Vascular Health and Risk Factors in Children With Down Syndrome

Pulse wave velocity (PWV) is a non-invasive imaging measure of arterial stiffness. Pulse wave velocity measures vascular stiffness by evaluating the time for a pressure wave to travel through the aorta. The velocity is determined by the elasticity and geometry of the vessel. PWV will be measured using a SphygmoCor device. With the participant in the supine position and ECG leads attached, the maximal pulsation of the right carotid and right femoral artery will be marked and measured from the suprasternal notch using a tape measure (carotid) and caliper (femoral). A tonometer will record the carotid and femoral impulses. The device calculates PWV as the difference in the carotid-to-distal path length divided by the difference in R-wave-to-waveform times (∆distance/∆time, m/sec). Measurements will be in triplicate and averaged. PWV can be completed in ~30 mins.

Carotid intimal medial thickness (CIMT) is a non-invasive imaging measure of carotid artery thickness. B-mode ultrasound with a high-resolution linear array vascular transducer will be used to record common, bulb, and internal CIMT.

Height (centimeters) will be measured using standard stadiometers and weight (kilograms) using a calibrated scale available at each site. BMI (kg/m2) will be calculated and converted to age- and sex-matched Down Syndrome percentiles. Measured at 1 time point.

Waist circumference will be measured at the top of the posterior iliac crest (NHANES standard) and normalized by calculating waist to height ratio. Measured at 1 time point.

A fasting lipid profile will be obtained to measure total cholesterol, triglycerides, and HDL cholesterol. Trained pediatric phlebotomists will perform the blood draw after the participant has fasted ≥10 hours. A standard lipid profile will provide total cholesterol, HDL cholesterol, and triglycerides. LDL will be calculated using the Friedwald equation when triglycerides are <400 mg/dL. For triglycerides ≥400 mg/dl, LDL will be measured directly via a homogeneous enzymatic assay. Measured at 1 time point.

Lipoprotein subfractions by NMR will be used to describe lipid particle number and size. These lipoprotein measurements likely estimate CV risk more accurately than a standard lipid profile alone. Lipoprotein sub-fractionation will be completed using proton NMR signals. Measured at 1 time point.

Insulin resistance will be assessed by fasting serum glucose, hemoglobin A1C, and insulin level since diabetes (fasting glucose ≥126 mg/dL or hemoglobin A1C ≥6.5%) is a major risk factor. Measured at 1 time point.

A detailed personal history for congenital heart disease (CHD) and associated surgery, sleep apnea, hypothyroidism, and cancer will be obtained as all are common in the population with Down Syndrome and increase the risk for cardiovascular disease in adulthood. The fundamental CHD and associated surgery will be obtained from the medical records. The parent/LAR will be questioned and the medical record reviewed for a history of sleep apnea, hypothyroidism, and cancer (yes/no). Measured at 1 time point.