Which of the following gene defect is associated with development of medullary carcinoma of thy roid-

Ans. is 'a' i.e., RET proto oncogene o RET protooncogene is a growth factor receptor (receptor tyrosine kinase)o The RET protein is a receptor for the glial cell lined derived neurotrophic factor and structurally related proteins that promote cell survival during neural development,o RET is normally expressed in the following cells# Parafollicular C cells of the thyroid# Adrenal medulla# Parathyroid cell precursors.o Point mutation in the RET protooncogenes are associated with the following disorders.MEN type 2 A -o There is point mutation in RET extracellular domain which causes constitutive dimerization and activation leading to:-Medullary thyroid carcinomaAdrenal and parathyroid tumoursMEN type2B-o Point mutation in the RET cytoplasmic catalytic domain alter the substrate specificity of the tyrosine kinase and leads to:-Thyroid tumoursAdrenal tumorsSporadic Medullary' thvroid carcinomao Somatic rearrangement of the RET geneHirschsprung diseaseo This is caused by complete loss of RET function.