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PHOX2A gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

PHOX2A gene

The PHOX2A gene provides instructions for a protein that is essential for the development of specific cranial nerves and the muscles that control eye movement.

Normal Function

The PHOX2A gene provides instructions for making a protein that is found in the nervous system. This protein acts early in development to help promote the formation of nerve cells (neurons) and regulate the process by which the neurons mature to carry out specific functions (differentiation).

The protein plays a critical role in the development of the autonomic nervous system, which controls involuntary body functions such as breathing, blood pressure, heart rate, and digestion. The PHOX2A protein is also involved in the formation of certain nerves in the head and face (cranial nerves). Specifically, it appears to be critical for the development and function of cranial nerves III and IV, which emerge from the brain and control many of the muscles that surround the eyes (extraocular muscles). These muscles direct eye movement and determine the position of the eyes.

Health Conditions Related to Genetic Changes

Congenital fibrosis of the extraocular muscles

At least four mutations in the PHOX2A gene can cause congenital fibrosis of the extraocular muscles (CFEOM). These mutations are responsible for a form of the disorder called CFEOM2, which has been identified in several families of Middle Eastern descent.

Most of the mutations that cause CFEOM2 result in the production of an abnormally short, nonfunctional version of the PHOX2A protein. A lack of this protein prevents the normal development of several cranial nerves and the extraocular muscles they control. Abnormal development and function of these muscles leads to the characteristic features of the disorder, including restricted eye movement and related problems with vision. Although the PHOX2A protein plays an important role in autonomic nervous system development, PHOX2A mutations do not seem to affect the function of this part of the nervous system.

Other Names for This Gene

  • aristaless homeobox homolog
  • aristaless homeobox protein homolog
  • ARIX
  • arix homeodomain protein
  • ARIX1 homeodomain protein
  • CFEOM2
  • FEOM2
  • MGC52227
  • NCAM2
  • paired like homeobox 2a
  • paired mesoderm homeobox protein 2A
  • paired-like homeobox 2a
  • PHX2A_HUMAN
  • PMX2A

Frequently Asked Questions

Most patients maintain stable eye function after appropriate surgery or vision therapy, but they may need ongoing ophthalmologic care to monitor for changes. The disorder does not typically affect other organ systems, so overall health can be normal. Early intervention and regular follow‑up help optimize quality of life.
Individuals with a PHOX2A mutation often have limited upward or outward eye movements, leading to double vision or a characteristic “downward” gaze. They may also have drooping eyelids or difficulty tracking moving objects. If a child or adult shows persistent eye misalignment or double vision, a neuro‑ophthalmologist can evaluate for congenital fibrosis of the extraocular muscles.
The diagnosis is confirmed by sequencing the PHOX2A gene from a blood sample. In addition, imaging studies such as MRI of the brain and orbits can show abnormal nerve or muscle structure. A comprehensive eye exam, including a cover test and measurement of eye movement, is also essential to assess functional impact.
Management is usually multidisciplinary. Surgical procedures can reposition extraocular muscles to improve alignment, while prism glasses or patching may help reduce double vision. In some cases, botulinum toxin injections can temporarily relax overactive muscles. Because the underlying nerve development is fixed, treatment focuses on improving visual function and comfort rather than curing the genetic defect.
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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