Familial Hypercholesterolemia (FH)
Definition
Familial hypercholesterolemia (FH) is a common autosomal codominant genetic disorder characterised by severely elevated LDL-C from birth due to impaired LDL receptor function. It is the most prevalent monogenic cause of premature ASCVD. Heterozygous FH (HeFH) affects 1 in 250–300 individuals (~20 million in the US); homozygous FH (HoFH) is rare (~1:300,000). Up to 90% of affected individuals are undiagnosed.
Key Concepts
Epidemiology and Genetics
- HeFH affects 1 in 250–300 (comparable to type 1 diabetes prevalence); by mid-forties ~20% of HeFH individuals have atherosclerotic conditions.
- LDLR actionable genotype lifespan impact (Iceland WGS; n=57,933): The LDLR c.694+2T→C splice variant (a CDC Tier 1 gene actionable genotype) was associated with a lifespan −6.47 years shorter (95% CI −9.91 to −3.03) than noncarriers in population-level survival analysis — the largest individual lifespan reduction of any non-cancer ACMG SF cardiovascular gene in Iceland. Among all 73 ACMG SF cardiovascular genes, LDLR was one of only two (alongside MYBPC3) showing an individual lifespan signal. (sources/genotype-lifespan-nejm-2023 — high) (sources/lipid-aha-2026, rating: very high; sources/inherited-basis-cad-nejm-2026, rating: high)
- Critical point: Even at identical LDL-C levels, persons with a genetically proven FH variant have a 2–3× higher CAD risk than those without the variant — confirming a genetic risk mechanism beyond what LDL-C alone captures, possibly from longer lifetime LDL-C exposure or variant-specific pleiotropic effects. (sources/inherited-basis-cad-nejm-2026, rating: high)
- Most common causative genes: LDLR (LDL receptor, ~70–80%), APOB (apolipoprotein B), PCSK9 (gain-of-function), LDLRAP1 (autosomal recessive FH)
- Elevated Lp(a) is common in FH (ascertainment bias — high Lp(a) increases clinical recognition); FH itself does not cause elevated Lp(a)
- Pathogenic variant prevalence: ~0.4% general population; ~3.5% in LDL-C >190 mg/dL; 5% probable FH, 24% definite FH by clinical scoring. (sources/inherited-basis-cad-nejm-2026, rating: high)
Other Monogenic Forms of CAD (Rare)
- Autosomal recessive hypercholesterolemia: LDLRAP1 variants — impaired LDL receptor adaptor protein; phenotype mimics HoFH. (sources/inherited-basis-cad-nejm-2026, rating: high)
- Sitosterolemia: ABCG5 and ABCG8 variants — impaired plant sterol excretion → premature CAD; often misdiagnosed as FH. (sources/inherited-basis-cad-nejm-2026, rating: high)
- Pseudoxanthoma elasticum: ABCC6 variants — premature CAD via calcification of elastic fibres and large vessels. (sources/inherited-basis-cad-nejm-2026, rating: high)
- Nitric oxide pathway: GUCY1A1 and PDE5A rare variants — dysfunctional NO signalling → premature MI; relevant to potential PDE5 inhibitor benefit (observational data only). (sources/inherited-basis-cad-nejm-2026, rating: high)
- Triglyceride regulation: APOA5 rare variants — markedly elevated TG → premature CAD. (sources/inherited-basis-cad-nejm-2026, rating: high)
- Cholesterol transport: SCARB1 rare variants — severe early-onset CAD via impaired reverse cholesterol transport. (sources/inherited-basis-cad-nejm-2026, rating: high)
- These genes are candidates for expanded molecular genetic evaluation panels alongside LDLR, APOB, PCSK9 for premature CAD evaluation. (sources/inherited-basis-cad-nejm-2026, rating: high)
Diagnosis and Screening
- FH phenotype: LDL-C ≥190 mg/dL (4.9 mmol/L) in adults (may be lower in children)
- Clinical diagnosis supported by Dutch Lipid Clinic Network (DLCN) or Simon Broome criteria (family history, physical signs such as tendon xanthomas/corneal arcus)
- Genetic panel testing for FH (LDLR, APOB, PCSK9, LDLRAP1 pathogenic/likely pathogenic variants): COR 2a in adults with LDL-C ≥190 mg/dL without secondary cause; COR 2a in children/adolescents with clinical FH presentation sources/lipid-aha-2026 (very high)
- AHA 2020 FH genetic testing criteria (Table 4): (sources/genetic-test-aha-2020 — high)
- Testing should be offered: (1) Children with persistent LDL-C ≥160 mg/dL or adults with LDL-C ≥190 mg/dL (no secondary cause) plus ≥1 first-degree relative with similar LDL-C or premature CAD, or when family history is unavailable; (2) Children with LDL-C ≥190 mg/dL or adults with LDL-C ≥250 mg/dL (no secondary cause), even without a positive family history
