<prompt> Medullary carcinoma of thyroid is associated with which of the following gene defect?Ret Proto OncogeneFAP geneRb geneBRCA 1 gene  <response>: Point mutation in RET proto-oncogene play an impoant role in the development of both familial sporadic medullary carcinomas. Medullary carcinoma is a neuroendocrine neoplasm of thyroid derived from the parafollicular cells or C-cells of thyroid. It secretes calcitonin. Tumor arise sporadically in 80 cases, remainder is associated with MEN Type IIA Or IIB syndrome. Most common presentation is mass in the neck. Ref: Genetics in Clinical Practice: New Directions for Nursing and Health Care By Dale Halsey Lea, Page 158 ; Robbins Pathologic Basis of Disease 6th Edition, Page 289, 292, 1145-6 