Prevention of Type 1 Diabetes

Marian Rewers, MD, PhD, and Georgeanna J. Klingensmith, MD

Type 1 diabetes is the third most prevalent severe chronic disease of childhood after asthma and mental retardation, affecting 0.5–1% of the general population during the life-span.₁ Globally, 10–20 million people are affected. In the United States alone, an estimated 123,000 children and 1.4 million adults have type 1 diabetes.² Annually, at least 60,000 children are diagnosed worldwide,³ including 12,000 in the United States.

Despite recent progress in our understanding of the genetics and immunology of the disease, its incidence continues to increase by 3–5% per year.⁴ The high and increasing incidence, associated severe morbidity,⁵ mortality,⁶ and enormous health care expenditures,^7,8 makes type 1 diabetes a prime target for prevention.

NATURAL HISTORY OF TYPE 1 DIABETES

The natural history of type 1 diabetes includes four distinct stages: 1) pre-clinical ß-cell autoimmunity with a progressive impairment of acute insulin response to intravenous or oral stimuli; 2) onset of clinical diabetes; 3) transient remission; and 4) established diabetes associated with acute and chronic complications and premature death (Table 1). Our understanding of the genetic and environmental determinants of the initiation and progression of this process is incomplete at best.

Prevention differs by stage and is classified here as primary, i.e., prevention of autoimmune destruction of ß- cells; secondary, i.e. prevention of diabetes after the onset of autoimmunity; and tertiary, i.e., prevention of complications and premature mortality. Similar to other recent reviews concerned with prevention of type 1 diabetes,^9-11 this article covers only primary and secondary prevention.

PRE-CLINICAL ß-CELL AUTOIMMUNITY

Type 1 diabetes results from a chronic autoimmune destruction of the pancreatic ß-cells, probably initiated by exposure of a genetically susceptible host to an environmental agent. While the candidate genetic and environmental factors are quite prevalent, ß-cell autoimmunity appears to develop in <5% and progresses to diabetes in <1% of the general population.

The autoimmune process is mediated by macrophages and T- and B-lymphocytes and is marked by circulating autoantibodies to ß-cell antigens.^12-16 Measurement of these autoantibodies requires less cost and smaller blood volume and is partially standardized across laboratories in contrast to the cellular markers. Earlier studies utilized the immunofluorescence test for islet-cell antibodies (ICA),¹² which has been difficult to standardize and is now replaced by a combination of several radioimmunoassays for antibodies against specific ß-cell antigens, such as insulin (IAA),^13,17 glutamic acid decarboxylase (GAD),^14,18 and IA-2 (ICA512).^16,19,20 Although these tests in combination are more sensitive and predictive than ICA^21,22 in high risk groups, e.g., relatives of type 1 diabetes patients, their value for a general population screening is unknown. The use of autoantibodies, rather than diabetes, as the main endpoint in future primary prevention trials may reduce the follow-up time, trial size, and cost.

Autoimmune destruction of ß-cells is thought to be completely asymptomatic until 80–90% of the cells are lost. However, some patients report hypoglycemia-like symptoms preceding the onset of diabetes by months or even years. This poorly documented phenomenon could be caused by a disordered release of insulin from damaged islets. ß-cell loss can be monitored, albeit with a significant intra- and interindividual variability, using acute insulin response to IV glucose.^23-32

PREVENTION OF AUTOIMMUNITY

In our opinion, large-scale prevention of type 1 diabetes will be most likely accomplished through primary prevention of autoimmunity. While not all people with ß-cell autoimmunity develop diabetes in their lifespan, prevention of autoimmunity would obviously prevent all cases of type 1 diabetes. The benefit would be even greater if remitting autoimmunity (e.g., in people with protective HLA genes) causes a permanent ß-cell defect and diabetes mascarading as type 2 later in life.33 Primary prevention of autoimmunity would have advantages over interventions at the point when autoimmunity has already spread to several ß-cell autoantigens (e.g., GAD, insulin, and IA-2, or ICA, as proposed by current trials), since these secondary interventions will be hampered by the multiplicity of immunological derangements that will need to be permanently reversed at this late stage in the process.

