Familiar hypercholesterolemia (FH) is the most common genetic disorder associated with the development of severe and premature coronary artery disease (CAD). The disorder is caused by mutations in the gene that encodes the low-density lipoprotein receptor (LDL-r), resulting in a lower expression of functional LDL-r in the liver. FH has autosomal dominant transmission with high penetrance and the prevalence of heterozygous individuals is one in 400 to 500 in the general population. To date, more than 800 different functional mutations of the LDL-r gene have been described worldwide, and more than 200 have been documented in Spain. In addition, a much less common disorder that resemble FH is familial defective apoB 100 disorder (FDB) produced by a mutation in the Apo B 100 gene. FDB accounts for a significant proportion of FH in some localized regions of Spain.