Decreased total, normal free (unbound) = Thyroid hormone-binding globulin deficiency
why can't "organification defect in T3 and T4" be the answer?
This is apparently congenital thyroid binding globulin deficiency
"Thyroxine-binding globulin deficiency — Thyroxine-binding globulin (TBG) deficiency is characterized by low serum total T4 but normal free T4 and TSH; the diagnosis is confirmed by measuring TBG concentrations. These infants have normal thyroid function and do not require treatment." - uptodate
*can't find in FA, maybe it is in there somewhere?