Of course, primary prevention of autoimmunity will require an understanding of its causes and identification of risk factors that can be modified. Despite an abundance of candidates, the genetic and environmental causes of ß-cell autoimmunity remain obscure. Current observational studies should focus on identification of environmental agents that trigger and sustain autoimmunity.

Genetic Causes of ß-cell Autoimmunity and Diabetes
It is not known which of the genetic markers associated with clinical diabetes are important for development of ß-cell autoimmunity and which determine progression to diabetes. Of 15 genetic loci linked to diabetes in NOD mice,³⁴ three may cause autoimmunity (insulitis) without diabetes (J. A.Todd, personal communication). A similar systematic exploration has not yet been carried out in humans.

No particular HLA genotype seems to be associated with the initiation of ß-cell autoimmunity in humans,³⁵ whereas the DRB1*0301/04, DQB1*0201/0302 genotype clearly promotes autoimmunity persistence and progression to diabetes.^35-37 Even within one locus, such as the human HLA-DQB1 gene, some alleles (*0302 or *0201) appear to be associated with progression of autoimmunity, while others (*0602) suppress progression from autoimmunity to diabetes.^38-40 More subjects with ß-cell autoimmunity need to be genotyped to precisely determine the role of HLA and additional type 1 diabetes candidate genes^41-50 in the initiation of autoimmunity and progression to diabetes. Even if this distant goal is accomplished, gene therapy is unlikely to become a practical option for a widespread prevention of autoimmunity.

Environmental Causes of ß-Cell Autoimmunity and Diabetes
Gluten-free diet—the current standard treatment for celiac disease—was reportedly established in a serendipitous way during the World War II famine in The Netherlands, when celiac children unexpectedly showed clinical improvement when deprived of wheat products. There is some evidence that, in recent years, delayed introduction of wheat into infant feeding has prevented a substantial number of symptomatic cases, though some of these prevented cases may manifest with milder symptoms later in life.

Rheumatic fever has been nearly eradicated with the introduction of antibiotics and guidelines for diagnosis and treatment of streptococcal infections. While only a small proportion of type 1 diabetes cases has ever been caused by congenital rubella infection, this is the only type of autoimmune diabetes that we can currently prevent (using live attenuated rubella vaccine—a component of the MMR vaccine).

Viruses. The role of viral infections in diabetes appears to be through initiation of autoimmunity rather than by precipitating diabetes through acute ß-cell destruction in subjects with autoimmunity. ICA or IAA has been detected after mumps,⁵¹ rubella, measles, chickenpox,⁵² Coxsackie,⁵³ and ECHO4⁵⁴ infections. Fetuses and newborns may be particularly at risk because of their propensity to develop persistent infection.

Congenital rubella infection can cause ß-cell autoimmunity in 70%⁵⁵ and diabetes in up to 40% of children infected in utero, but not in those infected postnatally.^52,55,56 The incubation period of type 1 diabetes in congenital rubella patients is 5–20 years,⁵⁷ and persistent rubella virus infection of the pancreas has been demonstrated in some cases. The infection can also trigger autoimmune thyroiditis.⁵⁸

While congenital rubella syndrome is not associated with particular HLA alleles, development of diabetes in these patients is associated with the HLA-DR3 and 4 alleles.⁵⁵ A molecular mimicry has been reported between a rubella virus protein and a 52-kDa ß-cell autoantigen.⁵⁹

Before the widespread use of the live attenuated rubella vaccine, only a very small proportion of type 1 diabetes had been caused by congenital rubella syndrome. Disappearance of the syndrome and associated diabetes cases following the introduction of universal rubella vaccination has proved that type 1 diabetes can be prevented by modification of environmental factors. Unfortunately, this is the only form of type 1 diabetes that we can prevent today.

There has been a recent resurgence of evidence that ß-cell autoimmunity⁶⁰ and diabetes⁶¹ may be caused by enteroviral infections, perhaps acquired in utero.^60,62 A molecular mimicry between the P2-C protein of Coxsackie virus and the GAD protein⁶³ could be responsible for ß-cell autoimmunity.

