Isolated Macroprolactinomas in Four Young Adult Males Harboring a Variant of the Aryl Hydrocarbon Interacting Protein (AIP) Gene: Isn’t It Too Much of a Coincidence?

Background: Germline mutations in the Aryl hydrocarbon receptor-Interacting Protein (AIP) gene are associated with pituitary adenomas in young patients usually in the setting of Familial Isolated Pituitary Adenomas (FIPA). The majority of these adenomas are somatotropinomas followed by prolactinomas, and rarely non-secreting adenomas. AIP-mutation-related prolactinomas predominantly affect men, as opposed to sporadic prolactinomas, that typically affect women. Clinical Case: We previously described an AIP gene mutation in two patients affected by prolactinomas. During the past years, we continued our study and have identified two more male patients with macroprolactinomas originally from the same small village and harboring the same AIP gene mutation. These male patients aged 19 to 44 years at the time of diagnosis. Two of them had neurological manifestations as the first clinical manifestation of the disease, one was studied because of hypogonadism and two patients had visual field defects. All of them had prolactin levels above 1000 ng/dl (mean 2946.5±948.7 ng/dl, reference range 10-21). In the imaging exams (CT/MRI) they presented pituitary adenomas larger than 20 mm (macroprolactinomas) and in two of the cases, the adenomas were even larger than 40 mm (giant prolactinomas). In order to exclude mutations most often associated with prolactinomas, DNA samples were obtained and analyzed by Next Generation Sequencing (NGS) using TruSightCancer Gene Set (Illumina) methodology. Investigation of significant deletions and/or duplications was performed using the MLPA (Multiplex ligation-dependent probe amplification) technique. None of the patients were positive for mutations of Multiple Endocrine Neoplasia type 1 (MEN1) gene. A variant of the AIP gene c.47G>A, expecting to lead to a substitution of arginine by histidine at position 16 (p.Arg16His) of the AIP was found in these four patients, including a father and his son. Seven asymptomatic carriers were identified among their first-degree relatives. In silico analysis and the information available in the literature, as well as in databases is not in agreement with the pathogenicity of this variant of the AIP gene. However, our findings point to a founder effect transmitted as a dominant trait with incomplete penetrance (4 out of 11 patients, 36%). Conclusion: The variant of the AIP gene identified in our patients behaved as a pathogenic mutation and was only associated with prolactinomas, including two giant prolactinomas.