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CHN1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CHN1 gene

The CHN1 gene provides instructions for making the N-chimaerin protein, which is essential for the development of the nervous system and specific cranial nerves.

Normal Function

The CHN1 gene provides instructions for making a protein called N-chimaerin. This protein plays an important role in the early development of the nervous system. In particular, it helps regulate complex signaling pathways during the development of nerve cells (neurons). N-chimaerin helps guide the growth of axons and dendrites, which are specialized extensions of neurons that transmit and receive nerve impulses throughout the nervous system.

N-chimaerin appears to be critical for the formation of certain nerves in the head and face, known as cranial nerves. The protein is necessary for the development and function of cranial nerve VI and, to a lesser extent, cranial nerve III. These two nerves emerge from the brain and control several of the muscles that surround the eyes (extraocular muscles). The extraocular muscles direct eye movement and determine the position of the eyes.

Health Conditions Related to Genetic Changes

Isolated Duane retraction syndrome

Variants (also called mutations) in the CHN1 gene have been identified in families with isolated Duane retraction syndrome. This condition prevents outward movement of the eye (toward the ear), and in some cases it may also limit inward eye movement (toward the nose). This condition is referred to as "isolated" because it causes eye problems with no other signs or symptoms.

CHN1 gene variants alter the structure and function of N-chimaerin in the developing nervous system. These variants are called "gain of function" variants because they appear to enhance the activity of the protein. This can disrupt the normal growth of neurons in certain parts of the brain. As a result, cranial nerves VI and III do not develop normally and cannot effectively control the extraocular muscles. Impaired function of these muscles leads to the characteristic features of isolated Duane retraction syndrome.

Other Names for This Gene

  • A-chimaerin
  • alpha-chimerin
  • CHIN_HUMAN
  • CHN
  • N-chimaerin
  • n-chimerin
  • RHOGAP2

Frequently Asked Questions

Treatment focuses on preserving binocular vision, preventing amblyopia (lazy eye), and eliminating compensatory head tilts. Mild cases may only require regular monitoring by a pediatric ophthalmologist. If a significant head turn is present, or if misaligned eyes cause double vision in primary gaze, corrective extraocular muscle surgery (such as muscle recession or transposition) can reposition the muscles to balance eye alignment and straighten head posture.
CHN1 mutations are typically gain-of-function variants that make the encoded N-chimaerin protein hyperactive. N-chimaerin normally halts axon growth at the proper developmental window. When it is hyperactive, the abducens nerve (cranial nerve VI) fails to develop properly or stops growing before reaching the lateral rectus muscle of the eye. Branches from the oculomotor nerve (cranial nerve III) then aberrantly innervate the lateral rectus, causing the eyeball to retract backward into the orbit when looking inward.
Isolated Duane retraction syndrome caused by CHN1 variants is inherited in an autosomal dominant pattern. This means a single altered copy of the gene in each cell is sufficient to cause the condition. An affected parent has a 50 percent chance of passing the variant to each child. However, the condition exhibits variable penetrance and expressivity, meaning family members carrying the same mutation may have differing degrees of eye movement limitation or even appear clinically unaffected.
Key signs include an inability to turn one or both eyes outward toward the ear (abduction deficit), narrowing of the eye opening (palpebral fissure) along with backward pulling of the eye when looking inward (adduction), and an involuntary upward or downward eye drift on inward gaze. Children often adopt a compensatory head turn to maintain binocular single vision and avoid double vision (diplopia).
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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