Diabetes related autoimmunity in gestational diabetes mellitus: Is it important?

Nutrition, Metabolism & Cardiovascular Diseases (2009) 19, 674e682 available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/nmcd

REVIEW

Diabetes related autoimmunity in gestational diabetes mellitus: Is it important? `, D. Fedele A. Lapolla*, M.G. Dalfra Department of Clinical and Surgical Sciences-Chair of Metabolic Disease, Padova University, Via Giustiniani n 2, 35100 Padova, Italy Received 24 September 2008; received in revised form 6 February 2009; accepted 1 April 2009

KEYWORDS Diabetes; Pregnancy; Autoimmunity

Abstract Some GDM women show autoantibody positivity during and after pregnancy and pancreatic autoantibodies can appear for the first time in some patients after delivery. Autoantibody positivity is often accompanied by a high frequency of DR3 and DR4 alleles, which are classically related to the development of type 1 diabetes and, although not all studies agree on this point, by an immunological imbalance expressed by the behaviour of the lymphocyte subpopulation, which can be seen as diabetic anomalies overlapping with the immunological changes that occur during pregnancy. It is worth emphasizing that such patients may develop classical type 1 diabetes during and/or after their pregnancy or they may evolve, often some years after their pregnancy, into cases of latent autoimmune diabetes of adulthood (LADA). Autoimmune GDM accounts for a relatively small number of cases (about 10% of all GDM) but the risk of these women developing type 1 diabetes or LADA is very high, so these patients must be identified in order to prevent the severe maternal and fetal complications of type 1 diabetes developing in pregnancy, or its acute onset afterwards. Since women with autoimmune GDM must be considered at high risk of developing type 1 diabetes in any of its clinical forms, these women should be regarded as future candidates for the immunomodulatory strategies used in type 1 diabetes. ª 2009 Elsevier B.V. All rights reserved.

Introduction

* Corresponding author. Department of Clinical and Surgical Sciences-Chair of Metabolic Disease, Padova University, Via Giustiniani n 2, 35100 Padova, Italy. Tel.: þ390498216848; fax: þ390498216838. E-mail address: [email protected] (A. Lapolla).

Gestational diabetes mellitus (GDM) is classically defined as a carbohydrate intolerance of variable severity that develops or is first recognized during pregnancy. It is the most common metabolic disorder in pregnancy, affecting 1e10% of all pregnancies [1,2]. Although all the physiopathological mechanisms leading to the onset of GDM are

0939-4753/$ - see front matter ª 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.numecd.2009.04.004

Diabetes related autoimmunity in gestational diabetes mellitus still not known, in most cases it is characterized by an increased insulin resistance in certain tissues, particularly the skeletal muscle, and a decline in insulin secretion [3,4], both defects characteristic of type 2 diabetes. Women with GDM are consequently at high risk of developing type 2 diabetes after their pregnancy [5], but some of them have symptoms typical of type 1 and/or latent autoimmune diabetes of adulthood (LADA) [6]. The aim of this review is to analyze the available literature on diabetes related autoimmunity in GDM to ascertain whether autoimmune GDM can really be considered as a clinical entity in its own right.

