Risk of diabetes in siblings of index cases with Type 2 diabetes: implications for genetic studies

Prevalence of gestational diabetes mellitus in women with a family history of type 2 diabetes in first- and second-degree relatives

AIMS

A family history of type 2 diabetes mellitus (T2DM) markedly increases an individual's lifetime risk of developing the disease. For gestational diabetes (GDM), this risk factor is less well characterized. This study aimed to investigate the relationship between family history of T2DM in first- and second-degree relatives in women with GDM and the differences in metabolic characteristics at early gestation.

METHODS

This prospective cohort study included 1129 pregnant women. A broad risk evaluation was performed before 16 + 0 weeks of gestation, including a detailed family history of the different types of diabetes and a laboratory examination of glucometabolic parameters. Participants were followed up until delivery and GDM assessed according to the latest diagnosis criteria.

RESULTS

We showed that pregnant women with first- (FHD1, 26.6%, OR 1.91, 95%CI 1.16 to 3.16, p = 0.005), second- (FHD2, 26.3%, OR 1.88, 95%CI 1.16 to 3.05, p = 0.005) or both first- and second-degree relatives with T2DM (FHD1 + D2, 33.3%, OR 2.64, 95%CI 1.41 to 4.94, p < 0.001) had a markedly increased risk of GDM compared to those with negative family history (FHN) (n = 100, 15.9%). The association was strongest if both parents were affected (OR 4.69, 95%CI 1.33 to 16.55, p = 0.009). Women with FHD1 and FHD1 + D2 had adverse glucometabolic profiles already in early pregnancy.

CONCLUSIONS

Family history of T2DM is an important risk factor for GDM, also by applying the current diagnostic criteria. Furthermore, we showed that the degree of kinship plays an essential role in quantifying the risk already at early pregnancy.

Association between Single-nucleotide Polymorphisms of RXRG and Genetic Susceptibility to Type 2 Diabetes in South China

OBJECTIVE

To investigate the relationship between genetic polymorphisms of RXRG rs1467664, rs3753898 and the genetic susceptibility of type 2 diabetes in the Chinese Han population from South China.

METHODS

In our case-control study, single-nucleotide polymorphisms (SNPs) rs1467664 and rs3753898 were genotyped by SNPscanTM kit in 1092 patients with T2D as cases and 1092 normal persons as controls. The distributions of genotype and allele frequencies in two groups were analyzed by the SPSS 20.0 software.

RESULTS

The distribution of genotypes and alleles of RXRG rs3753898 was statistically significant between the two groups, but there was no significant difference in the distribution of genotypes and alleles of the rs1467664. Before and after the adjustment of age, sex and BMI, rs3753898 in the two groups had statistical significance under the additive, dominant and recessive models (P<0.05), but no statistical differences were found under the overdominance and co-dominant genetic models (P>0.05). There was no significant difference in the genetic models of rs1467664 between the two groups (P>0.05). The haplotype, which consists of rs1467664 allele T and rs3753898 allele A was a high-risk factor for T2D, OR=1.27, 95% CI (1.09-1.47), Padj=0.002.

CONCLUSION

Our results showed that the single nucleotide polymorphism of RXRG rs3753898 may be related to genetic susceptibility of type 2 diabetes. The haplotype consisting of the allele T of rs1467664 and the allele A of rs3753898 is a risk factor for type 2 diabetes, suggesting that the genetic variation of RXRG gene may be the genetic cause of diabetes mellitus in the Chinese Han population.

Is diagnosis of type 2 diabetes a "teachable moment"? A qualitative study

AIMS

To explore the potential of type 2 diabetes diagnosis to be a "teachable moment".

METHODS

Semi-structured interviews were conducted with 23 participants (10 people with type 2 diabetes, 13 relatives of people with type 2 diabetes) in Scotland, UK. They explored cognitive, emotional and behavioural changes following diagnosis of type 2 diabetes in oneself or in a relative. Data were analysed using Framework approach.

RESULTS

Strong emotional responses are not always related to the occurrence of a teachable moment. Risk perception and outcome expectancy were found to be teachable moment factors for patients with type 2 diabetes and their offspring, but not their partners. Change in self-concept increases the likelihood of type 2 diabetes diagnosis to be a teachable moment for patients but not for relatives. In some cases, type 2 diabetes is perceived as incompatible with current roles thus hindering diabetes self-management. Relatives often engage in caring for patients and "policing" their behaviour but did not report perceived changes in social roles.

CONCLUSIONS

The study suggests that diagnosis of type 2 diabetes is a teachable moment for some patients and their relatives. These findings have implications for interventions to address diabetes self-management in patients and primary prevention in their relatives.

Barriers to intra-familial prevention of type 2 diabetes: A qualitative study on horizons of significance and social imaginaries

Objectives

In families living with type 2 diabetes, relatives have a significantly heightened risk of developing the disease. In many families, both the person with type 2 diabetes and his/her relatives lack detailed knowledge about this risk. One obstacle to constructive intra-familial prevention and risk reduction is the lack of perceived familial disease relevance. The objective of the present study is to explore barriers to prevention in families with at least one adult with type 2 diabetes.

Methods

Data were gathered during eight problem assessment and ideation workshops with families. The data were analyzed using radical hermeneutics and interpreted using Taylor’s concepts of social imaginaries and horizons of significance.

Results

The analysis revealed three main barriers: (1) Sole responsibilities and the absence of collective practices, (2) intra-familial differences in perceptions of risks and future health, and (3) lack of perceived disease significance and the ensuing lack of mutual care. The participating families all experienced one or more of the three identified primary barriers.

Discussion

The study has produced important knowledge about barriers to familial prevention of type 2 diabetes. The findings confirm that familial prevention is indeed a complex matter that calls for the use of complexity-oriented approaches in health care practice.

TCF7L2 polymorphism a prominent marker among subjects with Type-2-Diabetes with a positive family history of diabetes

The greatest risk of developing type2 diabetes (T2DM) was conferred by rs7903146 SNP of Transcription factor7-like2 (TCF7L2) gene in many ethnic populations. The aim was to investigate the association of TCF7L2 (rs7903146) gene polymorphism among newly diagnosed diabetes subjects with different parental diabetes registry. A total of 171 subjects were categorized into 3 groups based on parental diabetes registry i.e. Conjugal Diabetes Registry (CDR) (n = 50), One Parental Diabetes Registry (OPDR) (n = 56) and Non Parental Diabetes Registry (NPDR) (n = 62) (control group). Kompetitive allele specific PCR (KASP) genotyping assay was used in real time PCR for identifying the genotypes. None of the biochemical parameters showed any significant difference between groups except age at onset of diabetes (p = 0.001). The T allele of TCF7L2 (rs7903146) was associated with significant risk of diabetes. TT genotype which doubles the diabetes risk showed significant association among OPDR whereas in CDR both CT and TT genotypes showed significant association than CC wild type. The 'T' allele of TCF7L2 SNP was associated with significant risk when compared between OPDRvsNPDR (OR 2.45, p = 0.003) and CDRvsNPDR (OR 2.82, p = 0.0007). In conclusion, TCF7L2 gene polymorphism and positive family history of diabetes are strongly associated irrespective of the presence of other risk factors among diabetes subjects.

