Two new large deletions in the low density lipoprotein receptor (LDLR) gene not revealed by PCR-based molecular diagnosis of familial hypercholesterolemia.

In the French Canadian population six mutations appear to be responsible for about 85% of FH cases. Two of these mutations are large deletions. The most prevalent deletion is a >15 kb deletion of the promoter and first exon; the second, a 5 kb deletion that removes exons 2 and 3. The high frequency of these deletions in the French Canadian population has been attributed to a founder effect. Other mutations are present in the population but at a much lower prevalence. We recently identified two new large deletions in FH patients of French Canadian descent. Carriers of the new deletions were identified because of an unusual pattern of band migration on Southern blots. We have identified and sequenced the deletions' boundaries. The first deletion covers 3813 bp and removes exons 7 and 8. The second deletion covers 5994 bp and removes exons 3-6. These deletions have not been previously reported. They would have been missed if a PCR-based method had been used instead of Southern blot analysis.