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JPH3 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

JPH3 gene

The JPH3 gene provides instructions for making the junctophilin-3 protein, which is essential for signaling within and between nerve cells in the brain.

Normal Function

The JPH3 gene provides instructions for making a protein called junctophilin-3, which is found primarily in the brain. This protein plays a role in the formation of the junctional membrane complex, a structure that acts as a link between the inside and outside of the cell. It connects channels on the surface of the endoplasmic reticulum with channels at the cell surface. This complex is involved in transmitting signals after the release of charged calcium atoms (calcium ions), facilitating signaling within and between neurons.

One region of the JPH3 gene contains a CAG/CTG trinucleotide repeat, a segment of DNA building blocks that normally repeats 6 to 28 times.

Health Conditions Related to Genetic Changes

Huntington's disease-like 2

A specific mutation in the JPH3 gene causes Huntington's disease-like 2 (HDL2). The signs and symptoms of HDL2 resemble Huntington's disease and include:

  • Uncontrolled movements
  • Emotional problems
  • Loss of thinking ability

The variant associated with HDL2 increases the size of the CAG/CTG trinucleotide repeat. People with this condition have 40 or more repeats. Those with 29 to 39 repeats may or may not develop symptoms.

Researchers believe the altered JPH3 gene produces an altered version of messenger RNA (mRNA). This altered mRNA cannot produce a functional junctophilin-3 protein and forms clumps inside neurons that interfere with normal cell function. The lack of normal protein combined with the dysfunction and death of neurons in certain brain areas causes the symptoms of HDL2.

Other Names for This Gene

  • JP-3
  • JP3
  • JPH3_HUMAN
  • junctophilin type 3
  • junctophilin-3

Frequently Asked Questions

Diagnosis is confirmed by PCR‑based sizing of the CAG/CTG repeat in the JPH3 gene performed in a CLIA‑certified laboratory. Once a pathogenic expansion is identified, predictive testing can be offered to at‑risk adult relatives after thorough genetic counseling, because the result has implications for future planning and reproductive decisions.
Both disorders share similar movement (chorea, dystonia), psychiatric, and cognitive symptoms, but HDL2 is caused by an expanded CAG/CTG repeat in the JPH3 gene, whereas Huntington’s disease is due to a CAG repeat expansion in the HTT gene. HDL2 is much more common in individuals of African ancestry and may have a slightly later average onset (mid‑40s) compared with Huntington’s (30s‑40s). Genetic testing distinguishes the two conditions.
repeat length of 35 falls into the “intermediate” range (29‑39 repeats). Individuals in this range may remain asymptomatic or develop very mild symptoms later in life. No disease‑modifying therapy exists, but regular neurologic assessments, counseling about potential symptom onset, and lifestyle measures (exercise, cognitive stimulation) are recommended.
Currently, treatment is symptomatic: antichorea medications (e.g., tetrabenazine), psychiatric drugs for mood or psychosis, and cognitive therapies. Clinical trials are exploring antisense oligonucleotides and gene‑silencing approaches targeting the mutant JPH3 transcript, but these are experimental and not yet widely available.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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