Association between CUBN gene variants, type 2 diabetes and vitamin D concentrations in an elderly Greek population

Accumulating evidence suggests a potential implication of vitamin D biological network in the pathogenesis of diabetes mellitus. The megalin-cubilin endocytotic system constitutes a key transport structure, with a modulating role in vitamin D metabolism. We aimed to assess the contribution of variants in the CUBN gene to the genetic risk of Type 2 Diabetes Mellitus (T2DM). 95 polymorphisms within CUBN were genotyped in 716 patients with T2DM and 542 controls of Greek origin. Samples were analyzed on Illumina Human PsychArray. Permutation test analysis was implemented to determine statistical significance. Twenty-five-hydroxy-vitamin-D [25(OH)D)] levels were measured in a sub-group of participants (n = 276). Permutation analysis associated rs11254375_G/T (p_emp = 0.00049, OR = 1.482), rs6602175_G/T (p_emp = 0.016, OR = 0.822), rs1801224_G/T (p_emp = 0.025, OR = 0.830), rs4366393_A/G (p_emp = 0.028, OR = 0.829) and rs7071576_A/G (p_emp = 0.04, OR = 1.219) with T2DM. Mean 25(OH)D concentrations were significantly lower in patients with T2DM compared to controls (16.70 ± 6.69 ng/ml vs 18.51 ± 6.71 ng/ml, p < 0.001), although both groups were vitamin D deficient. In a further quantitative analysis, rs41301097 was strongly associated with higher 25(OH)D concentrations (p = 5.233e-6, beta = 15.95). Our results indicate a potential role of CUBN gene in T2DM genetic susceptibility in the Greek population. These findings may also denote an indirect effect of vitamin D metabolism dysregulation on the pathogenesis of T2DM. Further studies are required to replicate our findings and clarify the complex underlying mechanisms.

Implementing a research-based innovation to generate intra-familial involvement in type 2 diabetes self-management for use in diverse municipal settings: a qualitative study of barriers and facilitators

BACKGROUND

Involving family members in disease management is vital to people with type 2 diabetes. New innovations that support family members' involvement can help both the person with type 2 diabetes and the relatives to create the supportive environment they need. The objective of the present study is to examine what facilitates and obstructs implementation of an innovation that supports intra-familial involvement in life with type 2 diabetes.

METHODS

Of the 48 healthcare professionals trained in facilitating the innovation in municipal patient education courses, single, semi-structured interviews were conducted with 13 of them. The interviews were focused specifically on the implementation process. All interviews were transcribed verbatim and analyzed using radical hermeneutics.

RESULTS

The analysis revealed three distinct themes affecting implementation of the innovation. 1) Focusing on creating family involvement in patient education for people with type 2 diabetes was relevant and important to the healthcare professionals. 2) The dynamics of group-based patient education sessions changed when family members were involved, which affects healthcare professionals' group facilitation methods. 3) Implementing new methods in patient education requires great commitment and support from the organization and management.

CONCLUSION

Implementation of an innovation to involve families and close relatives in patient education in Danish municipalities is feasible, but highly dependent on the commitment of healthcare professionals and managers as well as their openness to new ways of facilitating group processes.

Are Malaysian Type 2 Diabetes patients willing to be trained to speak to their offspring about risk of diabetes and preventive measures?

Background

Offspring of type 2 diabetes patients have an absolute risk of 20–40% of developing the condition. Type 2 diabetes patients should be encouraged to speak to their offspring regarding diabetes risk and prevention strategies. The Health Belief Model conceptualises that the higher the perceived risk, the more likely an individual will modify their behaviour. The objectives of this study were to i) determine the distribution of type 2 diabetes patients regarding their willingness to accept training to speak to their offspring, ii) determine the distribution of type 2 diabetes patients regarding their willingness to accept training based on the HBM and iii) to determine the factors associated with their willingness to accept training.

Methods

This was a cross-sectional study amongst type 2 diabetes patients attending two primary care clinics in Malaysia. Sociodemographic data and knowledge of diabetes risk factors were collected. The adapted, translated and validated Diabetes Mellitus in the Offspring Questionnaire-Malay version (DMOQ-Malay) was self-administered. Statistical analysis included descriptive statistics, univariate and multiple logistic regression (MLogR).

Results

A total of 425 participants were recruited. Of these, 61.6% were willing to accept training. In MLogR, six variables were found to be significantly associated with willingness to accept training. These were i) positive family history [Adj. OR 2.06 (95% CI: 1.27, 3.35)], ii) having the correct knowledge that being overweight is a risk factor [Adj. OR 1.49 (95%CI: 1.01, 2.29)], iii) correctly identifying age ≥ 40 years old as a risk factor [Adj. OR 1.88 (95%CI: 1.22, 2.90)], iv) agreeing that speaking to their offspring would help them to prevent type 2 diabetes [Adj. OR 4.34 (95%: 1.07, 17.73)], v) being neutral with the statement ‘I do not have much contact with my offspring’ [Adj. OR: 0.31 (95% CI: 0.12, 0.810] and vi) being neutral with the statement ‘my offspring are not open to advice from me’ [Adj. OR: 0.63 (95% CI: 0.31, 0.84].

Conclusion

The majority of type 2 diabetes patients were willing to accept training to speak to their offspring to prevent diabetes. A training module should be designed to enhance their knowledge, attitude and skills to become family health educators.

Risk of diabetes among related and unrelated family members

AIMS

The aim was to explore familial aggregation of diabetes in genetically related and unrelated individuals.

METHODS

We included citizens from Danish nationwide registries between 1995 and 2018 and calculated rate ratios (RR) of diabetes based on family relation using Poisson regression.

RESULTS

Of 7.3 million individuals eligible for inclusion, we identified 343,237 (4.7%) with diabetes. The RR of diabetes was 2.02 (95% CI: 1.99-2.05; p < 0.0001) if any relative had diabetes, 1.79 (95% CI: 1.76-1.83) if a father had diabetes, and 2.06 (95% CI: 2.02-2.10) if a mother had diabetes. If both parents had diabetes, the RR was 3.40 (95% CI: 3.24-3.56). Among full siblings, the RR for developing diabetes was 2.77 (95% CI: 2.71-2.84) and 5.76 (95% CI: 5.00-6.63) for twins. For second-degree relatives, half siblings with a common mother had a RR of 2.35 (95% CI: 2.15-2.56), and with a common father 1.99 (95% CI: 1.81-2.17). Furthermore, the RR was 1.60 (95% CI: 1.56-1.64) if a wife had diabetes, and 1.41 (95% CI: 1.38-1.44) if a husband had diabetes. A subgroup analysis of individuals receiving insulin only treatment (N = 23,054) demonstrated a similar risk pattern, although with slightly higher risk estimates.

CONCLUSIONS/INTERPRETATION

Family aggregation of diabetes is associated with genetic disposition with maternal status being the predominant factor. Furthermore, we observed increased risk of diabetes in second-degree relatives, and between unrelated spouses, indicating that environmental factors influence diabetes risk substantially.

Mutual Involvement in Families Living with Type 2 Diabetes: Using the Family Toolbox to Address Challenges Related to Knowledge, Communication, Support, Role Confusion, Everyday Practices and Mutual Worries

Family involvement plays a key role in diabetes management. Challenges related to type 2 diabetes (T2D) often affect the whole family, and relatives are at increased risk of developing diabetes themselves. Creating family involvement in families living with T2D is a complex matter. This article studies potential effects of working with dialogue tools specifically developed to create family involvement. The data consist of 18 semi-structured family interviews. The data were analyzed using radical hermeneutics and theories on family identity and healthcare authenticity. The analysis revealed five themes: (1) Working with the tools created better and broader intra-familial involvement; (2) the tools enabled new roles and self-understandings for all family members; (3) the tools facilitated mutual insights into each other’s thoughts and worries; (4) after working with the tools, it was easier to discover potential challenges and possible behavior change; and (5) gaining new knowledge and the motivation to seek more knowledge was easier after working with the tools. Working with the tools changed how the families perceive themselves and the ways in which they can affect their own T2D-related health behavior together. This has direct implications for healthcare practitioners working with people with T2D.

Just Living With Obese Family Members Increases Your Risk of Type 2 Diabetes

IN BRIEF In this new era of accountable care and population health, large provider organizations are looking for new ways to predict diseases in their population, especially for people with diabetes. Although diabetes has been associated with the incidence of obesity, many diabetes patients are not obese. However, we find that just living in a household with one or more obese biologically related family members is a major risk factor for diabetes, even after accounting for all the other traditional risk factors.

