Moreover, although one case series confirmed that the TSH response is normal or exaggerated in RTHβ but blunted in TSHoma, with the authors specifying a greater than 5-fold TSH increase being a cut-off that differentiates these entities (60), there may be a “gray zone” (3- to 5-fold TSH response to thyrotropin-releasing hormone) compatible with either diagnosis (Gurnell, unpublished observations). This evidence concerns the gene TRH and TSH-secreting pituitary adenoma.