DEFB1 and preterm premature rupture of the membranes: 2009) Notable in this regard are the rare heterozygous damaging mutations in DEFB1, FUT2 and MBL2 that were found only in PPROM cases. Variation in these genes have been previously associated with increased risk of infection and in some cases preterm birth (Annells et al. 2005; Gibson et al. 2011; Jaffe et al. 2013).