Basically it is a genetic defect found in Nubians and their crosses. Affected goats will not live a long life, maybe 2 years at the max. Carriers only have one defective gene (all genes are found in pairs) and can live a long, normal life. Normal goats do not have either gene affected and when bred to another normal goat all kids will be normal. It is not something you have to test for every year because it is genetic. Once a goat has been tested, whatever they test as that is what they are. As long as you only breed normal to normal you don't have to test any kids and can call them "G6S normal by parentage".
The test can be done using blood or semen through TVMDL. I think it costs about $42 per goat.
It concerns me as well. I was so relieved when we got the test results back and our girls were normal! The lady who owns the buck we used also tested all of hers, and got normal results. I'm wondering if perhaps it's more prevalent in some parts of the country than others. I remember reading somewhere that they thought nearly a quarter of all nubians might have the defect :-( Scary indeed! I'll be very interested to see what more current research shows.
I think the problem with the statistics of it is that a lot of people who have tested don't share the results. Or, you only hear about the goats that do not test normal. Some bloodlines are said to be more likely to carry the defect, mostly the lines that are more tightly bred than lines that are complete out crosses. On the NubainTalk Yahoo group, under the Database there is a section for people to add their animals that are tested and their status. The more people that do this the easier it will be to know if an animal you are looking at is most likely normal, most likely a carrier, or possibly affected.
I think it would be really good if ADGA became more proactive in the awareness of the defect (for new Nubian owners) and also if they could add a section to their genetics look up where you can have TVMDL report your testing to ADGA and they can list what the goat is on the genetics site. Kind of like how they put if an animal is DNA'd, collected, has been LA'd or has a production eval. They could even list animals as normal that are normal by parentage. I also think eventually they should require that all bucks are either normal by parentage, or test normal before they can be registered. This would be expensive, but it would really help to eradicate the defect. They could eventually include does in this, but since bucks produce more kids than does that would be a good start. This would be similar to what the AQHA has done with HYPP in Quarter Horses. They passed a new rule that all Quarter Horses that are descendents of Impressive must be tested for HYPP before being registered. Any that test as affected (H/H) can not be registered since those animals will pass on the defective gene to every single foal they produce.