1 The Quebec Network of Genetic Medicine, Centre Hospitalier Université Laval, 2705, boulevard Laurier Ste-Foy (Qc) Canada, G1V 4G2
2 Service de Génétique et Maladies, Héréditaires du Métabolisme, Centre Hospitalo Universitaire, Hôpital C Husiez, Place Verdun, Lille, France
To the Editor.
We would like to respond to the allegation of Fisher et al1 that 10% to 15% of our treated hypothyroid children did not attain a normal development because they were undertreated at the time of therapy initiation. First, the Quebec cohort of patients do not include those who were treated with triiodothyronine (T3) because this clinical trial was accomplished early in our program (1974 to 1975). Thus goes the argument for the deleterious effect to T3 treatment vs thyroxine (T4) (ie, the majority of the T3 in brain originates from T4 to T3 conversion.