The importance of MEN1 gene variants in AIP mutation negative FIPA patients

Abstract

Introduction: Pituitary adenomas (PAs) that occur in a familial setting account for no more than 5%, which can be part of familial tumor syndromes such as Multiple Endocrine Neoplasia type 1 (MEN1) and type 4 (MEN4), Carney Complex (CNC) or Familial Isolated Pituitary Adenoma (FIPA). The presence of two or more cases of PAs without MEN1 or CNC characteristics in the same family, enable FIPA diagnosis. Heterozygous germline inactivating mutations in thearyl hydrocarbon receptor-interacting protein(AIP) gene confer predisposition to PAs in different races in the setting of FIPAs. However, we have previously reported our cohort of FIPA patients as negative forAIPpoint mutations. Therefore, the aim of this study was to detect copy number variations (CNVs) inAIPandMEN1, and to investigateMEN1gene variations in this cohort.Patients and methods: Seven families including 16 patients with FIPA diagnosis were involved in this study. Among these families, heterogenous and homogenous FIPA were composed of three and four families, respectively. All homogenous FIPA patients had somatotropinoma. Mean follow-up period of the cohort was 13 (5–40) years. Only 12 patients from these families were available for genetic analyses, who did not have hypercalcemia and other components of familial syndromes. Patients’ genomic DNA were isolated from peripheral blood. All exons, exon-intron boundaries and UTR regions ofAIPandMEN1genes were PCR amplified, followed by Sanger sequencing to detect point mutations. CLC Main Workbench 6.5 was used in sequence data analysis against the reference sequences NM_003977.3 and NM_000244.3 forAIPandMEN1genes, respectively. Multiplex ligation-dependent probe amplification (MLPA) was performed in CNV detection, where commercially obtained reagents and probe-mixes were used according to the manufacturer’s instructions (P244-AIP-MEN1-CDKN1B, MRC-Holland, the Netherlands).Results: In our cohort, initial screen ofAIPgene revealed no mutations and MLPA anlaysis also showed no CNVs. Afterthan,MEN1sequencing exhibited novel heterozygous variants including c.1846T>A (p.*616Argext*21); rs778272737:T>C; rs972128957:C>T in 2 families having patients diagnosed with Cushing disease, non-functional PA, and acromegaly, respectively. Among them, c.1846T>A (p.*616Argext*21) is a stop codon read-through, whereas the others are 3′UTR variations. Overall,MEN1variation frequency was detected 15% in our cohort.Conclusion: In the long term clinically followed-up of FIPA patients without hypercalcemia,MEN1gene can be of significance and screening should be offered especially to young first-degree relatives with or without MEN1 syndrome features.