TM6SF2 Determines Both the Degree of Lipidation and the Number of VLDL Particles Secreted by the Liver

In 2014, exome-wide studies identified a glutamine176lysine (p.E167K) substitution in a protein of unknown function named transmembrane 6 superfamily member 2 (TM6SF2). The p.E167K variant was associated with increased hepatic fat content and reduced levels of plasma TG and LDL cholesterol. Over the next several years, additional studies defined the role of TM6SF2, which resides in the ER and the ER-Golgi interface, in the lipidation of nascent VLDL to generate mature, more TG-rich VLDL. Consistent results from cells and rodents indicated that the secretion of TG was reduced in the p.E167K variant or when hepatic TM6SF2 was deleted. However, data for secretion of APOB was inconsistent, either reduced or increased secretion was observed. A recent study of people homozygous for the variant demonstrated reduced in vivo secretion of large, TG-rich VLDL1 into plasma; both TG and APOB secretion were reduced. Here we present new results demonstrating increased secretion of VLDL APOB with no change in TG secretion in p.E167K homozygous individuals from the Lancaster Amish community compared to their wild-type siblings. Our in vivo kinetic tracer results are supported by in vitro experiments in HepG2 and McA cells with knock-down or Crispr-deletions of TM6SF2, respectively. We offer a model to potentially explain all of the prior data and our new results.

Initial Insights into the Genetic Variation Associated with Metformin Treatment Failure in Youth with Type 2 Diabetes

Metformin is the first-line treatment for type 2 diabetes (T2D) in youth but with limited sustained glycemic response. To identify common variants associated with metformin response, we used a genome-wide approach in 506 youth from the Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study and examined the relationship between T2D partitioned polygenic scores (pPS), glycemic traits, and metformin response in these youth. Several variants met a suggestive threshold (P < 1 × 10-6), though none including published adult variants reached genome-wide significance. We pursued replication of top nine variants in three cohorts, and rs76195229 in ATRNL1 was associated with worse metformin response in the Metformin Genetics Consortium (n = 7,812), though statistically not being significant after Bonferroni correction (P = 0.06). A higher β-cell pPS was associated with a lower insulinogenic index (P = 0.02) and C-peptide (P = 0.047) at baseline and higher pPS related to two insulin resistance processes were associated with increased C-peptide at baseline (P = 0.04,0.02). Although pPS were not associated with changes in glycemic traits or metformin response, our results indicate a trend in the association of the β-cell pPS with reduced β-cell function over time. Our data show initial evidence for genetic variation associated with metformin response in youth with T2D.

Insights from rare variants into the genetic architecture and biology of youth-onset type 2 diabetes

Youth-onset type 2 diabetes (T2D) is a growing public health concern. Its genetic basis and relationship to other forms of diabetes are largely unknown. To gain insight into the genetic architecture and biology of youth-onset T2D, we analyzed exome sequences of 3,005 youth-onset T2D cases and 9,777 ancestry matched adult controls. We identified (a) monogenic diabetes variants in 2.1% of individuals; (b) two exome-wide significant (P < 4.3×10-7) common coding variant associations (in WFS1 and SLC30A8); (c) three exome-wide significant (P < 2.5×10-6) rare variant gene-level associations (HNF1A, MC4R, ATX2NL); and (d) rare variant association enrichments within 25 gene sets broadly related to obesity, monogenic diabetes, and β-cell function. Many association signals were shared between youth-onset and adult-onset T2D but had larger effects for youth-onset T2D risk (1.18-fold increase for common variants and 2.86-fold increase for rare variants). Both common and rare variant associations contributed more to youth-onset T2D liability variance than they did to adult-onset T2D, but the relative increase was larger for rare variant associations (5.0-fold) than for common variant associations (3.4-fold). Youth-onset T2D cases showed phenotypic differences depending on whether their genetic risk was driven by common variants (primarily related to insulin resistance) or rare variants (primarily related to β-cell dysfunction). These data paint a picture of youth-onset T2D as a disease genetically similar to both monogenic diabetes and adult-onset T2D, in which genetic heterogeneity might be used to sub-classify patients for different treatment strategies.

Using Workflow Modeling to Identify Areas to Improve Genetic Test Processes in the University of Maryland Translational Pharmacogenomics Project

Delivering genetic test results to clinicians is a complex process. It involves many actors and multiple steps, requiring all of these to work together in order to create an optimal course of treatment for the patient. We used information gained from focus groups in order to illustrate the current process of delivering genetic test results to clinicians. We propose a business process model and notation (BPMN) representation of this process for a Translational Pharmacogenomics Project being implemented at the University of Maryland Medical Center, so that personalized medicine program implementers can identify areas to improve genetic testing processes. We found that the current process could be improved to reduce input errors, better inform and notify clinicians about the implications of certain genetic tests, and make results more easily understood. We demonstrate our use of BPMN to improve this important clinical process for CYP2C19 genetic testing in patients undergoing invasive treatment of coronary heart disease.

Diabetes in the Old Order Amish: characterization and heritability analysis of the Amish Family Diabetes Study

OBJECTIVE

The Old Order Amish (OOA) are a genetically well-defined closed Caucasian founder population. The Amish Family Diabetes Study was initiated to identify susceptibility genes for type 2 diabetes. This article describes the genetic epidemiology of type 2 diabetes and related traits in this unique population.

RESEARCH DESIGN AND METHODS

The study cohort comprised Amish probands with diabetes who were diagnosed between 35 and 65 years of age and their extended adult family members. We recruited 953 adults who represented 45 multigenerational families. Phenotypic characterization included anthropometry, blood pressure, diabetes status, lipid profile, and leptin levels.

RESULTS

The mean age of study participants was 46 years, and the mean BMI was 26.9 kg/m2. Subjects with type 2 diabetes were older, more obese, and had higher insulin levels. The prevalence of diabetes in the OOA was approximately half that of the Caucasian individuals who participated in the Third National Health and Nutrition Examination Survey (95% CI 0.23-0.84). The prevalence of diabetes in the siblings of the diabetic probands was 26.5% compared with a prevalence of 7.0% in spouses (lambdaS = 3.28, 95% CI 1.58-6.80). The heritability of diabetes-related quantitative traits was substantial (13-70% for obesity-related traits, 10-42% for glucose levels, and 11-24% for insulin levels during the oral glucose tolerance test; P = 0.01 to <0.0001).

CONCLUSIONS

Type 2 diabetes in the Amish has similar phenotypic features to that of the overall Caucasian population, although the prevalence in the Amish community is lower than that of the Caucasian population. There is significant familial clustering of type 2 diabetes and related traits. This unique family collection will be an excellent resource for investigating the genetic underpinnings of type 2 diabetes.