FHNEXT

FHNext is a targeted panel for patients with familial hypercholesterolemia, one of the most common genetic conditions. Establishing a genetic diagnosis can direct medical management, treatment and help identify at-risk family members. 

PrintPrint

FHNext is a targeted panel for patients with familial hypercholesterolemia, one of the most common genetic conditions. Establishing a genetic diagnosis can direct medical management, treatment and help identify at-risk family members. 

FHNext is a next generation sequencing (NGS) panel of 4 genes associated with FH: APOB, LDLR, PCSK9, and LDLRAP1 (including deletion/duplication analysis of the APOB, LDLR, and PCSK9 genes). FHNext also includes analysis of the pharmacogenetic c.521T>C SNP in the SLCO1B1 gene. Specific Site Analysis is available for individual gene mutations identified in a family.

Disease Name 
Familial Hypercholesterolemia
Disease Information 

Familial hypercholesterolemia (FH) is typically an autosomal dominant disease characterized by extremely high levels of plasma LDL (low density lipoprotein) cholesterol in the body, causing atherosclerotic plaque formation in the arteries and therefore a significantly increased risk for premature coronary artery disease (CHD) and myocardial infarction.1 Rarely, FH may be also inherited in an autosomal recessive manner (such as the more severe form associated with biallelic pathogenic variants in the LDLRAP1 gene).2

Abnormally functioning LDL-receptors cause deposition of cholesterol in different parts of the body, including xanthelasma (skin), xanthomas (tendons), and coronary arteries (atherosclerosis).3,4

Historically, it has been estimated that 1 in 500 individuals has one LDLR mutation (“heterozygous” or “HeFH” – autosomal dominant form assumed) worldwide, while recent studies have suggested a higher prevalence of 1 in 200 individuals.6 It has been estimated that 1 in 160,000  individuals has two LDLR mutations (“homozygous” or “HoFH” – autosomal dominant form assumed) worldwide.1,7

Those with HeFH usually have a 2- to 3- fold elevation in plasma LDL-cholesterol and develop symptoms such as tendinous xanthomas, corneal arcus, and premature coronary artery disease.4,7 Those with HoFH also present planar xanthomas, with plasma LDL cholesterol increased 6- to 8-fold; death from myocardial infarctions during the first two decades of life is common.8 Due to a founder effect, FH is much more common in some population groups such as French Canadians, Afrikaners, Lebanese, Finns, and Ashkenazi Jews.9

When to Suspect FH5

Diagnostic clinical criteria have been published for FH and are based on extreme hypercholesterolemia, premature coronary artery disease (CAD), physical examination findings (e.g. xanthoma or corneal arcus), family history of hypercholesterolemia or CAD, and presence of a disease-causing mutation in an FH-related gene.

  • Dutch Lipid Clinic Network10 criteria include:
    • Total cholesterol and LDL-C measurements
    • Personal and family histories of CAD
    • Physical examination findings, and
    • Presence of a disease-causing mutation in an FH-related gene
  • Simon Broome Register Group11 criteria include:
    • Total cholesterol and LDL-C measurements
    • Family history
    • Physical examination findings, and
    • Presence of a disease-causing mutation in an FH-related gene
  • US Make Early Diagnosis Prevent Early Deaths Program (MEDPED)12 criteria include:
    • Total cholesterol and LDL-C measurements

Proper diet, exercise, and certain medications can help treat FH. Those with HeFH usually respond well with a combination of diet change and drugs (statins), while in some cases, additional therapies13 (LDL apheresis, MTP inhibitor, apoB antisense inhibitor, PCSK9 inhibitor) or liver transplantation may be recommended for those with HoFH or patients with FH who are intolerant of statins.14 A proactive diagnosis, in combination with selective treatments, can help decrease the incidence and progression of FH effects. 

1-5% of those treated with statins experience myalgia; this can be related to a specific pharmacogenetic marker.15 The c.521T>C SNP pharmacogenetic marker in SLCO1B1 confers an intermediate (in the heterozygous form) to high (in the homozygous form) simvastatin-induced myopathy risk; a lower dose of simvastatin or use of an alternative statin and routine creatine kinase (CK) surveillance are recommended in these cases.15

Genetic testing for FH

Genetic testing can:

  • Confirm a diagnosis, particularly when clinical criteria are unclear or borderline in an individual
  • Help tailor medical treatment, including avoiding/adjusting simvastatin use based on SLCO1B1 genotype
  • Clarify risks to family members, including the inheritance pattern

Data also support using genetic testing to offer cascade testing to family members, as it increases the detection of FH when compared to using serum cholesterol levels alone for diagnosis.5

