MEN1 Clinical Background

MEN1 mutations and potentially MEN1-targeting miRNAs are responsible for menin deficiency in sporadic and MEN1 syndrome-associated primary hyperparathyroidism

Inherited, germline mutations of menin-coding MEN1 gene cause multiple endocrine neoplasia type 1 (MEN1), while somatic MEN1 mutations are the sole main driver mutations in sporadic primary hyperparathyroidism (PHPT), suggesting that menin deficiency has a central role in the pathogenesis of PHPT. MiRNAs are small, noncoding RNAs posttranscriptionally regulating gene expression. Our aim was to investigate both the role of MEN1 mutations and potentially MEN1-targeting miRNAs as the underlying cause of menin deficiency in MEN1-associated and sporadic PHPT tissues. Fifty six PHPT tissues, including 16 MEN1-associated tissues, were evaluated. Diagnosis of MEN1 syndrome was based on identification of germline MEN1 mutations. In silico target prediction was used to identify miRNAs potentially targeting MEN1. Menin expression was determined by immunohistochemistry while expression of miRNAs was analyzed by quantitative real-time PCR. Sporadic PHPT tissues were subjected to somatic MEN1 mutation analysis as well. Lack of nuclear menin was identified in all MEN1-associated and in 28% of sporadic PHPT tissues. Somatic MEN1 mutations were found in 25% of sporadic PHPTs. The sensitivity and specificity of menin immunohistochemistry to detect a MEN1 mutation were 86 and 87%, respectively. Expression levels of hsa-miR-24 and hsa-miR-28 were higher in sporadic compared to MEN1-associated PHPT tissues; however, no difference in miRNA levels occurred between menin-positive and menin-negative PHPT tissues. Menin deficiency is the consequence of a MEN1 mutation in most menin-negative PHPT tissues. Elevated expression of hsa-miR-24 and hsa-miR-28 mark the first epigenetic changes observed between sporadic and MEN1-associated PHPT.

MEN1 and microRNAs: The link between sporadic pituitary, parathyroid and adrenocortical tumors?

Sporadic tumors of the pituitary, parathyroids and adrenal cortex are unique, as their benign forms are very common, but malignant forms are exceptionally rare. Hereditary forms of these tumors occur in multiple endocrine neoplasia syndrome type 1 (MEN1). We hypothesize that the pathogenic link among the sporadic tumors of these organs of different germ layers might be represented by common molecular pathways involving the MEN1 gene and microRNAs (miR). miR-24 might be a microRNA linking the three tumor entities, but other candidates such as miR-142-3p and microRNAs forming the DLK1-MEG3 miRNA cluster might also be of importance.

[Familial isolated pituitary adenoma syndrome]

Familial pituitary adenomas occur in multiple endocrine neoplasia type 1, Carney complex, as well as in familial isolated pituitary adenoma syndrome. Familial isolated pituitary adenoma syndrome is an autosomal dominant disease with incomplete penetrance. Pituitary adenomas occur in familial setting but without any other specific tumors. In 20-40% of families with this syndrome, mutations have been identified in the aryl hydrocarbon receptor interacting protein gene while in the rest of the families the causative gene or genes have not been identified. Families carrying aryl hydrocarbon receptor interacting protein gene mutations have a distinct phenotype with younger age at diagnosis and a predominance of somatotroph and lactotroph adenomas. Germline mutations of the aryl hydrocarbon receptor interacting protein gene can be occasionally identified in usually young-onset seemingly sporadic cases. Genetic and clinical testing of relatives of patients with aryl hydrocarbon receptor interacting protein gene mutations can lead to earlier diagnosis and treatment at an earlier stage of the pituitary tumor.