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Biology, Genetics, and Diagnosis: What’s Happening in the Brain?

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Hemiplegic migraine is a condition caused by genetic mutations that disrupt electrical signals in the brain. Diagnosis relies on specific symptoms, including fully reversible motor weakness, and tests like MRI or EEG to safely rule out similar conditions like stroke, TIA, or epilepsy.

Key Takeaways

  • • Hemiplegic migraine is a channelopathy caused by abnormal electrical signals and ion channels in brain cells.
  • • Familial cases are usually driven by mutations in the CACNA1A, ATP1A2, SCN1A, or PRRT2 genes.
  • • A formal diagnosis requires fully reversible motor weakness alongside other aura symptoms that spread gradually over five or more minutes.
  • • Doctors use tests like MRI and EEG to differentiate hemiplegic migraine from stroke, TIA, and epilepsy.

To understand hemiplegic migraine (HM), we have to look beneath the surface at the “instruction manual” of your brain cells—your genes. HM is a channelopathy, a condition where the “gates” (ion channels) that control the flow of electrical signals in your brain do not work correctly [1][2].

The Genetic Blueprint

Most cases of Familial Hemiplegic Migraine (FHM) are caused by mutations in one of three primary genes. These mutations change how brain cells handle electrical charges, making them more likely to trigger the “brain tsunami” (Cortical Spreading Depolarization) [3][4].

Gene Type Biological Mechanism Key Clinical Features
CACNA1A (FHM1) Gain-of-function The calcium “gates” stay open too long, letting in too much calcium [3]. Often includes cerebellar signs like ataxia (clumsiness) or nystagmus (jerky eye movements) [5][6].
ATP1A2 (FHM2) Loss-of-function The “pump” that clears out salt and chemicals fails, leading to a buildup of “trash” between cells [4]. Often linked to more severe attacks, including fever, seizures, or, very rarely, coma [7][8].
SCN1A (FHM3) Gain-of-function The sodium “gates” are hyperactive, causing brain cells to fire too easily [9][10]. Symptoms often start very rapidly [1]. There is a known overlap with epilepsy [11].
PRRT2 (FHM4) Dysfunctional Affects how brain cells release chemical messengers [4]. Often associated with movement disorders or childhood seizures [4].

Gain-of-function means the gene is working “too hard” or staying “on” when it shouldn’t, while loss-of-function means it isn’t doing its job well enough [3][4].

How Doctors Confirm the Diagnosis (ICHD-3)

Neurologists use the ICHD-3 (the international “rulebook” for headaches) to diagnose HM. To meet the criteria, an attack must include:

  1. Motor weakness that is fully reversible [12].
  2. At least one other aura symptom: visual changes, sensory changes (numbness), or speech/language trouble [12].
  3. The symptoms must spread gradually over 5 minutes or more and/or happen one after another [13][1].

If a close relative (parent, sibling, or child) has the same condition, it is Familial (FHM). If not, it is Sporadic (SHM) [12].

Ruling Out the “Mimics”

Because HM looks so much like other conditions, doctors use specific tests to tell them apart:

  • Stroke vs. HM: In a stroke, an MRI—specifically Diffusion-Weighted Imaging (DWI)—shows permanent tissue damage from lack of blood [14]. In HM, the brain often shows “rebound hyperperfusion”—a temporary surge of blood flow visible on an Arterial Spin Labeling (ASL) MRI scan [15][16].
  • TIA (Mini-Stroke): A TIA usually happens all at once, whereas HM symptoms “march” or spread gradually across the body over several minutes [13][17].
  • Todd’s Paralysis (Epilepsy): Weakness that happens after a seizure. An EEG (which records brain waves) helps tell the difference: HM shows “slow-wave” activity during the weakness, while epilepsy shows “spikes” or “discharges” [18][19].

Tests Your Doctor May Consider During Your Initial Workup

Hemiplegic migraine is fundamentally a clinical diagnosis based on the ICHD-3 criteria [20]. However, during your initial presentation, doctors may use the following tests to rule out mimics like stroke or epilepsy. Once a clear pattern is established, routine neuroimaging or EEG is usually not needed [21].

  • Genetic Panel: Testing for CACNA1A, ATP1A2, and SCN1A [22].
  • Multimodal MRI: Including ASL and DWI to check blood flow [15].
  • EEG: To rule out seizures as the cause of the weakness [18].
  • Neurological Exam: Checking for balance (ataxia) between attacks [5][6].

