confused by allele difference

[fibrodude84]

Genetic genie puts my risk allele at AA for MTHFR C677T yet Promethease has me as TT.

what's going on?

 

[fibrodude84]

How is it that genetic genie puts me as AA for C677T mutation and promethease puts me as TT.

 

[Critterina]

They are just looking at different strands (forward or reverse) of one helix of DNA. If you have A on forward, you have T on reverse. If you have C on forward, you have G on reverse. When 23andMe reports a result like AC, they aren't talking about the two nucleic acids facing each other, positive and negative, on the same strand, but what you got from each of your parents. The A will have a T facing it, and C will have a G facing it.

Also, I understand that 23and Me also reports the positive strands, and puts them in alphabetical order, so it will always be AC, not CA. If you have two results next to each other, AC, AC, you can't tell that the two As are from the same parent.

 

[adreno]

The short answer is that A = T and C = G.

 

[Sea]

The slightly longer answer is that you have to be aware of what is known as orientation. DNA has two strands, one is designated forward or plus and the other reverse or minus. (This has nothing to do with inheriting 2 sets of alleles from your parents) Genetic testing usually only reads one strand because the other is always known from reading one. The alleles are known as complementary. A always pairs with T and C always pairs with G. So, if a test says you have an A allele in the forward orientation you will have a T allele on the reverse and vice versa.

23andme do all their testing on the forward strand. Alleles reported in the research may be forward or reverse. The C677T mutation is reported on the reverse.

So Genetic Genie is reporting your alleles as found on 23andme (in forward orientation), Promethease is reporting as found in the research (in reverse orientation).