Genotyping Type 1 diabetes is characterized by a progressive destruction of pancreatic beta cells, giving rise to insulin deficiency and hyperglycaemia. It has been demonstrated that beta-cell destruction is the outcome of an autoimmune process mediated by T-cells and that this process is initiated by a series of environmental conditions, mostly as yet unidentified, in genetically susceptible individuals [7,8]. Studies on first-degree relatives of patients with type 1 diabetes have shown islet autoimmunity for months and even years before 70% of beta-cell function is lost and the typical symptoms of diabetes become clinically apparent [9]. Concerning genetic involvement, the major histocompatibility complex (MHC) on chromosome 6 in human leukocyte antigen (HLA) alleles at the class II DR and DQ loci is evident in 50% of family clusters of type 1 diabetes cases [10]. The HLA class II molecules present the antigenic peptides to helper cells (CD4). HLA class I molecules also have a role in this setting because they present the antigenic peptides to T cytotoxic cells (CD8). HLA typing is useful in assessing the risk of type 1 diabetes in relatives of type 1 diabetic patients. The DRB1*03,04DQBI*;0201,0302 (DR3,4-DQ2,8) sequence coincides with relatives having a more than 20-fold risk of developing diabetes and is associated with an earlier age at diagnosis [11]. The other characteristic sequences, such as DRB1*04,04; DQB1*0302,0302(DR4,4-DQ8,8), DRB1*03,03; DQB1*0302,Y(DR3,3-DQ8,Y),DRB1*04,03; DQB1*0302,Y(DR4,X-DQ8,Y) and DRB1*03,X, correlate with a lower risk of developing type 1 diabetes. However, even siblings with no haplotypes on either chromosome carry a 1:100 risk of developing diabetes, as compared with the 1:300 risk for the general population. In this context, it is worth emphasizing that it is crucial to identify protective markers against any future onset of type 1 diabetes in first-degree relatives too. HLA-DQ 6 (*0602) has been negatively associated with the onset of type 1 diabetes in childhood [12], but this association is lost in adult-onset type 1 diabetes [13]. Studies have demonstrated that DRB1*0403 is the marker associated with the strongest protective effect in Continental Europe [14] and in Italy [15]. As for the genetics of GDM, there has been relatively little research on these patients for a number of reasons. It is difficult, for instance, to study the twin concordance or to estimate the family risk or heritability due to the

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relatively low prevalence of GDM. In this setting, only one study [16] has shown a greater family cluster of diabetes on the maternal side of offspring with type 1 diabetes whose mothers had GDM. Studies on the HLA haplotype in GDM patients are inconsistent and this is due mainly to the ethnic heterogeneity of the populations considered and to the small numbers of patients involved (Table 1). Some authors have reported no association between HLA haplotype and GDM or islet autoimmunity [17e21], while others have found different results [22e25]. Rubinstein et al found no greater frequency of DR3 and DR4 in GDM patients than in normal controls, but 50% of ICA-positive GDM women were positive for the presence of DR3 or DR4 [22]. Freinkel et al [23] found a high frequency of DR3 and DR4 in GDM patients, which correlated positively with ICA positivity and progression to type 1 diabetes. Ferber et al reported similar results [24]. In a study of ours [25] that compared the frequency of HLA, antigen autoantibodies and T lymphocyte subpopulations in GDM women and normal pregnant women, only 1 in 2 patients with autoantibody positivity who developed type 1 diabetes tested positive for DR3 and DQw2. Finally, only Cw7 was found to be significantly higher than normal in GDM women and, in this context, it must be emphasized that HLA-Cw7 has only recently been related to the risk of type 1 diabetes development [26]. More recently, in a Swedish GDM population, Torn et al [27] showed that HLA-Dr3-DQ2 or Dr4-DQ8 and MICA5.0/5.1 were more common in GDM women with autoantibody positivity than in controls, whereas 4 other genotypes were more frequent in autoantibody-negative GDM women than in controls (i.e., HLA-DR7-DQ2, DR9-DQ9, DR14-DQ5 and MICA5.0/z). On the basis of their results, the authors speculated that the presence of these genotypes in nonautoimmune GDM women could be related to some condition associated with their non-autoimmune GDM, such as insulin resistance, hypertension and pre-eclampsia. Finally, Steinborn et al [28] found a significantly higher percentage of anti-HLA class II antibodies circulating in women with GDM, expressing the mother’s stronger humoral immune reaction to fetal class II HLA. This increased alloimmune response may be involved in the pathogenesis of GDM through activation of the inflammatory system thereby determining beta-cell apoptosis [29]. This fascinating new hypothesis, however, needs to be confirmed.

Islet antigen reactive T-cells Pregnancy is characterized by a particular immunological state: the fetus is seen as an allograft by the mother’s immunological system, continuously needing protection against rejection processes. Recognition of fetal antigens by the mother is probably a prerequisite for the normal course of gestation. A strong activation of the maternal immune system in response to the paternal antigens expressed by the fetus is normal in pregnancy [30], while low numbers of peripheral T helper and NK cells in late pregnancy are thought to play a part in maintaining gestation [31]. In diabetes, it has been demonstrated that beta-cell destruction is mediated by autoreactive T-cells, mainly CD8þTCR alphaebeta and CD3* CD4 CD8 TCR gammae delta [32,33] and that peripheral T cell distribution is impaired

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A. Lapolla et al.

