COL4A1 and achalasia-alacrima syndrome: Collagen IV has been identified as a protective agent against the development of abdominal aortic aneurysms (AAAs) by Steffensen et al., who developed a murine model showing knockout mice with a deficiency in COL4A1/2 correlated with AAA progression, in addition to a Danish human cohort demonstrating that increasing collagen IV degradation product levels correlate with the progression of AAAs [25].