Clinical genetics of multiple endocrine neoplasias, Carney complex and related syndromes

An Update on the Genetic Drivers of Corticotroph Tumorigenesis

The genetic landscape of corticotroph tumours of the pituitary gland has dramatically changed over the last 10 years. Somatic changes in the USP8 gene account for the most common genetic defect in corticotrophinomas, especially in females, while variants in TP53 or ATRX are associated with a subset of aggressive tumours. Germline defects have also been identified in patients with Cushing's disease: some are well-established (MEN1, CDKN1B, DICER1), while others are rare and could represent coincidences. In this review, we summarise the current knowledge on the genetic drivers of corticotroph tumorigenesis, their molecular consequences, and their impact on the clinical presentation and prognosis.

Update of Genetic and Molecular Causes of Adrenocortical Hyperplasias Causing Cushing Syndrome

Bilateral hyperplasias of the adrenal cortex are rare causes of chronic endogenous hypercortisolemia also called Cushing syndrome. These hyperplasias have been classified in two categories based on the adrenal nodule size: the micronodular types include Primary Pigmented Nodular Adrenocortical Disease (PPNAD) and isolated Micronodular Adrenal Disease (iMAD) and the macronodular also named Primary Bilateral Macronodular Adrenal Hyperplasia (PBMAH). This review discusses the genetic and molecular causes of these different forms of hyperplasia that involve mutations and dysregulation of various regulators of the cAMP/protein kinase A (PKA) pathway. PKA signaling is the main pathway controlling cortisol secretion in adrenocortical cells under ACTH stimulation. Although mutations of the regulatory subunit R1α of PKA (PRKAR1A) is the main cause of familial and sporadic PPNAD, inactivation of two cAMP-binding phosphodiesterases (PDE11A and PDE8B) are associated with iMAD even if they are also found in PPNAD and PBMAH cases. Interestingly, PBMAH that is observed in multiple familial syndrome such as APC, menin, fumarate hydratase genes, has initially been associated with the aberrant expression of G-protein coupled receptors (GPCR) leading to an activation of cAMP/PKA pathway. However, more recently, the discovery of germline mutations in Armadillo repeat containing protein 5 (ARMC5) gene in 25-50% of PBMAH patients highlights its importance in the development of PBMAH. The potential relationship between ARMC5 mutations and aberrant GPCR expression is discussed as well as the potential other causes of PBMAH.

Genetic Aspects of Pituitary Adenomas

Although most of pituitary adenomas are benign, they may cause significant burden to patients. Sporadic adenomas represent the vast majority of the cases, where recognized somatic mutations (eg, GNAS or USP8), as well as altered gene-expression profile often affecting cell cycle proteins have been identified. More rarely, germline mutations predisposing to pituitary adenomas -as part of a syndrome (eg, MEN1 or Carney complex), or isolated to the pituitary (AIP or GPR101) can be identified. These alterations influence the biological behavior, clinical presentations and therapeutic responses, and their full understanding helps to provide appropriate care for these patients.

A rare combination consisting of aldosterone-producing adenoma and adrenal myelolipoma in a patient with heterozygosity for retinoblastoma (RB) gene

Various pathological disorders have been associated with primary aldosteronism, including glucagonoma, phaeochromocytoma and primary hyperparathyroidism.

In this report, a case of adrenal myelolipoma (a rare non-functioning tumour composed of mature adipose tissue and normal haematopoietic elements similar to bone marrow cells), aldosterone-producing adenoma and a pituitary microadenoma coexisting in a 62-year-old man with a 15-year history of arterial hypertension, previous ablation of an autonomously-functioning thyroid adenoma, multiple lipomas and an heterozygosity of the retinoblastoma (RB) susceptibility gene is reported.

We believe that this case probably represents another variant of the multiple neoplasia syndrome and we speculate that structural alteration of the RB gene may play a role in the tumorogenesis.

