hey there -it is genetic and there are certain ppl who are in higher risk. I dont think they routinely screen for this in 12 wk tests. I am in a higher risk cat and I had the tests done to see if I am a carrier b4 i TTC, it involved taking a fair amt of blood and some blood screening tests. Are you in a high risk category for Tay Sachs? If so suggest you chat to your Dr.