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

SHH gene

The SHH gene provides instructions for the Sonic Hedgehog protein, a critical signaling molecule that guides the development of the brain, spinal cord, eyes, and limbs.

Normal Function

The SHH gene provides instructions for making a protein called Sonic Hedgehog. This protein functions as a chemical signal that is essential for embryonic development. Sonic Hedgehog plays a role in cell growth, cell specialization, and the normal shaping (patterning) of the body. This protein is important for development of the brain and spinal cord (central nervous system), eyes, limbs, and many other parts of the body.

Sonic Hedgehog is necessary for the development of the front part of the brain (forebrain). This signaling protein helps establish the line that separates the right and left sides of the forebrain (the midline). Specifically, Sonic Hedgehog establishes the midline for the underside (ventral surface) of the forebrain. Sonic Hedgehog and other signaling proteins are needed to form the right and left halves (hemispheres) of the brain.

Sonic Hedgehog also has an important role in the formation of the eyes. During early development, the cells that develop into the eyes form a single structure called the eye field. This structure is located in the center of the developing face. Sonic hedgehog signaling causes the eye field to separate into two distinct eyes.

Health Conditions Related to Genetic Changes

Nonsyndromic holoprosencephaly

More than 100 mutations in the SHH gene have been found to cause nonsyndromic holoprosencephaly. This condition occurs when the brain fails to divide into two hemispheres during early development. SHH gene mutations are the most common cause of nonsyndromic holoprosencephaly. These mutations reduce or eliminate the activity of Sonic Hedgehog. Without the correct activity of this protein, the eyes will not form normally and the brain does not separate into two hemispheres.

Other Names for This Gene

  • HPE3
  • SHH_HUMAN
  • sonic hedgehog homolog (Drosophila)
  • sonic hedgehog protein
  • sonic hedgehog protein preproprotein

Frequently Asked Questions

SHH-related holoprosencephaly can be inherited in an autosomal dominant pattern. If a parent carries the mutation, there's a 50% chance for each child to inherit it. However, penetrance can be incomplete, meaning not everyone with the mutation develops the condition. Genetic counseling is essential to understand recurrence risks and testing options for future pregnancies.
The Sonic Hedgehog protein is crucial for establishing the midline of the forebrain and ensuring it divides into two hemispheres. It also guides the separation of the single eye field into two distinct eyes. If the SHH gene is not working correctly, the brain may fail to divide (holoprosencephaly), and severe facial and eye abnormalities can occur.
SHH gene mutations are the most common genetic cause of nonsyndromic holoprosencephaly. While severity varies, SHH mutations often lead to a spectrum of features including facial anomalies like cyclopia, proboscis, or cleft lip/palate, alongside varying degrees of brain malformation. The specific presentation can differ from holoprosencephaly caused by other genes.
Management is highly individualized and focuses on supportive care. This often includes neurological monitoring for seizures, developmental therapies (physical, occupational, speech), nutritional support, and surgical interventions for associated conditions like hydrocephalus or severe facial clefts. A multidisciplinary team approach is crucial.
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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