Preliminary whole-exome sequencing reveals mutations that imply common tumorigenicity pathways in multiple endocrine neoplasia type 1 patients

Multiple endocrine neoplasia type 1 (MEN1) is a rare, autosomal-dominant disorder caused by alterations in the MEN1 gene on chromosome 11.1 Ninety percent of patients with MEN1 initially present with hyperparathyroidism (HPT), affecting men and women equally (unlike sporadic HPT) and at a younger age of onset (compared with sporadic HPT).2 Other commonly affected endocrine glands include the pancreas and pituitary; >20 different types of tumors have been described in MEN1 patients. Of particular concern is the development of pancreatic neuroendocrine tumors (PNET), some of which produce gastrin, insulin, or other secretory hormones; metastatic PNETs are the leading cause of disease-specific death in MEN1 patients.3,4 Identifying a cellular mechanism behind the multiple neoplasms occurring in MEN1 patients could eventually enable clinicians to predict and properly screen for the development of PNET at the time of HPT presentation has the important potential to prevent downstream morbidity and mortality. A number of genes are known to be involved in neuroendocrine tumorigenesis, including MEN1, RET, VHL, TSC1, and TSC2,5 with mutations in MEN1 remaining the most common form of genetic predisposition to neuroendocrine tumors. More than 1,300 mutations6 in the MEN1 gene have been reported in families with MEN1 syndrome, yet the exact mechanisms by which these mutations cause the MEN1-related pathologies are not known.3,7,8 The heterozygous germline-inactivating mutation in the MEN1 may be followed by loss of the normal copy of this gene or a somatic inactivating mutation (second hit), leading to complete loss of function of the encoded protein menin. However, genotype–phenotype analysis has not revealed a clear pattern of disease penetrance in MEN1 patients.9,10 Additionally, it is reported that 5–30% of MEN1 patients do not have an identifiable mutation by standard testing.7,11 Loss of heterozygosity (LOH) has been described in parathyroid tissue of sporadic HPT patients, particularly in chromosome 11 in association with MEN1 gene alterations.8,12 No relationship has been found between MEN1-related HPT and tumor suppressor genes, such as TP53,13 although mutations of this gene have been associated with other neuroendocrine tumors. In contrast, whole-exome sequencing of parathyroid tissue from sporadic HPT patients has not revealed clear mutation patterns. Somatic mutations in the MEN1 gene have been described in 15– 35% of non-MEN1 parathyroid adenomas and are implicated in the pathology of sporadic HPT.8,12,14 However, few other somatic variants have been found to be harbored with significant frequency in sporadic HPT adenomas.12 Whole-exome sequencing has previously been used to identify somatic mutations in samples from sporadic HPT adenomas, parathyroid carcinomas, and other sites (ie, PNET), but not MEN1-related HPT.8,12,15 Because of the known germline mutation in MEN1 patients, we hypothesized that whole-exome sequencing on blood and tissue samples of HPT patients could aid in the following goals: (1) Identify acquired somatic mutations involved in functional pathways and tumorigenic networks, and (2) elucidate additional germline risk factors associated with outcomes.