Inborn errors of iodine metabolism.

Garrod,4 in I908, introduced the term ' inborn errors of metabolism' to describe biochemical abnormalities which were genetically determined, present throughout life and relatively non-lethal. He suggested that it would ultimately be possible to attribute the biochemical aberrations found in these conditions to specific enzyme defects. Recent work5 has confirmed the validity of Garrod's ideas to a remarkable extent, and has extended them to a considerably greater range of conditions than the four originally considered by him (albinism, alcaptanuria, cystinuria and pentosuria). One of the most fruitful of these extensions has been to certain types of thyroid disease.16 These defects (collectively known as ' sporadic goitrous cretinism ') conform extremely well to Garrod's definition, for they are hereditary, congenital, persist through life, and are relatively non-lethal. The fact that they are accompanied by gross structural changes (goitre, cretinism) does not by any means exclude them from the group defined by Garrod, for these structural changes are merely anatomical reflections of the underlying biochemical defect. Although existing evidence cannot be regarded as conclusive, most authors are agreed that the biochemical defects consist essentially of absence or inadequacy of one or more of the enzyme systems which collectively enable the thyroid gland to produce its hormones (thyroxine and triiodothyronine).