Effect of parental history of diabetes on markers of inflammation, insulin resistance and atherosclerosis in first degree relatives of patients with type 2 diabetes mellitus

AIM AND OBJECTIVE

To study the effect of parental history of diabetes on markers of inflammation, insulin resistance, adiposity indices and carotid intima media thickness (cIMT) in first degree relatives of patients with type 2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

Normal glucose tolerant (NGT) first degree relatives of T2DM patients of age group 20-40 years designated as FH^positive were enrolled in the cross sectional study. Depending on the parental history of diabetes they were divided into three groups: family history positive in father (FH^father), family history positive in mother (FH^mother) and family history positive in both (FH^both). Age, sex and BMI matched controls without any history of diabetes in their parents designated as FH^negative were taken for comparison. All subjects underwent detailed clinical evaluation and biochemical investigations. cIMT and adiposity indices like visceral adipose tissue thickness (VAT) and subcutaneous adipose tissue thickness (SAT) were assessed using ultrasonography.

RESULTS

No difference existed with regards to BMI, hsCRP, degree of insulin resistance, adiposity markers and cIMT between FH^mother and FH^father group. Subjects in FH^both group had significantly higher degree of insulin resistance, subclinical inflammation, increased atherosclerosis and adiposity indices in contrast to those who have a single parent T2DM family history.

CONCLUSIONS

hsCRP and cIMT are significantly higher in the first degree relatives of type2 diabetes mellitus patients than controls. Individuals with history of T2DM in both parents have significantly worse glycemic status, increased cIMT and adverse cardiovascular risk profile than those with T2DM history in only single parent.

Adiposity and family history of type 2 diabetes in an admixed population of adolescents: Associations with insulin sensitivity, beta-cell function, and hepatic insulin extraction in BRAMS study

AIMS

Insulin resistance and beta-cell dysfunction manifest differently across racial/ethnic groups, and there is a lack of knowledge regarding the pathophysiology of type 2 diabetes mellitus (T2DM) for ethnically admixed adolescents. This study aimed to investigate the influence of adiposity and family history (FH) of T2DM on aspects of insulin sensitivity, beta-cell function, and hepatic insulin extraction in Brazilian adolescents.

METHODS

A total of 82 normoglycemic adolescents were assessed. The positive FH of T2DM was defined as the presence of at least one known family member with T2DM. The hyperglycemic clamp test consisted of a 120-min protocol. Insulin secretion and beta-cell function were obtained from C-peptide deconvolution. Analysis of covariance considered pubertal stage as a covariate.

RESULTS

Both lean and overweight/obese adolescents had similar glycemic profiles and disposition indexes. Overweight/obese adolescents had about 1/3 the insulin sensitivity of lean adolescents (1.1 ± 0.2 vs. 3.4 ± 0.3 mg·kg·min·pmol ∗ 1000), which was compensated by an increase around 2.5 times in basal (130 ± 7 vs. 52 ± 10 pmol·l·min) and total insulin secretion (130,091 ± 12,230 vs. 59,010 ± 17,522 pmol·l·min), and in the first and second phases of insulin secretion; respectively (p < 0.001). This increase was accompanied by a mean reduction in hepatic insulin extraction of 35%, and a 2.7-time increase in beta-cell glucose sensitivity (p < 0.05). The positive FH of T2DM was not associated with derangements in insulin sensitivity, beta-cell function, and hepatic insulin extraction.

CONCLUSIONS

In an admixed sample of adolescents, the hyperglycemic clamp test demonstrated that adiposity had a strong influence, and FH of T2DM had no direct influence, in different aspects of glucose metabolism.

A Drosophila model of insulin resistance associated with the human TRIB3 Q/R polymorphism

Members of the Tribbles family of proteins are conserved pseudokinases with diverse roles in cell growth and proliferation. Both Drosophila Tribbles (Trbl) and vertebrate Trib3 proteins bind to the kinase Akt (Akt1) to block its phosphorylation activation and reduce downstream insulin-stimulated anabolism. A single nucleotide polymorphism (SNP) variant in human TRIB3, which results in a glutamine (Q) to arginine (R) missense mutation in a conserved motif at position 84, confers stronger Akt binding, resulting in reduced Akt phosphorylation, and is associated with a predisposition to Type 2 diabetes, cardiovascular disease, diabetic nephropathy, chronic kidney disease and leukemogenesis. Here, we used a Drosophila model to understand the importance of the conserved R residue in several Trbl functions. In the fly fat body, misexpression of a site-directed Q mutation at position R141 resulted in weakened binding to Drosophila Akt (dAkt), leading to increased levels of phospho-dAkt, increased cell and tissue size, and increases in the levels of stored glycogen and triglycerides. Consistent with the functional conservation of this arginine in modulating Akt activity, mouse Trib3 R84 misexpressed in the fly fat body blocked dAkt phosphorylation with a strength similar to wild-type Trbl. Limited mutational analysis shows that the R141 site dictates the strength of Akt binding but does not affect other Trbl-dependent developmental processes, suggesting a specificity that could serve as a drug target for metabolic diseases.

Relationships between adiponectin levels, the metabolic syndrome, and type 2 diabetes: a literature review

Elevated hepatic glucose production, impaired insulin secretion, and insulin resistance - abnormalities of glucose metabolism typically found in subjects with obesity - are major factors underlying the pathogenesis of type 2 diabetes (DM2) and the metabolic syndrome (MS). Adiponectin is a major regulator of glucose and lipid homeostasis via its insulin-sensitizing properties, and lower levels seems to be associated with the development of DM2 and MS. The purpose of this review is to clarify the mechanisms whereby adiponectin relates to the development of DM2 and MS and the association between polymorphisms of the adiponectin gene, circulating levels of the hormone, and its relationships with DM2. In addition, the impact of dietary lipids in the circulating levels of adiponectin will be addressed. According to the literature, circulating adiponectin levels seem to decrease as the number of MS components increases. Lower adiponectin concentrations are associated with higher intra-abdominal fat content. Therefore, adiponectin could link intra-abdominal fat with insulin resistance and development of MS. Therapeutic strategies that target the MS and its components, such as lifestyle modification through physical activity and weight loss, have been shown to increase adiponectin concentrations. Possible roles of diets containing either low or high amounts of fat, or different types of fat, have been analyzed in several studies, with heterogeneous results. Supplementation with n-3 PUFA modestly increases adiponectin levels, whereas conjugated linoleic acid supplementation appears to reduce concentrations when compared with unsaturated fatty acid supplementation used as an active placebo.

Mutual Involvement in Families With Type 2 Diabetes Through Web-Based Health Care Solutions: Quantitative Survey Study of Family Preferences, Challenges, and Potentials

Background

Type 2 diabetes (T2D) is a prevalent chronic disease that affects not just patients but entire families. Both the patient and the rest of the family may benefit from gaining knowledge about the disease and from supportive interfamilial interaction. The Internet is becoming a widely-used resource for health information, so a Web-based solution could potentially promote awareness and knowledge on how to manage T2D as a family, while also providing support for the family.

Objective

We aim to assess the usage of online diabetes information by patients with T2D and their relatives, and explore the families’ needs and preferences regarding online information on diabetes.

Methods

A quantitative self-reported questionnaire survey was performed with Danish families that had at least one family member diagnosed with T2D. The survey consisted of 36 closed questions on demographics, usage of the Internet, preferences in the source of information, interest in online information on six problem domains within family life related to T2D, preferences towards the delivery format of online information, and peer-to-peer communication. Two open-ended questions were also included to elicit any additional comments or suggestions about improving online information on T2D regarding family life.

