None of the 63 patients with TD (41 females and 22 males) had mutations in the studied candidate genes PAX-8, TSH-R, NKX2-5 and HES-1. The candidate genes PAX-8, NKX2-5, TSH-R and HES-1 proposed as those being the most likely cause of TD (8,20-24) were not responsible for the TD confirmed in our cohort. Here, HES1 is linked to thanatophoric dysplasia.