A LDL receptor gene homozygous mutation: PCR amplification, direct genomic sequencing, associated haplotype, rapid screening for frequency.

Many mutations in the LDL receptor (LDLR) gene have now been identified mostly as gross gene rearrangements, however they only represent a weak percentage of all deleterious gene mutations causing Familial Hypercholesterolemia (FH). This discrepancy may be related to the difficulties in characterizing point or small defective mutations. In a three-generation family with Familial Hypercholesterolemia, one specific haplotype constructed with 12 intragenic restriction fragment length polymorphisms (RFLP) cosegregated with the disease, while in the consanguineous propositus there was homozygosity for this haplotype. By polymerase chain reaction (PCR) amplification followed by direct sequencing there was unequivocal evidence for a double dose of a unique mutation, (namely a duplication of 4 bases in exon 17), while there was a single dose in heterozygote relatives. We consequently screened a population selected under clinical and geographical criteria for this mutation by PCR and allele specific oligonucleotides (ASO) hybridization. None of the 158 type IIa individuals tested carried the same mutation. Herein, is a rapid combined genetic and molecular approach to characterize and evaluate the frequency of LDL Receptor gene mutations causing Familial Hypercholesterolemia, towards targeted prevention and therapy.