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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Genetics

Genetics, Inheritance, and the Health of Female Carriers

At a Glance

Christianson Syndrome is an X-linked disorder caused by a mutation in the SLC9A6 gene, which primarily causes severe symptoms in males. Female carriers can also experience symptoms, including learning challenges, mood disorders, and a risk for late-onset neurological issues like tremors.

Christianson Syndrome is caused by a change (mutation) in the SLC9A6 gene [1]. This gene is responsible for making a protein called NHE6 [2]. You can think of NHE6 as a “thermostat” or a “pH regulator” for the small transport bubbles inside your brain cells, called endosomes [3][4].

In a healthy cell, endosomes must maintain a specific level of acidity to move nutrients, recycle receptors, and clear out “trash” proteins like tau [5][6]. When the SLC9A6 gene is mutated, this thermostat breaks, and the endosomes become too acidic [2][3]. This “trash” begins to build up, and the cell can no longer communicate effectively with other cells, eventually leading to the symptoms seen in Christianson Syndrome [7][8]. (Note: While tau buildup is discussed in other neurodegenerative diseases, in Christianson Syndrome it is primarily linked to movement and coordination issues rather than Alzheimer’s disease).

Why Males Are Primarily Affected

The SLC9A6 gene is located on the X chromosome [1]. This is why the condition is called an X-linked disorder.

  • Males have one X chromosome and one Y chromosome. If their only X chromosome has the mutation, they do not have a backup copy of the gene, leading to the severe symptoms of Christianson Syndrome [9].
  • Females have two X chromosomes. If one has the mutation, the second, healthy X chromosome usually provides enough “working” NHE6 protein to prevent the full-blown syndrome [10].

Understanding the Female Carrier Experience

For many years, women who carried the mutation were called “asymptomatic carriers,” meaning they were thought to have no symptoms at all. However, research now shows that being a carrier can impact a woman’s health across her lifespan [11][12]. Because of a process called X-chromosome inactivation—where each cell “turns off” one of its two X chromosomes—a woman’s body becomes a mosaic of healthy cells and cells with the mutation [10][13].

1. Cognitive and Behavioral Health

Many female carriers (up to 85%) may experience subtle challenges in certain areas of brain function [12]. These can include:

  • Learning and Language: History of learning disabilities, speech delays, or difficulty with visuospatial tasks (like reading maps or 3D puzzles) [12][10].
  • Executive Function: Challenges with attention, planning, or organizing tasks [12].
  • Neuropsychiatric Symptoms: An increased likelihood of ADHD, anxiety, or depression [12][14].

2. Late-Onset Neurological Risks

As carriers age, the buildup of proteins in certain brain regions can lead to physical symptoms [15][13]. In some women, this may manifest as atypical parkinsonism later in life [12][16]. Symptoms can include:

  • Bradykinesia: Slowness of movement [16].
  • Rigidity: Stiffness in the arms or legs [16].
  • Tremors: Shaking, especially when at rest [16].
  • Corticobasal Degeneration: A rare condition that affects coordination and muscle control [12][17].

While these late-onset conditions are possible, it is important to know that their severity is highly variable, and they do not affect every carrier [12][16].

Empowering Carriers

If you are a mother and a carrier, it is easy to focus entirely on your child’s complex needs. However, understanding your own genetic profile is vital for your long-term health [17]. If you notice new stiffness, tremors, or significant changes in your memory or mood, it is important to consult a neurologist who understands the unique risks associated with the SLC9A6 mutation [15][13]. Making your own health a priority ensures you can continue to be the best advocate for your family.

Common questions in this guide

What causes Christianson Syndrome?
Christianson Syndrome is caused by a mutation in the SLC9A6 gene. This gene is responsible for making the NHE6 protein, which acts as a regulator for the small transport bubbles inside your brain cells. When this gene is mutated, brain cells cannot communicate properly.
Why does Christianson Syndrome mostly affect boys?
Because the condition is X-linked, it primarily affects males who only have one X chromosome. Females have two X chromosomes, so if one has the mutation, the healthy one usually produces enough functioning protein to prevent the most severe symptoms of the syndrome.
Can female carriers of Christianson Syndrome have symptoms?
Yes, research shows that female carriers can experience symptoms. Up to 85% of carriers may have cognitive or behavioral challenges, such as learning disabilities, ADHD, or anxiety, due to how the X chromosomes are activated in the body.
What are the long-term health risks for female carriers?
As female carriers age, they may be at risk for late-onset neurological issues like atypical parkinsonism. Symptoms to watch for include new slowness of movement, muscle stiffness, and resting tremors.
Should female carriers be monitored by a neurologist?
If you notice new tremors, stiffness, or changes in your memory or mood, it is highly recommended to consult a neurologist. Finding a specialist who understands the unique risks of the SLC9A6 mutation can help you proactively manage your health.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Based on my genetic test, what is the risk of my other children or future children having Christianson Syndrome?
  2. 2.Could my history of learning disabilities or ADHD be related to my status as a carrier?
  3. 3.Are there specific neurologists who specialize in 'atypical parkinsonism' should I develop movement symptoms later in life?
  4. 4.What screening or monitoring do you recommend for me as a carrier to stay ahead of potential cognitive or motor changes?
  5. 5.How does X-chromosome inactivation impact why my symptoms might be different from another carrier's?

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 (17)
  1. 1

    A novel splicing mutation in SLC9A6 in a boy with Christianson syndrome.

    Ieda D, Hori I, Nakamura Y, et al.

    Human genome variation 2019; (6()):15 doi:10.1038/s41439-019-0046-x.

