The TRH receptor gene is a single copy gene containing three exons and two introns and was assigned to the chromosome 8q23. A patient with congenital central hypothyroidism due to the mutations of the thyrotropin-releasing hormone receptor gene has been reported by Collu, et al: in 1997. His sole manifestation was short stature, and his plasma TSH and prolactin levels did not increase in TRH test. He was found to be a compound heterozygote of the mutations of the TRH receptor gene. Expression study using COS1 cells and HEK293 cells revealed that both mutations reduced or abolished the receptor activity.