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Frequently Asked Questions

What genes cause familial hemiplegic migraine?
Most cases are caused by mutations in the CACNA1A, ATP1A2, SCN1A, or PRRT2 genes. These genes control the electrical channels in your brain cells, and mutations can cause them to misfire and trigger a migraine attack.
What is the difference between familial and sporadic hemiplegic migraine?
If you have a close relative like a parent, sibling, or child with the condition, it is diagnosed as familial hemiplegic migraine. If no one else in your family has the condition, it is called sporadic hemiplegic migraine.
What does a gain-of-function mutation mean?
A gain-of-function mutation means the gene is working too hard or staying turned on when it shouldn't. This can cause the electrical gates in your brain cells to let in too much calcium or sodium, triggering a migraine attack.
How do doctors tell the difference between a hemiplegic migraine and a stroke?
Doctors use specialized MRI scans to tell them apart. A stroke shows permanent tissue damage from a lack of blood flow, while a hemiplegic migraine usually shows temporary changes in blood flow without causing permanent damage.
Why did my doctor order an EEG for my hemiplegic migraine?
An EEG records brain waves and helps rule out seizures as the cause of your weakness. During a hemiplegic migraine, the EEG typically shows slow-wave activity, whereas epilepsy typically shows sharp spikes.

Questions for Your Doctor

  • • Which of the four primary genes (CACNA1A, ATP1A2, SCN1A, or PRRT2) was included in my genetic testing panel?
  • • Can you explain if my specific mutation is a 'gain-of-function' or 'loss-of-function' and what that means for my treatment?
  • • Did my MRI include 'Arterial Spin Labeling' (ASL) to look at blood flow changes?
  • • If my EEG showed slow-wave activity, does that help confirm it was a migraine rather than a seizure?
  • • Should I see a neuro-ophthalmologist to check for subtle eye movement issues like nystagmus?

Questions for You

  • • Have you noticed any balance issues or 'clumsiness' even when you don't have a headache?
  • • Does anyone in your family have a history of 'weird' seizures or episodes of vertigo?
  • • How quickly do your symptoms spread? (e.g., from your hand to your arm over minutes, or all at once?)
  • • Has your doctor ruled out other conditions using both an MRI and an EEG?

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References

  1. 1

    [Familial hemiplegic migraine].

    Starikova NL, Kulesh AA

    Zhurnal nevrologii i psikhiatrii imeni S.S. Korsakova 2021; (121(7)):114-117 doi:10.17116/jnevro2021121071114.

    PMID: 34460166
  2. 2

    Familial Hemiplegic Migraine With Asymmetric Encephalopathy Secondary to ATP1A2 Mutation: A Case Series.

    Murphy OC, Merwick A, OʼMahony O, et al.

    Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society 2018; (35(1)):e3-e7 doi:10.1097/WNP.0000000000000387.

    PMID: 28445178
  3. 3

    Migraine: Calcium Channels and Glia.

    Kowalska M, Prendecki M, Piekut T, et al.

    International journal of molecular sciences 2021; (22(5)) doi:10.3390/ijms22052688.

    PMID: 33799975
  4. 4

    ATP1A2 Mutations in Migraine: Seeing through the Facets of an Ion Pump onto the Neurobiology of Disease.

    Friedrich T, Tavraz NN, Junghans C

    Frontiers in physiology 2016; (7()):239 doi:10.3389/fphys.2016.00239.

    PMID: 27445835
  5. 5

    Cerebellar function and ischemic brain lesions in migraine patients from the general population.

    Koppen H, Boele HJ, Palm-Meinders IH, et al.

    Cephalalgia : an international journal of headache 2017; (37(2)):177-190 doi:10.1177/0333102416643527.

    PMID: 27059879
  6. 6

    New Nonsense Variant c.2983G>T; p.Glu995* in the CACNA1A Gene Causes Progressive Autosomal Dominant Ataxia.

    Saathoff Y, Biskup S, Funke C, Roth C

    Journal of movement disorders 2021; (14(1)):70-74 doi:10.14802/jmd.20082.

    PMID: 33121221
  7. 7

    Familial hemiplegic migraine in pediatric patients: A genetic, clinical, and follow-up study.

    Mangano GD, Capizzi MR, Mantuano E, et al.

    Headache 2023; (63(7)):889-898 doi:10.1111/head.14582.

    PMID: 37326332
  8. 8

    Familial Hemiplegic Migraine with Severe Attacks: A New Report with ATP1A2 Mutation.

    Martínez E, Moreno R, López-Mesonero L, et al.

    Case reports in neurological medicine 2016; (2016()):3464285 doi:10.1155/2016/3464285.

