Type 2 diabetes mellitus (DM) is debilitating, deadly, and costly whose prevalence is increasing. Although the development of DM can be delayed or prevented by lifestyle changes, changes initiated too late may not delay DM onset indefinitely. Therefore, it is imperative to intervene earlier and to find new ways to increase motivation to initiate and maintain lifestyle changes. Risk communication is a key part of effective lifestyle behavior change strategies. Risk for DM has traditionally been estimated using patient age, sex, race, body mass index (BMI), family history of DM, and fasting plasma glucose (FPG) level. Genetic polymorphisms associated with the incidence of DM have been discovered and may further personalize risk, particularly because lifestyle changes can prevent DM even in patients with the polymorphisms. The ability of genetic test results to demonstrate improvement in patients’ health outcomes is unknown, posing a major obstacle to translation.
In this randomized trial, we examined whether supplementing conventional DM risk counseling with communication of DM-related genetic test results affected clinical and behavioral outcomes.
Participants were Veteran outpatients aged 21-65 with body mass index (BMI) ≥ 27 and without DM. At baseline, fasting plasma glucose (FPG), family history of DM, and lifetime DM risk (based on age, sex, race, and BMI) were assessed. Patients were randomized to the genetic test (CR+G) or attention control eye disease counseling (CR+EYE) arm; randomization was stratified by family history of DM (unknown/low vs. moderate/high) and BMI (<35 vs. ≥35). Two to four weeks following enrollment, participants attended a DM risk counseling session conducted by a genetic counselor. Participants received personalized DM risk estimates based on their baseline FPG, family history, and lifetime risk; for each risk factor, participants were classified as being at low, moderate, or high risk. The genetic counselor then opened an envelope to reveal the randomization assignment; participants received either DM genetic test results or attention control eye disease counseling immediately thereafter. The session concluded with brief goal setting related to weight loss, diet, and physical activity, followed by assessment of perceived risk and illness representations. Three and 6 months post-baseline, participants returned for outcome assessments. The primary outcome was weight at 3 months. Secondary outcomes included perceived risk immediately following counseling; HOMA-IR, self-reported dietary intake and physical activity, and perceived risk at 3 and 6 months; and weight at 6 months. Linear mixed models were fit for weight, perceived risk, HOMA-IR, and dietary variables; generalized linear mixed models using a negative binomial distribution with a log link were used for walking and moderate physical activity. Outcomes were transformed when necessary to meet normal distributional assumptions. Models included a common intercept, time effect, time*treatment interaction, and randomization stratification variables (family history and BMI).
A total of 601 participants were enrolled; 303 were randomized to CR+G and 298 to CR+G. Mean age was 54 years, 42% were White, 53% were Black, 80% were male, 30% had BMI ≥ 35, and 52% had moderate/high family-history-based DM risk. Estimated mean weight did not differ between arms at 3 months [(CR+G)−(CR+EYE) = 0.2 kg, 95 % CI: −0.3, 0.7; p = 0.44] or at 6 months (mean difference = 0.4 kg, 95 % CI: −0.3, 1.1; p = 0.27), nor did insulin resistance (HOMA2-IR) (p = 0.19 and 0.12 at 3 and 6 months, respectively). Daily calorie intake was lower in the CR+G arm than the CR+EYE arm at 3 months (p =0.05), but there was no difference between arms at 6 months (p = 0.20). The percentage of calories from carbohydrates, protein, fat, and saturated fat intake did not differ between arms at 3 or 6 months (all p ≥ 0.07). Monounsaturated fat and polyunsaturated fat were lower in the CR+G than the CR+EYE arm at 3 months (all p ≤ 0.04) but not at 6 months (all p ≥ 0.26). There were no between-arm differences in the estimated duration of moderate-intensity physical activity or walking at 3 or 6 months (all p > 0.22). Given an estimated $7.00 per session in overhead costs, genetic testing cost of $125, and blood draw cost of $3.00 per participant, the total intervention cost was $207.03 for the first genetic counselor and $178.78 for the second.
Providing patients with genetic test results was not more effective in changing patient behavior to reduce the risk of DM compared to conventional risk counseling. Because genetic testing for DM did not make a clinically important impact on patients at risk for DM, it may not be appropriate for widespread implementation.