SIX3

At least 60 mutations in the SIX3 gene have been found to cause nonsyndromic holoprosencephaly. This condition occurs when the brain fails to divide into two hemispheres during early development. SIX3 gene mutations are the third most common cause of nonsyndromic holoprosencephaly. Although mutations in this gene can cause mild to severe forms of the condition, they tend to result in more severe signs and symptoms than mutations in other genes that cause nonsyndromic holoprosencephaly

SIX3 gene mutations change the structure of the SIX3 protein in different ways; however, all of them disrupt the protein's ability to bind with DNA. As a result, the genes involved in normal eye and forebrain development are not properly activated or repressed. Without the correct activity of these genes, the eyes will not form normally and the brain does not separate into two hemispheres. The signs and symptoms of nonsyndromic holoprosencephaly are caused by abnormal development of the brain and face.

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