CLINICAL SCREENING AS COMPARED WITH DNA ANALYSIS IN FAMILIES WITH MULTIPLE ENDOCRINE NEOPLASIA TYPE 2A

Background. Multiple endocrine neoplasia type 2A (MEN-2A) is characterized by medullary thyroid carcinoma in combination with pheochromocytoma and sometimes parathyroid adenoma. Missense mutations in the RET proto-oncogene are associated with MEN-2A. Their detection by DNA analysis allows the identification of carriers of the gene, in whom the risk of medullary thyroid carcinoma is 100 percent. We compared the reliability of biochemical tests with that of DNA analysis in identifying carriers of the MEN2A gene. Methods. Starting in 1975, we screened 300 subjects in four large families with MEN-2A for expression of the disease, using measurements of plasma calcitonin after stimulation with pentagastrin or calcium and urinary excretion of catecholamines and catecholamine metabolites. We tested for carrier status by DNA analysis, including linkage analysis, and more recently by analysis of mutations in the RET gene. Results. Of 80 MEN2A gene carriers (in 61 of whom carrier status was proved by DNA analysis), 66 had abnormal plasma calcitonin values and medullary thyroid carcinoma. Fourteen young carriers had normal results of plasma calcitonin tests. In 8 of these 14, thyroidectomy revealed small foci of medullary thyroid carcinoma; the remaining 6 have not yet been operated on. Of the other 220 family members, 68 were found by DNA analysis not to carry the MEN2A gene. None of these 68 subjects had medullary thyroid carcinoma or pheochromocytoma; 6 had elevated plasma calcitonin concentrations and underwent thyroidectomy but had only C-cell hyperplasia. Conclusions. Unlike biochemical tests, DNA analysis permits the unambiguous identification of MEN2A gene carriers.