- Testing may be considered: (1) Children with LDL-C ≥160 mg/dL + parent LDL-C ≥190 mg/dL or family history of hypercholesterolemia + premature CAD; (2) Adults without pre-treatment LDL-C data but with personal premature CAD and family history of both hypercholesterolemia and premature CAD; (3) Adults with LDL-C ≥160 mg/dL + family history of hypercholesterolemia and premature CAD (personal or family history)
- Premature CAD thresholds: males ≤55 years, females ≤65 years
- Genetic confirmation identifies higher-risk individuals within the LDL-C ≥190 mg/dL group
- Lipid screening from age ≥2 y if family history of FH (cascade screening): identifies FH early for lifestyle and pharmacotherapy sources/lipid-aha-2026 (very high)
Risk Assessment Caveat
- PREVENT-ASCVD equations (and PCE) should NOT be used in HeFH (COR 3: Harm) — standard equations vastly underestimate lifetime ASCVD risk because they were not derived in FH populations sources/lipid-aha-2026 (very high)
- Lifetime cumulative LDL-C exposure (cholesterol-years concept) drives ASCVD risk; FH starts at birth
Treatment Goals — LDL-C Targets by Clinical Context
| HeFH Scenario | LDL-C Goal | Non-HDL-C Goal | Agents |
|---|---|---|---|
| No ASCVD, no additional risk factors, no coronary calcification | <100 mg/dL | <130 mg/dL | Maximally tolerated statin + ezetimibe/PCSK9 mAb/bempedoic acid (COR 1) |
| HeFH confirmed (clinical or genetic) OR additional risk factors OR coronary calcification, no ASCVD | <70 mg/dL | <100 mg/dL | Statin + ezetimibe/PCSK9 mAb/bempedoic acid (COR 1) |
| Clinical ASCVD | <55 mg/dL | <85 mg/dL | Statin + ezetimibe/PCSK9 mAb/bempedoic acid (COR 1) |
| LDL-C ≥100 mg/dL on max statin ± ezetimibe | Intensify to goals | — | Add inclisiran (COR 2a) |
HoFH (Homozygous FH) — Special Considerations
- Very severe hypercholesterolemia (LDL-C often 400–1000+ mg/dL); LDL receptor function near zero
- Standard statin therapy has limited effect (LDL receptor-dependent mechanism)
- PCSK9 mAbs in HoFH — genotype-specific response (evolocumab; TESLA Part B + TAUSSIG open-label) sources/pcsk9-inhibitors-nrc-2018 (very high):
LDLR Genotype Evolocumab LDL-C Reduction Two defective alleles (2–25% normal LDL uptake) ~47% One defective + one negative allele (<2% LDL uptake) ~25% Two negative alleles (null-null) No response APOB mutation ~47% Compound heterozygote (PCSK9 GoF + LDLR negative allele) ~6% - Overall TESLA Part B mean: 31% LDL-C reduction; TAUSSIG 420 mg monthly: 20%; uptitrated Q2W: 28%
- Patients with two negative (null-null) LDLR alleles do NOT respond to PCSK9 mAbs — evinacumab (LDLR-independent) is the key alternative
- Evinacumab (ANGPTL3 mAb, IV every 4 weeks): LDL receptor-independent mechanism; ~47–49% LDL-C reduction; 55% TG reduction; effective across both null-null and non-null LDLR genotypes (Raal Phase 3; n=65; 24 weeks) — see concepts/ANGPTL3-Inhibition and entities/Evinacumab for full trial data (sources/angptl3-inhibition-tcm-2024 — high)
- ACC/AHA 2026: COR 2b in HoFH with LDL-C ≥100 mg/dL on max statin + ezetimibe + PCSK9 mAb sources/lipid-aha-2026 (very high)
- ESC 2025: COR IIa B — should be considered in HoFH patients aged ≥5 years not at LDL-C goal despite maximum lipid-lowering therapy (ELIPSE HoFH trial + paediatric extension) sources/lipid-esc-2025 (very high)
- ESC recommendation is broader (IIa vs 2b) and explicitly includes paediatric patients ≥5 years; ACC/AHA 2026 recommendation is restricted to adults with LDL-C still ≥100 mg/dL on triple therapy
- LDLR-independent LDL-C lowering mechanism operates via endothelial lipase–dependent VLDL clearance — distinct from all other approved LDL-C-lowering agents that require functional LDLR (sources/angptl3-inhibition-tcm-2024 — high)
- Lomitapide (MTTP inhibitor): 40–50% LDL-C reduction; available through REMS program only; hepatotoxicity risk; daily fat-soluble vitamin supplements required
- Lipoprotein apheresis: available for refractory HoFH/HeFH with high Lp(a) ≥60 mg/dL + CAD/PAD
Statin Therapy in FH
- High-intensity statin is first-line; should be started early (children with FH from age 8–10 y in most guidelines)
- Paediatric statin RCTs show safety and LDL-C lowering in short/medium term; long-term follow-up of 1 RCT showed reduced premature ASCVD sources/lipid-aha-2026 (very high)
- Most HeFH patients will require statin + ezetimibe ± PCSK9 inhibitor to reach LDL-C <70 mg/dL
Cascade Screening