Table 1

Human leukocyte antigen (HLA) in GDM women.

Authors

HLA in GDM

Islet autoimmunity

Autoimmune diabetes mellitus after GDM

Rubinstein et al, 1981 [22] Freinkel et al, 1985 [23] Bell et al, 1990 [17] Strangenberg et al, 1990 [18] Damm et al, 1994 [19] Lapolla et al, 1996 [25] Vanbergue et al, 1997 [20] Ferber et al, 1999 [24] Torn et al, 2004 [27] Steinborn et al, 2006 [28]

no trend no no e no no no yes yes

yes no no e e no e yes yes e

e e e e trend e e yes yes yes

in diabetes, both at diagnosis and during the course of the disease [34,35]. As for the lymphocyte subsets in GDM patients (Table 2), Di Mario et al [36] reported a decline in T lymphocytes, and especially T helper/inducer cells, and Bompiani [37] found a drop in the ratio of T helper to T suppressor cells. In a previous paper we demonstrated a significant rise in the absolute number of total and activated T lymphocytes (CD3þHLA-DRþ), and a significant increase in the absolute number and percentage of suppressor/cytotoxic T lymphocytes (CD8) and NK lymphocytes (CD57) in GDM patients by comparison with normal pregnant women, suggesting that the immunological status of GDM women during pregnancy could be considered as the compound effect of diabetic anomalies and of the immunological changes occurring during pregnancy [25]. In future studies, we aim to establish whether T lymphocytes expressing the CD3 gammaedelta receptor are overexpressed in GDM patients, with a view to clarifying its possible role in the pathogenesis of subsequent type 1 diabetes. In a preliminary study, we showed that the percentage of CD3þTCR gammaedelta was significantly higher in GDM women than in their normal pregnant counterparts, but no relationship emerged with autoantibody positivity [38]. When we analyzed a large number of GDM women who were also tested for cytokines (IL-2, IL-2 soluble receptor and IL-5) [39], we found higher levels of lymphocytes, CD8 expressing TCR gammaedelta, and lower levels of CD3 expressing TCR alphaebeta in our GDM women than in normal pregnant women, thus confirming Lang

Table 2

Lymphocyte subsets in GDM women.

Authors

Di Mario et al, 1987 [36] Lapolla et al, 1996 [25] Lapolla et al, 1999 [42] Lapolla et al, 2000 [38] Lapolla et al, 2005 [39] Mahmoud et al, 2005 [43] a

et al’s finding [40]. Women requiring insulin therapy during pregnancy showed a drop in CD4 and a rise in CD8, so it would seem that a reduction in T helper lymphocytes and an increase in T suppressor cytotoxic lymphocytes have an important role in the future development of type 1 diabetes in more severe forms of GDM. Patients with autoantibody positivity also had significantly lower CD4 and higher CD8 levels, confirming the hypothesis that the initial betacell insult is caused by cytotoxic CD8 cells in a CD4dependent manner [41]. Autoantibody-positive GDM women also had lower IL-5 levels, further confirming an immunological imbalance that may play a part in the subsequent onset of type 1 diabetes in these women. In the same study, we also showed that the newborn of insulin-treated GDM mothers had significantly lower CD3 alphaebeta and higher CD16 levels, and that the newborn of autoantibody-positive GDM mothers had low CD4 and high CD8 levels, suggesting that the newborn of mothers with the more severe and the autoimmune forms of GDM also have an immunological imbalance that may correlate with a greater risk of developing type 1 diabetes [42]. In a more recent paper, Mahmoud et al [43] reported that GDM women had higher percentages of CD4þCD25þ, CD4þCD45ROþ and CD4þCD29þ, and significantly lower levels of CD4þCD45RAþ in comparison with normal pregnant women; their data partially confirming our own and seem to indicate that normal maternal immunosuppression is less effective in GDM women. It is worth noting that a limit of some published studies is that they describe the frequencies of particular T cell

GDM insulin treated.