Results

Fifty participants from 22 families with T2D answered the questionnaire individually. Relatives (25/28, 89%) and patients (22/22, 100%) indicated that information on T2D is relevant for them, while indicating that the Internet is the first or second preferred source when in need of information on T2D (25/28, 89% vs 21/22, 95%). Only a minority of the participants indicated that they had searched the Internet to gain knowledge on T2D regarding family life (9/28, 32% vs 10/22, 46%). Also, patients were more likely to have used the Internet to gain information on T2D (P=.027). Both groups indicated a preference for watching videos or reading about T2D in relation to family life while a minority of the participants indicated an interest in peer-to-peer communication. Regarding the six problem domains, the domains Support, Knowledge, and Everyday Life were slightly more popular. These three domains were considered interesting by at least 79% (22/28) and 73% (16/22) of the relatives and patients respectively, while the domains Communication, Worries, and Roles were considered interesting by at least 46% (20/28) and 50% (11/22).

Conclusions

Despite an interest in online information on T2D, there appears to be an unsatisfied need for more supportive online information on T2D aimed at Danish families with T2D. Based on family preferences, online information should focus on the six problem domains and be presented through text and videos by health care practitioners and peers. Peer-to-peer communication elements may be beneficial, but are only expected to be used by a very limited number of families.

Involvement of family members in life with type 2 diabetes: Six interconnected problem domains of significance for family health identity and healthcare authenticity

Objectives:

Family involvement plays a key role in diabetes management. Problems and challenges related to type 2-diabetes often affect the whole family, and relatives are at increased risk of developing diabetes themselves. We highlight these issues in our objectives: (1) to uncover specific family problems associated with mutual involvement in life with type 2-diabetes and (2) to analytically look at ways of approaching these problems in healthcare settings.

Methods:

Qualitative data were gathered in participatory problem assessment workshops. The data were analysed in three rounds using radical hermeneutics.

Results:

Problems were categorized in six domains: knowledge, communication, support, everyday life, roles and worries. The final cross-analysis focusing on the link between family identity and healthcare authenticity provided information on how the six domains can be approached in healthcare settings.

Conclusion:

The study generated important knowledge about problems associated with family involvement in life with type 2 diabetes and about how family involvement can be supported in healthcare practice.

Interventions for prevention of type 2 diabetes in relatives: A systematic review

The relatives and partners of people with type 2 diabetes are at increased risk of developing type 2 diabetes. This systematic review examines randomized controlled trials, written in English that tested an intervention, which aimed to modify behaviors known to delay or prevent type 2 diabetes, among the relatives or partners of people with type 2 diabetes. Study quality was assessed using the Cochrane Collaboration's tool for assessing risk of bias. Seven studies met the inclusion criteria. The majority of studies were at low risk of bias. Six studies tested an intervention in first-degree relatives of people with type 2 diabetes and one in partners. Intervention components and intervention intensity across studies varied, with those targeting diet and physical activity reporting the most significant changes in primary outcomes. Only one study did not observe significant changes in primary outcomes. There were three main recruitment approaches: advertising in the community, recruiting people through their relatives with diabetes, or identifying people as high risk by screening of their own health care contacts. Some evidence was found for potentially successful interventions to prevent type 2 diabetes among the relatives and partners of people with type 2 diabetes, although finding simple and effective methods to identify and recruit them remains a challenge. Future studies should explore the effect of patients' perceptions on their family members' behavior and capitalize on family relationships in order to increase intervention effectiveness.

Heritability, parental transmission and environment correlation of pediatric-onset type 2 diabetes mellitus and metabolic syndrome-related traits

AIM

To estimate the heritability, parental transmission and environmental contributions to the phenotypic variation in type 2 diabetes mellitus and metabolic syndrome-related traits in families of Mexican children and adolescents.

METHODS

We performed a cross-sectional study of 184 tri-generational pedigrees with a total of 1160 individuals (99 families with a type 2 diabetes mellitus proband before age 19). The family history of type 2 diabetes mellitus in three generations was obtained by interview. Demographic, anthropometric, biochemical and lifestyle information was corroborated in parents and offspring. We obtained correlations for metabolic traits between relative pairs, and variance component methods were used to determine the heritability and environmental components.

RESULTS

The heritability of early-onset of type 2 diabetes mellitus was 0.50 (p<1.0e-7). The heritability was greater than 0.5 for hypertension, hypoalphalipoproteinemia, hypercholesterolemia, body mass index, waist circumference, blood pressure, 2-h insulin, and cholesterol (p<0.001). In contrast, we observed a high environmental correlation (>0.50) for blood pressure, HbA1c and HDL-cholesterol after multivariate adjustment (p<0.05). Several traits, such as type 2 diabetes mellitus and insulin resistance, were significantly correlated only through the mother and others, such as hypertriglyceridemia, were significantly correlated only through the father.

CONCLUSION

This study demonstrates that type 2 diabetes mellitus and metabolic syndrome-related traits are highly heritable among Mexican children and adolescents. Furthermore, several cardiometabolic factors have strong heritability and/or high environmental contributions that highlight the complex architecture of these alterations.

Recent advances in the molecular genetics of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a complex disease in which both genetic and environmental factors interact in determining impaired β-cell insulin secretion and peripheral insulin resistance. Insulin resistance in muscle, liver and fat is a prominent feature of most patients with T2DM and obesity, resulting in a reduced response of these tissues to insulin. Considerable evidence has been accumulated to indicate that heredity is a major determinant of insulin resistance and T2DM. It is believed that, among individuals destined to develop T2DM, hyperinsulinemia is the mechanism by which the pancreatic β-cell initially compensates for deteriorating peripheral insulin sensitivity, thus ensuring normal glucose tolerance. Most of these people will develop T2DM when β-cells fail to compensate. Despite the progress achieved in this field in recent years, the genetic causes of insulin resistance and T2DM remain elusive. Candidate gene association, linkage and genome-wide association studies have highlighted the role of genetic factors in the development of T2DM. Using these strategies, a large number of variants have been identified in many of these genes, most of which may influence both hepatic and peripheral insulin resistance, adipogenesis and β-cell mass and function. Recently, a new gene has been identified by our research group, the HMGA1 gene, whose loss of function can greatly raise the risk of developing T2DM in humans and mice. Functional genetic variants of the HMGA1 gene have been associated with insulin resistance syndromes among white Europeans, Chinese individuals and Americans of Hispanic ancestry. These findings may represent new ways to improve or even prevent T2DM.

Simultaneous copy number losses within multiple subtelomeric regions in early-onset type 2 diabetes mellitus

Genetic factors play very important roles in the onset and progression of type 2 diabetes mellitus (T2DM). However, the genetic factors correlating with T2DM onset have not as yet been fully clarified. We previously found that copy number losses in the subtelomeric region on chromosome 4p16.3 were detected in early-onset Japanese T2DM patients (onset age <35 years) at a high frequency. Herein, we additionally found two novel copy number losses within the subtelomeric regions on chromosomes 16q24.2-3 and 22q13.31-33, which have significant associations with early-onset Japanese T2DM. The associations were statistically significant by Fisher's exact tests with P values of 5.19×10⁻³ and 1.81×10⁻³ and odds ratios of 5.7 and 4.4 for 16q24.2-3 and 22q13.31-33, respectively. Furthermore, copy number variation (CNV) analysis of the whole genome using the CNV BeadChip system verified simultaneous copy number losses in all three subtelomeric regions in 11 of our 100 T2DM subjects, while none of 100 non-diabetic controls showed the copy number losses in all three regions. Our results suggest that the mechanism underlying induction of CNVs is involved in the pathogenesis of early-onset T2DM. Thus, copy number losses within multiple subtelomeric regions are strongly associated with early-onset T2DM and examination of simultaneous CNVs in these three regions may lead to the development of an accurate and selective procedure for detecting genetic susceptibility to T2DM.

Joint effects of known type 2 diabetes susceptibility loci in genome-wide association study of Singapore Chinese: the Singapore Chinese health study

BACKGROUND

Genome-wide association studies (GWAS) have identified genetic factors in type 2 diabetes (T2D), mostly among individuals of European ancestry. We tested whether previously identified T2D-associated single nucleotide polymorphisms (SNPs) replicate and whether SNPs in regions near known T2D SNPs were associated with T2D within the Singapore Chinese Health Study.

