 Children participate in two 2-week study phases. Between the study phases the children will take 150 mgkg daily of a cholesterol preparation typically used to supplement cholesterol in patients in SLOS studies at NIH. In the study phases, the participants are randomly assigned to take either egg yolk or an egg yolk substitute, such as Egg Beaters, that does not contain cholesterol. The study is done at the participants home, and the cholesterol supplementation and eggegg substitute are sent to the home each day with instructions on how to take them. 