Inhibin A and pro-alpha C inhibin in Down syndrome and normal pregnancies

Using two enzyme-linked immunosorbent assays specific for inhibin A and pro-alpha C inhibin, levels of the two proteins were assessed in maternal serum from 43 Down syndrome and 300 chromosomally normal pregnancies at 15-17 weeks' gestation. Compared to the control pregnancies, both inhibin A and pro-alpha C inhibin were significantly elevated in the Down syndrome pregnancies with median levels, expressed as multiples of the normal median, of 1.53 MoM and 1.34 MoM, respectively (P < 0.001 and P = 0.046 compared to controls). Levels of inhibin A and pro-alpha C inhibin were weakly but significantly correlated in both the control and the Down syndrome sera (r = 0.25, P < 0.0001; r = 0.4, P = 0.008, respectively). These data suggest that the mechanism(s) underlying the elevated inhibin levels observed in Down syndrome may affect the regulation of both the inhibin alpha- and beta A-subunits.