Polymorphism in vitamin D-binding protein as a genetic risk factor in the pathogenesis of endometriosis.

ABSTRACT

CONTEXT Previous studies have implicated a deficiency in the inflammatory response in women who develop endometriosis. The specific immunological deficits have not been completely elucidated. OBJECTIVE: Our objective was to identify differences in protein expression in serum that might shed light on the pathophysiology of endometriosis. DESIGN AND SETTING: This cross-sectional study of women undergoing laparoscopy between 2003 and 2005 took place at a university medical center. PATIENTS Patients included consenting women age 18-49 yr undergoing surgery for pain and/or infertility or elective tubal ligation. Women with acute or chronic medical conditions were excluded. INTERVENTION Blood was collected preoperatively. MAIN OUTCOME MEASURE: Proteomic analysis of serum was done using two-dimensional difference gel electrophoresis. RESULTS: We found 25 protein spots with a significant difference in abundance between women with endometriosis and controls, including acute-phase proteins and complement components. The abundance of vitamin D-binding protein was higher in all endometriosis pools by a factor of approximately 3 compared with the control pool (P < 0.02). Analysis of specific allele products using nano-scale liquid chromatography-electrospray ionization-mass spectrometry indicated that it was the GC*2 allele product that was in greater concentration in serum pools, as well as in single validation samples, in women with endometriosis (P = 0.006). In contrast to the GC*1 allele product, which is readily converted to a potent macrophage factor (Gc protein-derived macrophage-activating factor), the GC*2 allele product undergoes practically no such conversion. CONCLUSIONS: We speculate that the inability to sufficiently activate macrophages' phagocytotic function in those carrying the GC*2 polymorphism (more prevalent in endometriosis) may allow endometriotic tissues to implant in the peritoneal cavity. Future studies evaluating specific vitamin D-binding protein polymorphisms as a risk factor for endometriosis in larger populations of women are warranted.