COL18A1

Knobloch syndrome

At least a dozen mutations in the COL18A1 gene have been identified in people with Knobloch syndrome, a condition characterized by severe vision problems and a skull defect called an occipital encephalocele. Most COL18A1 gene mutations lead to an abnormally short version of the genetic blueprint used to make the alpha 1 subunit of collagen XVIII. There are a few other mutations that replace single protein building blocks (amino acids) in the protein sequence. Although the process is unclear, the COL18A1 gene mutations result in the loss of collagen XVIII. Most COL18A1 gene mutations affect all isoforms of collagen XVIII, but at least one mutation affects only the short isoform. The loss of one or all isoforms of the collagen XVIII protein likely causes the signs and symptoms of Knobloch syndrome. It is unclear whether endostatin is involved in this condition.