Alterations of Phosphodiesterases in Adrenocortical Tumors

Alterations in the cyclic (c)AMP-dependent signaling pathway have been implicated in the majority of benign adrenocortical tumors (ACTs) causing Cushing syndrome (CS). Phosphodiesterases (PDEs) are enzymes that regulate cyclic nucleotide levels, including cyclic adenosine monophosphate (cAMP). Inactivating mutations and other functional variants in PDE11A and PDE8B, two cAMP-binding PDEs, predispose to ACTs. The involvement of these two genes in ACTs was initially revealed by a genome-wide association study in patients with micronodular bilateral adrenocortical hyperplasia. Thereafter, PDE11A or PDE8B genetic variants have been found in other ACTs, including macronodular adrenocortical hyperplasias and cortisol-producing adenomas. In addition, downregulation of PDE11A expression and inactivating variants of the gene have been found in hereditary and sporadic testicular germ cell tumors, as well as in prostatic cancer. PDEs confer an increased risk of ACT formation probably through, primarily, their action on cAMP levels, but other actions might be possible. In this report, we review what is known to date about PDE11A and PDE8B and their involvement in the predisposition to ACTs.

The complex of myxomas, spotty skin pigmentation and endocrine overactivity (Carney complex): imaging findings with clinical and pathological correlation

The complex of myxomas, spotty skin pigmentation and endocrine overactivity, or Carney complex (CNC), is a familial multiple endocrine neoplasia and lentiginosis syndrome. CNC is inherited in an autosomal dominant manner and is genetically heterogeneous. Its features overlap those of McCune-Albright syndrome and other multiple endocrine neoplasia (MEN) syndromes. Spotty skin pigmentation is the major clinical manifestation of the syndrome, followed by multicentric heart myxomas, which occur at a young age and are the lethal component of the disease. Myxomas may also occur on the skin (eyelid, external ear canal and nipple) and the breast. Breast myxomas, when present, are multiple and bilateral among female CNC patients, an entity which is also described as “breast-myxomatosis” and is a characteristic feature of the syndrome. Affected CNC patients often have tumours of two or more endocrine glands, including primary pigmented nodular adrenocortical disease (PPNAD), an adrenocorticotropin hormone (ACTH)-independent cause of Cushing’s syndrome, growth hormone (GH)-secreting and prolactin (PRL)-secreting pituitary adenomas, thyroid adenomas or carcinomas, testicular neoplasms (large-cell calcifying Sertoli cell tumours [LCCSCT]) and ovarian lesions (cysts and cancinomas). Additional infrequent but characteristic manifestations of CNC are psammomatous melanotic schwannomas (PMS), breast ductal adenomas (DAs) with tubular features, and osteochondromyxomas or “Carney bone tumour”.

Teaching Points

• Almost 60 % of the known CNC kindreds have a germline inactivating mutations in the PRKAR1A gene.

• Spotty skin pigmentation is the major clinical manifestation of CNC, followed by heart myxomas.

• Indicative imaging signs of PPNAD are contour abnormality and hypodense spots within the gland.

• Two breast tumours may present in CNC: myxoid fibroadenomas (breast myxomatosis) and ductal adenomas.

• Additional findings of CNC are psammomatous melanotic schwannomas (PMSs) and osteochondromyxomas.

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

Kidney donation from a patient with cardiac myxoma: a case report

INTRODUCTION

Renal transplantation has still become the preferred method to treat end-stage renal failure. The majority of organs are obtained from individuals with irreversible central nervous system injury. This group is nowadays unsatisfactory and small relative to the needs. A significant percentage of donors may be found among patients primarily suffering from benign neoplasms whose nature does not show malignant potential and do not metastasize. To date, there have been no reports about successful organ transplantation from an organ donor with cardiac myxoma.

AIM

The aim of this report was to present a successful transplantation of cadaveric kidney grafts from a 61-year-old female donor with a left atrial cardiac myxoma, which initially appeared as an embolic cerebral infarct. The kidney graft recipients were a 51-year-old woman and a 57-year-old man with long-lasting histories of chronic renal failure under treatment by hemodialysis. The transplant function of both kidneys has been satisfactory with a 5-year follow-up. For the present, apart from single event of acute rejection in a male recipient, the patients have maintained stable renal function. Routine accessory examinations did not reveal any changes within the kidney or other organs. To date, a renal biopsy has not been taken. Both recipients are undergoing special follow-up.

CONCLUSION

Patients with myxoma should be accepted as donors, since the risk of dying on the waiting list is greater than the tumor transfer risk. Exclusion of these potential donors decreases the donor pool and unnecessarily wastes valuable organs.