N

17 68 15 29 62 20

T lymphocyte (%) CD3

CD8

CD4

Y [ [ (absolute number) [ TCRgd [ TCRgd [a

Z [ [ (absolute number) e [ TCRgd [aCD3þCD8þ

Y [ [ (absolute number) e Z [aCD4þCD8þ

Diabetes related autoimmunity in gestational diabetes mellitus subsets in the plasma of their subjects and provide no evidence to prove that these cells are indeed autoreactive. The reported influence of pregnancy and GDM on T lymphocyte subsets consequently varies, but the more severe and the autoimmune forms of GDM seem to be characterized by lymphocyte alterations resembling those occurring in type 1 diabetes.

Islet antibodies The following antibodies have been identified as markers of beta cell autoimmunity: ICA (islet cell autoantibody), IAA (insulin autoantibody), GAD 65A (glutamic acid decarboxylase autoantibody), IA-2A (tyrosine phosphatase-like islet antigen autoantibody), and IA2beta (tyrosine phosphataselike islet antigen autoantibody). The sensitivity of ICA, GAD, IAA and IA-2Ab in diagnosing new cases of diabetes in pre-pubertal children is, respectively, 85%, 60%, 80% and 75%. It has been demonstrated that young relatives of patients with type 1 diabetes carry a greater risk of developing diabetes the more of these antibodies they have, i.e., diabetes developed within 5 years in 15% of relatives with 1 antibody, 44% of those with 2, and 100% of those with 3 antibodies [44]. Preliminary screening with GAD and IAA can pinpoint more than 85% of cases of newly diagnosed or future type 1 diabetes with a 98% specificity. IAA may be seen even before the appearance of GAD, so it should be included in the screening of pre-pubertal children. It is worth adding that, among these diabetes related autoantibodies, only GAD are not age-dependent, so they are sensitive markers for studying childhood and adult autoimmune diabetes (LADA). As shown by Vandewalle et al [45], GAD autoantibodies are the markers with the highest diagnostic sensitivity in LADA so they should be used to identify such patients. It is generally accepted that autoantibodies are markers of type 1 diabetes but are not directly involved in destroying beta cells. Wenzlau et al [46] recently found antibodies to a new antigen ZnT8S in type 1 diabetic patients previously classified as autoantibody-negative. Studies on a large series of diabetic patients and controls are currently underway to assess the sensitivity, specificity and potential clinical application of this marker.

Islet autoantibodies in GDM patients As for ICA assessment during pregnancy, Fig. 1 shows the most important published studies [9,17e19,23,25,47e63]: clearly, the frequency of ICA positivity in GDM patients varies considerably, ranging from 1% to 35%. It should be noted that the studies reporting a high frequency of ICA positivity, such as those by Rubinstein et al [22] and Ginsberg-Fellner et al [47], measured these antibodies using an indirect immunofluorescence method with a Bouin-fixed pancreas e a method that has yet to be standardized and that yields numerous false positive results. Subsequent studies reported a considerably lower frequency of ICA positivity using a standardized method based on indirect immunofluorescence testing on unfixed pancreas [48e63]. ICA titres were generally lower in GDM patients than in cases of newly diagnosed type 1 diabetes [19,50e53,57,61].

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Moreover, only some authors considered control groups, most of them finding ICA positivity more common in GDM patients than in controls [23,52,54,57,61,62]. Fig. 1 lists the studies that evaluated IAA frequency in GDM patients [6,19,50,53,59,64]. Here again, the antibody titres are lower in GDM patients than in cases of new-onset type 1 diabetes [53]. In addition, most of the studies on GDM report a low prevalence of IAA, while only 3 found a higher prevalence of IAA positivity in GDM patients than in the control population [62,64]. These data are consistent with the fact that IAA are more frequent in patients whose type 1 diabetes developed at an early age [65]. Fig. 1 lists most of the studies that evaluated GAD frequency in GDM patients [54,55,57e64,66e76]. GAD autoantibody titres in GDM patients are usually reportedly lower than in cases of type I diabetes [61,77]. The results of studies on GAD titres in GDM patients and controls also vary widely, some showing higher titres [54,57,61,62,70,71] and others showing no difference [68,69,72,75,76]. Such different results may be due to the different populations considered, since it is common knowledge that ethnicity plays an important part in determining beta-cell autoimmunity. As for the frequency of IA2 positivity this ranges from 0% to 62% in the published literature [54,55,57,60,62,64]. Some papers report a higher frequency in GDM patients than in normal controls [54,57,64], while others found no difference [53,62]. On the whole, IA2 titres were found to be lower in GDM patients than in type 1 diabetics [55] and this is important because their presence is associated with a rapid progression to insulinopenia [78]. When looking at combinations of autoantibodies in GDM patients, high antibody titres are rare [57,54,55,60,62] and this is in keeping with the slow progression of autoimmune disease in GDM patients.

