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Familial Hypercholesterolaemia

Familial Hypercholesterolaemia. The prevalence of heterozygous FH in the UK population is estimated to be 1 in 500 ~110,000 people are affected ↑ serum cholesterol concentration characterises heterozygous FH

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Familial Hypercholesterolaemia

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  1. Familial Hypercholesterolaemia • The prevalence of heterozygous FH in the UK population is estimated to be 1 in 500 • ~110,000 people are affected • ↑ serum cholesterol concentration characterises heterozygous FH • It leads to >50% risk of coronary heart disease in men by the age of 50 years and at least 30% in women by the age of 60 years.

  2. Simon Broome diagnostic criteria for index individuals Diagnose a person with definitefamilial hypercholesterolaemia (FH) if they have: • cholesterol concentrations as defined in table 1 and tendon xanthomas, or evidence of these signs in first- or second-degree relative OR • DNA-based evidence of an LDL-receptor mutation, familial defective apo B-100, or a PCSK9 mutation.

  3. Simon Broome diagnostic criteria for index individuals Table 1 Cholesterol levels to be used as diagnostic criteria for the index individual1 Total cholesterol LDL-C • Child/young person > 6.7 mmol/l > 4.0 mmol/l • Adult > 7.5 mmol/l > 4.9 mmol/l 1 Levels either pre-treatment or highest on treatment. LDL-C, low-density lipoprotein cholesterol.

  4. Simon Broome diagnostic criteria for index individuals Diagnose a person with possibleFH if they have cholesterol concentrations as defined in table 1 and at least one of the following. • Family history of MI < 50 years in second-degree relative or < 60 years in first-degree relative. • Family history of raised total cholesterol: > 7.5 mmol/l in adult first- or second-degree relative or > than 6.7 mmol/l in child, brother or sister under 16 years.

  5. NICE Guidelines FH • Family history of premature coronary heart disease should always be assessed in a person being considered for a diagnosis of FH (see Simon Broome criteria) • In children at risk of FH because of one affected parent, the following diagnostic tests should be carried out by the age of 10 years: • A DNA test if the family mutation is known • LDL-C concentration measurement if the family mutation is not known. • A further LDL-C measurement should be repeated after puberty because LDL-C concentrations change during puberty

  6. NICE Guidelines FH • Coronary heart disease risk estimation tools such as those based on the Framingham algorithm should not be used because people with FH are already at a high risk of premature coronary heart disease.

  7. NICE Guidelines FH - Identifying people with FH using cascade testing • Healthcare professionals should offer all people with FH a referral to a specialist with expertise in FH for • confirmation of diagnosis • initiation of cascade testing • Cascade testing using a combination of DNA testing and LDL-C concentration measurement is recommended. This should include at least the first- and second- and, when possible, third-degree biological relatives. • The use of a nationwide, family-based, follow-up system is recommended to enable comprehensive identification of people affected by FH.

  8. Scottish protocol • Eligible for testing: Simon Broome criteria positive • Lipid clinics to help to select patients for testing and manage affected cases • Genetics to do the cascade testing and refer as appropriate

  9. Laboratory Results • 556 patients tested in Aberdeen July (750) • 158 (28.4%) have mutation • 124 (78.5%) mutations identified in LDLR by sequencing • 20 were identified using MLPA (12.6%) • 14 had APOB R3572Q mutation (8.9%) • 0 had the PCSK9 D374Y mutation (0.0%)

  10. Laboratory Results • The LDLR mutations included – • 64 missense (51.5%) • 25 small deletions (20.2%) – 80% due to c.660delC & c.933delA • 24 nonsense (19.4%) • 9 splicing (7.3%) • 2 small insertions (1.6%)

  11. Laboratory Results • 36.3% (45/124) of all the LDLR sequence changes were found in exon 4. • Mainly c.660delC & c.682G>T - two of the more commonly found mutations in our samples • Without these changes the % of mutations in exon 4 would be 18.8%, which is closer to the LDLR mutation database which states 19.5%

  12. Laboratory Results • 7 novel changes not previously reported LDLR mutation database • 4 predicted to a premature stop codon • Remaining 3: one is a missense change and the other two are predicted to affect splicing. These three changes require further work to clarify their significance.

  13. Laboratory Results

  14. Laboratory Results Within Scotland FH test requests now outnumber those for BRCA1 gene screening. Uptake of predictive testing has lagged behind diagnostic testing. However, numbers of predictive tests are rapidly increasing month by month.

  15. Laboratory Results • The provision of a service for FH testing in Scotland has led to over 500 samples being tested to date and mutations being identified in 158 patients. The identification of familial mutations will allow for testing of family members to identify at risk individuals. • Mutations have been identified throughout the LDLR gene, 5 of these mutations have been identified in 5 or more apparently unrelated patients. • Our data support a continuing strategy of full gene screening in this patient group in our population. A targeted screening approach, such as the Elucigene FH20 would only detect ~33% of the mutations found. • NICE review ongoing • Similar to most other disorders - unclassified variants are problematic from a diagnostic point of view and require further time and work to clarify their significance.

  16. Mutation detection rates for FH in Scotland (2007-2010)

  17. Mutation detection rate by centre • Average mutation detection rate • Aberdeen 24% • Dundee 27% • Edinburgh 34% • Glasgow 32% Note: PM requests n=7 (1 mutation positive) = 12% of all Aberdeen requests

  18. Request and Mutation Rate by Centre (2007-2010) Note: PM requests n=7 (1 mutation positive) = 12% of all Aberdeen requests

  19. Mutation detection rate by centre Total requests: Aberdeen 9%; Dundee 8%; Edinburgh 53%; Glasgow 27% Note: PM requests n=7 (1 mutation positive) = 12% of all Aberdeen requests

  20. Scottish FH Testing Programme • FH DNA testing is happening due to national funding of genetic testing • Effective management in place, at least for those patients with FH that are known to NHS. • “Low hanging fruit approach”- Scotland over taken England <2 yrs • Despite no specific funding for FH services funding of genetic testing has been sufficient to allow services to become established- paediatric “buy-in” now. • A specifically funded, population wide screening strategy may be ideal, but our pragmatic approach at least gives benefit to some of the most needy patients at minimal cost in a time of severe funding constraints. • More detail coming on differences in referral rates • To audit rates of probable vs unclassifed and test sources, beware small nos.

  21. Acknowledgements • Bill Simpson • Steven Tennant, Christine Bell & DNA lab • Claire Parsons • Catriona Brown paper on children testing • Scottish Lipid Forum • Scottish Molecular Genetics Consortium steering group & Clinical Genetics Forum

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