METHODS

2338 cases and 2339 T2D controls from the Singapore Chinese Health Study were genotyped for 507,509 SNPs. Imputation extended the genotyped SNPs to 7,514,461 with high estimated certainty (r(2)>0.8). Replication of known index SNP associations in T2D was attempted. Risk scores were computed as the sum of index risk alleles. SNPs in regions ± 100 kb around each index were tested for associations with T2D in conditional fine-mapping analysis.

RESULTS

Of 69 index SNPs, 20 were genotyped directly and genotypes at 35 others were well imputed. Among the 55 SNPs with data, disease associations were replicated (at p<0.05) for 15 SNPs, while 32 more were directionally consistent with previous reports. Risk score was a significant predictor with a 2.03 fold higher risk CI (1.69-2.44) of T2D comparing the highest to lowest quintile of risk allele burden (p = 5.72 × 10(-14)). Two improved SNPs around index rs10923931 and 5 new candidate SNPs around indices rs10965250 and rs1111875 passed simple Bonferroni corrections for significance in conditional analysis. Nonetheless, only a small fraction (2.3% on the disease liability scale) of T2D burden in Singapore is explained by these SNPs.

CONCLUSIONS

While diabetes risk in Singapore Chinese involves genetic variants, most disease risk remains unexplained. Further genetic work is ongoing in the Singapore Chinese population to identify unique common variants not already seen in earlier studies. However rapid increases in T2D risk have occurred in recent decades in this population, indicating that dynamic environmental influences and possibly gene by environment interactions complicate the genetic architecture of this disease.

Diabetes in first-degree family members: a predictor of type 2 diabetes in 159 nonscreening Alabama hemochromatosis probands with HFE C282Y homozygosity

OBJECTIVE We sought to identify predictors of diabetes diagnosed before hemochromatosis. RESEARCH DESIGN AND METHODS We studied these 16 variables in 159 nonscreening hemochromatosis probands with HFE C282Y homozygosity: age; sex; BMI; diabetes reports in first-degree family members (dichotomous); heavy ethanol consumption; cigarette smoking; elevated serum alanine aminotransferase/aspartate aminotransferase levels; nonalcoholic fatty liver; chronic viral hepatitis; cirrhosis; hand arthropathy; iron removed by phlebotomy; and positivity for HLA-A*01, B*08; A*03, B*07; and A*03, B*14 haplotypes. We performed univariable and multivariable analyses. RESULTS Twenty-three probands (14.5%) had diabetes; 19 were men. Each of the 23 probands had type 2 diabetes. Mean BMI was greater in probands with diabetes (31.7 ± 8.5 [SD] kg/m(2) vs. 27.6 ± 5.1 kg/m(2); P = 0.032). Reports of any first-degree family member with diabetes were more prevalent in probands with than in probands without diabetes (69.6 vs. 17.6%; P < 0.0001). In probands with diabetes, the odds ratio (OR) of maternal diabetes was 6.7 (95% CI 2.3-19.7; P = 0.0005) and of sibling diabetes was 11.7 (3.0-45.5; P = 0.0004). In a logistic regression model, predictors of diabetes at hemochromatosis diagnosis in 159 probands were diabetes reports in family members (OR 8.5 [95% CI 2.9-24.8]; P < 0.0001) and BMI (1.1 [1.0-1.2]; P = 0.049). This model explained 26.0% of total deviance contributing to diabetes. CONCLUSIONS In nonscreening hemochromatosis probands with HFE C282Y homozygosity, a heritable factor(s) increases the risk of diabetes diagnosed before hemochromatosis.

Evaluating empirical bounds on complex disease genetic architecture

The genetic architecture of human diseases governs the success of genetic mapping and the future of personalized medicine. Although numerous studies have queried the genetic basis of common disease, contradictory hypotheses have been advocated about features of genetic architecture (for example, the contribution of rare versus common variants). We developed an integrated simulation framework, calibrated to empirical data, to enable the systematic evaluation of such hypotheses. For type 2 diabetes (T2D), two simple parameters--(i) the target size for causal mutation and (ii) the coupling between selection and phenotypic effect--define a broad space of architectures. Whereas extreme models are excluded by the combination of epidemiology, linkage and genome-wide association studies, many models remain consistent, including those where rare variants explain either little (<25%) or most (>80%) of T2D heritability. Ongoing sequencing and genotyping studies will further constrain the space of possible architectures, but very large samples (for example, >250,000 unselected individuals) will be required to localize most of the heritability underlying T2D and other traits characterized by these models.

Estimating sibling recurrence risk in population sample surveys

BACKGROUND/AIMS

Sibling recurrence risk (SRR) is a measure of familial aggregation of a disease and is often used in family-based studies in genetic epidemiology to indicate the existence of possible genes conferring susceptibility of disease. Estimating SRR requires information about the disease status of sibships of families with two or more siblings where at least one is affected. Since family-based studies are not usually random samples, estimates of SRR derived from these studies may be biased. Network sampling used in survey research offers a way to ascertain the disease status of sibships from interviewed individuals in household survey samples, in order to obtain (approximately) unbiased estimators of SRR and its related SRR ratio (SRR divided by the prevalence of disease).

METHODS

Two methods of ascertaining sibships of affected families are considered: in one method the siblings' affected status is reported by an individual, regardless of the individual's affected status, and in the other method only affected individuals can report their siblings' affected status. Network estimators of SRR and SRR ratio and estimators of their standard errors are provided.

RESULTS

Reported diabetes for siblings from the 1976 National Health Interview is used to illustrate the estimation methods. The SRR ratio for diabetes among living siblings was 5.79% [relative standard error (RSE) = 5.12%], and for living or deceased siblings, it was 7.66% (RSE = 3.76%).

CONCLUSIONS

Network sampling estimators can provide population estimates of SRR and SRR ratio for diseases such as diabetes.

Genetic prediction of common diseases. Still no help for the clinical diabetologist!

Genome-wide association studies (GWAS) have identified several loci associated with many common, multifactorial diseases which have been recently used to market genetic testing directly to the consumers. We here addressed the clinical utility of such GWAS-derived genetic information in predicting type 2 diabetes mellitus (T2DM) and coronary artery disease (CAD) in diabetic patients. In addition, the development of new statistical approaches, novel technologies of genome sequencing and ethical, legal and social aspects related to genetic testing have been also addressed. Available data clearly show that, similarly to what reported for most common diseases, genetic testing offered today by commercial companies cannot be used as predicting tools for T2DM and CAD. Further studies taking into account the complex interaction between genes as well as between genetic and non-genetic factors, including age, obesity and glycemic control which seem to modify genetic effects on the risk of T2DM and CAD, might mitigate such negative conclusions. Also, addressing the role of relatively rare variants by next generation sequencing may help identify novel and strong genetic markers with an important role in genetic prediction. Finally, statistical tools concentrated on reclassifying patients might be a useful application of genetic information for predicting many common diseases. By now, prediction of such diseases, including those of interest for the clinical diabetologist, have to be pursued by using traditional clinical markers which perform well and are not costly.

Expanded Criteria Living Donors: How Far Can We Go?

In an effort to expand the deceased donor pool, transplant centers have accepted expanded criteria donors as appropriate for many of the patients in the deceased donor pool. Translating this into the living donor pool is more complex. One must consider not only the quality of the organ procured but the consequences that the nephrectomy might have on the living donors for the rest of their lives. This review examines the available data on higher risk donors and the appropriateness, or lack thereof, of accepting them as kidney donors.