Autoantibodies and predicting future diabetes in women with GDM A number of studies have considered the potential predictive role of autoantibodies vis-a `-vis the onset of type 1 diabetes after delivery in GDM patients and most of them have confirmed the predictive role of positivity for ICA [19,47,56,62,64,68], GAD [62,63,68,78] and the presence of 2 or more autoantibodies [62,64,68,78,79e81], but not for IA2 [54,62]. Most of the studies confirming the predictive value of antibodies refer to a long follow-up such as the study by Ivarsson et al on type 1 diabetes developing 18 years after pregnancy [63], while it does not come to light after a short- or medium-term follow-up. In a Finnish population, Ja ¨rvela ¨ et al [62] found that 10% of GDM women developed diabetes within 6 years; aged less than 30 years, the need for insulin therapy during pregnancy, and ICA and GAD positivity coincided with a high risk of developing type 1 diabetes, accounting for half of the women who became diabetic after their pregnancy. None of the women who developed type 1 diabetes tested positive for IAA in this study, confirming the results reported by Fuchtenbusch et al [54]. As for IA2 behaviour, Lo ¨bner et al [79] showed an 8year postpartum diabetes risk of 52.7% in GDM women, and higher still in those who were GAD and/or IA2 positive.

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A. Lapolla et al. ICA

GAD

IAA

IA2

GAD+IA2

Murgia 2008 (64) Jarvela,2006(62) Damanhouri,2005(75) Bo,2003(61) Albareda,2003(60) Lapolla,2002(59) Balaji,2002(73) Weng,2002(72) Kousta,2001(71) Bartha,2001(58) Mitchell,2000(70) Kinalski,1999(57) Panczel,1999(56) Whittingham,1997(55) Fallucca,1997(69) Fuchtenbusch,1997(54) Ivarsson 1997 (63) Dozio,1997(53) Lapolla,1996(25) Petersen,1996(68) Mauricio,1996(6) Beischer,1995(67) Tuomilehto,1994(66) Damm,1994(19) Ziegler,1993(9) Mauricio,1992(52) Strangerberg,1990(18) Bell,1990(17) Catalano,1990(51) Stowers,1985(50) Freinkel,1985(23) Fallucca,1985(49) Ginsberg-Fellner,1980(47) Steel,1980(48) 0

5

10

15

20

25

30

35

40

45

50

Figure 1 Frequency (%) of islet cell autoantibody (ICA) , glutamic acid decarboxylase autoantibody (GAD) ,, insulin autoantibody (IAA) , tyrosine phosphatase-like islet antigen autoantibody (IA2) -,glutamic acid decarboxylase and IA2 in GDM women.

Women developing type 1 diabetes after pregnancy had a normal BMI and a higher prevalence of HLA DR3 or DR4 DQ8 haplotypes, and most of them required insulin therapy during pregnancy. The frequency of autoantibody positivity was globally low in the Lo ¨bner et al’s study, but any such positivity coincided with a high risk of developing type 1 diabetes after pregnancy. More recently, Nilsson et al [82] reported a 6% positivity for at least one autoantibody (ICA, GAD or IA-2A) in GDM women. In a follow-up lasting 8 years, 50% of the autoantibody-positive women developed type 1 diabetes and 21% had impaired fasting and/or impaired glucose tolerance e a significantly higher rate than in autoantibody-negative GDM patients. Of the women who developed type 1 diabetes (all GADA-positive), this happened within 6 months of delivery in 41% of cases and within a year in 50%. These findings emphasize the importance of autoantibody screening during and after pregnancy to ensure the early recognition of type 1 diabetes. We measured ICA, GAD and IA2 in GDM women during and after pregnancy. One of 70 patients was positive for both ICA and GAD during pregnancy, while one other was positive for ICA; none were positive for IA2. During the follow-up, the situation remained unchanged in the 2 positive cases, and 4 previously negative patients became positive (1 for ICA and GAD, and 3 for GAD alone). Type 1 diabetes developed in 2 of the 6 patients with pancreatic autoimmunity over a 5-year follow-up [59]. This study confirms the low rate of pancreatic autoimmunity in GDM patients and shows that GAD antibodies can sometimes appear after delivery. This may be because the mother’s typical immunodepressed state during pregnancy causes a drop in the titre of some organ-specific autoantibodies. So