Conservative management of bilateral Sertoli cell tumors of the testicle in association with the Carney complex: a case report

Large cell calcifying Sertoli cell tumor of the testicle is a rare, hormonally active sex cord-stromal tumor seen in patients with Carney complex. When such tumors occur bilaterally, treatment options for preserving fertility and addressing the secondary effects of excess hormone production must be considered. The availability of specific antiestrogen drugs means that bilateral orchiectomy for this benign tumor may no longer be warranted. Testicular-sparing surgery and advances in reproductive technology may also improve the overall prognosis for fertility. Gynecomastia in prepubescent boys can be emotionally very distressing. Approximately two thirds of teenaged boys will develop some degree of breast enlargement that spontaneously regresses as testosterone levels rise (Ill Med J 1938;73:113). In all cases, a thorough history and physical examination are required to exclude nonphysiologic causes such as drugs, pulmonary disease, chronic liver disease, exogenous estrogens, and estrogen-producing tumors (Seashore J. Disorders of the breast. In: Rowe MI, O'Neill JA, Grosfeld JL et al, editors. Pediatric surgery, 5th ed. St Louis (MO): Mosby Year Book, 1998). We report on a child who presented with a 2-year history of gynecomastia with associated bilateral testicular swellings and discuss a novel treatment strategy for managing bilateral testicular tumors in the context of the Carney complex.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

An Unusual Association of Cerebral Meningioma, Parathyroid Adenoma and Thyroid Papillary Carcinoma

The case of a 50-year-old woman with cerebral meningioma and concomitant parathyroid adenoma and papillary thyroid carcinoma is presented. She complained of neurological symptoms characterized by right hemiparesis and dysarthria. Cerebral CT and MRI scans revealed a left voluminous frontal parasagittal lesion with the characteristics of a meningioma. Routine laboratory analysis revealed altered values of calcium-phosphorus metabolism. Intravenous infusion of saline solution at 0.9% of NaCI resulted in a reduction of serum ionized calcium. A left craniotomy was performed and a fibroblastic meningioma of 5 cm in diameter was removed. Even though the patient's clinical condition was good, a calcium-phosphorus metabolism test confirmed high plasma levels of ionized calcium and parathyroid hormone. Thyroid and parathyroid ultrasonography revealed multinodular goiter and a parathyroid lesion confirmed by99mTc-TCO4/99mTc-MIBI scintigraphy. A left superior parathyroidectomy and total thyroidectomy were performed. Histological examination revealed a parathyroid adenoma and a small papillary carcinoma of 0.4 cm in the right thyroid lobe. As far as we know, this patient is the third case of meningioma associated with parathyroid adenoma and papillary thyroid carcinoma described in the literature.

Hereditary hormone excess: genes, molecular pathways, and syndromes

Hereditary origin of a tumor helps toward early discovery of its mutated gene; for example, it supports the compilation of a DNA panel from index cases to identify that gene by finding mutations in it. The gene for a hereditary tumor may contribute also to common tumors. For some syndromes, such as hereditary paraganglioma, several genes can cause a similar syndrome. For other syndromes, such as multiple endocrine neoplasia 2, one gene supports variants of a syndrome. Onset usually begins earlier and in more locations with hereditary than sporadic tumors. Mono- or oligoclonal ("clonal") tumor usually implies a postnatal delay, albeit less delay than for sporadic tumor, to onset and potential for cancer. Hormone excess from a polyclonal tissue shows onset at birth and no benefit from subtotal ablation of the secreting organ. Genes can cause neoplasms through stepwise loss of function, gain of function, or combinations of these. Polyclonal hormonal excess reflects abnormal gene dosage or effect, such as activation or haploinsufficiency. Polyclonal hyperplasia can cause the main endpoint of clinical expression in some syndromes or can be a precursor to clonal progression in others. Gene discovery is usually the first step toward clarifying the molecule and pathway mutated in a syndrome. Most mutated pathways in hormone excess states are only partly understood. The bases for tissue specificity of hormone excess syndromes are usually uncertain. In a few syndromes, tissue selectivity arises from mutation in the open reading frame of a regulatory gene (CASR, TSHR) with selective expression driven by its promoter. Polyclonal excess of a hormone is usually from a defect in the sensor system for an extracellular ligand (e.g., calcium, glucose, TSH). The final connections of any of these polyclonal or clonal pathways to hormone secretion have not been identified. In many cases, monoclonal proliferation causes hormone excess, probably as a secondary consequence of accumulation of cells with coincidental hormone-secretory ability.

