Connexin 26

Definition: Connexin 26 is a protein that belongs to the connexin family.
- It plays a role in forming gap junctions, specifically gap junction beta 2 (GJB2), which encodes for a gap junction.
- Gap junctions are essential for permitting the transport of ions, molecules, and other substances between cells.
Location:
- Found in the skin.
- Present in the cells lining the airways and the digestive system.
- Specifically located in the cochlea of the inner ear.
Clinical Relevance:
- It is associated with non-syndromic hearing loss, particularly congenital sensorineural hearing loss (SNHL) that can progress over time.

Proper auditory function necessitates the maintenance of appropriate potassium levels in the inner ear.
Roles:
- Connexin 26 is responsible for maintaining a high concentration of potassium ions in the endolymph fluid of the cochlea.
- It facilitates the recycling of potassium from the perilymph back into the endolymph.
Impairments leading to Hearing Loss:
- Mutations in connexin 26 can lead to:
- A buildup of potassium ions
- A deficiency in potassium recycling
- Overall disruptions in potassium homeostasis
Impact on Hearing:
- Any of these disruptions can cause various forms of hearing loss.

Statistical Information:
- Mutations in the Connexin 26 protein account for approximately 20% of all genetic hearing loss and about 10% of all cases of childhood hearing loss in recent studies.
Types of Hearing Loss Associated with Connexin 26:
- DFNB1:
- Pattern of Inheritance: Autosomal recessive.
- Characteristics:
  - Ranges from mild to profound hearing loss.
  - Present before a child learns to speak.
  - The severity does not increase over time.
- Illustration of Genetic Inheritance Structure:
  - Involves affected and carrier parents transmitting the gene variant.
- DFNA3:
- Pattern of Inheritance: Autosomal dominant.
- Characteristics:
  - Hearing loss may be prelingual or postlingual.
  - Severity ranges from mild to profound and worsens over time.
  - Particularly impacts the ability to hear high-frequency sounds.
  - Illustration of Genetic Structure:
  - Shows affected and unaffected offspring from parents.

Current Status:
- There is no definitive cure for Connexin 26 mutations.
Available Treatments:
- Cochlear implants and hearing amplifiers are recommended for individuals with profound hearing loss.
- Assistive learning devices can also aid in communication, especially effective when combined with cochlear implants or hearing amplifiers.

Bart-Pumphrey Syndrome:
- Characterized by leukonychia (whitening of the nails), palmoplantar keratoderma (thickening of the skin on the palms and feet), and hearing loss.
Hystrix-like Ichthyosis with Deafness (HID):
- Involves ichthyosis (dry skin) and almost always results in profound hearing loss.
Keratitis-Ichthyosis-Deafness (KID) Syndrome:
- Involves inflammation of the cornea, ichthyosis (dry skin), and deafness.
Vohwinkel Syndrome:
- Includes loss of hearing and skin abnormalities, such as tight bands of abnormal fibrous tissue around fingers and toes, which can constrict blood flow and may lead to spontaneous amputation.

Green et al. (2002, May 1). Performance of cochlear implant recipients with Gjb2-related deafness. American journal of medical genetics. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3212411/
Kemperman et al. (2002, April). Hearing loss and connexin 26. Journal of the Royal Society of Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1279509/
U.S. National Library of Medicine. (n.d.). Gjb2 gene: Medlineplus genetics. MedlinePlus. https://medlineplus.gov/genetics/gene/gjb2/