The relation between size at birth and risk of type 1 diabetes is not influenced by adjustment for the insulin gene (-23HphI) polymorphism or HLA-DQ genotype

The Bell Curve Revisited: Testing Controversial Hypotheses with Molecular Genetic Data

In 1994, the publication of Herrnstein's and Murray's The Bell Curve resulted in a social science maelstrom of responses. In the present study, we argue that Herrnstein's and Murray's assertions were made prematurely, on their own terms, given the lack of data available to test the role of genotype in the dynamics of achievement and attainment in U.S. society. Today, however, the scientific community has access to at least one dataset that is nationally representative and has genome-wide molecular markers. We deploy those data from the Health and Retirement Study in order to test the core series of propositions offered by Herrnstein and Murray in 1994. First, we ask whether the effect of genotype is increasing in predictive power across birth cohorts in the middle twentieth century. Second, we ask whether assortative mating on relevant genotypes is increasing across the same time period. Finally, we ask whether educational genotypes are increasingly predictive of fertility (number ever born [NEB]) in tandem with the rising (negative) association of educational outcomes and NEB. The answers to these questions are mostly no; while molecular genetic markers can predict educational attainment, we find little evidence for the proposition that we are becoming increasingly genetically stratified.

Insulin gene VNTR polymorphisms -2221MspI and -23HphI are associated with type 1 diabetes and latent autoimmune diabetes in adults: a meta-analysis

AIMS

A variable number of tandem repeat (VNTRs) region in the insulin gene (INS) possibly influences the progression of type 1 diabetes (T1D) and latent autoimmune diabetes in adults (LADA). However, effects of INS VNTR polymorphisms in these contexts remain inconclusive.

METHODS

We performed a systematic review of work on the INS VNTR -2221MspI and -23HphI polymorphisms to estimate the overall effects thereof on disease susceptibility; we included 17,498 T1D patients and 24,437 controls, and 1960 LADA patients and 5583 controls.

RESULTS

For T1D, the C allele at -2221MspI and the A allele at -23HphI were associated with estimated relative risks of 2.13 (95 % CI 1.94, 2.35) and 0.46 (95 % CI 0.44, 0.48), which contributed to absolute increases of 46.76 and 46.98 % in the risk of all T1D, respectively. The estimated lambda values were 0.44 and 0.42, respectively, suggesting that a co-dominant model most likely explained the effects of -2221MspI and -23HphI on T1D. For -23HphI, the A allele carried an estimated relative risk of 0.55 (95 % CI 0.50, 0.61) for LADA and increased the risk of all LADA by 36.94 %. The λ value was 0.43, suggesting that a co-dominant model most likely explained the effect of -23HphI on LADA.

CONCLUSIONS

Our results support the existence of associations of INS with T1D and LADA.

The prenatal environment and type 1 diabetes

There is ample evidence that environmental factors are involved in the aetiology of type 1 diabetes, but the nature and timing of the interactions are poorly understood. The intrauterine environment is known to play a role in the later development of type 2 diabetes, and this review considers a possible role in type 1 diabetes. Autoimmune type 1 diabetes is rare in those diagnosed before 6 months of age, but endogenous autoantibodies predictive of future type 1 diabetes may be detectable by 6-12 months of age, suggesting that environmental factors may operate before this age in some cases. Indirect evidence of a protective effect for the intrauterine environment comes from the observation that mothers with type 1 diabetes are less likely than affected fathers to transmit diabetes to their offspring, although the precise role (if any) is unclear. The risk of childhood-onset type 1 diabetes increases with maternal age at delivery, and with high birthweight, but these associations are weak and heterogeneous, and these factors are unlikely to be directly causally related to type 1 diabetes. No firm conclusion can be drawn from studies of maternal enteroviral infection or from various nutritional exposures. The birth process itself may play a role, as suggested by the slightly increased risk in children born by Caesarean section; lack of contact with maternal bacteria is one suggested mechanism. In sum, there is circumstantial evidence, but no proof of principle, that maternal or intrauterine conditions may modulate genetic risk of type 1 diabetes. The disease process culminating in type 1 diabetes typically begins in early life, but it is not clear whether the trail begins before or after birth.

Does the relative risk for type 1 diabetes conferred by HLA-DQ, INS, and PTPN22 polymorphisms vary with maternal age, birth weight, or cesarean section?

