Zinc transporter 8 autoantibodies: what is their clinical relevance in gestational diabetes?

Aims To investigate the prevalence, clinical significance and antepartum to postpartum trajectory of zinc transporter 8 autoantibodies, a novel marker of islet autoimmunity, in women with gestational diabetes mellitus. Methods A total of 302 consecutive women attending a multi‐ethnic Australian gestational diabetes clinic were prospectively studied. Zinc transporter 8 autoantibodies were measured at gestational diabetes diagnosis and 3 months postpartum using an enzyme‐linked immunosorbent assay, and were correlated with maternal phenotype, antepartum and postpartum glucose tolerance, treatment and perinatal outcomes. Results Of the 302 women, 30 (9.9%) were positive for one islet autoantibody antepartum. No participant had multiple islet autoantibodies. Zinc transporter 8 autoantibodies were the most prevalent autoantibody [zinc transporter 8 autoantibodies: 13/271 women (4.8%); glutamic acid decarboxylase 7/302 women (2.3%); insulinoma‐associated antigen‐2: 6/302 women (2.0%); insulin: 4/302 women (1.3%)]. Zinc transporter 8 autoantibody positivity was associated with a higher fasting glucose level on the antepartum oral glucose tolerance test, but not with BMI , insulin use, perinatal outcomes or postpartum glucose intolerance. Five of the six women who tested positive for zinc transporter 8 autoantibodies antepartum were negative for zinc transporter 8 autoantibodies postpartum, which corresponded to a significant decline in titre antepartum to postpartum (26.5 to 3.8 U/ml; P =0.03). This was in contrast to the antepartum to postpartum trajectory of the other islet autoantibodies, which remained unchanged. Conclusions Zinc transporter 8 autoantibodies were the most common islet autoantibody in gestational diabetes. Zinc transporter 8 autoantibody positivity was associated with slightly higher fasting glucose levels and, unlike other islet autoantibodies, titres declined postpartum. Zinc transporter 8 autoantibodies may be a marker for islet autoimmunity in a proportion of women with gestational diabetes, but the clinical relevance of zinc transporter 8 autoantibodies in pregnancy and gestational diabetes requires further investigation.