Does anyone understand enzymes in genetic testing?

[Cindy1802]

This might be a long shot but hoping to find someone who understands the role of enzymes in genetic testing on DNA.

I'm currently undergoing some testing for a genetic disease. The standard process is that they run 2 tests, using 2 different enzymes. However I got a call yesterday saying once they extracted the DNA from the sample I gave, there wasn't actually enough DNA in it to run 2 tests - so they would only be able to run one, meaning they wouldn't be able to give complete confidence in the result. They are culturing more DNA to be able to run the second test, but that is likely to mean the 2nd result won't be for another few weeks.

So what I'm trying to understand is, how accurate will the one test be? Does using 2 different enzymes show 2 different things, or is it more of a sense check? I only got the phone call last thing yesterday so now have to wait til Monday to ask more questions!

Note, I am aware that if they find the genetic disease with 1 enzyme that is pretty much confirmed, it's more that if they DONT find it, what are the chances of a different enzyme finding it?

Surely you can ask the body carrying out the tests?

I think anyone answering this question on mumsnet would be reckless to do so

@Jazzappledelish I can't ask til Monday. And I'm not actually expecting anyone to tell me how accurate the test will be, I'm asking if anyone can explain the role of enzymes to me. I'm trying to understand the process here rather than someone tell me re. the result.

What are they testing for?

I'd potentially be able to explain if you were happy to share what they're testing for, but understand if you're not comfortable with that.

Was it bloods you gave or tissue sample? If bloods can't you just give more to speed up the process?

Same as above. Without knowing what disease/ gene it is for, it would be impossible to answer.

Culturing a sample for additional DNA (genetic test) if there is insufficient to meet quality standards, is a routine practise. It does tend to take a couple of weeks.

Enzyme testing is a chemical test. It looks for too much or too little of a particular enzyme. Depending on the suspected condition results may be enough to make a diagnosis. In other circumstances , it may identity the chemical pathway involved, but not the exact condition. In these circumstances enzyme results may need to be combined with a DNA test ( a genetic test) to confirm the diagnosis.

It sounds like your situation is scientifically complex. Call your clinicians on Monday and ask them to explain again.

It is complex. We're prenatal testing for FSHD. I'm definitely going to speak to my geneticist on Monday, but as you can imagine my mind is in overdrive and wondered if I could find anyone on here who understood it!

Ok. So they are looking for a section of DNA which is shorter than it should be. As this is what causes the fshd.

The first test should find it if it is there but there are a small number of people who have an extremely similar bit of DNa on a different chromosome, which can sometimes show up as a sort of false positive. Sometimes they are different enough that they can be told apart on the first test and sometimes they need the second test to check where the shorter bit of DNa is from. The way they check the differences between the DNA from the different bits is by using an enzyme which recognises the DNA sequence and only cuts at certain places.

Hope that helps?

@Geneticsbunny that's helpful thank you. What about a negative result if they don't find it with the first enzyme - does the second test/second enzyme look for something different, or is it more of a sense check?

We will absolutely wait for the second test to confirm everything, but just wondering how confident we can be either way with the first enzyme test...

If it is the same testing as the one I found, which is likely, then a negative on the first test is a true negative. The second test just helps to eliminate false positives. Definitely check with the genetic counsellors though.

Will do. Thanks @Geneticsbunny, really helpful while my mind is in overdrive!