Despite the identification of a familial component to NMTCs, the recognition that some NMTCs are occasionally seen in association with rare cancer predisposition syndromes coupled with major advances in mapping predisposition loci in large NMTC-segregating families, there has been little progress in unequivocally identifying the disease-causing alleles accounting for familial NMTC outside that seen in rare cancer predisposition syndromes such as Cowden syndrome. The paucity of unequivocally identified disease-causing alleles has hampered the clinical management of familial NMTC, compared to medullary thyroid cancer, and means that germline gene testing in affected individuals in familial or early onset NMTC is limited to those in which there is a high likelihood of an underlying cancer predisposition syndrome.
Individuals with Cowden and other such syndromes should receive genetic counseling. Guidelines for diagnosis, counseling, and screening for associated disease with these syndromes are discussed elsewhere [36,89]. Families of probands should also be screened for NMTC, given their increased risk.
In patients with PTC, a family history should be extracted with special reference to family members with either NMTC or PRN. Presence of either of these should suggest a familial PTC syndrome. If such a familial PTC syndrome is identified, the first-degree relatives should be screened for underlying thyroid disease. The optimum screening method has yet to be identified. Although indicated in families with MEN2A and MEN2B, the value of prophylactic thyroidectomy has not been proven and should not routinely be recommended, not only since PTC is generally more indolent than medullary thyroid cancer, but also since no germline mutations can be unequivocally associated with affection status. There has yet to be formal consensus on the most effective screening program for PTC in high risk families. First-degree relatives of affected familial PTC kindred members should be assessed with a yearly physical examination of the thyroid gland, probably starting at the age of 20 years. The role of ultrasound monitoring of the thyroid gland may also be of use due to its greater sensitivity and ability to identify unrelated and clinically unimportant abnormalities. The role of ultrasound in screening for PRN is limited, as an increased incidence of PRN is not observed in most familial PTC kindreds. Moreover, in those kindreds segregating PTC and PRN, the frequency of PRN is far lower than that of PTC.
Finally, any size of families segregating NMTC, from affected sibling pairs upwards, should be accrued whenever possible, after host institution ethical review board approval, for gene mapping studies. If participating in such studies, and when disease-causing alleles have not been unequivocally identified, results should not influence clinical management of participating families, due to the statistical probabilities concerned and the lack of an identified mutant allele.
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