Pathophysiology/Complications N A L
A R T I C L E
Low Prevalence of Islet Autoantibodies in Patients With Gestational Diabetes Mellitus NlCOLETTA DOZIO, MD ANGELO BERETTA, MD CRISTINA BELLONI, DIP APPL SCI MARIATERESA CASTIGLIONI, MD
SUSANNA ROSA, MD EMANUELE BOSI, MD Ezio BONIFACIO, PHD
Subjects
OBJECTIVE — To determine the proportion of patients with gestational diabetes mellitus (GDM) who have serological characteristics typical of 1DDM. RESEARCH DESIGN A N D METHODS— Islet cell antibodies (ICAs), insulin autoantibodies (lAAs), GAD65, and IA-2 antibodies were measured in 145 pregnant women with GDM, 33 with impaired glucose tolerance (IGT), and in 73 with normal glucose tolerance (NGT). ICAs were measured by indirect immunofluorescence; GAD65 and IA-2 antibodies, by a radio-ligand immunoassay incorporating 35S-labeled recombinant antigen; and LAAs, by a liquid-phase radiobinding assay. RESULTS — The prevalences of islet autoantibodies were low and not significantly different between groups. ICAs were detected at levels ranging from 5 to 45 Juvenile Diabetes Foundation U in 14 (10%) women with GDM, 2 (6%) women with IGT, and in 4 (5%) women with NGT. IAAs were detected at levels between 3 and 4 SD above the mean in 4 (3%) women with GDM, 0 women with IGT, and in 1 (1%) woman with NGT. None had both ICAs and IAAs. Neither GADM nor IA-2 antibodies, which have been detected in the majority of pre-IDDM and 1DDM patients, were found in NGT, IGT, or GDM patients. CONCLUSIONS — Low-titer ICAs and IAAs are not infrequent in pregnant women, but multiple islet autoantibodies and antibodies to GAD65 or IA-2 were not found in GDM. These findings suggest that the serological characteristics of IDDM are rare in GDM.
G
estational diabetes mellitus (GDM) is a heterogeneous group of disorders with a high incidence of diabetes in the years following the affected pregnancy (1-3). The majority of patients develop N1DDM, and the proportion that progresses to IDDM varies from 2 to 4% (3-6). Among factors predicting the progression to diabetes are the fasting blood glucose level at diagnosis and the prepregnancy BM1 (1,5), but it is nevertheless unclear which factors predict progression to IDDM in GDM patients. IDDM is an autoimmune disease that may have a long preclinical phase characterized by the presence of islet autoantibodies (7,8). It is therefore conceivable that islet autoimmunity may char-
acterize a subgroup of GDM patients with increased risk for the development of IDDM. Islet cell antibodies (ICAs), the traditional marker of IDDM, have been detected in GDM patients at prevalences ranging from 2 to 36% (4,6,9-11). Little, however, has been known up until now about the prevalence of other humoral markers of IDDM, including autoantibodies to GAD65 (12,13), IA-2 (14,15), and insulin (4,5,10,16), that, when present together with ICAs, confer a higher predictive value for the development of disease (17-19). The aim of this study was to determine whether a subgroup of patients with IDDM-associated islet autoantibodies could be identified among GDM women.
From the Department of Medicine (N.D., A.B., C.B., E.Bos., E.Bon.) and the Department of Obstetrics and (iynecology (M.C, S.R.), H. San Raffaele Scientific Institute, University of Milano, Milan, Italy. Address correspondence and reprint requests to Nicoletta Dozio, MD, Department of Medicine 1, H. San Kallaele Scientific Institute, Via Olgettina 60, 20132 Milano, Italy. E-mail:
[email protected]. Received for publication 13 June 1996 and accepted in revised form 22 September 1996. GDM, gestational diabetes mellitus; IAA, insulin autoantibody; 1CA, islet cell antibody; IGT, impaired glucose tolerance; NGT, normal glucose tolerance; OGTT, oral glucose tolerance test.