Presence of antibodies against enteroviruses in people with autoimmunity does not, however, prove a causal relationship. People with autoimmunity may be more prone to enteroviral infection, may have a stronger humoral response to infection due to their particular HLA genotypes, or may be in a nonspecific hyperimmune state marked by elevation of antibody levels to a variety of exogenous antigens.⁶⁴ However, if the enteroviral infections are indeed associated with triggering both autoimmunity and diabetes, one of the following mechanisms could operate.

• Several distinct infections are necessary. The first, early in ontogenesis, leads to a low-grade persistent infection, while the subsequent infections with antigenetically similar viruses initiate and sustain autoimmunity until the final "hit" results in ß-cell loss sufficient to cause diabetes.^65,66

• Enteroviral infection does not trigger autoimmunity, but recurrent acute lytic infections of ß-cells promote ß-cell loss and diabetes in people with autoimmunity.

• Persistent enteroviral infection of ß-cells impairs insulin secretion with out cell lysis and promotes diabetes in people with autoimmunity.

• An acute or chronic enteroviral infection of peninsular tissue leads to ß-cell destruction from abundance of free radicals—the "innocent bystander" theory."

These hypotheses are based on extensive studies in animal models (reviewed in⁶⁷), but they have been extremely difficult to test in human populations because of the need to prospectively follow large groups of young children at risk for type 1 diabetes.

In mice, immunization with a nondiabetogenic strain of the virus can induce immunity to antigenetically similar diabetogenic strains and protects from autoimmunity and diabetes.⁶⁸ Evidence for such a protective effect in humans is not available. Measles, but not polio, immunization has been reported to be associated with lower risk of type 1 diabetes.⁵⁶ However, the effects of current mass immunization programs against potentially diabetogenic viruses are virtually unknown.

Autoimmunity/diabetes prevention trials using interventions focused on prevention of enteroviral infections are unlikely in the near future because there is no enteroviral vaccine approved for human use (other than the polio vaccine). The interactions between HLA, antigen, and T-cell receptor, as well as the genetic determinants of viral diabetogenicity, are being disentangled. It may become possible to design recombinant vaccines that would provide optimal antigenic stimulus in the context of the host’s HLA, providing long-term protection against diabetogenic strains and avoiding adverse effects. Alternative approaches to vaccination include antiviral agents.⁶⁹

A recent unconfirmed report has suggested that ß-cell autoimmunity and diabetes may be related to expression of a human endogenous retrovirus,⁷⁰ perhaps via superantigen activation of autoreactive T-cells.⁷¹ At the present time, any intervention options seem unclear.

Dietary factors. A proposed protective effect of breastfeeding on the incidence of type 1 diabetes⁷² has attracted enormous interest. The association between cow’s milk and autoimmunity and diabetes remains controversial.^73-75 If real, it could be due to a molecular mimicry between bovine serum albumin and pancreatic autoantigen ICA6973,⁷⁴ or to the effect of casein-immunostimulating hexapeptide present in enzymatic hydrolysate of milk from Bos taurus cows, but not from Bos indicus cows (RB Elliott, NJ Bibby, unpublished).

Subsequent human studies have shown varying results:

• Diabetic children were significantly less likely to have been breastfed than nondiabetic children,^76-78

• There was no significant difference in the frequency of breastfeeding between diabetic and nondiabetic children,^79-88 or

• Diabetic children were significantly more likely to have been breastfed than nondiabetic children.⁸⁹

Certain studies suggested that the longer children had been breastfed, the lower was their risk for developing diabetes.^77,78,90,91 Other studies did not show increased protection with longer duration of breastfeeding.^85,87,89,92 A meta-analysis of selected studies suggested that children with diabetes are 60% more likely to have had an early exposure to cow’s milk than nondiabetic children.⁹³

A major limitation of most of the aforementioned studies is that the infant diet data were based on long-term maternal recall, which is subject to error.⁹⁴ In fact, studies using prospectively collected records to assess infant diet^85,87,95 did not find the associations between type 1 diabetes and infant diet exposures found in studies that relied on recalled data. This suggests that there may be bias in the retrospective assessment of infant diet.

The Diabetes Autoimmunity Study in the Young has found no association between early exposure to cow’s milk and ß-cell autoimmunity in young siblings and offspring of diabetic patients.⁹⁶ This was also true when the analyses were restricted to the highest- risk HLA genotypes: DR3/4, DQB1*0302, DR3/3 or DRx/4, DQB1*0302.