BACKGROUND AND OBJECTIVE

Maternal age at birth, birth weight, and cesarean section has been associated with a weak but significant increase in risk of type 1 diabetes. The objective was to assess whether the relative risk for type 1 diabetes conferred by established susceptibility loci human leukocyte antigen (HLA)-DQ, INS, and PTPN22 differed depending on these perinatal factors.

METHODS

We employed a case-control study with 456 cases of type 1 diabetes diagnosed before 15 yr of age and 1377 population-based control children. HLA genotypes were divided into high to moderate risk (DQ8/DQ2, DQ8/DQ8, DQ8/X, DQ2/DQ2) vs. all other genotypes. Case-only analysis using logistic regression was used to test for significant interaction.

RESULTS

There was no significant difference in the relative risks conferred by HLA-DQ, INS, or PTPN22 by maternal age, birth weight, or mode of delivery, except the relative risk conferred by PTPN22 which was 2.11 [95% confidence interval (CI): 1.64-2.72] for those born vaginally and 0.99 (95% CI: 0.50-1.99) for those born by cesarean section [p(interaction) = 0.028].

CONCLUSION

The relative risks conferred by the three established susceptibility genes investigated here were independent of the perinatal factors, apart from a possible interaction between PTPN22 and mode of delivery.

Birthweight and the risk of childhood-onset type 1 diabetes: a meta-analysis of observational studies using individual patient data

AIMS/HYPOTHESIS

We investigated whether children who are heavier at birth have an increased risk of type 1 diabetes.

METHODS

Relevant studies published before February 2009 were identified from literature searches using MEDLINE, Web of Science and EMBASE. Authors of all studies containing relevant data were contacted and asked to provide individual patient data or conduct pre-specified analyses. Risk estimates of type 1 diabetes by category of birthweight were calculated for each study, before and after adjustment for potential confounders.Meta-analysis techniques were then used to derive combined ORs and investigate heterogeneity between studies.

RESULTS

Data were available for 29 predominantly European studies (five cohort, 24 case-control studies), including 12,807 cases of type 1 diabetes. Overall, studies consistently demonstrated that children with birthweight from 3.5 to 4 kg had an increased risk of diabetes of 6% (OR 1.06 [95% CI 1.01-1.11]; p=0.02) and children with birthweight over 4 kg had an increased risk of 10% (OR 1.10 [95% CI 1.04-1.19]; p=0.003), compared with children weighing 3.0 to 3.5 kg at birth. This corresponded to a linear increase in diabetes risk of 3% per 500 g increase in birthweight (OR 1.03 [95% CI 1.00-1.06]; p=0.03). Adjustments for potential confounders such as gestational age, maternal age, birth order, Caesarean section, breastfeeding and maternal diabetes had little effect on these findings.

CONCLUSIONS/INTERPRETATION

Children who are heavier at birth have a significant and consistent, but relatively small increase in risk of type 1 diabetes.

The current state of birth outcome and birth defect surveillance in northern regions of the world

OBJECTIVES

Little is known about the rates of congenital anomalies in the northernmost regions of the world. As in other parts of the world, it is crucial to assess the relative rates and trends of adverse birth outcomes and birth defects, as indicators of population health and to develop public health strategies for prevention. The aim of this review is to catalogue existing and developing birth outcome and birth defect surveillance within and around the geographic jurisdiction of the International Union of Circumpolar Health (IUCH).

STUDY DESIGN

Descriptive study.

METHODS

The representatives of the IUCH Birth Defects Working Group catalogued existing and developing birth and birth defect surveillance systems and the extent of information they contain to determine inter-regional comparability.

RESULTS

Systematic population-based registration of birth outcomes including birth defects occurs to some degree in all circumpolar countries, but the quality of collection and the coverage in northernmost regions vary. There are limited circumpolar jurisdictions with surveillance systems collecting birth defect information beyond the perinatal period. Efforts are underway in Canada and Russia to improve the quality and comprehensiveness of the information collected in the northern regions.

CONCLUSIONS

Although there is variability in the comprehensiveness of information collected in northern jurisdictions limiting sophisticated comparative analyses between regions, there is untapped potential for baseline analyses of specific risks and outcomes that could provide insight into geographic differences and gaps in surveillance that could be improved.

