Several mutations in the COL1A1 gene are responsible for the ‘Arthrochalasia Type’ of Ehlers-Danlos Syndrome (EDS). These genetic changes lead to the production of defective pro-α1 (I) chain with missing a critical segment. The absence of this segment interferes with the assembly and structure of type I collagen molecules and the processing of these molecules into collagen fibrils.
Tissues that are rich in type I collagen — such as the skin, bones, and tendons are most affected by this change.
A mutation in the COL1A1 gene has also been shown to cause the ‘Classic Type’ of Ehlers-Danlos syndrome. This mutation changes one of the amino acids used to build the pro-α1 (I) chain. Specifically, this genetic change replaces the amino acid ‘arginine’ with the amino acid ‘cysteine’ at position 134. The altered protein interferes with other collagen-building proteins, disrupting the structure of type I collagen fibrils and trapping collagen in the cell. But researchers believe that this COL1A1 mutation only rarely underlies the signs and symptoms of classic Ehlers-Danlos syndrome.