Leptin and bone turnover in monochorionic twins complicated by twin-twin transfusion syndrome

To test the hypothesis that the bone metabolism of a growth-restricted foetus is regulated by genetic, placental and/or foetal factors through leptin, we investigated the foetal bone turnover in monochorionic pregnancies complicated with or without twin-twin transfusion syndrome (TTTS).

Maternal and cord bloods were collected from gestational-age-matched monochorionic twins with (n=15) and without (n=15) TTTS. The samples were assayed for leptin, cross-linked carboxyl terminal telo-peptide (ICTP, a marker of bone resorption) and pro-peptide (PICP, a marker of bone formation) of type I collagen by radioimmunoassay (RIA).

In the growth-restricted donor twin, the plasma concentration of leptin (P < 0.001), PICP (P < 0.001) was lower, while that of ICTP (P < 0.001) was higher than the recipient twin of the TTTS group. In contrast, leptin, PICP and ICTP were comparable in non-TTTS twins. In the recipient twin of TTTS and non-TTTS twins, leptin was positively associated with PICP (r=0.73; n=45, P < 0.001) and negatively with ICTP (r=-0.68; n=45; P < 0.001). No such association was found between leptin and bone marker in the growth-restricted donor twin of the TTTS group.

Our data suggest that, in AGA twins, leptin maintains bone metabolism by inhibiting resorption and enhancing bone formation. In contrast, growth-restricted donor twins have high bone turnover and this does not seem to be due to leptin deficiency.