Anti GAD - GABA

[Grunch]

I was searching to find out what this GAD thing was and I found this:

In mammals, GAD exists in two isoforms encoded by two different genes - Gad1 and Gad2. These isoforms are GAD67 and GAD65 with molecular weights of 67 and 65 kDa, respectively.[1] GAD1 and GAD2 are expressed in the brain where GABA is used as a neurotransmitter, GAD2 is also expressed in the pancreas.

If the GAD antibodies attack the pancreas shouldn't they attack the brain also or something like that?

I didn't really understand exactly what GAD is and what this antibodies attack.

What about the other 2 antibodies found in type 1. Do they all destroy beta cells? Or if someone has insulin antibodies do they just destroy insulin leaving the cells alone? Not sure if antibodies can attack molecules, I think not.

[Dogen]

You know, I can't answer all of your questions, but I can explain why attacks on the pancreas don't translate into attacks on the GABA receptors in the brain: the blood-brain barrier prevents most molecules from getting into the brain.

The barrier is less a wall and more a combination of special blood vessels and glial cells in the brain. Normally the cells that make up your blood vessels have space between them that allow nutrients, antibodies, etc. to pass in and out on the way to cells. In the brain the cells are jammed close together, making the spaces much smaller and harder for things to pass through - they have to be very small chain molecules (one of the reasons it's difficult to make medicines that work on the brain directly).

Glia are a type of call found in the central nervous system, along with neurons. One type of glial cell, called astrocytes, have arms which connect to neurons on one side and the blood vessels on the other. The exact effect of astrocytes on the blood-brain barrier is being studied, but they appear to control blood flow into the brain.

GAD - glutamic acid decarboxylase - is an enzyme, not an antibody. The antibodies attack the GAD enzyme, destroying it. This has been linked with both IDDM and LADA. Antibodies in general are too large to pass through the small spaces between epithelial cells in the blood vessels of the brain, and thus can't get in to attack your GABA receptors.

[foxl]

I actually found an article on this on wikipedia some time ago.

The two GAD enzymes, named the same because they serve similar purposes, in two different tissues, brain and pancreas. The one in the brain differs by having a molecular weight of 2000 more than the one in the pancreas. Apparently they are quite different. Interestingly, GAD-67 in the brain is also vulnerable to autoimmune attack -- believed to result in bipolar disorder.

Evidently, the antibodies are very specific and do not cross-react between the two enzymes.

[sarahspins]

GAD enzymes are not the bad thing.. the bad thing that is tested for is antibodies against GAD-65

[Dogen]

GAD enzymes are not the bad thing.. the bad thing that is tested for is antibodies against GAD-65

Exactly. We'd be in pretty bad shape without it. GAD is necessary for the creation of the transmitter GABA from glutamate, and without GABA we couldn't live... it's one of the most prolific neurotransmitters in the brain.

Sadly, I don't know anything about what happens on the outside of the blood-brain barrier (like the function of GAD in the pancreas) - not my area of expertise. ;)