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Pregnant women attending the obstetric clinic of our institution were routinely assessed according to American Diabetes Association recommendations (20). When glucose intolerance had not been identified earlier via the presence of risk factors or altered routine blood tests, the pregnant women were screened for glucose intolerance with a 50-g oral glucose load between weeks 24 and 28 of gestation. Those pregnant women with a 1-h plasma glucose level ^ 1 3 5 mg/dl or ^ 7 . 5 mmol/1 subsequently underwent a full 100-g oral glucose tolerance test (OGTT). From February 1988 to March 1994,214 pregnant women without previous GDM or previous known glucose intolerance underwent a 3-h 100-g OGTT and were included in this study. An additional 37 women with NGT underwent the 100-g OGTT without previous selection because they served as controls for a separate study. From the total of 251 women included in this study, 145 were classified as having GDM according to the criteria recommended by Carpenter and Coustan (21) (i.e., two plasma glucose ^ 5 . 3 , 10, 8.6, and 7.8 mmol/1 at 0, 60,120, and 180 min, respectively). Their mean BMI was 23.8 (range, 16-44). Of these women, 18 were diagnosed before the 24th week of gestation and 51 (35%) had a family history of diabetes. Furthermore, 33 women were classified as having impaired glucose tolerance (IGT) when one abnormal value was found after the oral glucose load, and the remaining 73 had normal glucose tolerance (NGT). All women gave their informed consent to be included in this study. Serum samples were collected either at the time of the OGTT or at delivery and were kept frozen. GDM patients were followed in a single outpatient clinic by one team, and insulin treatment was started on the basis of capillary blood glucose self-determination with fasting values ^ 5 . 8 mmol/1 or postprandial values ^ 6 . 7 mmol/1 following a moderately hypocaloric regimen. GDM patients with islet autoantibodies were followed for the development of diabetes and autoantibody measurement, and
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Islet autoantibodies
in GDM
Table 1— Islet autoantibody pre\alences during pregnancy
GDM IGT NGT
n
ICAs
lAAs
145 33 73
14(10) 2(6) 4(5)
4(3) 0(0)
KD
GAD65 antibodies
IA-2 antibodies
0(0) 0(0) 0(0)
0(0) 0(0) 0(0)
Data are n (%).
75-g OGTTs were performed in a subgroup of patients 3-7 years after the index pregnancy. Methods ICAs were measured by indirect immunofluorescence on fresh frozen pancreas and quantified in Juvenile Diabetes Foundation (JDF) units (detection limit, 5 JDF U) (22). IAAs were measured by competitive liquidphase radiobinding assay, using 125I-Tyr A14 human insulin, as described (23), with one extra washing after polyethylene glycol precipitation. The threshold for positivity was selected at the 99th centile of 326 normal control subjects. GAD65 and IA-2 antibodies were detected by radio-ligand immunoassay of 35S-labeled in vitro translated recombinant antigen. The threshold for positivity was selected at 3 U, representing the 99th centile of control samples for GADM and IA-2 antibodies (15,24).