Test Description 

FHNext includes 4 genes associated with FH: APOB, LDLR, PCSK9, and LDLRAP1. Genomic deoxyribonucleic acid (gDNA) is isolated from the patient’s specimen using a standardized kit and quantified. Sequence enrichment of the targeted coding exons and adjacent intronic nucleotides is carried out by a bait-capture methodology using long biotinylated oligonucleotide probes, followed by polymerase chain reaction (PCR) and NGS. Sanger sequencing is performed for any regions missing or with insufficient read depth coverage for reliable heterozygous variant detection. Reportable small insertions and deletions, potentially homozygous variants, variants in regions complicated by pseudogene interference, and single nucleotide variant calls not satisfying 100x depth of coverage and 40% het ratio thresholds are verified by Sanger sequencing.16 This assay targets all coding domains, and well into the flanking 5’ and 3’ ends of all the introns and untranslated regions. Gross deletion/duplication analysis is performed utilizing a targeted chromosomal microarray for APOB, LDLR, and PCSK9. Analysis of the pharmacogenetic c.521T>C SNP in the SLCO1B1 gene is performed. If Specific Site Analysis is requested, only specific region(s) of DNA is (are) amplified by PCR and sequenced.

Mutation Detection Rate 

~70% of patients with a diagnosis of FH have a mutation in one of the FHNext genes (clinical sensitivity). FHNext can detect >99.9% of described mutations in the included genes, when present (analytic sensitivity).

Specimen Requirements 

Complete specimen requirements are available here or by downloading the PDF found above on this page.

Turnaround Time 
TEST CODE TECHNIQUE TURNAROUND TIME (Weeks)
8680 FHNext  2-3 

 

Specialty 
Genes 
APOB
LDLR
PCSK9
LDLRAP1
SLCO1B1
Tests 
References 
  1. Hopkins PN. Familial hypercholesterolemia—improving treatment and meeting guidelines. International Journal of Cardiology. 2003;89:13-23.
  2. Youngblom BA and Knowles JW. Familial Hypercholesterolemia. 2014 Jan 2 GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2016.
  3. Schmidt HH, et al. Delayed low density lipoprotein (LDL) catabolism despite a functional intact LDL-apolipoprotein B particle and LDL-receptor in a subject with clinical homozygous familial hypercholesterolemia. J Clin Endocrinol Metab. 1998;83(6):2167-74.
  4. Varret M, et al. Genetic heterogeneity of autosomal dominant hypercholesterolemia. Clin Genet. 2008:73:1–13. 
  5. Goldberg AC, et al.  Familial hypercholesterolemia: screening, diagnosis, and management of pediatric and adult patients.  J Clin Lip. 2011; 5: S1-S8.
  6. Benn M, et al. Mutations causative of familial hypercholesterolaemia: screening of 98,098 individuals from the Copenhagen General Population Study estimated a prevalence of 1 in 217. Euro Heart J. 2016 May 1;37(17):1384-94.
  7. Hobbs H, et al. The LDL receptor locus in familial hypercholesterolemia: mutational analysis of a membrane protein. Ann Rev Genet. 1990;24:133-70. 
  8. Bertolini S, et al. Analysis of LDL receptor gene mutations in Italian patients with homozygous familial hypercholesterolemia. Arterioscler Thromb Vasc Biol. 1999;19:408-418. 
  9. Austin M, et al. Genetic causes of monogenic heterozygous familial hypercholesterolemia: a HuGE prevalence review. Am J Epidemiol. 2004;160:407–420.
  10. World Health Organization Human Genetics Programme. Familial Hypercholesterolaemia (FH): Report of a second WHO Consultation. Geneva, 1999. (WHO Publication No. WHO/HGN/FH/CONS/99.2).
  11. Scientific Steering Committee on behalf of the Simon Broome Register Group. Risk of fatal coronary heart disease in familial hypercholesterolaemia. BMJ. 1991 Oct 12;303(6807):893-6.
  12. Williams RR, et al. Diagnosing heterozygous familial hypercholesterolemia using new practical criteria validated by molecular genetics. Am J Cardiol. 1993 Jul 15;72(2):171-6.
  13. Watts GF, et al. Integrated guidance on the care of familial hypercholesterolemia from the International FH Foundation. Int J Cardiol. 2014 Feb 15;171(3):309-25.
  14. Rader DJ, et al. Monogenic hypercholesterolemia: new insights in pathogenesis and treatment. J Clin Invest. 2003;111:1795-1803.
  15. Ramsey LB et al. The clinical pharmacogenetics implementation consortium (CPIC) guideline for SLCO1B1 and simvastatin-induced myopathy: 2014 update. Clin Pharmacol Ther. 2014 Oct;96(4):423-8. 
  16. Mu W, et al. Sanger confirmation is required to achieve optimal sensitivity and specificity in next-generation sequencing panel testing. J Mol Diagn. 2016. 18(6):923-932.