7 DNA POLYMORPHISMS IN THE LDL RECEPTOR GENE - APPLICATION TO THE STUDY OF FAMILIAL HYPERCHOLESTEROLEMIA IN SPAIN

We have performed restriction fragment length polymorphism (RFLP) anal ysis at the low density lipoprotein receptor (LDLR) locus in order to investigate the molecular genetics of familial hypercholesterolemia (F H) in Spain. Firstly, a sample of 50 unrelated patients with a clinica l diagnosis of FH was screened for the presence of major rearrangement s at this locus by Southern blot analysis of BglII digested genomic DN A. Four different mutations were detected, accounting for 8% of the mu tant alleles in the Spanish FH sample. Then, we determined the relativ e allele frequency and estimated linkage disequilibrium between seven RFLPs of the LDLR gene in the remaining 46 FH patients and in 61 normo lipidemic controls. HincII, AvaII, PvuII, MspI, and NcoI are the most polymorphic sites with individual PIC values higher than 0.28, whereas the TaqI and StuI sites display low levels of polymorphism. The usefu lness of the seven RFLPs to confirm a clinical diagnosis of FH was inv estigated in 15 FH-families, consisting of 118 individuals, in whom th e presence of Familial Defective Apolipoprotein B-100 (FDB) due to the apoB(3500) mutation was excluded. Independent haplotypes were constru cted for 71 chromosomes: 15 FH and 56 control haplotypes. A total of 1 4 different haplotypes was found. In 12 families, clinical diagnosis o f FH was confirmed by cosegregation analysis, which makes these RFLPs useful for studying the inheritance of the LDLR gene in 80% of Spanish families with FH. Comparison of haplotypes found in the Spanish sampl e with those found in Swiss and Norwegians suggests heterogeneity of h aplotypes among European populations.