This study will assess the cardiovascular disease (CVD) risk in Phenylketonuria (PKU) patients on a low-phenylalanine diet (LPD). Ultrasound tests, diet information and routine blood samples will be collected once per patient at their next outpatient appointment. 32 adults with PKU will be studied and compared to reference data for healthy people. The results will show if the PKU CVD risk differs from healthy people, and if CVD risk varies within people with PKU.
Cardiovascular disease (CVD) is the largest cause of deaths worldwide each year. Many factors affect CVD including diet, genetics, exercise and smoking. It is unclear if Phenylketonuria (PKU) and the low-phenylalanine diet (LPD) affect CVD risk. CVD risk can be predicted by measuring the thickness of the artery wall in the neck which supplies blood to the head. Thickness is measured using a non-invasive, safe ultrasound test (similar to pregnancy jelly scans). A wall thicker than normal indicates an increased CVD risk. A wall thinner than normal indicates a lower CVD risk.
Study Type
OBSERVATIONAL
Enrollment
32
CIMT is a measurement of the thickness of the two inner layers of the common carotid artery wall. Using ultrasound, a linear array transducer is placed on the surface of the skin at the neck. Electrocardiogram(ECG) electrodes are placed on each wrist and one on the ankle. An image of the common carotid artery (CCA) is then produced in anterior, posterior and lateral views, and saved along with the ECG recording. The wall thickness can then be measured at the same point in the cardiac cycle using semi-automated detection software (Philips QLAB), which can reduce observer variability. The CIMT will be averaged across left and right CIMTs, as the control reference values use an average of both sides.
The PWV measures the speed of a pulse wave travelling between two points in the vascular systems of known distance between them. PWV will be measured by the gold standard carotid-femoral PWV method which is a direct measurement of aortic stiffness. A 3-Lead ECG is connected alongside measurements of the blood velocity trace for the left CCA 2cm proximal to the bifurcation, and for the left common femoral artery origin.
A blood pressure cuff is placed around the ankle and upper arm of the participant. A continuous wave Doppler probe is used over the surface of the skin to locate the artery distal to the cuff (such as the brachial artery in the arm, or the anterior tibial and posterior tibial arteries in the ankle). The cuff is then inflated, and the systolic pressure identified by listening cessation of the sounds produced by the probe corresponding to blood flow in the artery. The ABPI is then the ratio of the highest systolic ankle pressure divided by the highest systolic brachial pressure for the left and right sides of the body.
Dietary information will be collected in two formats. One will be a 14-item questionnaire (Martínez-González et al., 2012), which is a simplified version of a comprehensive food frequency questionnaire. This provides a quick measure of compliance to a Mediterranean dietary pattern and a rough measure of protective and adverse dietary factors that could affect individual CVD risk. The second will be a 3-day diet diary (3DDD). This will consist of participants recording the foods that they consume and the quantities, which will then be analysed for macro- and micronutrient composition once completed.
Blood samples will be taken from participants during their outpatient appointment. Patients routinely have blood samples taken during this clinic. The study will use the results from the routine blood tests, and also extra blood samples to collect data on other biomarkers. The laboratory facilities at Guy's and St Thomas Hospitals will be used to conduct analysis, no other laboratories will be used. Data will be collected on Phenylalanine levels, lipids, vitamin B12 and related biomarkers.
Guy's and St Thomas' NHS Foundation Trust
London, United Kingdom
RECRUITINGA single carotid-intima media thickness (CIMT) measurement in Phenylketonuria (PKU) participants and the corresponding age- and gender-matched controls.
A single CIMT measurement in PKU participants at their most recent outpatient appointment, and the corresponding age- and gender-matched CIMT, generated from the male (1) or female (2) equation for a healthy population using each participants' age and gender (Engelen et al., 2013).
Time frame: 10 minutes
Pulse Wave Velocity (PWV)
will be compared to PKU patient biomarkers (median annual Phenylalanine levels, biomarkers and dietary factors) to assess if there is any correlation between compliance to diet and variation in cardiovascular risk within PKU patients.
Time frame: 10 minutes
Ankle brachial pressure index (ABPI)
will be compared to PKU patient biomarkers (median annual Phe levels, biomarkers and dietary factors) to assess if there is any correlation between compliance to diet and variation in cardiovascular risk within PKU patients.
Time frame: 10 minutes
Vitamin B12 levels from blood sample
will be compared to PKU patient measures (PWV, ABPI and CIMT) to assess if there is any correlation between compliance to diet and variation in cardiovascular risk within PKU patients.
Time frame: 5 minutes
Blood Phenylalanine levels
will be compared to PKU patient measures (PWV, ABPI and CIMT) to assess if there is any correlation between compliance to diet and variation in cardiovascular risk within PKU patients.
Time frame: 5 minutes
Blood low-density lipoprotein (LDL) cholesterol levels
will be compared to PKU patient measures (PWV, ABPI and CIMT) to assess if there is any correlation between compliance to diet and variation in cardiovascular risk within PKU patients.
Time frame: 5 minutes
Diet diary and diet questionnaire (Mediterranean Adherence Screener, 0-14 scale, 14 indicating full adherence, 0 indicating no adherence)
will be compared to PKU patient measures (PWV, ABPI and CIMT) to assess if there is any correlation between compliance to diet and variation in cardiovascular risk within PKU patients.
Time frame: 3 days
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