    PMID: 27818813
  9. 9

    Gain of Function for the SCN1A/hNav1.1-L1670W Mutation Responsible for Familial Hemiplegic Migraine.

    Dhifallah S, Lancaster E, Merrill S, et al.

    Frontiers in molecular neuroscience 2018; (11()):232 doi:10.3389/fnmol.2018.00232.

    PMID: 30038559
  10. 10

    Modeling NaV1.1/SCN1A sodium channel mutations in a microcircuit with realistic ion concentration dynamics suggests differential GABAergic mechanisms leading to hyperexcitability in epilepsy and hemiplegic migraine.

    Lemaire L, Desroches M, Krupa M, et al.

    PLoS computational biology 2021; (17(7)):e1009239 doi:10.1371/journal.pcbi.1009239.

    PMID: 34314446
  11. 11

    The gain of function SCN1A disorder spectrum: novel epilepsy phenotypes and therapeutic implications.

    Brunklaus A, Brünger T, Feng T, et al.

    Brain : a journal of neurology 2022; (145(11)):3816-3831 doi:10.1093/brain/awac210.

    PMID: 35696452
  12. 12

    Hemiplegic migraine.

    de Boer I, Hansen JM, Terwindt GM

    Handbook of clinical neurology 2024; (199()):353-365 doi:10.1016/B978-0-12-823357-3.00015-X.

    PMID: 38307656
  13. 13

    Pathophysiology of migraine aura.

    Sanchez Del Rio M, Cutrer FM

    Handbook of clinical neurology 2023; (198()):71-83 doi:10.1016/B978-0-12-823356-6.00016-0.

    PMID: 38043972
  14. 14

    Serial magnetic resonance imaging findings during severe attacks of familial hemiplegic migraine type 2: a case report.

    Fear D, Patel M, Zand R

    BMC neurology 2021; (21(1)):173 doi:10.1186/s12883-021-02201-z.

    PMID: 33882852
  15. 15

    Time Course of Cerebral Perfusion Changes in Children with Migraine with Aura Mimicking Stroke.

    Cobb-Pitstick KM, Munjal N, Safier R, et al.

    AJNR. American journal of neuroradiology 2018; (39(9)):1751-1755 doi:10.3174/ajnr.A5693.

    PMID: 29903927
  16. 16

    A case report of sporadic hemiplegic migraine associated cerebral hypoperfusion: comparison of arterial spin labeling and dynamic susceptibility contrast perfusion MR imaging.

    Kim S, Kang M, Choi S

    European journal of pediatrics 2016; (175(2)):295-8 doi:10.1007/s00431-015-2609-2.

    PMID: 26250760
  17. 17

    Familial Hemiplegic Migraine Type 3 (FHM3) With an SCN1A Mutation in a Chinese Family: A Case Report.

    Shao N, Zhang H, Wang X, et al.

    Frontiers in neurology 2018; (9()):976 doi:10.3389/fneur.2018.00976.

    PMID: 30498473
  18. 18

    Clinical and electroencephalographic abnormalities during the full duration of a sporadic hemiplegic migraine attack.

    Chastan N, Lebas A, Legoff F, et al.

    Neurophysiologie clinique = Clinical neurophysiology 2016; (46(4-5)):307-311 doi:10.1016/j.neucli.2016.03.004.

    PMID: 27155821
  19. 19

    Relationships between migraine and epilepsy: Pathophysiological mechanisms and clinical implications.

    Demarquay G, Rheims S

    Revue neurologique 2021; (177(7)):791-800 doi:10.1016/j.neurol.2021.06.004.

    PMID: 34340811
  20. 20

    Familial hemiplegic migraine in Indian children-a tertiary center experience.

    Saini L, Gunasekaran PK, Tiwari S, et al.

    Journal of tropical pediatrics 2024; (70(3)) doi:10.1093/tropej/fmae008.

    PMID: 38580379
  21. 21

    A case report of atypical hemiplegic migraine with nonheadache onset in a Chinese child.

    Chen H, Sun X, Wang R, et al.

    BMC neurology 2021; (21(1)):267 doi:10.1186/s12883-021-02302-9.

    PMID: 34229663
  22. 22

    CACNA1A-p.Thr501Met mutation associated with familial hemiplegic migraine: a family report.

    Romozzi M, Primiano G, Rollo E, et al.

    The journal of headache and pain 2021; (22(1)):85 doi:10.1186/s10194-021-01297-5.

    PMID: 34320921

This page explains hemiplegic migraine genetics and diagnosis for educational purposes. It does not replace professional medical advice. Always consult your neurologist to interpret your test results and genetic panels.

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