There are different causes for high cholesterol in the blood. Sometimes, it is because of faulty genes that people inherit from their parents. ‘Polygenic hypercholesterolaemia’ is a condition where the cholesterol is raised because of the combined effect of several faulty genes together. ‘Familial hypercholesterolaemia’ is caused by a severe problem with one gene, rather than many. We know that having high cholesterol could cause heart attack or stroke. In this study we will find out to what extent cholesterol deposits in the neck artery of children with polygenic hypercholesterolaemia and how does it compare to children who have familial hypercholesterolaemia and those who don’t have and cholesterol problems. There are currently no data supporting a treatment of children with polygenic high cholesterol.