While we believe that current data are insufficient to support a trial of cow’s milk avoidance for prevention of ß-cell autoimmunity and type 1 diabetes, other groups proposed to gather definitive data through such a trial in newborn relatives with high-risk HLA genotypes.^97,98 In a pilot study, one child in the intervention group (n = 10) developed type 1 diabetes at the age of 14 months despite perfect compliance with the intervention (breastfeeding or casein hydroly-sate until the age of 9 months) and prevention of BSA antibody development.⁹⁹ This raises questions as to whether BSA exposure is not relevant or whether it should be avoided for a period longer than 9 months—perhaps for life—similar to gluten elimination in celiac disease.

Environmental toxins. Toxic doses of nitrosamine compounds can cause diabetes^100-102 due to the generation of free radicals. The effect of dietary nitrate, nitrite, or nitrosamine exposure on human type 1 diabetes risk is less clear.^103-105 Breast milk and vitamin supplements are important sources of antioxidants and may theoretically reduce the concentration of free radicals and, thus, the risk of ß-cell damage.

A number of additional environmental toxins have been implicated in type 1 diabetes etiology¹⁰⁶ but never explored in a cohort study. Anecdotal reports have shown that toxic doses of nitrosamine-containing compounds can cause diabetes.⁵⁹107 Multiple exposures to dietary ß-cell toxins may render genetically resistant individuals susceptible to diabetogenic viruses leading to type 1 diabetes.¹⁰⁸ No human intervention trials appear imminent in this area.

Gene-Environment Interaction as the Cause of Type 1 Diabetes
The cause of ß-cell autoimmunity appears to be multifactorial and includes the effects of multiple genes interacting with several plausible environmental agents. Characterization of these environmental factors and the understanding of how they interact with the susceptibility or protective genotypes is the subject of intense research.

The Diabetes Autoimmunity Study in the Young (DAISY) is studying relatives of type 1 diabetic patients and children from the general population in the first few years of life, when ß-cell autoimmunity predominantly develops.^109,110 Similar cohort studies have been set up in Germany,¹¹¹ Finland,¹¹² and Sardinia.¹¹³ In some of these cohorts, participants have been selected using relatively simple and highly reliable PCR-based screening for susceptibility HLA-DR, DQ alleles.^109,114

While type 1 diabetes is polygenic in nature, the IDDM1 locus, including the HLA-DR and DQ genes, is the only major genetic determinant, accounting for up to 50% of the familiar clustering of the disease.^42,43 The DRB1*0301/04, DQB1*0201/ 0302 heterozygotes account for only 2% of the general population, but this genotype is present in 30–40% of type 1 diabetes patients115 (in up to 52% of those who develop diabetes in the first 10 years of life¹¹⁶). Thus, a great deal can be learned about the causes of type 1 diabetes by studying the interactions between plausible environmental causes and the HLA-DR, DQ genotypes. First-degree relatives with these genotypes are the natural candidates for initial trials to prevent autoimmunity and diabetes.

PROGRESSION FROM ß-CELL AUTOIMMUNITY TO DIABETES

The duration of pre-clinical ß-cell autoimmunity is variable and precedes the diagnosis of diabetes by up to 9–13 years.^117,118 In most people with persistent autoantibodies, there is an early loss of spontaneous pulsatile insulin secretion; progressive reduction in the acute insulin response to an intravenous glucose load, followed by a decreased response to other ß-cell secretagogues; and then impaired oral glucose tolerance and fasting hyperglycemia.¹¹⁹ However, a nonprogressive ß-cell defect can exist for many years in some monozygotic twins and other relatives of people with type 1 diabetes.

Studies in first-degree relatives of type 1 diabetes patients ^118,120,121 and in school children with no family history of type 1 diabetes^{36,37,122-124} have reported ICA "remission" rates between 10 and 78%. It is unclear whether such remissions really occur or are an artifact of low specificity of autoantibody assays. If autoimmunity remits at the reported rates, only 1 in 2–8 autoimmune children will develop diabetes by the age of 20 years. In those who lose their autoantibodies or remain autoimmune but do not progress to diabetes, the penetrance or number of susceptibility genes or the causative environmental exposures are insufficient to cause clinical disease.

