Extension of type 2 diabetes genome-wide association scan results in the diabetes prevention program

OBJECTIVE— Genome-wide association scans (GWASs) have identified novel diabetes-associated genes. We evaluated how these variants impact diabetes incidence, quantitative glycemic traits, and response to preventive interventions in 3,548 subjects at high risk of type 2 diabetes enrolled in the Diabetes Prevention Program (DPP), which examined the effects of lifestyle intervention, metformin, and troglitazone versus placebo.RESEARCH DESIGN AND METHODS— We genotyped selected single nucleotide polymorphisms (SNPs) in or near diabetes-associated loci, including EXT2, CDKAL1, CDKN2A/B, IGF2BP2, HHEX, LOC387761, and SLC30A8 in DPP participants and performed Cox regression analyses using genotype, intervention, and their interactions as predictors of diabetes incidence. We evaluated their effect on insulin resistance and secretion at 1 year.RESULTS— None of the selected SNPs were associated with increased diabetes incidence in this population. After adjustments for ethnicity, baseline insulin secretion was lower in subjects with the risk genotype at HHEX rs1111875 (P = 0.01); there were no significant differences in baseline insulin sensitivity. Both at baseline and at 1 year, subjects with the risk genotype at LOC387761 had paradoxically increased insulin secretion; adjustment for self-reported ethnicity abolished these differences. In ethnicity-adjusted analyses, we noted a nominal differential improvement in β-cell function for carriers of the protective genotype at CDKN2A/B after 1 year of troglitazone treatment (P = 0.01) and possibly lifestyle modification (P = 0.05).CONCLUSIONS— We were unable to replicate the GWAS findings regarding diabetes risk in the DPP. We did observe genotype associations with differences in baseline insulin secretion at the HHEX locus and a possible pharmacogenetic interaction at CDKNA2/B.The increasing incidence of diabetes continues to have a tremendous impact on diabetes-related morbidity and mortality around the world. Although much emphasis has been placed on the contribution of a Western lifestyle characterized by increasing caloric intake and physical inactivity to the diabetes epidemic, the role genetics plays in the development of diabetes is generally poorly understood. Additional insight into the contribution of genetic variants to diabetes incidence, gene-lifestyle interactions, and pharmacological response to antidiabetes medications is required to slow this tragic epidemic.The recent implementation of genome-wide association scans (GWASs) as an investigative tool has resulted in a qualitative leap in identifying diabetes-related genes (1,2). These surveys, which are agnostic to candidate genes, can cover ∼80% of common human genome variants with current technology, thus providing unprecedented insight into the genetic architecture of type 2 diabetes. In 2007, the first published type 2 diabetes GWAS confirmed the important impact of TCF7L2 on diabetes incidence (odds ratio [OR] 1.65, P < 1.0 × 10⁻⁷) and identified several new type 2 diabetes loci, SLC30A8 (1.26, P = 5.0 × 10⁻⁷), HHEX (1.21, P = 9.1 × 10⁻⁶), LOC38771 (1.14, P = 2.9 × 10⁻⁴), and EXT (1.26, P = 1.2 × 10⁻⁴) (3). SLC30A8 encodes a zinc transporter protein that carries zinc from the cytoplasm into insulin secretory vesicles within the pancreatic β-cell, an important step in insulin synthesis and secretion (4). HHEX is essential for the development of the pancreas and liver and is a target of the Wnt signaling pathway (5).After the initial GWAS publication, four other high-density scans were published simultaneously by different groups, confirming many of the initial findings. In addition to replicating the prior associations of TCF7L2, HHEX, and SCL30A8, investigators from Iceland identified CDK5 regulatory subunit associated protein 1-like 1 (CDKAL1) as another potential diabetes-related gene (OR 1.2, P = 1.8 × 10⁻⁴) (6). This gene is hypothesized to lead to β-cell degeneration by modulating CDK5/CDK5R1 activity. The Diabetes Genetics Initiative, the Wellcome Trust Case Control Consortium, and the Finland–U.S. Investigation of Type 2 Diabetes Genetics concomitantly published GWASs that were combined in a preliminary meta-analysis of >30,000 samples (7–9). Again, the above findings were confirmed, and novel diabetes loci in or near IGF2BP2 (1.14, P = 8.9 × 10⁻¹⁶) and CDKN2A/B (1.2, P = 7.8 × 10⁻¹⁵) were identified. The EXT2 and LOC387761 gene regions have not been replicated in these or additional studies (10,11). Taken together, these studies support the potential power of GWASs in unraveling the genetic basis of type 2 diabetes.Several studies have attempted to characterize the physiological mechanisms affected by these genetic variants. Pascoe et al. (12) performed 75-g oral glucose tolerance tests (OGTTs) and hyperinsulinemic-euglycemic clamps on 1,276 healthy European subjects and demonstrated that common variants in CDKAL1 and HHEX are associated with decreased pancreatic β-cell function. Grarup et al. (13) reported that variants of HHEX, CDKN2A/B, and IFG2BP2 are associated with type 2 diabetes, and single nucleotide polymorphisms (SNPs) within the HHEX and CDKN2A/B loci impaired glucose-induced insulin release in healthy subjects, emphasizing the central role of pancreatic β-cell dysfunction in disease pathogenesis. Staiger et al. (14) found that the major alleles of the SLC30A8 and the HHEX SNPs associate with reduced insulin secretion stimulated by orally administered glucose but not with insulin resistance; the other reported type 2 diabetes SNPs within the EXT2 and LOC387761 loci did not associate with insulin resistance or β-cell dysfunction. Finally, a quantitative trait analysis of GWAS-identified type 2 diabetes susceptibility loci was recently completed by Palmer et al. (15) in their analysis of the Insulin Resistance Atherosclerosis Family Study (IRAS-FS). This study of 1,268 Hispanic and 581 African American subjects revealed that the increase in diabetes risk associated with variants in GWAS-identified gene regions, including CDKAL1, IGF2BP2, SLC30A8, and LOC387761, is mediated in part via defects primarily in insulin secretion. In Hispanic Americans, the acute insulinogenic response to glucose challenge decreased in high-risk genotype subjects at CDKAL1 (P = 0.005), and the disposition index was reduced in subjects with the high-risk genotype at IGF2BP2 (P = 0.01). Paradoxically, in Hispanic Americans, the previously identified risk allele of LOC387761 was significantly associated with an increased acute insulin response (P = 0.005) and disposition index (P = 0.036). IGF2BP2 rs4402960 was the only GWAS-identified SNP that associated with type 2 diabetes as a categorical trait (P = 0.02). Even fewer studies have attempted to analyze the influence of these genetic variants on response to pharmacological or behavioral interventions (16,17).The current study attempts to replicate and extend recent GWAS findings in the Diabetes Prevention Program (DPP) cohort. As a multiethnic, interventional study of >3,000 people at high risk for diabetes who have been carefully characterized, the DPP provides the opportunity to study insulin dynamics according to genotype and potential drug-genotype interactions. Studying pre-diabetic subjects as opposed to patients with overt diabetes provides insight into the role of genetic variation in the early stages of disease progression. As a longitudinal interventional study, the DPP provides the opportunity to carefully study the impact of genetic variation on insulin secretion and resistance over time. Finally, having multiple treatment arms allows for the identification of potential interactions of genotype with the results of the interventions. Studying gene-treatment interactions helps elucidate mechanisms of disease, identify specific treatments that may ameliorate the genetic predisposition to disease, and focus on subgroups that respond particularly well (or poorly) to specific therapies.     

