Familial Hypercholesterolemia

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Familial Hypercholesterolemia

• Stephen Tennant
• Aberdeen Molecular Genetics
• Scottish Genetic Laboratories Consortium Meeting
• 26th November 2008

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Familial Hypercholesterolemia

• Autosomal dominant disorder causing high levels
  of low density lipoprotein cholesterol which
  frequently leads to early coronary heart disease.
• Prevalence of FH is 1 in 500 ( 12,000 affected
  in Scotland)
• Homozygous form the disease affects 1
  /1,000,000
• Patients have a greatly increased risk of heart
  disease (100 fold for males 20-40yrs)
• 50 risk of coronary heart disease by the
  age of 50 yrs in men and at least 30 in women by
  the age of 60 years
• A significant reduction in morbidity can be
  achieved through changes in lifestyle and the use
  of statins to lower cholesterol.

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Familial Hypercholesterolemia

• Through early identification, more powerful drugs
  (statins), stop smoking, good diet and annual
  checks
• life expectancy of FH is now the same as the
  general population.
• But the vast majority (85) of affected
  individuals remain undiagnosed (10,000 cases
  in Scotland).
• Low prevalence of young people with FH, many
  undiagnosed
• Identification of individuals with FH using
  cascade testing
• identify mutation in proband gt test relatives
  for familial mutation gt identify patients younger
  gt reduce no. of CHD deaths especially in 20-40
  year olds.

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Familial Hypercholesterolemia - phenotype

• Simon Broome Criteria
• (a) 16yrs Total cholesterol gt7.5mmol/l or
  LDL-C gt4.9mmol/l
• u16 yrs Total cholesterol gt6.7mmol/l or
  LDL-C gt4.0mmol/l
• (b) Tendon xanthoma in patient or 1st or 2nd
  degree relative
• (c) FH of MI lt60 yrs in 1st degree relative or FH
  of MI lt50 yrs in 2nd
• degree relative
• (d) FH of total cholesterol gt7.5mmol/l in 1st or
  2nd degree relative

Definite FH ab must be present Possible FH
ac or ad
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Genetics of FH

• FH is caused by mutations in 3 genes identified
  so far

Low-density lipoprotien receptor gene
(LDLR) Apoliprotein B-100 gene (APOB) involved
in LDLR binding Proprotein convertase
subtilisin/kexin type 9 (PCSK9) cholesterol
homeostasis
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LDLR

• 93 of all mutations described so far are in LDLR
• Coding region of 5kb, 18 exons.
• Over 1000 mutations reported, no hotspots
• In the UK it is rare for a mutation to reach
  frequency of 10
• Reported that 5 mutation may be due to large
  deletions or duplications MLPA kit

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APOB

• Only one mutation in APOB is reported R3527Q
  and is 5 of FH cases in the UK.
• Founder effect, not found in Finland, China or
  Japan
• PCSK9
• Common mutation is D374Y reported to be 1-2 of
  FH cases.
• PCKS9 is very polymorphic
• R46L is associated with lower LDL-C and lower
  cardiovascular risk
• Because of this Belfast do not routinely screen
  PCSK9 unless specifically requested due to the
  difficulty in interpretation of the results
  very rare in probands can be found when testing
  their family members

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Testing in London

• Pre-screen using Tepnel FH20 ARMS kit - 18
  mutations in LDLR APOB R3527Q PCSK9 D374Y
• Developed in collaboration with GOSH in London,
  this kit will detect 45 of mutations in their
  population

Sequence to confirm if a mutation has been
identified. If no mutation detected sequence the
entire coding region of LDLR and use MLPA to look
for large deletions or duplications in
LDLR. London detect a mutation in 80 of
definite FH cases
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Testing in Belfast

• Belfast iPLEX MassARRAY assay which will detect
  57 mutations 55 LDLR common APOB PCSK9
• MALDI-TOF
• This detects 82 of NI mutations and 70-80 of
  known common UK mutations.
• If no mutation detected then screen LDLR coding
  region and MLPA analysis 1kb of APOB ex26 which
  includes R3527Q. PCSK9 testing upon request
• Mutation identified in 95 of definite cases in
  NI
• - Is this due to better referrals than london or
  new genes or mutations yet to be identified ??

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FH testing service

• In order to establish the mutation spectrum in
  Scotland all samples are going to be testing by
  MLPA and sequencing.
• MLPA kit available form MRC Holland which
  contains probes for each of the 18 LDLR exons.
• 20 fragments 18 LDLR (1 exon per fragment) and
  APOB R3527Q and PCSK9 D374Y.
• Probands referred from Lipid clinics ? mutation
  identified ? testing of other family members ?
  early treatment ? less death

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Results so far

• Tested all patients referred for FH since 1999
• No clinical information given so do not know if
  the patients fit Simon Broome criteria
• Mutations identified in 8/20 patients 7
  different mutations, 2 patients were father and
  daughter and had the same mutation
• All 7 mutations are on the LDLR mutation database
• 4/7 would be detected by NI iPLEX, 3/7 would be
  detected by FH20
• 
  
  
  
  
  
  
  
  
  

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Future plans

• To test all the samples that are referred and to
  review this information to find out
• If there are any common Scottish mutations that
  could be used in a pre-screen before sequencing ,
  would the existing FH20 ARMS kit be a use in the
  Scottish population
• What is the pick up rate for definite FH
  samples and how does this compare with the rest
  of the UK
• How many samples have more than one pathogenic
  mutation and therefore might be missed by a
  pre-screen and have an effect on future familial
  testing ?
• To keep an eye on the literature to see
  if any other genes are identified or if any other
  pathogenic mutations are identified in APOB

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Scottish Lipid Forum - 19th 20th November,
Dunkeld

• Meeting discussed an FH service and involved
  lipidiologists, genetic clinicians and lab staff.
• Talks from other countries on how they do it
  Holland NI
• Cascade screening to be introduced
• Inform the lipid clinics that testing is
  available at the Aberdeen lab and that samples
  will start arriving soon.
• Lots of discussion about ethics, databases, who
  does what in the service, how proactive about
  getting samples
• NI put a genetic nurse in lipid clinics, all
  about funding and time

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Summary

• The service will involve interaction between
  lipid clinics and genetics
• FH service now available in Aberdeen
• Need to establish information about our
  population
• Possibly introduce a pre-screen in the future