Genetic analysis spots hereditary cases of medullary thyroid cancer

A significant percentage of medullary thyroid cancer (MTC) cases are hereditary, caused by a genetic mutation that researchers recently sought while examining the DNA of Middle Eastern adults with apparently sporadic cases of the disease.

Among 55 Iranian patients who had undergone thyroidectomies for what was initially diagnosed as non-hereditary MTC, nine tested positive for genetic mutations that increase the risk of the disorder, according to a study published in the journal Thyroid.

While the majority of MTC cases are sporadic - meaning random or unrelated to genetic predisposition - between 20 and 25 percent are connected to changes in the Rearranged during Transfection (RET) proto-oncogene, the National Cancer Institute (NCI) estimates.

The RET proto-oncogene is a segment of DNA that controls a certain set of tyrosine kinase receptors in the endocrine system. Changes to the RET proto-oncogene can lead to multiple endocrine neoplasia (MEN) type 2, a disorder that confers a high lifetime risk of MTC.

Mutations to the RET proto-oncogene can be passed from mother and father to child, even if only one parent carries this trait.

To determine the rate of this hereditary disease among the MTC-afflicted Iranian population, researchers at the Tehran University of Medical Sciences sequenced the DNA of participants who had been treated for MTC between 1999 and 2006.

All patients had been previously diagnosed with a sporadic form of the illness. Testing revealed that nearly 18 percent of patients had in fact suffered from the hereditary form of the condition. This finding falls firmly in line with the expected rate of MEN-associated MTC, the study's authors noted.

After subsequent genetic tests were conducted among first-degree relatives of the participants, four otherwise asymptomatic people were found to carry the mutation. In this way, the advent of genetic sequencing in Iran may help diagnose MEN type 2 before it causes MTC, the team concluded.

In the U.S., all forms of MTC account for 2 to 3 percent of thyroid cancer diagnoses each year, according to the NCI.