Genetics and Genetic Testing
Chat Highlights
September 17, 2003

Norma Devine, Editor

On Wednesday, September 17, 2003, Dr. George Spaeth, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Genetics and Genetic Testing."

Moderator:  Welcome back, Dr. Spaeth.  Our topic tonight is "Genetics and Genetic Testing."  

Dr. George Spaeth:  Sorry to be late.  I had a computer problem.   

Moderator:  Some patients in here have also being having computer problems.  I think we're ready to start now, if you are.

Dr. George Spaeth:  I'm ready.  Any questions?

P:  Yes.  What's new in genetics? 

Dr. George Spaeth:  Genetic causes for glaucoma have been known for years, but only by observing families.  Now actual molecular biologic defects are being identified, and some are able to be changed.  

Moderator:  Can you give us an example?

Dr. George Spaeth:  Yes.  The glaucoma that is most common in young adults is caused by an abnormality in chromosome 1.  If a person has that abnormality, he or she is going to get glaucoma.  Thus, if you test a person at risk for glaucoma because he or she is related, you can rule in or rule out the likelihood that the person will get glaucoma.

P:  Can you predict age, type, and severity?

Dr. George Spaeth:  Yes.  One defect, mt.1, is associated with severity, but only in young people.  When old people have that defect, it doesn't seem to matter, but when a young person with POAG (primary open-angle glaucoma) has the mt.l defect, he or he has an 80% chance of getting markedly worse.

P:  Should patients receive counseling before genetic testing?  

Dr. George Spaeth:  It is essential to counsel patients, because most think that a gene test is like a pregnancy test.  Usually, however, the test only gives likelihoods, and usually the likelihoods are hard to pin down.

P:  How is genetic testing conducted? 

Dr. George Spaeth:  The usual way is to take a blood specimen, but swabbing the inside of the cheek also works well for certain genes.  Open-angle glaucoma in adults is strongly familial, but not strongly expressed.  If one parent has glaucoma, you are five times as likely to get glaucoma yourself.

P:  Does genetic testing test for all types of diseases or does it test just for one disease like glaucoma?

Dr. George Spaeth:  When there are associated findings, sometimes the gene defects are very predictive. 

P:  What kind of associated findings would that be?

Dr. George Spaeth:  If you have abnormal nails, kneecaps, and pigment in the eye, you will almost certainly get glaucoma.  

P:  How might gene research help glaucoma patients?  

Dr. George Spaeth:  The real excitement now lies in learning how to modify the way the genes work. There are genes in the trabecular meshwork that help regulate the outflow of aqueous. These can be made to work better -- up-regulate or, worse, down- regulate.  Certain drugs, however, such as  cortisone products, cause a change in the way one of the genes, MYOC/TIGR, works, and causes the pressure to rise.  That only happens in people with that particular gene.

P:  What types of glaucoma are hereditary?

Dr. George Spaeth:  Almost all the types that occur without a specific cause are at least partially hereditary. Thus POAG,  juvenile POAG,  infantile glaucoma, and pigmentary glaucoma  are all partially hereditary.  The type of glaucoma that comes from a blow to the eye, or an inflammation, or secondary to surgery, is not hereditary.

P:  Are there known genetic markers for all types of glaucoma?

Dr. George Spaeth:  No.  The so-called "secondary" glaucomas don't have genetic markers.

P:  Is there only one kind of POAG? 

Dr. George Spaeth:  What is becoming apparent is that some types of glaucoma that were thought to be one type, such as POAG,  are now being found to be associated with different genes.  That means there are many different types of POAG. 

P:  Dr. Spaeth, what is a phenotype? 

Dr. George Spaeth:  The way a person looks is called the phenotype.  The genes a person has is called the genotype.

[Editor's note:  Computer problems persisted throughout the chat.  Dr. Spaeth kept trying, but finally had to give up.] 

P:  Such a disappointment tonight.  The topic is so interesting.

P:  Too bad, this would have been one of the more interesting chats, but we're spoiled because it goes so well, week after week.  Glitches are going to happen once in a while.

Moderator:  Dr. Spaeth and I appreciated your patience and understanding.  Perhaps we can continue with this topic another time.

P:  Anyone in hurricane Isabel's path, take care. 

End of highlights for September 17, 2003.

On September 24, Dr. Werner discussed "Pain and the Glaucoma Patient" in the Chat room. Click here for highlights of that meeting.

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