Genetic Risk Factor for Heat Stroke

Exploring a Common Genetic Risk Factor for Heat Stroke and Dehydration

The goal of this observational study is to examine the effect of the Cystic Fibrosis (CF) Carrier state on the risk for dehydration and other CF-specific fluid-and-electrolyte disorders in male and female adults.

The primary aim of the study is to estimate the risk of electrolyte disorders attributable to the CF carrier state in a genotyped cohort.

This will be accomplished with two smaller projects- Aim 1 and Aim 2.

Aim 1 will consist of 100 CF Carriers and 100 age- and sex-matched controls. Participants in this aim will be asked to complete a Participant Info and Temperature Survey consisting of questions about race, ethnicity, medical history, and how they experience heat.

Aim 2 will consist of a subset of 25 CF Carriers and 25 age- and sex-matched controls from Aim 1. Participants in this aim will be scheduled for a visit to complete a heat challenge. At this visit, they will also complete the Participant Info and Temperature Survey. They will also sit in a sauna at 62 - 63 degrees Celsius for 45 minutes.

Study Overview

• Status: Recruiting
• Conditions: Dehydration; Carrier State; Heat Stroke
• Intervention / Treatment: Procedure: Heat Challenge

• Study Type: Observational
• Enrollment (Estimated): 200

Contacts and Locations

• Study Contact: Name: Shelby L Francis, PhD; Phone Number: 319-678-8037; Email: shelby-francis@uiowa.edu
• Study Contact Backup: Name: Aaron Miller, PhD; Phone Number: (319) 335-3053; Email: aaron-miller@uiowa.edu

Study Locations

• United States
  • Iowa
    • Iowa City, Iowa, United States, 52242
      • Recruiting
      • University of Iowa Health Care
      • Contact: Shelby L Francis, PhD; Phone Number: 319-678-8037; Email: shelby-francis@uiowa.edu
      • Principal Investigator: Aaron Miller, PhD

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Individuals who have previously been genotyped as CF Carriers or Controls.

Description

Inclusion Criteria:

• Previously genotyped as a CF carrier or control
• Comfortable speaking/reading English

Exclusion Criteria:

• Previously genotyped as a CF patient
• Diagnosis of Type 1 or Type 2 diabetes
• History of heart attack, stroke, heart failure, or atherosclerosis
• Currently pregnant
• Currently taking beta blockers or diuretics
• Prisoner status
• Unable to provide own written informed consent

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
CF Carriers; Participants who have previously been genotyped as CF Carriers.	Procedure: Heat Challenge; Participants will be asked to arrive well-hydrated and to refrain from exercise, alcohol, caffeine, and smoking for 24 hours prior to the visit. Height, weight, blood pressure, and body fat percentage will be measured. Blood (15.5 ml) and urine will be collected. Participants will wear a heart rate monitor and sit in a heat chamber at 62-63 degrees Celsius for 45 minutes. Heart rate will be measured continuously. Body temperature and a self-report of their comfort (1-4 scale) and thermosensation (1-7 scale) will be measured before the challenge, every 15 minutes during the challenge, and after the challenge. During the challenge, a sample of sweat will be collected to measure electrolyte loss. Participants will consume 16 ounces of water at their own pace during the 45 minutes. If they become too uncomfortable to continue or their body temperature rises above 39 degrees Celsius, the challenge will be stopped. All baseline measures except body fat percentage will be measured again.
Controls; Participants who have previously been genotyped as controls and are age- and sex-matched to a CF Carrier.	Procedure: Heat Challenge; Participants will be asked to arrive well-hydrated and to refrain from exercise, alcohol, caffeine, and smoking for 24 hours prior to the visit. Height, weight, blood pressure, and body fat percentage will be measured. Blood (15.5 ml) and urine will be collected. Participants will wear a heart rate monitor and sit in a heat chamber at 62-63 degrees Celsius for 45 minutes. Heart rate will be measured continuously. Body temperature and a self-report of their comfort (1-4 scale) and thermosensation (1-7 scale) will be measured before the challenge, every 15 minutes during the challenge, and after the challenge. During the challenge, a sample of sweat will be collected to measure electrolyte loss. Participants will consume 16 ounces of water at their own pace during the 45 minutes. If they become too uncomfortable to continue or their body temperature rises above 39 degrees Celsius, the challenge will be stopped. All baseline measures except body fat percentage will be measured again.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Participant Scores for Temperature Sensitivity and Regulation Survey	Individual and composite scores for 5 components of the Temperature Sensitivity Survey (Heat- and Activity-Induced Autonomic Thermoregulation; Heat-Induced Behavioral Thermoregulation; Heat Perception; and Heat- and Activity-Induced Fatigue). For these 5 components, there are a total of 25 questions. All questions are on a 7-point scale, with the highest representing the most sensitive to heat and the lowest being the least sensitive. We will add up the scores for each question to arrive at a composite score for each component and the component scores will be added to arrive at a total score. Scores will be compared between groups.	Baseline
Change in Weight	Weight will be measured in kilograms pre- and post-heat challenge. We will compare change in weight between groups.	Up to 45 minutes
Change in Sodium Concentration	Sodium concentration will be measured pre- and post-heat challenge by blood draw and urine sample. Sodium concentration will be compared between groups.	Up to 45 minutes
Change in Potassium Concentration	Potassium concentration will be measured pre- and post-heat challenge by blood draw and urine sample. Potassium concentration will be compared between groups.	Up to 45 minutes
Concentration of Sweat Chloride	Sweat chloride will be measured pre- and post-heat challenge by sweat collection. Sweat chloride will be compared between groups.	Up to 45 minutes
Final Score on Comfort Scale	Participants will rate their level of comfort on a scale of 1-4 at the end of the heat challenge. Scores will be compared between groups.	Up to 45 minutes
Final Score on Thermosensation Scale	Participants will rate their level of thermosensation on a scale of 1-7 at the end of the heat challenge. Scores will be compared between groups.	Up to 45 minutes

Collaborators and Investigators

• Sponsor: University of Iowa
• Investigators: Principal Investigator: Aaron Miller, PhD, University of Iowa

Study record dates

Study Major Dates

• Study Start (Actual): November 19, 2025
• Primary Completion (Estimated): December 1, 2026
• Study Completion (Estimated): December 1, 2026

Study Registration Dates

• First Submitted: February 14, 2025
• First Submitted That Met QC Criteria: February 20, 2025
• First Posted (Actual): February 26, 2025

Study Record Updates

• Last Update Posted (Actual): April 27, 2026
• Last Update Submitted That Met QC Criteria: April 21, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Wounds and Injuries; Pathologic Processes; Metabolic Diseases; Water-Electrolyte Imbalance; Heat Stress Disorders; Pathological Conditions, Signs and Symptoms; Nutritional and Metabolic Diseases; Dehydration; Heat Stroke
• Other Study ID Numbers: 202308319

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No