RecruitingNatural History of Uncommon Dyslipidemias, Rare Lipid Disorders and Unusual Atherosclerotic ConditionsBackground: The right amount of fats in the blood (cholesterol and triglycerides) are a key part of a healthy organism. Too much or too little of these fats may manifest as diseases (dyslipidemia). There are many causes for these abnormalities, but some are genetically determined and we would like to better understand the progression of these conditions over time. Objective: This natural history study aims to learn more about dyslipidemias; how they change over time; and how they respond to therapy. We also want to develop new diagnosis methods for these conditions. With the knowledge we will acquire we hope to provide new insights, new approaches and improve the overall health of these patients. Eligibility: Individuals aged 10 years and older, residing both within and outside the United States, who have or are suspected of having a disorder that causes changes in the levels of fats in their blood (genetic dyslipidemias). Design: Participants residing within and outside the United States will be screened. Their medical records may be reviewed. They may talk to researchers about their medical history by phone, telehealth, or in person. All study visits are optional. Participants may visit the NIH up to 15 times per year, if needed. Each visit may include a physical exam and blood tests. Participants may also have an electrocardiogram (EKG). The EKG measures the electrical activity when the heart beats. In some cases, participants may remain in the study for up to 20 years.