It is possible that ß-cell autoimmunity remits spontaneously in genetically resistant people or when the offending factor is removed, similar to celiac disease. Age also plays a role, because children younger than 10 years have a threefold increased risk of progressing from autoimmunity to type 1 diabetes compared to older relatives.¹²⁵

It is possible that ß-cell autoimmunity may remit and reappear in the course of viral infections or variable exposure to dietary causal factors. The cumulative ß-cell damage and increases in insulin resistance with obesity and physical inactivity may eventually cause diabetes at a later age.³³ Those people in whom the disease process is slow may present with type 2 diabetes as adults, develop diabetes that does not require insulin treatment, or even fail to develop diabetes altogether. Markers of autoimmunity can be detected in 14–33% of type 1 diabetes patients^126,127 and are associated with early failure of oral hypoglycemic drug therapy and insulin dependence in these patients.

Both genetic and environmental factors may influence the progression of autoimmunity to overt diabetes. An understanding of these factors is crucial to identification of successful intervention strategies.

Genetic Factors
While the polygenic nature of type 1 diabetes makes prevention through genetic counseling impossible, family history and genetic markers are essential factors in selecting high-risk individuals for the initial prevention trials. In the United States, the risk of type 1 diabetes by the age of 15 years is approximately 1/400.1 The risk is increased to about 1/40 in offspring of type 1 diabetes fathers and to 1/66 in offspring of type 1 diabetes mothers. The risk to siblings ranges from 1/12 to 1/35^145,146 and is further increased, to 1/4, in HLA-identical siblings. It is estimated that by the age of 60 years, ~10% of the relatives develop type 1 diabetes.¹⁴⁷

Family history is a surrogate measure of the combination of type 1 diabetes genes and environmental exposures shared by family members. "Familial" cases represent about 10% of type 1 diabetes and do not appear to be etiologically different from "sporadic" cases in HLA gene frequencies, seasonality of onset, prevalence of various ß-cell autoantibodies, or IgM against Coxsackie B.¹⁴⁸ "Familial" cases tend to have lower glycated hemoglobin and higher C-peptide levels than "sporadic" cases because relatives recognize diabetes symptoms earlier. However, these differences disappear soon after diagnosis.

The primary locus of susceptibility to type 1 diabetes includes the HLA-DR and DQ genes,^38-40,115 but new candidate loci outside the HLA region are being identified.^41-50

While 50% of non-Hispanic whites in the United States have the HLA-DR3 or DR4 allele, at least one of these alleles is present in 95% of patients with type 1 diabetes. The estimated risk to HLA-DR3/4 children in the general population ranges from 1/35 to 1/90.³ The risk is further increased in those with HLA-DR3/4,DQB1*0302 genotype—about 2.2% of the general population¹⁰⁹ versus 30–52% of type 1 diabetes patients.^114-116 Diabetes risk differs for DRB1*04 variants of this genotype, with the *0403 and *0406 alleles being relatively protective and the *0401 and *0402 alleles further increasing the risk. The DRB1*03/*0401(0402),DQB1*0201/*0302 genotypes, present in only in 0.73% of the general U.S. population and in 25% of type 1 patients, increase type 1 risk 40 times. Since 8.7% of children with these genotypes develop type 1 diabetes by the age of 20 years, they offer an attractive target for primary prevention of type 1 diabetes in the population.¹⁴⁹

Environmental Factors
The environmental factors suspected of triggering ß-cell autoimmunity that we discussed above—entroviruses and cow’s milk—have also been linked to the onset of clinical diabetes. In the DAISY, we have been unable to reproduce earlier cross-sectional studies indicating that acute enteroviral infections trigger autoimmunity or precipitate diabetes in people with autoimmunity.¹⁵⁰ If, however, many type 1 diabetes cases are indeed caused by a persistent viral infection similar to the congenital rubella model, eradication of diabetes would require a universal vaccination to build up population immunity. Women of reproductive age may need to be targeted to prevent in utero and prenatal infections, which are more likely to persist.