Statistics Differences in antibody prevalences between groups were analyzed using the x 2 test or Fishers exact test, when appropriate. Analysis of variance was performed to compare mean blood glucose levels between groups. R E S U L T S — Of the 251 women, 145 were classified as having GDM (median age, 31 years; range, 21-43 years), 33 as having IGT (median age, 31 years; range, 23-38 years), and 73 as having NGT (median age, 30 years; range, 21-41 years). No significant differences were observed between the prevalence of islet autoantibodies in these groups (Table 1). ICAs at relatively low titers (5-45 JDF U) were found in 14 (10%) women with GDM, 2 (6%) women with IGT, and in 4 (5%) women with NGT. There were no differences in ICA levels between groups. Similarly, those few subjects with IAAs all had low levels (3-4 SD above the mean). None had both ICAs and IAAs. Antibodies to
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GAD65 and IA-2 were not found in any subject. Twenty-one GDM patients required insulin therapy. Insulin-treated patients had higher basal plasma glucose levels at the OGTT (6 ± 1.1 vs. 5 ± 0.6 mmol/1, P < 0.0001), but no one of the insulin-treated patients had islet antibodies. Patients with ICAs or IAAs did not have higher blood glucose levels at any time during the OGTT. Three to seven years after the index pregnancy, it was possible to contact 13 of the 14 GDM women with ICAs and 3 of the 4 GDM women with IAAs. None had developed IDDM. At the same time, a 75g OGTT was performed in 7 of the 14 women with ICAs and in 2 of the 4 women with IAAs. Glucose tolerance was classified as normal in two of these women, impaired in three, and abnormal (although not diagnostic for diabetes) in the remaining four. Two patients had developed low levels of IA-2 antibodies, one with NGT and one with IGT. No other islet autoantibodies were detected in the follow-up samples. C O N C L U S I O N S — GDM encompasses all forms of glucose intolerance diagnosed for the first time during pregnancy. It includes heterogeneous diseases such as IDDM, which occasionally develops during pregnancy, and glucose intolerance associated with gross obesity. GDM is associated with increased perinatal morbidity, and a large proportion of GDM patients develop NIDDM and a few develop IDDM in later life (1-4). While there is general consensus on the need for diagnosis during pregnancy, the criteria for diagnosis of GDM are still debated (20,25). Nevertheless, screening procedures for glucose intolerance during pregnancy are now routine, and it is possible to identify a large number of women at risk for the development of diabetes. The proportion of GDM women who develop IDDM varies among the different cohorts studied, but is generally low. The
progression to IDDM has been reported to be associated with the presence of islet autoantibodies during gestation (4,6). The presence of these serological markers is a typical finding in the majority of subjects with glucose intolerance who later develop IDDM (7,17-19,26,27). To determine the proportion of GDM patients with evidence of islet autoimmunity, we measured islet autoantibodies in pregnant women classified after an OGTT. None of the patients studied had serological characteristics typical of pre-lDDM or IDDM. While 13% of GDM patients had either ICAs or IAAs, their prevalence was not significantly higher than in pregnant women with NGT, and none had both antibodies. Importantly, neither GAD65 nor IA2 antibodies, which have been found in 90% of IDDM patients before and at onset of disease, were found in GDM patients. The presence of ICAs or IAAs alone did not appear to be related to a more severe insulin secretion impairment, since it was not associated with insulin requirements during pregnancy nor with higher blood glucose levels in the OGTT. Moreover, none of the GDM patients with islet antibodies had developed IDDM 3-7 years postpartum. Two patients developed low titer IA-2 antibodies, but no other islet antibodies were present, and indeed, in the majority tested, no islet antibodies could be detected in the follow-up sample, suggesting that the absence of multiple islet autoantibodies was unlikely to be because the samples were obtained too early in the disease process, but that the detection of single islet autoantibodies of low titer is not a specific marker of progression to IDDM. In this study, the prevalence of GDM patients requiring insulin during pregnancy was lower than in previous reports (2,10). This discrepancy may reflect differences in patient selection and patient management, since GDM patients were treated with a strict slightly hypocaloric dietary regimen (25-30 kcal/kg prepregnancy ideal body weight). The low antibody prevalence may further reflect the low incidence rate of IDDM in Northern Italy, which is one of the lowest in Europe (28). In conclusion, the findings of this study suggest that serological characteristics of the progression to IDDM are rare in pregnancies complicated with GDM. The study also supports the hypothesis that the detection of single islet autoantibodies of low titer does not indicate a significantly increased risk for the development of
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IDDM. Because multiple islet autoantibodies are rare in GDM, studies in very large cohorts will be required to assess their sensitivity and positive predictive value for future IDDM in these patients.
Acknowledgments— The authors are grateful to Elena Bazzigaluppi for help in the islet autoantibody measurements and to Andrea Moreschi, MD, for skillful help in the collection of data.
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