it is important to repeat autoantibody screening a few months after delivery [82]. Murgia et al [64] recently reported finding a high prevalence (38.8%) of autoantibodies in GDM patients from Sardinia (an Italian region where type 1 diabetes is relatively common). Judging from these data, it would make sense to recommend screening for autoantibodies in areas with high rates of type 1 diabetes. In conclusion, pancreatic autoimmunity is rare in GDM patients, but its presence coincides with a high risk of developing type 1 diabetes after pregnancy and it is, therefore, important to screen these patients during and after pregnancy to recognize type 1 diabetes early on.

GDM and LADA Though the rationale for defining LADA has recently been questioned [83] because the diagnosis is still imprecise, it is important to retain the word ‘‘latent’’ to distinguish slowonset type 1 diabetes from classical adult type 1 diabetes [84]. The prevalence of LADA varies, depending on the population studied and the autoantibody screening method used [85e87]. For example, in the general population of northern Italy its prevalence is 0.19% (95% CI: 0.05e0.5), representing only a small minority of cases of adult diabetes [87]. The diagnosis of LADA is generally based on 3 criteria. (1) Adult age at onset of diabetes; (2) the presence of circulating islet antibodies and; (3) lack of a requirement for insulin for at least 6 months after diagnosis [83,84,88e 91]. Furthermore the Immunology of Diabetes Society has

Diabetes related autoimmunity in gestational diabetes mellitus proposed that an age of 30 years has to be used as a cut-off when using the age criteria [12]. As for genetic factors, LADA has a genetic susceptibility generally resembling the situation seen in adult-onset type 1 diabetes [85,86]. HLA-DQ 6 (*0602) has been negatively associated with the onset of type 1 diabetes in childhood [12], but this association is lost in adult-onset type 1 diabetes [13], so it is not clear whether this disease is controlled by distinct genetic markers or due to the action of protective environmental factors on a genetic predisposition to diabetes. Concerning autoantibodies, LADA is usually diagnosed by the presence of GAD, with or without ICA and/or IA2 antibodies [84,86,90]. The results of an Italian nationwide survey on Non-Insulin-Requiring Autoimmune Diabetes (NIRAD), conducted on 4250 type 2 diabetic patients has added to our understanding of LADA: 4.5% of patients reveal GAD and/or IA-2A antibodies and, among them, those with high GAD titres have a more prominent insulin deficiency, a lower BMI, a lower prevalence of the metabolic syndrome and a higher prevalence of IA-2A5, TPO antibodies, and DRB1*0602 and DRB1*06403. So GAD titres identify 2 subgroups of LADA patients with distinct clinical, autoimmune and genetic factors [92]. Among patients with a clinical diagnosis of type 2 diabetes in which the frequency of GAD 65 autoantibodies was 10.7%, Falorni et al [93] found that the majority of GADpositive patients had autoantibodies directed against both middle (GAD 65-MAb) and COOH-terminal (GAD 65-CAb) epitopes, and the presence of GAD 65-CAb antibodies was strongly associated with the need for insulin therapy. So this study clearly demonstrated that an epitope-specific antibody assay is useful in improving the diagnostic specificity of GAD antibodies. A further improvement in LADA diagnosis came from the results of the NIRAD Study 2 [94]: the authors evaluated the frequency of 7 IA2 construct fragments and found that IA2[256e760] was the most sensitive marker for detecting IA-2A immunoreactivity in LADA patients. This marker proved to be strongly associated with HLA diabetes genotypes and with a higher risk of developing thyroid autoimmunity. So IA-2A immunoreactivity in LADA patients has

