Dopamine D2 receptor gene polymorphisms and response to cabergoline therapy in patients with prolactin-secreting pituitary adenomas.

Dopamine-agonist cabergoline (CB) reduces prolactin (PRL) secretion and tumor size in 80% of patients with prolactin-secreting adenomas (PRL-omas) by binding type 2 dopamine receptor (DRD2). The mechanisms responsible for resistance to CB remain largely unknown. To assess the association of DRD2 with sensitivity to CB, TaqI-A1/A2, TaqI-B1/B2, HphI-G/ T and NcoI-C/ T genotypes were determined in a cross-sectional retrospective study, including 203 patients with PRL-oma. DRD2 alleles frequencies did not differ between patients and 212 healthy subjects. Conversely, NcoI-T allele frequency was higher in resistant rather than responsive patients, considering both PRL normalization (56.6 vs 45.3%, P 0.038) and tumor shrinkage (70.4 vs 41.4%, P = 0.006). Finally, [TaqI A1 -/TaqI B1 -/ HphI T -/ NcoI T-] haplotype was found in 34.5% of patients normalizing PRL with <= 3 mg/ week of CB vs 11.3% of resistants (P = 0.021). In conclusion, resistance to CB was associated with DRD2 NcoI-T+ allele, consistent with evidence suggesting that this variant may lead to reduction and instability of DRD2 mRNA or protein.