Multiple endocrine neoplasia type 2A (MEN 2A) is a dominantly inherited cancer syndrome that affects tissues derived from neural ectoderm. It is characterized by medullary thyroid carcinoma (MTC) and phaeochromocytoma. The MEN2A gene has recently been localized by a combination of genetic and physical mapping techniques to a 480-kilobase region in chromosome 10q11.2 (refs 2,3). The DNA segment encompasses the RET proto-oncogene, a receptor tyrosine kinase gene expressed in MTC and phaeochromocytoma and at lower levels in normal human thyroid. This suggested RET as a candidate for the MEN2A gene. We have identified missense mutations of the RET proto-oncogene in 20 of 23 apparently distinct MEN 2A families, but not in 23 normal controls. Further, 19 of these 20 mutations affect the same conserved cysteine residue at the boundary of the RET extracellular and transmembrane domains.

We have analysed 118 families with inherited medullary thyroid carcinoma (MTC) for mutations of the RET proto-oncogene. These included cases of multiple endocrine neoplasia types 2A (MEN 2A) and 2B (MEN 2B) and familial MTC (FMTC). Mutations at one of 5 cysteines in the extracellular domain were found in 97% of patients with MEN 2A and 86% with FMTC but not in MEN 2B patients or normal controls. 84% of the MEN2A mutations affected codon 634. MEN 2A patients with a Cys634 to Arg substitution had a greater risk of developing parathyroid disease than those with other codon 634 mutations. Our data show a strong correlation between disease phenotype and the nature and position of the RET mutation, suggesting that a simple, constitutive activation of the RET tyrosine kinase is unlikely to explain the events leading to MEN 2A and FMTC.

The susceptibility loci for the three multiple endocrine neoplasia (MEN) type 2 syndromes have been mapped to the region of chromosome 10q11.2 containing the RET proto-oncogene, which codes for a receptor tyrosine kinase. The majority of MEN 2A and familial medullary thyroid carcinoma results from missense mutations within one of five cysteine codons in the extracellular domain of the RET proto-oncogene. We now report a missense mutation, resulting in the substitution of a threonine for a methionine at codon 918 in the tyrosine kinase catalytic domain, in the germline of 26 of 28 apparently distinct families with MEN 2B. DNA from five of 13 apparently sporadic MTC and one of 12 apparently sporadic phaeochromocytomas harboured a similar mutation, but the corresponding germline DNA was wildtype in each case.

Multiple endocrine neoplasia type 2 (MEN 2) is a familial cancer syndrome arising from mutation at a locus or loci in chromosome region 10p11.2-q11.2. The disease is characterized by medullary thyroid carcinoma (MTC) and pheochromocytoma (Pheo). To assess the genetic events in tumour initiation and progression in this disease, we have compiled an allelotype for MTC and Pheo tumours using polymorphic marker loci from each chromosome arm. Using a panel of 58 tumours, we found frequent allele losses on chromosome arms 1p (42%), 3p (30%), 3q (38%), 11p (11%), 13q (10%), 17p (8%), and 22q (29%). Loss of heterozygosity (LOH) for loci on chromosome 10 was detected in a single tumour where one whole chromosome copy was lost. We used a panel of polymorphic markers for each of chromosomes 1, 3, 11, and 17 to define a shortest region of overlap for these regions. The most frequent allele losses were on chromosome 1, spanning the entire short arm of the chromosome but not loci on 1q. LOH on chromosome 3 encompassed a minimal common region of 3q12-qter. The regions of allelic deletion on chromosome 11 (11pter-p13), 17 (17pter-p11.2), and 13 (13q) encompass known tumour suppressor loci (WTI, TP53, RBI) which must therefore be candidates for genes contributing to MTC and Pheo development. Our data suggest allele loss on chromosome 11, 13, or 17 occurs predominantly in tumours with losses on chromosome 3, potentially reflecting the accumulation of genetic change in tumour progression. These events may be associated with more advanced disease in MTC. We suggest that at least 7 genes contribute to tumour development in MEN 2, including an initiating locus on chromosome 10 and loci on chromosomes 1, 3, 11, 13, 17, and 22 which have a progressional role in these tumours.