Table 3 Clinical characteristics related to islet autoimmunity in GDM women [61]. Characteristics

Abþ vs Ab p

Age Prepregnancy BMI No risk factor for GDM Weight gain BMI at screening Waist Fasting plasma insulin HOMA

0.19 0.31 0.009 0.039 0.035 0.022 0.0004 0.20

p Express the significance of differences (evaluated as mean value or frequency) between GDM women with positive autoantibodies (Abþ) and GDM women with negative autoantibodies (Ab).

679

been underestimated in the past and the IA-2A[256e60] autoantibody may be a novel diagnostic tool to use in the diagnosis of LADA. As for LADA and GDM, a very elegant paper by de Mauricio et al [95] showed an impaired acute insulin response to intravenous glucose and persistently low levels of ICA positivity (<20JDF) in prior ICA-positive GDM patients, even if their glucose tolerance was normal 13 months after pregnancy. Such behaviour is similar to the one recently emerging in first-degree relatives of LADA patients in a Finnish study [96], thus showing that there are similarities between GDM and LADA. Bo et al [61] assessed the prevalence of beta-cell autoantibodies in women with GDM, impaired glucose tolerance and normal glucose tolerance: autoantibody positivity was 8.9%, 17.9% and 0.3%, respectively, in the 3 groups of patients. Autoantibody-positive hyperglycaemic patients had fewer previous pregnancies, a lower BMI, a smaller waist-to-hip ratio, and a smaller weight gain during pregnancy than their autoantibody-negative counterparts. Their fasting insulin levels were significantly lower and correlated inversely with the presence of autoantibodies, the lowest values being found in anti-GADpositive patients. Finally, autoantibody-positive patients needed insulin more often than autoantibody-negative patients (Table 3). Thus, autoantibody-positive GDM patients display fewer features of insulin resistance and bear some resemblance to LADA patients. In this context it would be interesting to ascertain the frequency of the novel marker identified in LADA patients [93,94] in the GDM population.

Conclusions From the studies discussed in this review and in agreement with de Leiva et al [97], it is clear that some GDM women have autoantibody positivity during and after pregnancy, and that pancreatic autoantibodies can appear only after delivery in some patients. Autoantibody positivity is often accompanied by a high frequency of DR3 and DR4 alleles, which are classically related to the development of type 1 diabetes and, although not all studies agree on this point, by an immunological imbalance expressed by the behaviour of the lymphocyte subpopulation, which can be seen as diabetic anomalies overlapping with the immunological changes that occur during pregnancy. It is worth emphasizing that such patients may develop classical type 1 diabetes during and/or after their pregnancy, or they may evolve e often some years after their pregnancy e into cases of LADA. Therefore, 20 years on, we still agree with Freinkel et al [23] that GDM is a heterogeneous disease with a genotypic and phenotypic diversity that also includes patients who progress to type 1 diabetes. Autoimmune GDM accounts for a relatively small proportion of cases (about 10% of all GDM), but the risk of these patients developing type 1 diabetes or LADA is very high, so these patients should be identified to avoid the severe maternal and fetal complications of type 1 diabetes developing during pregnancy, or an acute onset of diabetes afterwards.

680 On the basis of this literature review, we can recommend that autoimmune GDM be considered as a distinct clinical entity and this means that we have to think about revising the classification of diabetes in pregnancy to include this form of GDM too. This does not mean that all GDM patients must be screened for autoantibodies because the procedure is too expensive, but we would recommend that GDM patients with clinical features suggestive of autoimmune disease (e.g., young age, no family history of type 2 diabetes, belonging to ethnic groups with a high prevalence of type 1 diabetes, a low BMI, an early diagnosis of GDM, an early need for insulin therapy) be screened for autoantibodies. Women with autoimmune GDM must be considered at high risk of developing type 1 diabetes in any of its clinical forms, so they should be regarded as potential future candidates for immunomodulatory strategies, as in type 1 diabetes.

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