Functional analysis of AIP variants in a cohort of neuroendocrine neoplasms

Loss-of-function (LOF) germline AIP variants are the main genetic cause of familial isolated pituitary adenoma and gigantism. A role for this defect in other neoplasms has been suggested, but remains unclear. We investigated the frequency, associated phenotypes, and in vitro functional effects of germline AIP variants in a cohort of Mexican patients with neuroendocrine neoplasms (NENs). Blood DNA samples from 101 adults (70.3% females) with isolated or syndromic NENs (50 with pituitary neuroendocrine tumors, PitNETs) were analyzed using a next generation sequencing panel. Targeted Sanger screening was carried out in additional family members and tumor samples. Missense and intronic variants were functionally assessed via cycloheximide chase assays or quantitative polymerase chain reaction plus sequence analysis of blood cDNA, as appropriate. Two rare likely benign defects (c.787 + 9C>T and p.T231M), two variants of uncertain significance (p.R106C and p.V291_L292del), one likely pathogenic (LP, p.C238Y), and one pathogenic (p.R304*) variant were found in six cases (5.9%). One individual was diagnosed with multiple gastric NENs and five carried PitNETs. Variant p.V291_L292del produced an unstable protein (P < 0.0001 for half-life curve, compared with wild type) and was reclassified to LP. Loss of heterozygosity in a gastric neuroendocrine tumor and nonsignificantly increased protein stability were observed for p.R106C. No deleterious effects were documented for c.787 + 9C>T. In conclusion, we determined the prevalence of AIP variants in a cohort of NENs and reclassified one VUS to LP. Our findings support the causal association of AIP LOF with PitNETs, but cannot rule out a role for AIP in other NENs.