Supplement Series Volume No. 21 Hormone and Metabolic Research Editors in Chief: Assistant Editors: Guest Editors: E. F. Pfeiffer, Ulm W. D. Hetzel, Ulm F. Raue, Heidelberg G. M. Reaven, Palo Alto A. R. Hoffman, R. F. Gagel, Houston Palo Alto 1989 Georg Thieme Verlag Stuttgart • New York Thieme Medical Publishers, Inc., New YorkMultiple Endocrine Neoplasia Type 2 International Symposium at the International Wissenschaftsforum, Heidelberg 1987 11 Figures, 23 Tables 1989 Georg Thieme Verlag Stuttgart • New York Thieme Medical Publishers, Inc., New YorkThe Mapping of the Locus for Multiple Endocrine Neoplasia Type 2A by Linkage with Chromosome 10 Markers Nancy E. Simpson1 and K. K. Kidd2 1 Division of Medical Genetics, Department of Paediatrics, Queen's University, Kingston, Ontario, Canada 2 Department of Human Genetics, Yale University School of Medicine, New Haven, Connecticut, U. S. A. Summary The sequence of studies leading to the assignment of the locus for multiple endocrine neoplasia (MEN2A) to chromosome 10 are described. They began with the exclusion of linkage between the disease locus and loci for conventional markers and a deletion site reported to be associated with the disease on chromosome 20. After 32% of the genome had been excluded, a “hint” of linkage was found but considerable additional family data were necessary in order to establish linkage to the marker locus DIOS5. The DNA marker DIOS5 was assigned to chromosome 10 by in situ hybridization and tests of linkage between the marker and disease loci were significant. The assignment of the marker and the linkage implied that the disease gene was on chromosome 10. The assignment was confirmed by the demonstration of an additional linkage, between the disease locus and the gene for interstitial retinol binding protein (RBP3) that had also been assigned to chromosome 10. Closer and flanking markers are now being sought as steps to providing better than Mendelian risks for the MEN2A genotype and for the ultimate identification of the gene. Key Words: Mapping, Multiple Endocrine Neoplasia Type 2A Introduction Our interest in mapping the locus for the dominantly inherited cancer, multiple endocrine neoplasia type 2A (MEN2A) using linkage was twofold. Linked markers (genes or loci with detectable normal variation of known chromosomal location) could identify family members with the genotype for the disease with a better probability than by using the Mendelian risk. Since the life threatening aspects of the disease are curable if recognized early, identification of the genotype seemed particularly desirable. In addition, linked markers would make it possible ultimately to map the disease locus and thereby identify the genotype with certainty. Secondly, identification of the gone would provide a probe for finding the protein it encodes, a stop that would lead to the understanding of the inherited basis of MEN2A. The most frequent and aggressive tumor of the disease is the medullary thyroid carcinoma (MTC). At present, MTC or6 Nancy E. Simpson and K. K. Kidd its presumed precursor, C–cell hyperplasia, is commonly ascertained prosymptomatically by a diagnostic rise in serum calcitonin after calcium infusion or pentagastrin. nose patients with a positive screening test are treated by a prophylactic thyroidectorny. Because the disease is inherited in an autosomal dominant fashion all of the children of an affected patient are screened although it is known from genetic theory that only half of the children have the gene. Not knowing which half necessitates the biochemical screening of all children. The pentagastrin stimulation test has unpleasant side-effects and thus often results in a lack of compliance thereby rendering the test less effective than it otherwise could be. Linked markers to the locus for MEN2A would improve the probability of the genotype for family members over the Mendelian probability. The degree of improvement will depend on three factors. The closer the marker(s) are to the disease locus, the better the probability will be. The closer the allele frequencies are to each other the more often they will be informative in families. If the marker loci flank the disease locus then the probability of the genotype will be better than when the marker loci are on the same side. However, markers will not be informative in all families but are the stepping stones that lead to the actual disease locus. Once the actual locus is found it will be possible to determine the genotype of family members with certainty. The Search for the MEN2A Locus on Chromosome 20 The long history of the search for the locus for MEN2A has been reviewed in Simpson (1984) and Simpson and Kidd (1987). The search began with studies of conventional markers, followed by a concentrated search for chromosome 20 DNA sequences that detect restriction fragment length polymorphisms (RFLPs). The latter studies were stimulated by the reporting of an interstitial deletion at 20pl2 associated with the disease (VanDyke, Jackson and Babu 1982; VanDyke, Babu and Jackson 1984; Babu, VanDyke and Jackson 1984; Butler, Rames and Joseph 1987). It had been suggested that the locus for MEN2A was in the site of the deletion. In our studies, two DNA sequences that detected RFLPs were found to map to the site of the deletion (Goodfellow, White, Holden, Duncan, Sears, Wang, Berlin, Kidd and Simpson 1985 , Goodfellow, Duncan, Farrer, Holden, White, Kidd, Kidd and Simpson 1987). Linkages between the two chromosome 20 loci and that for MEN2A were excluded at recombination frequencies of 0.13 and 0.15 (Farrer, Goodfellow, White, Holden, Kidd, Simpson and Kidd 1987). These data suggested that the locus for MEN2A was not likely in the deletion, a hypothesis that was further supported by studies using a q arm marker at D20S4 which virtually excluded the disease locus from chromosome 20 (Farrer et al. 1987). The Search for the MEN2A Locus on Chromosome 10 From the above data it seemed that we were left with no clues as to where to look for the locus for MEN2A. The chromosome 20 exclusion data had come primarily from the thesis of P. J. Goodfellow. Towards the end of his studies he had tested for linkage between several sequences (chosen randomly) that detected RFLPs and the locus for the disease. These sequences had been isolated for other purposes in the laboratory of B. N. White at