Brent - you are missing the GSTT1 (Glutathione S-tranferase theta-1). While this isn't uncommon (around 15% of the population is missing this gene), it's still not good. And I'd be curious if you are missing the GSTM1 gene as well (as that would make the glutathione and detoxification propecia theory a lot more interesting).
A genetic test isn't going to tell you if you have low glutathione. However, the methylation panel at Vitamin Diagnostics is quite different and looks at your glutathione, SAMe, and folic acid byproducts directly. However, to order the test online it is $399 dollars but you can find coupon codes - at the top of the site it looks like they are offering 7% off ending today. You can have your doctor order this test for you, but sometimes it's hard finding that willing doctor. Below is a link to order it yourself.
http://www.truehealthlabs.com/methylation-pathway-test-health-diagnosics/
Alternatively, you or your doctor can order a glutathione test through LabCorp (reduced glutathione). It's not nearly as good or comprehensive at the Vitamin Diagnostics test, but it's easier to interpret as you are just looking at glutathione alone. Unfortunately, the test only looks at whole blood and not RBC glutathione, so it may not as accurately determine your glutathione levels. It is $119, but you can use that 7% coupon to save some money.
http://www.truehealthlabs.com/glutathione-test/
If you have insurance, the LabCorp test may be partially or completely covered (depending on your insurance plan) if ordered through your doctor. The Vitamin Diagnostics test is not likely covered by insurance, but you can try submitting for partial reimbursement.
If your levels come back low, and B12/Folate, etc doesn't seem to be making a difference, I highly recommend the supplement S-Acetyl-Glutathione to boost glutathione (as well as intracellular glutathione). Other forms typically don't work. This partcular supplement can be quite expensive though.
Some excellent Whey proteins that boost glutathione levels include Immunocal (very expensive), ImmunoPro Rx, and Vital Whey. I don't recommend picking up Whey at your local store as the brands they typically carry don't work very well to boost glutathione (despite manufacturer's claims). Immunocal has been scientifically proven, and the others I mention have been around for a while with a lot of anectodal evidence of effectiveness.