A new Apa LI restriction fragment length polymorphism in the low density lipoprotein receptor gene

The existence of a new Apa LI restriction fragment length polymorphism in the third intron of the low density lipoprotein (LDL) receptor gene was described. As a gene probe we used a newly constructed derivative of pLDLR 3 which did not contain the highly repetitive Alu-sequences in exon 18. This new gene probe detected all exon sequences containing restriction fragments, and enabled us to demonstrate all described polymorphisms, which might be useful for genetic linkage studies. Based on analysis of 72 unrelated normo- and hypercholesterolaemic persons, the frequency of the allele A2, which showed the additional cutting site, was determined to be 0.05. With the simplified gene probe, pLDLR delta, we also studied other polymorphisms. A clear linkage disequilibrium between the Pvu II and Msp I polymorphisms was detected. This, and the previously described linkage disequilibrium of the two Msp I polymorphisms, demonstrate that the LDL receptor gene is apparently less heterogeneous than expected from the number of described polymorphisms.