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What is The expression of the following oncogene is associated with a high incidence of Medullary carcinoma of thyroid - and explain in detail?
RET protooncogene is a growth factor receptor (receptor tyrosine kinase) 
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.
RET is normally expressed in the following cells


Parafollicular C cells of the thyroid
Adrenal medulla


Parathyroid cell precursors. Point mutation in the RET protooncogenes are associated with the following disorders.

 (i) MEN type 2A -


There is point mutation in RET extracellular domain which causes constitutive dimerization and activation leading to:-
Medullary thyroid carcinoma
Adrenal and parathyroid tumours

(ii) MEN type 2B -
Point mutation in the RET cytoplasmic catalytic domain alter the substrate specificity of the tyrosine kinase and leads to:-
Thyroid tumours
Adrenal tumors
(iii) Sporadic Medullary thyroid carcinoma 

Somatic rearrangement of the RET gene

(iv) Hirschsprung disease

This is caused by complete loss of RET function.