Joint effects of HLA, INS, PTPN22 and CTLA4 genes on the risk of type 1 diabetes

BACKGROUND/HYPOTHESIS

HLA, INS, PTPN22 and CTLA4 are considered to be confirmed type 1 diabetes susceptibility genes. HLA, PTPN22 and CTLA4 are known to be involved in immune regulation. Few studies have systematically investigated the joint effect of multiple genetic variants. We evaluated joint effects of the four established genes on the risk of childhood-onset type 1 diabetes.

METHODS

We genotyped 421 nuclear families, 1,331 patients and 1,625 controls for polymorphisms of HLA-DRB1, -DQA1 and -DQB1, the insulin gene (INS, -23 HphI), CTLA4 (JO27_1) and PTPN22 (Arg620Trp).

RESULTS

The joint effect of HLA and PTPN22 on type 1 diabetes risk was significantly less than multiplicative in the case-control data, but a multiplicative model could not be rejected in the trio data. All other two-way gene-gene interactions fitted multiplicative models. The high-risk HLA genotype conferred a very high risk of type 1 diabetes (OR 20.6, using the neutral-risk HLA genotype as reference). When including also intermediate-risk HLA genotypes together with risk genotypes at the three non-HLA loci, the joint odds ratio was 61 (using non-risk genotypes at all loci as reference).

CONCLUSION

Most established susceptibility genes seem to act approximately multiplicatively with other loci on the risk of disease except for the joint effect of HLA and PTPN22. The joint effect of multiple susceptibility loci conferred a very high risk of type 1 diabetes, but applies to a very small proportion of the general population. Using multiple susceptibility genotypes compared with HLA genotype alone seemed to influence the prediction of disease only marginally.

Early infant feeding and risk of type 1 diabetes mellitus-a nationwide population-based case-control study in pre-school children

BACKGROUND

The evidence on the role of environmental factors in the development of type 1 diabetes is conflicting. Reducing potential bias and the variety of exposures, we investigated the association between type 1 diabetes risk and nutritional and environmental exposures in pre-school children.

METHODS

This nationwide population-based case-control study included 760 cases under 5 years of age newly diagnosed with type 1 diabetes during 1992-1995. From the general population, 1,871 controls were randomly selected and individually matched on age ( +/- 1 year), sex, and residence. Information on infant diet, foetal, perinatal and socio-economic factors, and familial diabetes was obtained by a parent-administered questionnaire. Data were analysed by multiple conditional logistic regression.

RESULTS

Duration of breastfeeding and age at introduction of bottle-feeding were inversely associated with type 1 diabetes risk according to a dose-response relationship (trend test p < 0.05). Adjusted odd ratios (95% CI) for a long breastfeeding period and a late introduction of bottle-feeding (>or=5 month versus < 2 weeks) were 0.71 (0.54-0.93) and 0.80 (0.62-1.04), respectively. Familial type 1 diabetes, maternal age > 40 years, and low birth weight were found more frequently among diabetic than among control children. Current cow's milk consumption, higher social status, and a larger family were associated with a reduced diabetes risk. Up to one half of the diabetic cases in the population could be attributed to modifiable exposures.

CONCLUSIONS

Our findings indicate that infant feeding is associated with type 1 diabetes risk and that a considerable part of new type 1 diabetic cases is potentially preventable.

Peroxisome proliferator-activated receptor-gamma2 Pro12Ala polymorphism, cod liver oil and risk of type 1 diabetes

OBJECTIVE

We have previously described an association between use of cod liver oil (a dietary n-3 fatty acid supplement) and reduced risk of type 1 diabetes. n-3 fatty acids are ligands for the peroxisome proliferator-activated receptor-gamma (PPARG), which has recently been implicated in the control of inflammation and possibly autoimmunity. We aimed to estimate the association between the common Pro12Ala polymorphism of PPARG2 and risk of type 1 diabetes, and to test whether there is gene-environment interaction with use of cod liver oil in the first year of life or gene-gene interaction with the established insulin gene (INS) and human leukocyte antigen DQ (HLA-DQ) genetic susceptibility loci.

METHODS

We designed a population-based case-control study of childhood-onset type 1 diabetes in Norway with information on use of cod liver oil in the first year of life from questionnaires and PPARG2 genotype data for 483 cases and 1520 control subjects. We used logistic regression for analysis.