Our data from the DAISY are inconsistent with a major role for early infancy exposure to cow’s milk in triggering autoimmunity. However, prolonged exposure has not been ruled out as the promoter of progression to clinical diabetes. If celiac disease is a good model for diet-induced autoimmune diabetes, chronic exposure to cow’s milk or milk products may be as important as early introduction of these nutrients in infant diet. Consequently, life-long elimination of cow’s milk products from the diet may be necessary to prevent autoimmunity, but shorter or less stringent dietary restrictions may suffice to prevent diabetes. The stringency of the elimination diet necessary for diabetes prevention may depend on the genetic make-up of the child. Clearly, more cohort studies powered to test hypotheses concerning gene-environment interactions are needed to answer these questions.

PREVENTION OF DIABETES IN PEOPLE WITH ß-CELL AUTOIMMUNITY

ICA-positive relatives of type 1 diabetes patients have become the primary target of clinical trials to prevent type 1 diabetes.¹²⁸ Some of the proposed interventions are associated with significant adverse effects,^129-131 while the effectiveness of others, e.g., oral nicotinamide, have not gained wide acceptance.

Promising results of a pilot trial¹³² gave impetus to a large, randomized, unmasked trial of low-dose parenteral insulin in first- and second-degree relatives with confirmed ICA positivity and low acute insulin response to IV glucose (the Diabetes Prevention Trial-1). This important national trial is currently recruiting subjects into multiple regional centers. (Call 1-800-425-8361 to receive a screening packet and a directory of screening sites nationwide.) The results of this trial will be known in 2002.

A second arm of the study is a randomized, masked trial of a specially prepared oral insulin in relatives with confirmed ICA positivity, but with normal acute insulin response to IV glucose. The results of this aspect of the trial will not be known until 2003.

Trials involving induction of tolerance (clonal anergy) to ß-cell autoantigens, such as GAD^133,134 or insulin,^135,136 are being tested in animal models.

CLINICAL ONSET OF TYPE 1 DIABETES

In industrialized countries, 20–40% of type 1 diabetes patients younger than 20 years present in diabetic ketoacidosis (DKA).^137-140 Younger age, female gender, HLA-DR4 allele,¹⁴¹ lower socioeconomical status, and lack of family history of diabetes have been associated with more severe presentation. Severe presentation in younger children may result from a greater ß-cell destruction at diagnosis: an average of 80% of the islets are damaged at diagnosis in children younger than 7 years, 60% in those 7–14 years old, and 40% in those older than 14 years.¹⁴² Case fatality in industrialized countries ranges from 0.4 to 0.9%,¹⁴³ but little is known concerning its predictors.

Both DKA and onset death are largely preventable because most patients have typical symptoms of polyuria, polydipsia, and weight loss 2–4 weeks before diagnosis. The diagnosis is straightforward in almost all cases and can be based on the symptoms, random blood glucose >200 mg/dl, and/or HbA_1c >7%.

Traditionally, nearly all children with newly diagnosed type 1 diabetes were hospitalized. More recently, an increasing proportion of new-onset children have been managed on an outpatient basis, especially in urban centers with specialized diabetes education and treatment facilities. In Colorado, the proportion of children receiving only outpatient care at diabetes diagnosis increased from 6% in 1978 to 35% in 1988,¹⁴⁴ and to an estimated 60–65% in 1996. Hospitalization at onset does not improve short-term outcomes, such as readmission for DKA or severe hypoglycemia.^137,140 Onset hospitalizations and acute complications have similar biological (younger age, lower endogenous insulin secretion) and psychosocial (lower socioeconomic status, limited access to health care, dysfunctional family) determinants.

REMISSION ("HONEYMOON PERIOD")

The understanding of the natural history of ß-cell function and autoantibody levels following the diagnosis of diabetes is crucial for interpretation of previous intervention trials and for designing new ones aimed at induction and "consolidation" of remission in newly diagnosed patients.

After clinical onset, most type 1 diabetes patients experience a transient fall in insulin requirements associated with improved ß-cell function, with a maximum usually at 1–6 months after diagnosis. Total and partial remissions have been reported in, respectively, 2–12% and 18–62% of young patients.^140,151,152 Older age and less severe initial presentation of type 1 diabetes^151-153 and low or absent ICA154,155 or GAD autoantibodies¹⁵⁶ have been consistently associated with deeper and longer remission.