    PMID: 30937176
  2. 2

    NHE6 depletion corrects ApoE4-mediated synaptic impairments and reduces amyloid plaque load.

    Pohlkamp T, Xian X, Wong CH, et al.

    eLife 2021; (10()).

    PMID: 34617884
  3. 3

    A potential gain-of-function variant of SLC9A6 leads to endosomal alkalinization and neuronal atrophy associated with Christianson Syndrome.

    Ilie A, Gao AYL, Boucher A, et al.

    Neurobiology of disease 2019; (121()):187-204 doi:10.1016/j.nbd.2018.10.002.

    PMID: 30296617
  4. 4

    A Christianson syndrome-linked deletion mutation (∆(287)ES(288)) in SLC9A6 disrupts recycling endosomal function and elicits neurodegeneration and cell death.

    Ilie A, Gao AY, Reid J, et al.

    Molecular neurodegeneration 2016; (11(1)):63 doi:10.1186/s13024-016-0129-9.

    PMID: 27590723
  5. 5

    Early lysosome defects precede neurodegeneration with amyloid-β and tau aggregation in NHE6-null rat brain.

    Lee Y, Miller MR, Fernandez MA, et al.

    Brain : a journal of neurology 2022; (145(9)):3187-3202 doi:10.1093/brain/awab467.

    PMID: 34928329
  6. 6

    Reversal of ApoE4-induced recycling block as a novel prevention approach for Alzheimer's disease.

    Xian X, Pohlkamp T, Durakoglugil MS, et al.

    eLife 2018; (7()).

    PMID: 30375977
  7. 7

    Amyloid clearance defect in ApoE4 astrocytes is reversed by epigenetic correction of endosomal pH.

    Prasad H, Rao R

    Proceedings of the National Academy of Sciences of the United States of America 2018; (115(28)):E6640-E6649 doi:10.1073/pnas.1801612115.

    PMID: 29946028
  8. 8

    Loss of Christianson Syndrome Na+/H+ Exchanger 6 (NHE6) Causes Abnormal Endosome Maturation and Trafficking Underlying Lysosome Dysfunction in Neurons.

    Pescosolido MF, Ouyang Q, Liu JS, Morrow EM

    The Journal of neuroscience : the official journal of the Society for Neuroscience 2021; (41(44)):9235-9256 doi:10.1523/JNEUROSCI.1244-20.2021.

    PMID: 34526390
  9. 9

    Syndrome of X linked intellectual disability, epilepsy, progressive brain atrophy and large head associated with SLC9A6 mutation.

    Padmanabha H, Saini AG, Sahu JK, Singhi P

    BMJ case reports 2017; (2017()) doi:10.1136/bcr-2017-222050.

    PMID: 29275387
  10. 10

    X-linked Christianson syndrome: heterozygous female Slc9a6 knockout mice develop mosaic neuropathological changes and related behavioral abnormalities.

    Sikora J, Leddy J, Gulinello M, Walkley SU

    Disease models & mechanisms 2016; (9(1)):13-23 doi:10.1242/dmm.022780.

    PMID: 26515654
  11. 11

    The expanding phenotypic spectrum of female SLC9A6 mutation carriers: a case series and review of the literature.

    Sinajon P, Verbaan D, So J

    Human genetics 2016; (135(8)):841-50 doi:10.1007/s00439-016-1675-5.

    PMID: 27142213
  12. 12

    Complex Neurological Phenotype in Female Carriers of NHE6 Mutations.

    Pescosolido MF, Kavanaugh BC, Pochet N, et al.

    Molecular neuropsychiatry 2019; (5(2)):98-108 doi:10.1159/000496341.

    PMID: 31192222
  13. 13

    A Homozygous PTRHD1 Missense Variant (p.Arg122Gln) in an Individual with Intellectual Disability, Generalized Epilepsy, and Juvenile Parkinsonism.

    Gebert J, Brunet T, Wagner M, et al.

    Neuropediatrics 2024; (55(3)):209-212 doi:10.1055/a-2256-0722.

    PMID: 38286424
  14. 14

    A new family with an SLC9A6 mutation expanding the phenotypic spectrum of Christianson syndrome.

    Masurel-Paulet A, Piton A, Chancenotte S, et al.

    American journal of medical genetics. Part A 2016; (170(8)):2103-10 doi:10.1002/ajmg.a.37765.

    PMID: 27256868
  15. 15

    SLC9A6-Linked Parkinson Syndrome in Female Heterozygotes Is Associated With PET-Detectable Tau Pathology.

    Yamamoto Y, Takahata K, Seki M, et al.

    Neurology. Genetics 2025; (11(1)):e200235 doi:10.1212/NXG.0000000000200235.

    PMID: 39810750
  16. 16

    Novel SLC9A6 Variation in Female Carriers With Intellectual Disability and Atypical Parkinsonism.

    Nan H, Kim YJ, Tsuchiya M, et al.

    Neurology. Genetics 2022; (8(1)):e651 doi:10.1212/NXG.0000000000000651.

    PMID: 35198730
  17. 17

    NDPACX: a newly defined X-linked Parkinsonian syndrome associated with SLC9A6 hemizygote mutation.

    Okochi R, Nihei Y, Ito D

    Brain communications 2025; (7(6)):fcaf435 doi:10.1093/braincomms/fcaf435.

    PMID: 41357349

This page explains the genetics of Christianson Syndrome and female carrier health for educational purposes. Always consult a genetic counselor or neurologist regarding your specific carrier risks and symptoms.

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