INCIDENCE OF TRANSIENT CONGENITAL HYPOTHYROIDISM DUE TO MATERNAL THYROTROPIN RECEPTOR-BLOCKING ANTIBODIES IN OVER ONE MILLION BABIES

To determine the incidence of transient congenital hypothyroidism due to TSH receptor-blocking antibodies, we screened dried blood specimens obtained from 788 neonates identified as having possible congenital h ypothyroidism (from a total population of 1,614,166 babies) and 121 co ntrols. ARRA was used. The potency of blood spot TSH binding inhibitor y activity was compared with the severity of congenital hypothyroidism to assess the possible etiological relationship. Maternal serum was s tudied to confirm the presence of blocking antibodies by both RRA and bioassay. Blood spots obtained from 9 infants contained potent TSH rec eptor-blocking activity. Samples from 2 additional babies, studied bec ause of clinical suspicion of the disease, were also positive. Long te rm outcome was known in of the 11 babies, and all had transient diseas e. Neonates with TSH receptor-blocking activity greater than 132 U/L h ad a significantly lower T-4 level (P < 0.05) and higher TSH (P < 0.00 5) than those in whom TSH binding-inhibitory activity was less than 13 2 U/L. All 9 mothers had autoimmune thyroid disease, and 3 had more th an 1 affected child. Potent blocking activity was present in 7 materna l serum samples as long as 7 yr after the births of their affected bab ies. We conclude that measurement of TSH binding-inhibitory activity i n dried neonatal blood specimens is a simple and effective method to p redict the occurrence of transient congenital hypothyroidism. The inci dence of this disorder in North America is 1 in 180,000 normal infants , or approximately 2% of babies with congenital hypothyroidism.