Exploring Sympathetic Nervous System Function in Individuals With Down Syndrome

Summary

Down syndrome (DS), the most common genetic cause of intellectual disability, is associated with widespread organ dysfunction, including abnormalities in the autonomic nervous system (ANS). The ANS regulates critical functions such as heart rate (HR) and blood pressure (BP), both essential for maintaining homeostasis and supporting physical activity. Individuals with DS often exhibit blunted HR responses to exercise-typically \~30 beats per minute below expected levels-suggesting reduced sympathetic nervous system (SNS) activity. The SNS governs rapid changes in HR and BP during stress by releasing catecholamines: epinephrine (from the adrenal medulla) and norepinephrine (from sympathetic nerve endings). Despite its importance, SNS function has not been comprehensively assessed among individuals with DS. This study addresses a critical knowledge gap by evaluating SNS responses to physiological stressors in individuals with DS. The investigators will measure beat-to-beat HR and BP, along with plasma catecholamine levels, in response to sympathetic activation, comparing individuals with DS to age- and sex-matched controls. Understanding the mechanisms of SNS dysfunction in DS is vital, as it likely underlies reduced exercise capacity and contributes to broader clinical challenges. These insights may guide targeted interventions to improve cardiovascular function, physical capacity, and overall quality of life in this understudied population.

Eligibility

Inclusion Criteria:

* 18-50 yrs old and apparently healthy individuals
* Ability to understand the study and give assent to participate
* Has a study partner who can attend all visits for the individuals with DS, and answer questionnaires, provide consent when necessary
* Corrected or non-existent congenital heart disease
* Euthyroid or on stable thyroid medication dose for at least 6 months
* Free from cardiovascular, pulmonary, inflammatory, or metabolic disease in the past 6 months that would prevent participation in study procedures
* BMI \<45kg/m2
* Ability to tolerate repeated blood draws / catheter placement

Exclusion Criteria:

* Hypertension (resting systolic blood pressure \[SBP\] ≥140 and/or diastolic blood pressure \[DBP\] ≥90 mmHg) this includes those on medications to treat hypertension
* Hypotension (resting BP of \<90/60 mmHg)
* Cancer in the last six months
* Any heart-rate-altering medications or any other medication that may modify metabolic responses
* Self-reported diabetes or use of glucose-lowering medication
* Tobacco products, including vaping, or marijuana use
* Currently pregnant
* Post-menopausal women

Specific Exclusion Criteria for Certain Stressors:

* Orthopedic limitations that would prohibit exercise or movement for exercise
* Fracture of limb to be immersed for CPT
* Open cut or sore on hand to be immersed for CPT
* Raynaud's syndrome for CPT
* Chronic caffeine drinkers for caffeine stressor (consumption of caffeine in the last 7 days)

Conditions3

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