Neonatal Thyrotoxicosis: Report of Three Cases Involving Four Infants

SUMMARY Four cases of neonatal hyperthyroidism are described. The condition was shown to be transient and associated with thyrotoxicosis in the mothers of the patients. Assays for long‐acting thyroid stimulator (L.A.T.S.) were performed on plasma samples from the neonatal hyperthyroid subjects and their mothers. It was shown that L.A.T.S. was present in all the patients and the mothers, and that it disappeared in the neonate after a few weeks. It is concluded that L.A.T.S. is the pathogenetic agent responsible for the hyperthyroidism by passage across the placenta from the maternal circulation. This finding is consistent with recent chemical evidence that L.A.T.S. is a 7S gamma globulin.