Additional investigation includes ultrasound-guided FNA cytology, but ordinary cytology analysis may be insufficient for diagnosis. Measurement of PTH in the aspirate and the use of immunohistochemical markers like thyroid transcription factor 1 (thyroid-specific) and chromogranin A (parathyroid indicator) may be particularly useful to differentiate a parathyroid adenoma from lymphatic or thyroid tissue in challenging cases [7,11]. The gene discussed is NKX2-1; the disease is parathyroid gland adenoma.