In vivo response of Plasmodium falciparum to different doses of chloroquine in semi-immune children in Liberia, West Africa

The efficacy of different doses of chloroquine in suppressing patent parasitaemia was investigated in 326 children two to 12 years old, living in six villages with holoendemic malaria. The children were given single doses (2, 3, 5-7 or 9-12 mg base kg-1) or a standard treatment over three days (25 mg base kg-1). Parasite prevalences were recorded after one, two, three, four, six and eight weeks. Complete clearance of Plasmodium falciparum trophozoites (TC) by day 7 was achieved by a dosage of 9-12 mg kg-1. By probit analysis of log dose response, 50% clearance (TC50) was established at about 1.5 mg kg-1, whereas a TC95 required 5.5 mg kg-1. The reappearance of patent parasitaemia was dependent on the dose of chloroquine given and on malaria transmission. After the standard dose treatment, only one re-infection in 56 children appeared within 21 days despite high sporozoite inoculation rates in the area. The dosage of 9-12 mg kg-1 yielded a hundredfold reduction of mean parasite density in the children if calculated over a four-week period. It may represent a suitable monthly regimen in a malaria control scheme in a holoendemic area with high P. falciparum sensitivity to chloroquine.     

Nursing home staff perspectives on adoption of an innovation in goals of care communication

Nursing homes (NH) are important settings for end-of-life care, but limited implementation may impede goals of care discussions. The purpose of this study was to understand NH staff perceptions of adoption and sustainability of the Goals of Care video decision aid for families of residents with advanced dementia. Study design was a cross-sectional survey of staff at 11 NHs in North Carolina who participated in the Goals of Care (GOC) cluster randomized clinical trial. Staff perceived the GOC decision aid intervention as a positive innovation; it was perceived as more compatible with current practices by male staff, nurses, and more experienced NH staff. Perceptions were correlated with experience, implying that experience with an innovative approach may help to promote improved GOC communication in nursing homes. Nurses and social work staff could be effective champions for implementing a communication technique, like the GOC intervention.     

Rapid Response Events in Hospitalized Patients: Patient Symptoms and Clinician Communication

Context

Patients triggering rapid response team (RRT) intervention are at high risk for adverse outcomes. Data on symptom burden of these patients do not currently exist, and current symptom management and communication practices of RRT clinicians are unknown.

Do Live Discharge Rates Increase as Hospices Approach Their Medicare Aggregate Payment Caps?

Context

The rate of live discharge from hospice and the proportion of hospices exceeding their aggregate caps have both increased for the last 15 years, becoming a source of federal scrutiny. The cap restricts aggregate payments hospices receive from Medicare during a 12-month period. The risk of repayment and the manner in which the cap is calculated may incentivize hospices coming close to their cap ceilings to discharge existing patients before the end of the cap year.