Identificación y caracterización del primer español con defecto homocigoto familiar de unión de la apolipoproteína B

Evaluation of clinical diagnosis criteria of familial ligand defective apoB 100 and lipoprotein phenotype comparison between LDL receptor gene mutations affecting ligand-binding domain and the R3500Q mutation of the apoB gene in patients from a South European population

Familial hypercholesterolemia (FH) and familial defective apoB 100 (FDB) are characterized by increased plasma low-density lipoprotein cholesterol (LDLc) levels and risk of coronary heart disease (CHD). FDB is clinically indistinguishable from FH. The aims of this study were to evaluate clinical diagnosis criteria for FDB and to compare the lipoprotein phenotype between carriers of LDL receptor (LDLR) gene mutations that affect the ligand-binding domain and subjects with the R3500Q mutation in apoB gene. We studied 213 subjects (113 probands) with FH and 19 heterozygous FDB subjects. Genetic diagnosis was determined by following a protocol based on Southern blot and polymerase chain reaction-single strand conformation polymorphism (SSCP) analysis. Thirty FH carriers of LDLR gene missense mutations that affect ligand-binding domain were matched by age, gender, and body mass index to the 19 FDB subjects (R3500Q mutation). Lipoprotein phenotype comparison was conducted between the 2 groups. FH patients showed plasma total and LDL cholesterol levels significantly higher than those in FDB patients. Three FDB showed plasma total and LDLc values in the normal range. Using the 1999 clinical Med-Ped criteria for diagnosis of genetic hypercholesterolemia, no FDB subjects had a confirmed diagnosis; it was probable in 36% of the subjects, it was possible in 32% of the subjects, and it could be excluded in the remaining 32% of the subjects. We conclude that the FDB lipoprotein phenotype was significantly less severe than that observed in FH carriers of LDLR gene missense ligand-binding domain mutations. Clinical Med-Ped diagnosis criteria tend to under-diagnose FDB.

Estudio del defecto familiar de unión de la apolipoproteína B100 en una población mediterránea

BACKGROUND AND OBJECTIVE

To compare the lipoprotein phenotype between FDB and heterozygous familial hypercholesterolemia (FH); to study the prevalence and possible founder effect of familial ligand-defective apo B100 (FDB) in a Mediterranean population, and to analyze the clinical and biochemical characteristics of FDB patients.

SUBJECTS AND METHOD

We studied 19 heterozygous FDB subjects (8 males) from 12 related families, carriers of the R3500Q mutation on the apo B gene, and 57 heterozygous FH (24 males) genetically characterized, randomly selected from a total of 213 FH. The genetic diagnosis was established with Southern blot analysis, PCR-SSCP analysis and automatic sequencing. In all subjects, plasma lipids and apolipoprotein levels were determined with standard procedures.

RESULTS

We demonstrated a founder effect for the R3500Q mutation in a geographically isolated rural area from our community. The prevalence of FDB in this area is high: 4/350. Heterozygous FDB subjects showed a statistical significantly lower prevalence of xanthomas and coronary heart disease, plasma concentrations of total and LDL cholesterol, HDL cholesterol, apo B and apo A-I values than heterozygous FH subjects.

CONCLUSIONS

A founder effect for the R3500Q mutation was found in a rural population with a high prevalence of FDB. In our population, FDB patients showed a mild clinical expression and lipoprotein phenotype compared with FH patients.

Influence of LDL receptor gene mutations and the R3500Q mutation of the apoB gene on lipoprotein phenotype of familial hypercholesterolemic patients from a South European population

Few data are available on genotype-phenotype interactions among familial hypercholesterolemia (FH) patients in South European populations and there are no data about the influence of R3500Q mutation on lipoprotein phenotype compared to low-density lipoprotein receptor (LDLR) mutations. The objective of the study is to analyze the influence of mutations in the LDLR and apolipoprotein B (apoB) genes on lipoprotein phenotype among subjects clinically diagnosed of FH living in East Spain. In all, 113 FH index patients and 100 affected relatives were studied. Genetic diagnosis was carried out following a protocol based on Southern blot and PCR-SSCP analysis. A total of 118 FH subjects could be classified into three groups according to the type of LDLR mutations (null mutations, missense mutations affecting the ligand binding 3-5 repeat, and missense mutations outside this domain). In addition, the lipoprotein phenotype of these FH groups was compared with 19 heterozygous subjects with familial ligand-defective apoB (FDB), due to R3500Q mutation. FH patients carrying missense mutations affecting the ligand binding repeat 3-5 showed total and LDL cholesterol levels significantly higher than FH patients with missense mutations in other LDLR domains or FDB patients. FH subjects carrying null mutations showed lower high-density lipoprotein cholesterol plasma values compared to FH carrying missense mutations. FDB subjects showed the lowest total and LDL cholesterol plasma values. In conclusion, the type of LDLR gene mutation and R3500Q mutation influences the lipoprotein phenotype of FH population from East Spain.