Sequencing of the coding exons of the LRP1 and LDLR genes on individual DNA samples reveals novel mutations in both genes

Five coding polymorphisms in de LRP1 gene, i.e. A217V. A775P, D2080N, D2632 E and G4379S were discovered by sequencing its 89 exons in three test-group s of 22 healthy individuals, 29 Alzheimer patients and 18 individuals with different clinical and molecularly uncharacterized lipid metabolism problem s. No genetic defect was evident in the LRP1 gene of any of the Alzheimer's disease (AD) patients, further excluding LRP1 as a major generic problem i n AD. Lipoprotein receptor related protein (LRP) A217V (exon 6) was clearly present in all groups as a polymorphism, while D2632E was observed only on ce in a healthy volunteer. On the other hand. LRP1 alleles A775P, D2080N, a nd G4379 were encountered only in patients with FH or with undefined proble ms of lipid metabolism. This finding forced one to also analyze the LDL rec eptror (LDLR) gene, for which a method was devised to sequence the entire r egion comprising LDLR exons 2-18. The resulting sequence contig of 33567 nu cleotides yielded finally an exact physical map that corrects published and listed LDLR gene maps in many positions. In addition, next to known mutati ons in LDLR that cause FH. four novel LDLR defects were defined, i.e. del e 7-10, exon 9 mutation N407T, a 20 bp insertion in exon 4, and a double muta tion C292W/K290R in exon 6. No evidence for pathology connected to the LRP1 'mutations' was obtained by subsequent screening for the five LRP1 variant s in larger groups of 110 FH patients and 118 patients with molecularly und efined, clinical problems of cholesterol and/or lipid metabolism. In three individuals with a mutant LDLR gene a variant LRP1 allele was also present, but without direct. obvious clinical compound effects, indicating that the variant LRP1 alleles must, for the present, be considered polymorphisms. ( C) 2001 Elsevier Science Ireland Ltd. All rights reserved.