This Figure from the lab of Rob Hegele, who has done a lot of sequencing in patients from Ontario and Quebec with heterozygous FH, illustrates the wide spectrum of different mutations that are found in patients with heterozygous FH.  This illustrates how many different mutations result in loss-of-function of the LDL receptor and underlines why simply genotyping for one specific mutation is not sufficient.  In fact, sequencing of the exons, of the coding portion of the gene, is really necessary in order to do molecular diagnosis of FH.  Importantly, major gene deletions or rearrangements are not detected by routine sequencing of the exons.