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PubMed This is a summary of 14 peer-reviewed journal articles Updated
Neurology · Hot Water Epilepsy

The Biology and Genetics of Hot Water Epilepsy

At a Glance

Hot Water Epilepsy (HWE) involves a hyper-sensitive brain response to temperature, often linked to mutations in the SLC1A1 or SYN1 genes. While routine MRIs appear normal, advanced imaging reveals subtle brain differences that make individuals susceptible to seizures from thermal stress.

While Hot Water Epilepsy (HWE) is triggered by an external event, its roots lie deep within the brain’s biological and genetic “blueprint.” Understanding these internal factors can help clarify why some people are sensitive to hot water while others are not, and why the condition often appears in certain families. For more on what to expect, see the Long-Term Outlook page.

The Genetics: More Than One Blueprint

Scientists have discovered that HWE is genetically heterogeneous, meaning that several different genetic variations can lead to the same symptoms [1]. Two main genes have been identified as key players:

  • SLC1A1: This gene helps manage glutamate, a chemical that tells brain cells to “fire.” In people with certain SLC1A1 variants, the brain may struggle to clear out glutamate quickly enough, making the neurons more likely to misfire when stressed by heat [2].
  • SYN1: This mutation is primarily linked to “Bathing Epilepsy” (where water triggers a seizure regardless of temperature). Because it is X-linked, it often affects males more severely [3][4]. It affects Synapsin I, a protein that regulates how brain cells communicate [5][6].

(Note: While other genes like SYNGAP1 also cause reflex epilepsy, they are typically associated with different triggers, such as eating or chewing [7][8].)

The Thermoregulatory “Misfire”

In a typical brain, the thermoregulatory system handles heat without issue. However, in HWE, the brain’s “thermostat” is hyper-sensitive. When hot water (usually 40°C–50°C) hits the scalp, it triggers a rapid response in the brain’s sensory networks [9][10]. In genetically predisposed individuals, this sudden “thermal stress” causes an electrical overload, resulting in a seizure [9].

What the Brain Looks Like: MRI vs. fMRI

If you or your child has had a routine MRI, the results were likely reported as “normal” [11][12]. This is common in HWE. However, advanced research tools like fMRI (functional MRI) and voxel-based morphometry (a way to measure brain tissue in high detail) show that there are subtle differences in the brain’s structure:

  • The Amygdala: Research has shown subtle structural differences or a slight enlargement in the amygdala, a part of the brain that processes emotions and sensory input [13].
  • The Cortical Ribbon: There are often measurable differences in the cortical ribbon—the outer layer of the brain—suggesting that HWE may be a unique variant of temporal lobe epilepsy [13].

These findings show that while the brain looks healthy on standard tests, it is “wired” to be more responsive to specific thermal and sensory triggers [13][14].

Common questions in this guide

Why does hot water trigger seizures in some people?
In individuals with this condition, the brain's temperature-regulating system is hyper-sensitive. When hot water hits the scalp, it triggers a rapid sensory response that causes an electrical overload, leading to a seizure.
What genes are linked to Hot Water Epilepsy?
Researchers have identified mutations in the SLC1A1 and SYN1 genes as key factors. The SLC1A1 gene affects how the brain clears certain chemicals, while the SYN1 gene is often linked to 'Bathing Epilepsy,' where water contact itself triggers a seizure.
Are routine MRI results usually normal for Hot Water Epilepsy?
Yes, routine MRI scans typically look completely normal in people with Hot Water Epilepsy. However, more advanced research imaging, like functional MRI, can reveal very subtle structural differences in specific areas of the brain.
Is Hot Water Epilepsy passed down in families?
Yes, the condition can be inherited, and specific genetic mutations have been identified. Because certain variants like SYN1 are X-linked and often affect males more severely, doctors may recommend testing female family members to see if they are carriers.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does my (or my child's) seizure pattern suggest a temperature-sensitive SLC1A1 variant or a water-contact SYN1 variant?
  2. 2.Since routine MRIs are often normal, would a specialized analysis like voxel-based morphometry be useful to look for subtle brain changes?
  3. 3.Given that SYN1 is X-linked, should we test female family members for carrier status?
  4. 4.How do the structural changes in the 'cortical ribbon' mentioned in research relate to the specific symptoms we are seeing?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (14)
  1. 1

    A genetic locus for sensory epilepsy precipitated by contact with hot water maps to chromosome 9p24.3-p23.

