Collagen II & III, Ehlers-Danlos syndrome

Type II collagen

• Notably found in cartilage, nucleus pulposus, and vitreous body

Reticulin, early wound healing, and uterus are type III collagen.

Bone and late wound healing are type I collagen.

Stickler syndrome

• Approximately 75% of Stickler syndrome cases are due to mutations in COL2A1.
• Most important feature is deafness.
• Since type II collagen is an essential component of vitreous body, these patients also frequently have ocular problems.

Type III collagen

• Found in granulation tissue (early wound healing)
• Also in blood vessels, uterus, and fetal tissue

Collagen III is the main component of reticulin

• Reticular cells secrete reticulin, a connective tissue protein composed of type III collagen
• Found predominantly in liver and bone marrow

Late wound healing is type I collagen.

Vitreous body is type II collagen.

Glomerular basement membrane is type IV collagen.

Although keloid scars have ↑↑ production of both types I and III collagen, USMLE questions occasionally assess keloid scars = ↑ type III collagen.

Collagen IV disorders include Alport syndrome (mutation in collagen IV) and Goodpasture syndrome (antibodies against type IV collagen).

Collagen XVII autoantibodies are seen in bullous pemphigoid. Collagen XVII is in hemidesmosomes.

Ehlers-Danlos syndrome (EDS)

• Hyperextensible skin, joint hypermobility, and joint subluxations are common in EDS.
• ↑ risk of aortic aneurysm + rupture
• Mitral valve prolapse and aortic regurgitation are the two murmurs you should think about if you get a stethoscope question.
• ↑ risk of circle of Willis berry (saccular) aneurysms, leading to subarachnoid hemorrhage (exceedingly HY)

Circle of Willis aneurysms lead to subarachnoid hemorrhage and are almost always in the anterior communicating or posterior communicating arteries (i.e., ACom and PCom), not the anterior cerebral or posterior cerebral arteries (i.e., not ACA, PCA).