[Familial medullary thyroid cancer. Contribution of genealogy and genetics to the study of two families].
A geneological study made it possible to establish a link between two medullary thyroid carcinoma families from Normandy totalling 9 sick subjects, and a probable link with a third family. The study contributed to the diagnosis of multiple endocrine neoplasia type IIa, whereas the condition had been diagnosed for 6 years as familial medullary thyroid carcinoma, without phaechromocytoma. Group in these two families together increased the number of subjects tested, thereby facilitating genetic link analysis and enabling the link with markers of the disease on chromosome 10 to be asserted. The genetic study can now be used to detect individuals at risk, and with regular laboratory tests the diagnosis will be made at the "precancerous" stage. A genealogical study going back to the family-founding couple will increase the population which will benefit from screening in this region north of Rouen.