Gene-environment interactions in the development of type 2 diabetes: recent progress and continuing challenges

Type 2 diabetes (T2D) is thought to arise from the complex interplay of both genetic and environmental factors. Since the advent of genome-wide association studies (GWAS), we have seen considerable progress in our understanding of the role that genetics and gene-environment interactions play in the development of T2D. Recent work suggests that the adverse effect of several T2D loci may be abolished or at least attenuated by higher physical activity levels or healthy lifestyle, whereas low physical activity and dietary factors characterizing a Western dietary pattern may augment it. However, there still remain inconsistencies warranting further investigation. Lack of statistical power and measurement errors for the environmental factors continue to challenge our efforts for characterizing interactions. Although our recent focus on established T2D loci is reasonable, we may be overlooking many other potential loci not captured by recent T2D GWAS. Agnostic approaches to the discovery of gene and environment interactions may address this possibility, but their application to the field is currently limited and still faces conceptual challenges. Nonetheless, continued investment in gene-environment interaction studies through large collaborative efforts holds promise in furthering our understanding of the interplay between genetic and environmental factors.

Frequent loss of genome gap region in 4p16.3 subtelomere in early-onset type 2 diabetes mellitus

A small portion of Type 2 diabetes mellitus (T2DM) is familial, but the majority occurs as sporadic disease. Although causative genes are found in some rare forms, the genetic basis for sporadic T2DM is largely unknown. We searched for a copy number abnormality in 100 early-onset Japanese T2DM patients (onset age <35 years) by whole-genome screening with a copy number variation BeadChip. Within the 1.3-Mb subtelomeric region on chromosome 4p16.3, we found copy number losses in early-onset T2DM (13 of 100 T2DM versus one of 100 controls). This region surrounds a genome gap, which is rich in multiple low copy repeats. Subsequent region-targeted high-density custom-made oligonucleotide microarray experiments verified the copy number losses and delineated structural changes in the 1.3-Mb region. The results suggested that copy number losses of the genes in the deleted region around the genome gap in 4p16.3 may play significant roles in the etiology of T2DM.

Quantifying the underestimation of relative risks from genome-wide association studies

Genome-wide association studies (GWAS) have identified hundreds of associated loci across many common diseases. Most risk variants identified by GWAS will merely be tags for as-yet-unknown causal variants. It is therefore possible that identification of the causal variant, by fine mapping, will identify alleles with larger effects on genetic risk than those currently estimated from GWAS replication studies. We show that under plausible assumptions, whilst the majority of the per-allele relative risks (RR) estimated from GWAS data will be close to the true risk at the causal variant, some could be considerable underestimates. For example, for an estimated RR in the range 1.2–1.3, there is approximately a 38% chance that it exceeds 1.4 and a 10% chance that it is over 2. We show how these probabilities can vary depending on the true effects associated with low-frequency variants and on the minor allele frequency (MAF) of the most associated SNP. We investigate the consequences of the underestimation of effect sizes for predictions of an individual's disease risk and interpret our results for the design of fine mapping experiments. Although these effects mean that the amount of heritability explained by known GWAS loci is expected to be larger than current projections, this increase is likely to explain a relatively small amount of the so-called “missing” heritability.

Genome-wide association studies (GWAS) exploit the correlation in genetic diversity along chromosomes in order to detect effects on disease risk without having to type causal loci directly. The inevitable downside of this approach is that, when the correlation between the marker and the causal variant is imperfect, the risk associated with carrying the predisposing allele is diluted and its effect is underestimated. Using simulations, where we know the true risk at the causal locus, we quantify the extent of this underestimation. We show that, for loci which have a modest effect on disease risk and are common in the population, the risk estimated from the most associated SNP is very close to the truth approximately two thirds of the time. Although the extent of the underestimation depends on assumptions about the frequency and strength of the risk allele, we predict that fine mapping of GWAS loci will, in rare cases, identify causal variants with considerably higher risk. Using three common diseases as examples, we investigate the expected cumulative effects of underestimation at multiple loci on our ability to stratify individuals by disease risk and to explain disease heritability.

Cultural variations in attitudes towards family risk of diabetes

AIMS

To examine differences in attitudes and behaviours towards familial risk of type 2 diabetes in populations in Ireland and Bahrain.

METHODS

Cross-sectional ecological study. Questionnaires were developed and administered to patients with diabetes and their first degree relatives in both Bahrain and Ireland. Data was analysed using non-parametric tests of association.

RESULTS

Responses were compared between 297 patients with diabetes from Ireland and 201 from Bahrain and between 364 relatives of patients with diabetes in Ireland and 244 from Bahrain. Relatives in Bahrain had more knowledge of risk factors for diabetes and an increased perception of the seriousness of diabetes but a more external, chance locus of control and perceived more barriers to changing lifestyles than those in Ireland. There was no difference in perception of personal risk of diabetes.

CONCLUSIONS

Knowledge of risk factors and seriousness of diabetes are higher in Bahrain than in Ireland but perception of personal risk of diabetes and intention to adopt risk reducing behaviours are no different. There is a need to develop models of behavioural change that are more relevant to the needs of the Bahraini population in reducing their risk of diabetes.

Evidence that BMI and type 2 diabetes share only a minor fraction of genetic variance: a follow-up study of 23,585 monozygotic and dizygotic twins from the Finnish Twin Cohort Study

AIMS/HYPOTHESIS

We investigated whether BMI predicts type 2 diabetes in twins and to what extent that is explained by common genetic factors.

METHODS

This was a population-based twin cohort study. Monozygotic (n = 4,076) and dizygotic (n = 9,109) non-diabetic twin pairs born before 1958 answered a questionnaire in 1975, from which BMI was obtained. Information on incident cases of diabetes was obtained by linkage to nationwide registers until 2005.

RESULTS

Altogether, 1,332 twins (6.3% of men, 5.1% of women) developed type 2 diabetes. The HR for type 2 diabetes increased monotonically with a mean of 1.22 (95% CI 1.20-1.24) per BMI unit and of 1.97 (95% CI 1.87-2.08) per SD of BMI. The HRs for lean, overweight, obese and morbidly obese participants were 0.59, 2.96, 6.80 and 13.64 as compared with normal weight participants. Model heritability estimates for bivariate variance due to an additive genetic component and non-shared environmental component were 75% (men) and 71% (women) for BMI, and 73% and 64%, respectively for type 2 diabetes. The correlations between genetic variance components (r (g)) indicated that one fifth of the covariance of BMI and type 2 diabetes was due to shared genetic influences. Although the mean monozygotic concordance for type 2 diabetes was approximately twice the dizygotic one, age of onset of diabetes within twin pair members varied greatly, irrespective of zygosity.

CONCLUSIONS/INTERPRETATION

A 28-year follow-up of adult Finnish twins showed that despite high trait heritability estimates, only a fraction of covariation in BMI and incident type 2 diabetes was of genetic origin.

The clinical relevance of genetic susceptibility to osteoarthritis

Osteoarthritis is a major musculoskeletal cause of disability in the elderly, but current therapeutic approaches are insufficient to prevent initiation and progression of the disease. Genetic studies in humans have identified molecules involved in signalling cascades that are important for the pathology of the joint components. These include the bone morphogenetic protein (BMP) signalling, the wingless-type signalling and the thyroid pathway as well as apoptotic-related molecules. There is emerging evidence indicating that inflammatory molecules related to cytokine production, prostaglandin and arachidonic acid metabolism are also involved in susceptibility to osteoarthritis. All of these pathways are likely targets for pharmacological intervention. Genetic variation also affects pain due to osteoarthritis highlighting molecular mechanisms for pain relief. Moreover, combinations of genetic markers can be used to identify individuals at high risk of osteoarthritis and risk of total joint arthroplasty failure, which should facilitate the application of preventive and disease management strategies.