Multiple endocrine neoplasia type I in a cat

A 13-year-old 4.6-kg (10.2-lb) neutered male domestic long hair cat was evaluated because of a history of lethargy, exercise intolerance, and ventroflexion of the cervical portion of the vertebral column. After extensive assessment at the Veterinary Teaching Hospital at Michigan State University, the clinical signs were attributed to an aldosterone-secreting tumor of the adrenal gland. Subsequently, an insulin-secreting tumor of the pancreas as well as a functional parathyroid gland adenoma were diagnosed. All 3 masses were surgically removed, and the cat made a full recovery with complete resolution of clinical signs. The syndrome of multiple endocrine neoplasia is well described in humans, and the heritability of the condition has been confirmed. In cats and other species with 1 or more endocrine neoplasms, it is important to perform thorough clinical assessments of patients to identify other endocrine organs that may also be affected concurrently with neoplastic disease.

Chondrosarcoma in association with primary hyperparathyroidism

We describe two female patients, 66 and 36 years of age, with both primary hyperparathyroidism and chondrosarcoma. Case 1 had a chondrosarcoma of the right scapula, and case 2 had chondrosarcoma of the left proximal tibia. Both patients underwent surgical resection of their chondrosarcoma and subsequent parathyroid surgery. Histological analysis of the excised parathyroid in case 1 showed a parathyroid carcinoma and in case 2 showed a parathyroid adenoma. Including these two patients, there is now a total of six cases that have been reported in the literature describing the association between hyperparathyroidism and bone malignancy. We believe that this small number makes it unlikely that there is an association between these two conditions, although we speculate that there may be an underlying genetic basis.

The clinically inapparent adrenal mass: update in diagnosis and management

Clinically inapparent adrenal masses are incidentally detected after imaging studies conducted for reasons other than the evaluation of the adrenal glands. They have frequently been referred to as adrenal incidentalomas. In preparation for a National Institutes of Health State-of-the-Science Conference on this topic, extensive literature research, including Medline, BIOSIS, and Embase between 1966 and July 2002, as well as references of published metaanalyses and selected review articles identified more than 5400 citations. Based on 699 articles that were retrieved for further examination, we provide a comprehensive update of the diagnostic and therapeutic approaches focusing on endocrine and radiological features as well as surgical options. In addition, we present recent developments in the discovery of tumor markers, endocrine testing for subclinical disease including autonomous glucocorticoid hypersecretion and silent pheochromocytoma, novel imaging techniques, and minimally invasive surgery. Based on the statements of the conference, the available literature, and ongoing studies, our aim is to provide practical recommendations for the management of this common entity and to highlight areas for future studies and research.

GH-secreting pituitary adenomas infrequently contain inactivating mutations of PRKAR1A and LOH of 17q23-24

OBJECTIVE

The molecular events leading to the development of GH-secreting pituitary tumours remain largely unknown. Gsalpha (GNAS1) mutations are found in 27-43% of sporadic GH-secreting adenomas in the Caucasian population, but the frequency of GNAS1 mutations in Japanese and Korean acromegalic patients was reported to be lower, 4-9% and 16%, respectively. Other genes responsible for the tumourigenesis of GH-secreting pituitary adenomas have not been detected yet. PRKAR1A, which codes for the RIalpha regulatory subunit of cyclic AMP-dependent protein kinase A (PKA) on 17q23-24, was recently reported to contain inactivating mutations in some Carney complex families, which involved GH-secreting adenomas in about 10%. We re-evaluated the frequency of GNAS1 mutations and investigated PRKAR1A on the hypothesis that it might play a role in the tumourigenesis of GH-secreting adenomas.

DESIGN

We analysed exons 8 and 9 of GNAS1 and all exons and the exon-intron boundaries of PRKAR1A with the PCR and by direct sequencing using genomic DNA extracted from 32 GH-secreting pituitary adenomas (30 GH-secreting adenomas, two GH and PRL-secreting adenomas) and 28 corresponding peripheral blood samples, and performed loss of heterozygosity (LOH) analysis of 17q23-24 with four microsatellite markers and intragenic markers of PRKAR1A.

RESULTS

Seventeen of 32 (53.1%) tumours showed somatic-activating mutations of GNAS1: 16 (53.3%) of 30 GH-secreting adenomas and one of two GH and PRL-secreting adenomas. Neither inactivating somatic mutations of PRKAR1A nor LOH of 17q23-24 were detected in any of the tumours examined.

CONCLUSION

We reconfirm the important role of activating mutations of GNAS1 in GH-secreting adenomas, and conclude that PRKAR1A does not play a significant role in the tumourigenesis.

