Pituitary-thyroid feedback hypersensitivity as a novel cause of hypothyroidism in children.

Recognition and treatment of childhood hypothyroidism is essential to prevent serious developmental abnormalities, and neonatal screening based on detection of raised thyrotropin concentrations is routine. We investigated an adolescent who had developmental retardation because of an undiagnosed and novel cause of childhood hypothyroidism associated with normal circulating thyrotropin concentrations. Dynamic testing showed a hypersensitive pituitary-thyroid feedback axis with no evidence of other pituitary or hypothalamic disease, and sequence analysis of four candidate causative genes was negative. A high index of suspicion is required to diagnose and treat this disorder to prevent the consequences of long-term hypothyroidism on development.