Monozygotic Twin Boys Concordant for Congenital Hypothyroidism: Two Cases

Twins or multi-pregnancy is reported to have much higher risks for congenital hypothyroidism (CH), and most twins are discordant for CH. Monozygotic twins concordant for CH are rare. We describe two monozygotic twin-pairs concordant for CH. Filter paper screening was performed and a blood spot thyroid- stimulating hormone (TSH) value higher than 9 mU/L led to recall for whole blood evaluation. One of each twin pairs was normal at initial neonatal screening, while delayed TSH elevation and low T4 level were found in the diagnosis testing 2-3 weeks later. The L-thyroxine (L-T4) replacement therapy was initiated when the diagnosis was made. The initial dosage of L-T4 for the twins was 8 µg/d/kg. After 16 months of follow-up, thyroid function and development were all normal for the twin pairs.