Comparative genomic hybridization analysis of adrenocortical tumors

Comparative genomic hybridization (CGH) is a molecular cytogenetic technique that allows the entire genome of a tumor to be surveyed for gains and losses of DNA copy sequences. A limited number of studies reporting the use of this technique in adult adrenocortical tumors have yielded conflicting results. In this study we performed CGH analysis on 13 malignant, 18 benign, and 1 tumor of indeterminate malignant potential with the aim of identifying genetic loci consistently implicated in the development and progression of adrenocortical tumors. Tissue samples from 32 patients with histologically proven adrenocortical tumors were available for CGH analysis. CGH changes were seen in all cancers, 11 of 18 (61%) adenomas, and the 1 tumor of indeterminate malignant potential. Of the adrenal cancers, the most common gains were seen on chromosomes 5 (46%), 12 (38%), 19 (31%), and 4 (31%). Losses were most frequently seen at 1p (62%), 17p (54%), 22 (38%), 2q (31%), and 11q (31%). Of the benign adenomas, the most common change was gain of 4q (22%). Mann-Whitney analysis showed a highly significant difference between the cancer group (mean changes, 7.6) and the adenoma group (mean changes, 1.1) for the number of observed CGH changes (P < 0.01). Logistic regression analysis showed that the number of CGH changes was highly predictive of tumor type (P < 0.01). This study has identified several chromosomal loci implicated in adrenocortical tumorigenesis. Activation of a protooncogene(s) on chromosome 4 may be an early event, with progression from adenoma to carcinoma involving activation of oncogenes on chromosomes 5 and 12 and inactivation of tumor suppressor genes on chromosome arms 1p and 17p.

Ovarian tumors associated with multiple endocrine neoplasias and related syndromes (Carney complex, Peutz-Jeghers syndrome, von Hippel-Lindau disease, Cowden's disease)

Despite the relatively high prevalence of ovarian cancer (1% of American women will develop this disease in their lifetime) and recent developments in its molecular genetic understanding (several proto-oncogenes, such as AKT2 and cKRAS, and tumor suppressor genes, such as BRCA1 and BRCA2, have been implicated), little is known about the presence of ovarian tumors and cancer in women already diagnosed with other familial multiple tumor syndromes. In this review, we focus on the possible association of ovarian tumors with multiple endocrine neoplasias (MENs) and their related syndromes, such as Carney complex (CNC), Peutz-Jeghers syndrome (PJS), von Hippel-Lindau disease (VHLD), and Cowden's disease (CD). These conditions recently have been molecularly elucidated, and some of the genes responsible for them (including STK11/LKB1 and PTEN, the genes responsible for PJS and CD, respectively) have already been investigated in series of sporadic ovarian lesions, mostly carcinomas. A brief description of each disease is followed by a literature search for affected patients with ovarian tumors; we review our own experience with CNC patients and ovarian tumors. An association between PJS and CNC and ovarian neoplasms seems likely; carcinoids of the ovary may occur in patients with MEN 1. Only few patients with CD and VHLD have any ovarian pathology, but PTEN, the CD gene has been investigated in sporadic ovarian tumors. The aim of the present report is to alert clinicians who care for patients with MENs, CNC, PJS, VHLD, CD, and other syndromes for possible associations between various types of ovarian tumors and these conditions.

MEN1 gene alterations do not correlate with the phenotype of sporadic primary hyperparathyroidism

Loss of heterozygosity (LOH) in the MEN1 region on chromosome 11q13 and MEN1 gene mutations have been found in a subset of sporadic parathyroid tumors. The question of whether these genetic abnormalities in the parathyroid tumors might influence the clinical and biochemical characteristics of primary hyperparathyroidism (PHPT) remains to be elucidated. The aim of the present study was to correlate the presence of MEN1 gene alterations in PHPT tumors with the clinical phenotype. Using microsatellite analysis for LOH at 11q13 and DNA sequencing of the coding exons, the MEN1 gene was studied in 38 parathyroid tumors of patients with sporadic PHPT. Fourteen tumors showed LOH at 11q13, and mutations of MEN1 gene were detected in 7 cases. The clinical and biochemical characteristics of patients were unrelated to the presence or absence of LOH and/or MEN1 gene mutations. In conclusion, MEN1 gene alterations are rather common in sporadic PHPT and their presence does not correlate with the clinical manifestations of the disease.