Umbilical waist-to-height ratio and trunk fat mass index (DXA) as markers of central adiposity and insulin resistance in Argentinean children with a family history of metabolic syndrome

Central adiposity is increasing in childhood. To find a simple index of central fatness that accurately predicts insulin resistance we studied 55 obese children and 53 siblings, aged 6-16 years. We recorded the family metabolic score, calculated clinical and DXA-derived fat distribution indexes and HOMA-IR. Umbilical waist-to-height ratio (W-to-Ht) had the best combination of ROC area (0.99, IC95: 0.93 to 1.0), Youden's index (0.976), coefficient of variation (4.9) and correlation with HOMA-IR (r = 0.58, p < 0.0001); it also correlated (p < 0.001) with BMI (r = 0.95) and DXA-trunk fat mass index (r = 0.93). It was the best predictor of insulin resistance in a multiple regression model (p < 0.0001). Odds ratios for insulin resistance were 9.33 when the family score was >10 (p < 0.01) and 14.35 when umbilical W-to-Ht was >0.54 (p < 0.0001). Umbilical W-to-Ht, a simple marker of central adiposity, strongly relates to children's DXA-trunk fat mass index and insulin resistance.

On the use of sibling recurrence risks to select environmental factors liable to interact with genetic risk factors

Gene-environment interactions are likely to be involved in the susceptibility to multifactorial diseases but are difficult to detect. Available methods usually concentrate on some particular genetic and environmental factors. In this paper, we propose a new method to determine whether a given exposure is susceptible to interact with unknown genetic factors. Rather than focusing on a specific genetic factor, the degree of familial aggregation is used as a surrogate for genetic factors. A test comparing the recurrence risks in sibs according to the exposure of indexes is proposed and its power is studied for varying values of model parameters. The Exposed versus Unexposed Recurrence Analysis (EURECA) is valuable for common diseases with moderate familial aggregation, only when the role of exposure has been clearly outlined. Interestingly, accounting for a sibling correlation for the exposure increases the power of EURECA. An application on a sample ascertained through one index affected with type 2 diabetes is presented where gene-environment interactions involving obesity and physical inactivity are investigated. Association of obesity with type 2 diabetes is clearly evidenced and a potential interaction involving this factor is suggested in Hispanics (P=0.045), whereas a clear gene-environment interaction is evidenced involving physical inactivity only in non-Hispanic whites (P=0.028). The proposed method might be of particular interest before genetic studies to help determine the environmental risk factors that will need to be accounted for to increase the power to detect genetic risk factors and to select the most appropriate samples to genotype.

Reducing health risk in family members of patients with type 2 diabetes: views of first degree relatives

Background

Patients with type 2 diabetes can have an important role in discussing health risk within families. This study aimed to establish the acceptability to first degree relatives towards their relative with type 2 diabetes intervening as health promoters in their own families, using the Health Belief Model as a theoretical framework for evaluation.

Methods

Cross-sectional questionnaire design. Survey questionnaire for first degree relative (sibling or child) mailed to a random sample of patients with type 2 diabetes registered with an urban hospital diabetes clinic (n = 607 eligible patients). Patients were asked to pass on questionnaires to one to two first degree relatives.

Results

Questionnaires were returned from 257 families (42% response rate) with two responses provided by 107 families (a total of 364 questionnaires). The majority (94%) of first degree relatives of patients with type 2 diabetes would like to be informed about reducing their risk. Half (48%) of respondents reported being spoken to by a relative with type 2 diabetes about their risk of diabetes. Those spoken to were more likely to see themselves at risk of diabetes, to worry about developing diabetes and to view diabetes as a serious condition.

Conclusions

A role for patients with type 2 diabetes in discussing health risk in their family appears to be acceptable to many relatives. Discussion of risk and interventions to reduce health risk with their relatives should be encouraged in patients with type 2 diabetes.

Insulin signaling regulating genes: effect on T2DM and cardiovascular risk

Type 2 diabetes mellitus (T2DM) is a complex disorder that has a heterogeneous genetic and environmental background. In this Review, we discuss the role of relatively infrequent polymorphisms of genes that regulate insulin signaling (including the K121Q polymorphism of ENPP1, the G972R polymorphism of IRS1 and the Q84R polymorphism of TRIB3) in T2DM and other conditions related to insulin resistance. The biological relevance of these three polymorphisms has been very thoroughly characterized both in vitro and in vivo and the available data indicate that they all affect insulin signaling and action as well as insulin secretion. They also affect insulin-mediated regulation of endothelial cell function. In addition, several reports indicate that the effects of all three polymorphisms on the risk of T2DM and cardiovascular diseases related to insulin resistance depend on the clinical features of the individual, including their body weight and age at disease onset. Thus, these polymorphisms might be used to demonstrate how difficult it is to ascertain the contribution of relatively infrequent genetic variants with heterogeneous effects on disease susceptibility. Unraveling the role of such variants might be facilitated by improving disease definition and focusing on specific subsets of patients.

Neighborhood resources for physical activity and healthy foods and incidence of type 2 diabetes mellitus: the Multi-Ethnic study of Atherosclerosis

BACKGROUND

Despite increasing interest in the extent to which features of residential environments contribute to incidence of type 2 diabetes mellitus, no multisite prospective studies have investigated this question. We hypothesized that neighborhood resources supporting physical activity and healthy diets are associated with a lower incidence of type 2 diabetes.

METHODS

Person-level data came from 3 sites of the Multi-Ethnic Study of Atherosclerosis, a population-based, prospective study of adults aged 45 to 84 years at baseline. Neighborhood data were derived from a population-based residential survey. Type 2 diabetes was defined as a fasting glucose level of 126 mg/dL or higher (> or =7 mmol/L) or taking insulin or oral hypoglycemic agents. We estimated the hazard ratio of type 2 diabetes incidence associated with neighborhood (US Census tract) resources.

RESULTS

Among 2285 participants, 233 new type 2 diabetes cases occurred during a median of 5 follow-up years. Better neighborhood resources, determined by a combined score for physical activity and healthy foods, were associated with a 38% lower incidence of type 2 diabetes (hazard ratio corresponding to a difference between the 90th and 10th percentiles for resource distribution, 0.62; 95% confidence interval, 0.43-0.88 adjusted for age, sex, family history of diabetes, race/ethnicity, income, assets, educational level, alcohol use, and smoking status). The association remained statistically significant after further adjustment for individual dietary factors, physical activity level, and body mass index.

CONCLUSION

Better neighborhood resources were associated with lower incidence of type 2 diabetes, which suggests that improving environmental features may be a viable population-level strategy for addressing this disease.

IRS1 G972R polymorphism and type 2 diabetes: a paradigm for the difficult ascertainment of the contribution to disease susceptibility of 'low-frequency-low-risk' variants

AIMS/HYPOTHESIS

The aim of the study was to determine the association between IRS1 G972R polymorphism and type 2 diabetes; published data concerning this association have been conflicting. To obtain further insight into this topic, we performed a meta-analysis of all available case-control studies.

METHODS

We performed a meta-analysis of 32 studies (12,076 cases and 11,285 controls).

RESULTS

The relatively infrequent R972 variant was not significantly associated with type 2 diabetes (OR 1.09, 95% CI 0.96-1.23, p = 0.184 under a dominant model). Some evidence of heterogeneity was observed across studies (p = 0.1). In the 14 studies (9,713 individuals) in which the mean age at type 2 diabetes diagnosis was available, this variable explained 52% of the heterogeneity (p = 0.03). When these studies were subdivided into tertiles of mean age at diagnosis, the OR for diabetes was 1.48 (95% CI 1.17-1.87), 1.22 (95% CI 0.97-1.53) and 0.88 (95% CI 0.68-1.13) in the youngest, intermediate and oldest tertile, respectively (p = 0.0022 for trend of ORs).

CONCLUSIONS/INTERPRETATION

Our findings illustrate the difficulties of ascertaining the contribution of 'low-frequency-low-risk' variants to type 2 diabetes susceptibility. In the specific context of the R972 variant, approximately 200,000 study individuals would be needed to have 80% power to identify a 9% increase in diabetes risk at a genome-wide significance level. Under these circumstances, a strategy aimed at improving outcome definition and decreasing its heterogeneity may critically enhance our ability to detect genetic effects, thereby decreasing the required sample size. Our data suggest that focusing on early-onset diabetes, which is characterised by a stronger genetic background, may be part of such a strategy.

