Familial hyper-cholesterolemia is a potentially fatal autosomal dominant disorder characterized by increased plasma levels of total cholesterol. Because screens for mutations in LDLR, APOB, and PCSK9 can be used to accurately diagnose FH, the UK's National Institute for Health and Clinical Excellence established guidelines for the 'cascade screening' of FH patients and their relatives in 2007. In a recent Clinical Genetics paper, the Great Ormond Street Hospital for Children's Alison Taylor et al. report results from a pilot project involving 635 probands and 296 of their relatives. Genome Technology's Tracy Vence recently spoke with Taylor about her team's findings.
Genome Technology: What was your initial motivation to investigate the mutation rates in patients diagnosed with FH?
Alison Taylor: We wanted to define the relative genetic contribution of mutations in LDLR in these two conditions. … The UK cascade project was undertaken to demonstrate the utility of large-scale population screening for FH and the observed detection rate and demand for cascade testing.
GT: For FH samples in which you did not detect mutations, you used a combination of techniques to identify possible LDLR deletions or duplications. Which methods gave the most robust results?
AT: Both sequence analysis and multiplex ligation-dependent probe amplification are robust and sensitive techniques which have been used in the laboratory for a number of years ... [for] a number of disorders, including FH. Sequence analysis is used to look for point mutations and small insertions and deletions, whereas MLPA will pick up large rearrangements, such as deletions or duplications of one or more exons. Such large rearrangements wouldn't be detected by sequence analysis.
GT: In your paper, you note that "sequencing is still required in a comprehensive diagnostic service for FH." What are your expectations for the future?
AT: We envisage that next-generation sequencing will be used for FH screening in the future. We're currently evaluating this technique in our lab, and in the future hope to be able to screen patients for all of the known genes associated with FH — such as PCSK9, APOB, and LDLRAP1 — rather than just focusing our efforts on LDLR. This technology may also provide us with the opportunity to increase our understanding of a variety of other types of hyperlipidemia — in particular, combined hyperlipidemia — by offering the possibility of sequencing the entire lipid exome.
GT: Do you plan to investigate the clinical utility of molecular detection methods further?
AT: We recently evaluated the Fluidigm BioMark platform for the detection of 48 mutations ... associated with FH, including the common mutations in APOB and PCSK9, in order to increase the pick-up rate of our initial screen. ... Our current data indicate that, in combination with MLPA, this first-level screening strategy will pick up approximately 66 percent of mutations, up from 44 percent using our previous first level [Elucigene FH20 amplification refractory mutation system] screen. … We now offer this new initial [Fluidigm BioMark] screen as a service.
GT: Do you have an idea of the uptake of cascade screening in UK clinics?
AT: Although DNA testing is recommended by NICE, it doesn't fall within specialized commissions groups' guidelines — as referrals are mainly from lipidologists, not clinical genetics centers. Genetics commissioners don't see FH as strictly a genetic condition, but rather a treatable cardiac problem. Most [National Health Service] trusts have been unable to find the funding for DNA testing and the support staff to carry out cascade family testing. Our lab's current aim is to drive down the cost of analysis and improve the efficacy of our initial screen.