Molecular investigation of familial hypercholesterolaemia: from gene to genome

[Truncated] Familial hypercholesterolaemia (FH) is considered to be the most common genetically definable heritable form of hypercholesterolaemia with a frequency of 1 in 500 in most countries. The distinguishing features of FH in adults include xanthomas of the Achilles tendons and digital extensor tendons; xanthelasmas involving the skin of the ocular orbit and lipoidal deposits in the cornea caused by a lifetime exposure to increased concentrations of low-density lipoprotein (LDL) in blood. Coronary events are almost inevitable in untreated FH cases, with FH homozygotes being at very high cardiovascular risk in early childhood. FH is caused by the lack or malfunctioning of LDL-receptors (LDLRs) expressed on liver cells responsible for the removal of LDL-particles via receptor-mediated endocytosis. Although mutations in five genes have now been shown to result in the FH phenotype, the majority of mutations occur within the LDLR gene.
More than 1200 unique mutations in the LDLR have been identified in patients with FH. The current success rates of finding a pathogenic mutation in genetic screening programs of patients with a clinical diagnosis of FH range from 30% to best reported rates of 70%. This has been attributed to both the genetic heterogeneity of the disorder and the surprisingly frequent occurrence of large LDLR gene rearrangements and splice variants.
The aims of this thesis were to compare variant detection between Ion Torrent semiconductor sequencing on a Personal Genome Machine (PGM) and Sanger sequencing in clinically diagnosed FH patients, to also compare this with the LDLR messenger RNA (mRNA) sequence, and to establish the genomic breakpoints for the large deletions identified in LDLR in FH patients by multiplex ligation-dependent probe amplification analysis.