Abstract

INTRODUCTION Familial hypercholesterolemia (FH) is an autosomal dominant genetic disorder caused, in the majority of cases, by a partial or total lack of functional low density lipoprotein receptors (LDLR). Mutations in the LDLR gene lead to increased plasma cholesterol levels, resulting in cholesterol deposition in the arteries, thereby increasing the risk of premature coronary heart disease. The homozygous form of FH is rare but heterozygous FH is common, although underdiagnosed in many populations, including the Portuguese. In 1999 the Portuguese Familial Hypercholesterolemia Study was begun at the National Institute of Health.

OBJECTIVES The aim of the Portuguese Familial H ypercholesterolemia Study is to perform an epidemiological study to determine the prevalence and distribution of FH in Portugal and to better understand the pathophysiology of coronary heart disease in these patients. The aim of the present work is to present the study's criteria and organization as well as its preliminary results.

METHODS The study population consists of individuals of both sexes and all ages with a clinical diagnosis of FH, with biochemical and molecular characterization being performed. The clinical criteria used for the diagnosis of FH were adapted from those of the Simon Broome Heart Research Trust. The study is organized in five stages: 1. selection of individuals with a clinical diagnosis of FH; 2. completion of a clinical questionnaire and declaration of informed consent; 3. collection of blood samples; 4. biochemical characterization; 5. molecular study of three genes associated with the FH phenotype: LDLR, apolipoprotein B (APOB) and proprotein convertase subtilisin/kexin type 9 (PCSK9).

RESULTS Between 1999 and June 2006 the LDLR gene and the APOB gene of 141 index cases (38 children and 103 adults) were studied. In 78 of these index cases (76 heterozygotes and two homozygotes) 50 different mutations in the LDLR gene were identified, and two unrelated individuals were found to have the ApoB3500 mutation. The PCSK9 gene was also studied in individuals in whom a mutation in the LDLR or APOB genes was not found, which identified two index cases with a mutation in this gene. The study of 62 families led to the identification of an additional 117 individuals with FH, 90 adults and 27 children (86 adults and 27 children with mutations in the LDLR gene, two adults with the ApoB3500 mutation, and two adults with a mutation in the PCSK9 gene).

CONCLUSIONS Genetic diagnosis enables correct identification of the disease and provides the basis for more aggressive pharmacologic therapeutic interventions to reduce cardiovascular risk in affected individuals. At present thirteen clinicians are collaborating in the Portuguese FH Study, but it is extremely important to obtain the collaboration of more physicians throughout the country, so that the prevalence and distribution of FH in the Portuguese population can be characterized and a greater number of individuals can benefit from appropriate and early therapy.