749E -4 R1648C -6 F1661S -8 -10 0 50 100 150 200 Pulse Duration (ms) 50 ms 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%
  25. 25. Familial 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, CACNA1A FHM2 1q21-q23 Na-K ATPase α2 subunit, ATP1A2 2 FHM3 2q22-24 Voltage-gated Na channel α subunit, SCN1A
  26. 26. SCN1A – a novel locus for familial hemiplegic migraine SCN1A – a novel locus for familial hemiplegic migraine Dichgans, et al., Lancet 2005
  27. 27. Recovery at –100 mV Expression in SCN5A Voltage-dependence of recovery from inactivation
  28. 28. Properties 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 current impaired recovery from inactivation Enhanced slow inactivation* Enhanced use-dependence * Novel features Kris Kahlig, Tommy Rhodes
  29. 29. Properties of SCN1A Mutant in FHM Increased persistent sodium current Impaired recovery from inactivation WT 1.0 Q1489K Normalized Current 0.8 WT 0.6 Q1489K WT 0.4% Q1489K 1.48 % 0.4 -10 mV ∆t – 120 mV 0.2 1 10 100 1000 50 ms Recovery period [ms] WT Q1489K τ1 (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) Kris Kahlig, Tommy Rhodes
  30. 30. Properties of SCN1A Mutant in FHM Abnormal use-dependence 1 Normalized current 0.75 0.5 WT Q1489K 0.25 0 20 40 60 80 100 120 140 Frequency (Pulses/Second)
  31. 31. Properties of SCN1A Mutant in FHM Abnormal use-dependence 1 Normalized current 0.75 Epilepsy 0.5 R1648H R1648C 0.25 WT Q1489K Migraine 0 20 40 60 80 100 120 140 Frequency (Pulses/Second)
  32. 32. Cortical Spreading Depression (CSD) of Leão Cortical spreading depression, a transient depolarization wave that moves across the cortex, explains migraine aura. Leão, J Neurophysiol 1944
  33. 33. Role of CSD in Migraine Pathogenesis
  34. 34. Summary and Conclusions • Mutations in brain voltage-gated Na channels are associated with a diverse group of human epilepsy syndromes and rare cases of familial migraine. • Functional defects range from loss- to gain-of-function • Relationship between clinical syndrome and biophysical phenotypes is complex • Other genetic, developmental and environmental factors may influence the clinical expression channel mutations • Computational modeling offers opportunities to define the mechanistic basis for Na channel dysfunction and may help with the design of targeted therapies.

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