A susceptibility gene for type 2 diabetes confers substantial risk for diabetes complicating cystic fibrosis

AIMS/HYPOTHESIS

Insulin-requiring diabetes affects 25-50% of young adults with cystic fibrosis (CF). Although the cause of diabetes in CF is unknown, recent heritability studies in CF twins and siblings indicate that genetic modifiers play a substantial role. We sought to assess whether genes conferring risk for diabetes in the general population may play a risk modifying role in CF.

METHODS

We tested whether a family history of type 2 diabetes affected diabetes risk in CF patients in 539 families in the CF Twin and Sibling family-based study. A type 2 diabetes susceptibility gene (transcription factor 7-like 2, or TCF7L2) was evaluated for association with diabetes in CF using 998 patients from the family-based study and 802 unrelated CF patients in an independent case-control study.

RESULTS

Family history of type 2 diabetes increased the risk of diabetes in CF (OR 3.1; p = 0.0009). A variant in TCF7L2 associated with type 2 diabetes (the T allele at rs7903146) was associated with diabetes in CF in the family study (p = 0.004) and in the case-control study (p = 0.02; combined p = 0.0002). In the family-based study, variation in TCF7L2 increased the risk of diabetes about three-fold (HR 1.75 per allele, 95% CI 1.3-2.4; p = 0.0006), and decreased the mean age at diabetes diagnosis by 7 years. In CF patients not treated with systemic glucocorticoids, the effect of TCF7L2 was even greater (HR 2.9 per allele, 95% CI 1.7-4.9, p = 0.00011).

CONCLUSIONS/INTERPRETATION

A genetic variant conferring risk for type 2 diabetes in the general population is a modifier of risk for diabetes in CF.

The emerging role of TRIB3 as a gene affecting human insulin resistance and related clinical outcomes

Type 2 diabetes is becoming epidemic. The personal and social burden imposed by diabetes will increase in the close future as its prevalence is expected to double in the next 15-20 years. Type 2 diabetes is caused by the combination of resistance to insulin action and inadequate insulin secretion. Despite the role of profound changes in individual environmental exposure is incontrovertible, several findings clearly indicate that type 2 diabetes and insulin resistance are also heritable. Among the several inhibitors of insulin signalling, which have been recently proposed as determinants of insulin resistance, is TRIB3, a mammalian tribbles homolog which affects insulin signalling at the level of Akt-2, a key modulator of insulin action in target cells. We here report data on a prevalent Q84R TRIB3 missense single nucleotide polymorphism (rs2295490) we first described few years ago. Several lines of evidences indicate that this amino-acid change is, in fact, a gain of function mutation with the potential to affect insulin signalling and thus, to increase the risk of insulin resistance and related clinical outcomes.

Agreement among type 2 diabetes linkage studies but a poor correlation with results from genome-wide association studies

AIMS/HYPOTHESIS

Little of the genetic basis for type 2 diabetes has been explained, despite numerous genetic linkage studies and the discovery of multiple genes in genome-wide association (GWA) studies. To begin to resolve the genetic component of this disease, we searched for sites at which genetic results had been corroborated in different studies, in the expectation that replication among studies should direct us to the genomic locations of causative genes with more confidence than the results of individual studies.

METHODS

We have mapped the physical location of results from 83 linkage reports (for type 2 diabetes and diabetes precursor quantitative traits [QTs, e.g. plasma insulin levels]) and recent large GWA reports (for type 2 diabetes) onto the same human genome sequence to identify replicated results in diabetes genetic 'hot spots'.

RESULTS

Genetic linkage has been found at least ten times at 18 different locations, and at least five times in 56 locations. All replication clusters contained study populations from more than one ethnic background and most contained results for both diabetes and QTs. There is no close relationship between the GWA results and linkage clusters, and the nine best replication clusters have no nearby GWA result.

CONCLUSIONS/INTERPRETATION

Many of the genes for type 2 diabetes remain unidentified. This analysis identifies the broad location of yet to be identified genes on 6q, 1q, 18p, 2q, 20q, 17pq, 8p, 19q and 9q. The discrepancy between the linkage and GWA studies may be explained by the presence of multiple, uncommon, mildly deleterious polymorphisms scattered throughout the regulatory and coding regions of genes for type 2 diabetes.

Sibling and parental history in type 2 diabetes risk among ethnic Chinese: the Chin-Shan Community Cardiovascular Cohort Study

BACKGROUND

This study aims to compare various family history profiles as predictors of diabetes in a community-based prospective cohort because few prospective studies have examined the association of family history with diabetes risk in ethnic Chinese populations.

METHODS

Among 2960 participants free from baseline diabetes through the Chin-Shan Community Cardiovascular Cohort Study, there were 548 cases that developed diabetes after a median 9 years of follow-up.

RESULTS

After multivariate adjustment, sibling history was associated with diabetes [Relative risk (RR): 2.08, 95% confidence interval (CI): 1.42-3.06, P=0.0002]. Both maternal and paternal histories had similar effects (RR: 1.62, 95% CI: 1.04-2.51 for paternal history, RR: 1.36, 95% CI: 0.98-1.89 for maternal history). Obese participants with sibling history increased the risk of diabetes by 4.6-fold (RR: 4.61, 95% CI: 2.93-7.26), compared with those with neither obesity nor family history.

CONCLUSION

The findings support the hypothesis that sibling history is more important than parental history for diabetes risk.

Genetic modifiers play a substantial role in diabetes complicating cystic fibrosis

CONTEXT

Insulin-requiring diabetes affects 7-15% of teens and young adults, and more than 25% of older adults with cystic fibrosis (CF). Pancreatic exocrine disease caused by CF transmembrane conductance regulator (CFTR) dysfunction underlies the high rate of diabetes in CF patients; however, only a subset develops this complication, indicating that other factors are necessary.

OBJECTIVE

Our objective was to estimate the relative contribution of genetic and nongenetic modifiers to the development of diabetes in CF.

DESIGN/PATIENTS

This was a twin and sibling study involving 1366 individuals at 109 centers in the CF Twin and Sibling Study, from which were derived 68 monozygous twin pairs, 23 dizygous twin pairs, and 588 sibling pairs, all with CF.

MAIN OUTCOME MEASURE

Chronic, insulin-requiring diabetes in the setting of CF, as established using longitudinal clinical and biochemical data, was studied.

RESULTS

About 9% of this predominantly pediatric population (mean age = 15.8 yr) had diabetes. Key independent risk factors identified by regression modeling included having a twin or sibling with CF and diabetes, increasing age, pancreatic exocrine insufficiency or two mutations causing severe CFTR dysfunction, decreased lung function or decreased body mass index, and longer duration of glucocorticoid treatment. The concordance rate for diabetes was substantially higher in monozygous twins (0.73) than in dizygous twins and siblings with CF (0.18; P = 0.002). Heritability was estimated as near one (95% confidence interval 0.42-1.0).

CONCLUSIONS

Diabetes is a frequent complication of CF that is associated with worse outcomes. Although a nongenetic factor (steroid treatment) contributes to risk, genetic modifiers (i.e. genes other than CFTR) are the primary cause of diabetes in CF.

Will people with type 2 diabetes speak to family members about health risk?

OBJECTIVE

This study aimed to assess the potential for communication of familial risk by patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A questionnaire was completed by a random sample of patients with type 2 diabetes registered with a hospital diabetes clinic.

RESULTS

Two-thirds of patients (65%) had spoken to at least one sibling or child about diabetes risk. They were more likely to believe their family was at risk, to worry about their family developing diabetes, and to be aware of the seriousness of diabetes. The results revealed greater awareness of family risk of type 2 diabetes compared with those from previous studies.

CONCLUSIONS

Many patients with type 2 diabetes had already taken the initiative, without formal prompting, to talk to family members about their risk of diabetes. Discussion of risk and interventions to reduce risk should be encouraged within families.