Cool Stuff, advances in genetic screening for Down’s Syndrome, Trisomy 18 and 13
For years one of the greatest challenges in Obstetrics has been to design a test for Down’s syndrome, Trisomy 18 and 13 that is accurate as well as non-invasive. Although amniocentesis and CVS remain as the golden standards, they are invasive tests that carry a small risk of pregnancy loss. We have non-invasive tests available, but they carry significant false positive and negative rates. This means that you can have a test indicating something is wrong when it is not, and less likely a screen test that is negative when in fact there may be an issue with the baby. Non-invasive testing for these syndromes has improved throughout the years, and in fact non-invasive first trimester screening is now up to 90% as accurate as invasive tests…but again not where we would like to be.
In medical school and residency, we were always taught that fetal (baby) cells and maternal (mom) cells never mixed…and that in fact, if that ever were to happen it was indicative of a problem. Well we now know for a fact that there is fetal DNA found in maternal plasma, and by extracting this DNA (through a simple blood test) we can test for Down’s syndrome, Trisomy 18 and 13.
The data on the MaterniT21 PLUS test is impressive. For T21 showed it detected 210/212 cases. Trisomy 18 and 13 are less common syndromes, yet the test picked out 59/59 and 11/12 cases respectively.
Downside in my opinion? Well of course being a new test the number of cases is not as large as with some other tests. Also, insurance may not cover it, and out of pocket expense is steep (around $2000). I anticipate these 2 issues will improve with time. Also the test is not as comprehensive as invasive testing in terms of being able to detect other conditions (for example, if muscular dystrophy runs in a family, invasive testing can be done for this condition). I also anticipate this will improve with time.
So, cool stuff…