The complex molecular genetics of familial hypercholesterolaemia.

Familial hypercholesterolaemia is the most commonly encountered genetic condition that predisposes individuals to premature cardiovascular disease. Nevertheless, most patients are undiagnosed, and treatment is often suboptimal even when the diagnosis seems certain. Advances in molecular technologies are reshaping our understanding of this condition, including revision upwards of the population prevalence. Furthermore, the underlying pathophysiological complexity has been exposed by the range of causative genetic loci, breadth of types and classes of rare disease-causing variants, and polygenic basis of the phenotype in many patients. Genetic testing is not always helpful or definitive. Familial hypercholesterolaemia can be envisioned as a group of related disorders, of which the classic 'textbook' phenotype is a subset. Features such as clinical stigmata, family history of dyslipidaemia or cardiovascular disease, and presence of a rare pathogenic variant all increase diagnostic certainty. However, even in the absence of these elements, the essential feature remains an elevated level of plasma LDL cholesterol, which alone should prompt a dialogue between the care provider and the patient on lifestyle modification and lipid-lowering therapy as the foundation of a long-term strategy to prevent or delay the onset of cardiovascular disease.