BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS 227, 736–742 (1996) ARTICLE NO. 1578 Clonal Analysis by Chromosome 11 Microsatellite-PCR of Microdissected Parathyroid Tumors from MEN 1 Patients A. Morelli, A. Falchetti, A. Amorosi,* F. Tonelli,² I. Bearzi,‡ R. Ranaldi,‡ P. Tomassetti,§ and M. L. Brandi 1 Endocrine and ² Surgical Pathology Units, Department of Clinical Physiopathology, and *Institute of Pathological Anatomy and Histopathology, University of Florence, 50139 Florence; ‡Institute of Pathological Anatomy and Histopathology, University of Ancona, 60128 Ancona; and §Gastroenterology and Medical Clinical Institute, University of Bologna, 40126 Bologna, Italy Received September 6, 1996 Loss of heterozygosity (LOH) at chromosome 11q13 loci has been described in the majority of larger parathyroid tumors from patients affected by Multiple Endocrine Neoplasia type 1 (MEN 1) syndrome. Since classical histology of the whole parathyroid gland does not permit a clear morpho-genetic correlation, the clonal composition of abnormal parathyroid tissue was analyzed in DNA obtained from single nodules and non-nodular areas within MEN 1 parathyroid lesions. Microdissected sections were analyzed by chromo- some 11q13 microsatellite-PCR for LOH and by patterns of X-inactivation. We detected LOH for chromo- some 11q13 loci in at least one microdissected area for each familial MEN 1 patient, but not in the single sporadic case. X-inactivation pattern of two ‘‘clonal’’ tumors exhibited a polyclonal cell composition of these microdissected samples, indicating the existence of a genetic heterogeneity in MEN 1 parathyroid microareas exhibiting a ‘‘clonal’’ pattern for allelic losses.  1996 Academic Press, Inc. MEN 1 is an autosomal dominant inherited disorder characterized by hyperfunction and development of tumors of the parathyroid glands, of the anterior pituitary and of the gastroenter- opancreatic endocrine system. Moreover, carcinoids, lipomas, pinealomas, adrenocortical and thyroid follicular tumors occur in MEN 1 patients at higher frequency than in the general population [1]. The putative men 1 gene has been localized to chromosome 11q region 13 by linkage analysis [2]. Combined linkage and tumor deletion studies have provided evidence that the men 1 gene acts as a tumor suppressor gene [3], since both parathyroid and pancreatic neoplasms from MEN 1 patients exhibited loss of the constitutional allele inherited from the unaffected parent [3, 4]. Allelic losses at 11q12-13 have been preferentially detected in larger MEN 1 parathyroid tumors [5]. Similarly, larger parathyroid glands in uremic patients have been shown to exhibit allelic losses on chromosome 11 [6]. LOH can be interpreted as an indirect evidence of clonality. Indeed, recent studies on chromosome X- inactivation pattern have confirmed tumor monoclonality in 38% of patients with primary parathyroid hyperplasia and 64% of patients with uremic parathyroid hyperplasia [7]. However, in familial cases LOH cannot necessarily represent an indirect evidence of a monoclonal pattern of growth, owing the possibility that polyclonal and monoclonal tu- mors exhibit similar patterns of LOH [8]. It is of interest the recent observation of different patterns of allelic loss at 11q12-13 in diverse endocrine-associated tumors in a single MEN 1 patient [9]. The possibility that similar events happen within a given endocrine tumor is, therefore, plausible, as also supported by the lack of unequivocal correlation 1 To whom correspondence should be addressed at Endocrine Unit, Department of Clinical Physiopathology, Viale G. Pieraccini, 6, 50139 Florence, Italy. Fax: (39)-55-641026. 0006-291X/96 $18.00 Copyright  1996 by Academic Press, Inc. All rights of reproduction in any form reserved. 736