RESULTS

The odds ratio for the PPARG2 Ala/Ala or Pro/Ala vs. Pro/Pro genotype and type 1 diabetes was 0.89 (95% CI: 0.69-1.13, p = 0.33). There was no significant interaction with cod liver oil in the first year of life [P (interaction) = 0.35] or with the INS polymorphism [P(interaction) = 0.42].

CONCLUSIONS

Although the association between PPARG2 and type 1 diabetes was not significant, the observed odds ratio was almost identical to that observed in two previous studies and can contribute to meta-analysis indicating a weak but significant association. Our hypothesized interaction between cod liver oil and PPARG2 in reducing type 1 diabetes risk was not supported.

Early environmental exposure and the development of lupus

Systemic lupus erythematosus (SLE) is a complex trait with evidence of polygenic inheritance influenced by environmental factors. However, the precise underlying causes of SLE remain unclear. A number of environmental exposures have been associated with lupus or related autoimmune phenomena. Evidence suggests that some environmental exposures need to be present many years before the onset of SLE. Both SLE and rheumatoid arthritis (RA) can occur in very young children and this supports the possibility that important environmental factors must be present during or before this time. In addition, the immune pathology, including autoantibody production, in adult lupus may begin years before clinical disease. There is also evidence that the developing immune system demonstrates developmental plasticity and can be permanently altered or 'programmed' by the early environment. We describe how early life environmental influences including infectious exposure may lead to autoantibody production in later life thus beginning the journey that leads to autoimmune diseases such as lupus in susceptible individuals.

Fetal growth is increased by maternal type 1 diabetes and HLA DR4-related gene interactions

AIMS/HYPOTHESIS

Intrauterine growth in non-diabetic pregnancies is reported to be influenced by type 1 diabetes susceptibility genes. In particular, the high-risk HLA DR4_DQB1*0302 haplotype is associated with increased birthweight. The aim of this study was to determine whether HLA DR4 was associated with increased birthweight in a maternal diabetes environment and whether effects persisted during early childhood.

SUBJECTS AND METHODS

Birthweight and gestational age were obtained in singleton births from mothers with type 1 diabetes (n = 1161) or whose fathers or siblings have type 1 diabetes (n = 872). Weight and height at ages 2 and 5 years were obtained from paediatric records. Data were adjusted for (gestational) age and sex and expressed as percentiles of German reference data. HLA DR typing was obtained for all children and 1090 children also had insulin gene (INS) variable number of tandem repeats (VNTR) typing.

RESULTS

Maternal type 1 diabetes was associated with increased birthweight, gestational age and birthweight percentiles (all p < 0.0001). In children of mothers with type 1 diabetes, birthweight percentile was further related to maternal HbA(1c) during pregnancy (r = 0.26; p < 0.0001) and was independently increased if children had HLA DR4 alleles (76th vs 64th percentile; p < 0.0001). HLA DR4 was not associated with birthweight in children of non-diabetic mothers. Birthweight was not associated with INS VNTR genotypes. High birthweight, but not HLA DR4 was associated with increased weight and BMI at ages 2 and 5 years (p < 0.0001).

CONCLUSIONS/INTERPRETATION

Our findings are consistent with the hypothesis that a diabetic intrauterine environment interacts with gene(s) marked by the type 1 diabetes susceptibility HLA DR4 alleles to increase fetal growth.

Environmental factors in the development of Type 1 diabetes

Environmental factors appear to play an important role in the pathogenesis of childhood-onset type 1 diabetes (T1D). The most important factors are thought to be infectious, dietary, perinatal, and psychosocial. Enteroviruses (especially Coxsackie B virus), breastfeeding, the early presence or lack of certain foods, birth weight, childhood over-nutrition, maternal islet autoimmunity, and negative stress events have been shown to be related to the prevalence of T1D. However, clear conclusions to date are limited because most studies lacked power to detect exposure/disease associations, were not prospective or long-term, did not start in infancy, had imprecise or infrequent exposure estimates, had confounding exposures, and failed to account for genetic susceptibility. In addition to the identification of specific antigenic triggers, several more general hypotheses, including the accelerator and hygiene hypotheses, are testable approaches worth pursuing.