In my case, FT3/FT4 levels are within range (upper limit of FT3) but the pituitary hormone TSH has not been responding to thyroid replacement as I previously posted on.
More investigation reveals that I carry the Thr92AlaD2 variant which predisposes me to a T4-T3 conversion defect (+/+ [C/C] for this SNP) via decreased DIO2 enzyme. This may be why some patients seem to fail T4 monotherapy. There may also be as-yet unknown thyroid hormone resistance selective pituitary variants in my genome that could be why my TSH hasn't suppressed on meds.
Combination (T4/T3) therapy is warranted, but at what ratio? NDT has a 4:1 T4 to T3 ratio and there is some dispute as to whether that is an optimal level for functioning (some say too much T3), as research suggests there is a wide variance in the ratio in humans.
Some people have dropped the dose of NDT and added T4 to adjust the ratio to a tolerable level. Lots of tweaking involved.
Bottom line: In addition to everything else discussed here, it would seem that individual thyroid genetics need to be taken into account as well.
More investigation reveals that I carry the Thr92AlaD2 variant which predisposes me to a T4-T3 conversion defect (+/+ [C/C] for this SNP) via decreased DIO2 enzyme. This may be why some patients seem to fail T4 monotherapy. There may also be as-yet unknown thyroid hormone resistance selective pituitary variants in my genome that could be why my TSH hasn't suppressed on meds.
Combination (T4/T3) therapy is warranted, but at what ratio? NDT has a 4:1 T4 to T3 ratio and there is some dispute as to whether that is an optimal level for functioning (some say too much T3), as research suggests there is a wide variance in the ratio in humans.
Some people have dropped the dose of NDT and added T4 to adjust the ratio to a tolerable level. Lots of tweaking involved.
Bottom line: In addition to everything else discussed here, it would seem that individual thyroid genetics need to be taken into account as well.
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