Gender problems in cornea transplants

Organ donations are noble gestures. Instead of wasting the organs after the brain death of a person, if his or her organs are donated, some patients who are in need of them can use them. That is the reason why I donated my mother's eyes - I couldn't do that when my father died because the cause of his death is septicemia. 

Cornea (picture source: centre for eye sight )

I am so glad corneas of my mother are still living and working and making two blind persons see this world again and work without any assistance. I want to donate my organs, especially my eyes too. 

Therefore, I read all the research coming from the donation turf with interest. A recent paper caught my attention. Why? 

Because till now the medical fraternity thought that  corneas are gender neutral and recent research shows that is not the case always. 

In transplanting complex organs (but not small tissue grafts), the larger blood vessels of the organ are surgically connected to those of the recipient. Connective tissue cells gradually link together the graft and host tissue. The main obstacle to successful transplantation is the rejection of foreign tissue by the host . Transplanted tissue from another individual (i.e., homograft, or allograft, tissue) contains antigens that stimulate an immune response from the host's lymphocytes. Homograft tissue is normally destroyed within a few weeks; the rejection mechanism is similar to that by which the body resists infection. The greater the number of foreign antigens on the donor organ, the more rapid and severe the rejection reactions.

The cornea is the front part of the eye that gives it its curvature and two thirds of its refracting power. Injury, infection or disease can damage the cornea, limiting vision and potentially leading to blindness. In such cases transplants can bring back sight to these people.

Corneal transplants have a high success rate largely because there are so few blood vessels in the cornea that corneal antigens may never enter the host's system to stimulate an immune reaction. So anybody can get corneas from any person.  Right? Uhhh, no, not really!

It seems gender matters when it comes to cornea transplants — at least for women in some cases.

A new study in the U.K. has found that female patients do better if they get their new corneas from other women rather than men! The study of more than 18,000 patients in the U.K. found that female transplant recipients were more likely to have successful transplants if they got a woman’s cornea—but there was no gender difference in failure rates for men receiving women’s tissue. With one corneal disease, called Fuchs endothelial dystrophy, women’s transplants were 40 percent less likely to fail if they received another woman’s cornea instead of a man’s, according to the study published  recently in the American Journal of Transplantation.

The researchers suspect the problem is the H-Y antigen, found on the surface of most cells in a man’s body. The gene that encodes H-Y is on the Y chromosome, so women don’t have it. If their immune systems haven’t encountered the H-Y antigen before, women’s bodies may take it as a sign of a foreign invader and attack the transplant, says study coauthor Stephen Kaye, an ophthalmologist at the Royal Liverpool University Hospital in England. H-Y appears to be more of an issue in the cornea than in other organs.

Researchers, however,  are speculating that this need  not be the true with regard to cornea transplants in other countries because the results could be at least partly due to the fact that donors and patients in the U.K. are matched differently than they are in many other parts of the world.

In the U.K. and Europe, where the populations are relatively homogeneous, donors are often matched according to their human leukocyte antigen (HLA) status. HLA proteins help the body identify which cells belong to it and which are foreign. In the U.S. and Australia HLA matching is not done for corneal transplants—because with their more diverse populations it is not considered to make a significant difference. It is possible that gender only matters for cornea transplants in populations where HLA matching has already been done. In other words, an effect of gender might be expected in well HLA-matched pairs, but not in unmatched pairs. The vast majority of patients in this study were not HLA matched. The gender effect was strongest in patients with certain diseases, such as Fuchs endothelial dystrophy—but less evident in other higher-risk conditions. Patients in the U.K. may have different outcomes from those in other countries because of procedural differences.

The amount of tissue transplanted may also make a difference in rejection rates. Most patients only need to replace the crucial back layer of cells, which account for 10 to 20 percent of the cornea. Transplanting fewer cells may mean a lower chance of rejection—and gender would therefore matter less to the outcome.

This research is still at the preliminary stage  and more work needs to be done to come to firm conclusions and using the knowledge for cornea transplants.