    Karan KR, Satishchandra P, Sinha S, Anand A

    Journal of genetics 2018; (97(2)):391-398.

    PMID: 29932058
  2. 2

    Rare SLC1A1 variants in hot water epilepsy.

    Karan KR, Satishchandra P, Sinha S, Anand A

    Human genetics 2017; (136(6)):693-703 doi:10.1007/s00439-017-1778-7.

    PMID: 28324217
  3. 3

    X-linked focal epilepsy with reflex bathing seizures: Characterization of a distinct epileptic syndrome.

    Nguyen DK, Rouleau I, Sénéchal G, et al.

    Epilepsia 2015; (56(7)):1098-108 doi:10.1111/epi.13042.

    PMID: 26096837
  4. 4

    Hot water epilepsy and SYN1 variants.

    Peron A, Baratang NV, Canevini MP, et al.

    Epilepsia 2018; (59(11)):2162-2163 doi:10.1111/epi.14572.

    PMID: 30390306
  5. 5

    Neuromodulator Signaling Bidirectionally Controls Vesicle Numbers in Human Synapses.

    Patzke C, Brockmann MM, Dai J, et al.

    Cell 2019; (179(2)):498-513.e22 doi:10.1016/j.cell.2019.09.011.

    PMID: 31585084
  6. 6

    Impaired GABAB-mediated presynaptic inhibition increases excitatory strength and alters short-term plasticity in synapsin knockout mice.

    Valente P, Farisello P, Valtorta F, et al.

    Oncotarget 2017; (8(52)):90061-90076 doi:10.18632/oncotarget.21405.

    PMID: 29163811
  7. 7

    The epilepsy phenotype in adult patients with intellectual disability and pathogenic copy number variants.

    d'Orsi G, Martino T, Palumbo O, et al.

    Seizure 2017; (53()):86-93 doi:10.1016/j.seizure.2017.11.009.

    PMID: 29156220
  8. 8

    Clinical and behavioural features of SYNGAP1-related intellectual disability: a parent and caregiver description.

    Wright D, Kenny A, Eley S, et al.

    Journal of neurodevelopmental disorders 2022; (14(1)):34 doi:10.1186/s11689-022-09437-x.

    PMID: 35655128
  9. 9

    Hot water epilepsy: A form of reflex epilepsy - from infancy to adolescence.

    Pejaver R, Srinivasa V, Basavanthappa SP, Murthy CL

    Journal of neurosciences in rural practice 2015; (6(4)):607-9 doi:10.4103/0976-3147.169782.

    PMID: 26752913
  10. 10

    A Rare Reflex Epilepsy: Bathing-Related Epilepsy.

    Altun Y, Çelik M, EKMEKÇi B, et al.

    Noro psikiyatri arsivi 2017; (54(2)):193-194 doi:10.5152/npa.2017.15955.

    PMID: 28680322
  11. 11

    Clinical, Demographic, and Electroencephalographic Profile of Hot-Water Epilepsy in Children.

    Bharathi NK, Shivappa SK, Gowda VK, et al.

    Indian journal of pediatrics 2021; (88(9)):885-891 doi:10.1007/s12098-020-03570-y.

    PMID: 33417183
  12. 12

    Reflex Epilepsy with Hot Water: Clinical and EEG Findings, Treatment, and Prognosis in Childhood.

    Hanci F, Türay S, Balci P, Kabakuş N

    Neuropediatrics 2020; (51(5)):336-340 doi:10.1055/s-0040-1709455.

    PMID: 32294767
  13. 13

    Cortical-Subcortical morphometric signature of hot water epilepsy patients.

    Kenchaiah R, Satishchandra P, Bhargava Goutham K, et al.

    Epilepsy research 2020; (167()):106436 doi:10.1016/j.eplepsyres.2020.106436.

    PMID: 32846313
  14. 14

    Reduced small world brain connectivity in probands with a family history of epilepsy.

    Bharath RD, Chaitanya G, Panda R, et al.

    European journal of neurology 2016; (23(12)):1729-1737 doi:10.1111/ene.13104.

    PMID: 27564534

This page provides educational information about the genetics and biology of Hot Water Epilepsy. It does not replace professional medical advice, diagnosis, or genetic counseling from your healthcare provider.

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