Evidence relating non-Caucasian origin, HLA-DR3 allele, female gender, and family history of type 1 diabetes to a less severe presentation, greater frequency of remission, and slower deterioration of insulin secretion is inconclusive. Previous reports may have been severely biased by including patients with mature-onset diabetes of the young (MODY) or early-onset type 2 diabetes.

Most studies,^151,155 but not all,^152,153 agree that preserved ß-cell function is associated with better glycemic control (lower HbA_1c) and preserved ß-cell glucagon response to hypoglycemia.¹⁵⁴ The prevalence of ICA (but not GAA) decreases from 87% at the time of type 1 diabetes diagnosis to 38–62% 2–3 years later.^154,158 This occurs faster in young boys, subjects lacking HLA-DR3 and 4, and those diagnosed between July and December.¹⁵⁸

The natural remission is always temporary, ending with a gradual or abrupt increase in exogenous insulin requirements. Destruction of ß-cells is complete within 3 years of diagnosis in most young children, especially those with the HLA-DR3/4 phenotype.¹⁵⁹ It is much slower and often only partial in older patients,¹⁶⁰ 15% of whom still have some ß-cell function preserved 10 years after diagnosis.¹⁶¹

Secondary Prevention (Induction and Consolidation of Remission) in New-Onset Diabetic Patients

A number of placebo-controlled, randomized trials using azathioprine, cyclosporin A, nicotinamide, prednisone, and other immunosuppressive agents have attempted to increase the rate and the duration of type 1 diabetes remission. These studies have been elegantly reviewed elsewhere.¹⁰ Only cyclosporin A treatment has been shown to be partially effective, inducing total remission in 25–40% and sustaining it for 1 year in 18–24% of newly diagnosed patients, compared with 0–10% in the placebo group.^162,163 However, the drug is nephrotoxic, of little value in children, and effective for only as long as it is administered,¹⁶⁴ rendering this approach to prevention unacceptable. More recent trials using intensive insulin treatment¹⁶⁵ and immunomodulation^166,167 have not been more successful.

Newly diagnosed patients offer a valuable population in which to test new preventive interventions. These people understand the importance of diabetes research, are highly motivated, and are available on a routine basis to clinical investigators who work on prevention of diabetes. It is tempting to test new interventions in this group, using as the endpoint the rate of decline in stimulated C-peptide levels or autoantibody levels. Unfor-tunately, these outcomes are largely dependent on factors over which the investigators have no control: age, ethnicity, gender, HLA genotype, and severity of the presentation. Without careful attention to these prognostic variables, results of interventions are not interpretable.

Using newly diagnosed patients, while convenient, also poses an ethical dilemma. Frankly, for most of the participants there is little to gain from the intervention, and the risks (e.g., allergy to insulin, induction of autoimmunity to other organs, im-munosuppression) should not exceed potential modest benefits. The patients should be informed openly that their participation is necessary mainly to collect safety data. Na-turally, safety monitoring has to be a major part of these studies.

CONCLUSIONS

The existing cohort studies of relatives, schoolchildren, and newborns from the general population should collaborate closely to identify modifiable environmental causes of autoimmunity and diabetes. Additional observational studies in diverse populations and including newborns and infants are needed to fully understand the causes, gene-environmental interactions, the natural history, and the best ways to prevent prediabetic autoimmunity and type 1 diabetes.

Primary prevention of autoimmunity and type 1 diabetes may become possible as the existing cohort studies define the triggers of prediabetic autoimmunity. Initial trials will enroll newborn and infant relatives of people with diabetes and/or infants without diabetic relatives but with the highest-risk genotype, HLA-DRB1*03/0401(2),DQB1*0302.

The next generation of secondary prevention trials (to prevent development of diabetes in people with autoimmunity) will likely target children without a diabetic relative found to have at least two antigen-specific autoantibodies (e.g., to insulin, GAD65, or IA-2) on a simple screening test.

Trials to prevent autoimmunity and type 1 diabetes will require, among other things, an effective and safe intervention, adequate funding, and multicenter collaboration.

Acknowledgment
This work has been supported by the NIH, NIDDK grant DK-32493 (MR and GJK). Additional support from the Eli Lilly Co (MR) allowed completion of this manuscript.

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