- After index case identified: screen all first- and second-degree relatives with fasting lipid profile (COR 2a)
- Can be performed from age ≥2 years for early adoption of lifestyle and timely pharmacotherapy
- "Reverse cascade screening" — screening relatives of FH probands identifies other affected family members and may be cost-effective
- Genetic testing improves cascade yield (vs lipid testing alone)
DTC-GT for FH — Emerging Role
- DTC genetic testing panels include the key FH genes: LDLR, APOB, PCSK9, LDLRAP1; these have ClinGen definitive/strong evidence and are ACMG SF v3.2 actionable secondary findings (sources/consumer-genetictest-aha-2025 — high)
- Gene-first FH screening is likely cost-effective in US adults ≤50 years — this represents one of the stronger clinical utility arguments for DTC-GT in cardiovascular medicine; however confirmatory CLIA-certified testing remains recommended before management changes (sources/consumer-genetictest-aha-2025 — high)
- DTC-GT for FH uses SNP-chip genotyping, which captures common known variants but not all novel LDLR mutations — a negative DTC result does NOT exclude FH in a patient with LDL-C ≥190 mg/dL (sources/consumer-genetictest-aha-2025 — high)
- GINA 2008 protects against genetic discrimination in health insurance but NOT life, disability, or long-term care insurance — relevant when FH identified through DTC-GT channels (sources/consumer-genetictest-aha-2025 — high)
- For comprehensive DTC-GT framework, see concepts/DTC-Genetic-Testing
Emerging Gene Editing — PCSK9 Base Editing in HeFH
- VERVE-102 (Heart-2; NEJM 2026; Phase 1; NCT06164730): Single IV infusion of GalNAc-LNP delivering ABE8.8 mRNA + gRNA targeting PCSK9 splice site; in 35 participants (HeFH or premature CAD on max statin ± ezetimibe); at 1.0 mg/kg: mean PCSK9 −88%, LDL-C −62% (absolute −78 mg/dL; 128→51 mg/dL); stable to ≥18 months; no dose-limiting toxicity; no deaths; GalNAc-LNP favorable safety vs predecessor VERVE-101 (sources/verve102-pcsk9-nejm-2026 — high)
- Mechanism mirrors naturally occurring cardioprotective PCSK9 LoF variants (88% lifetime CHD risk reduction in genetic LOF carriers) — single-infusion replication of a lifelong genetic advantage
- HeFH and premature CAD patients were the enrolled population; however because the mechanism requires functional LDL receptor (PCSK9 editing spares LDLR from degradation), efficacy in HoFH with null-null LDLR genotype is expected to be limited — same limitation as PCSK9 inhibitors; ANGPTL3 editing (LDLR-independent) remains the gene editing strategy for HoFH
- Not yet guideline-recommended; VERVE-102 Heart-2 study ongoing (up to 85 participants); 15-year long-term follow-up regulatory requirement
Emerging Oral Therapies — Obicetrapib in HeFH
- 17% of BROADWAY participants had HeFH (on maximum tolerated statins ± ezetimibe ± PCSK9 inhibitors); within this subgroup obicetrapib achieved comparable LDL-C reductions to the overall trial (−32.6 pp between-group difference) sources/obicetrapib-broadway-nejm-2025 (high)
- Offers an oral daily add-on option for HeFH patients unable or unwilling to use injectable PCSK9 inhibitors
- The simultaneous Lp(a) lowering by ~33.5% is notable in FH given the high co-prevalence of elevated Lp(a) in this population (ascertainment bias) — no approved Lp(a)-specific therapy currently exists
- Not yet guideline-recommended or approved; see concepts/CETP-Inhibitors for full context and ongoing BROOKLYN outcomes trial sources/obicetrapib-broadway-nejm-2025 (high)
Referral to Lipid Specialist
- All patients with diagnosed or suspected FH
- HeFH not achieving treatment targets on maximally tolerated statin + nonstatin therapy
- HeFH with statin-attributed side effects on ≥2 statins including at lowest dose
- HoFH (always)
Contradictions / Open Questions
- Genetic FH diagnosis confers 2-3× additional CAD risk at same LDL-C: Even after matching for LDL-C, a confirmed FH pathogenic variant carries 2-3× higher CAD risk. This implies that phenotypic FH diagnosis (based on LDL-C and clinical scoring alone) underestimates risk in genetically confirmed cases, and that genetic testing should influence both target-setting and screening intensity beyond what LDL-C alone dictates. (sources/inherited-basis-cad-nejm-2026, rating: high)
- Debate on when to start statins in children with FH: ACC/AHA recommends age 8–10 in US guidelines; some European guidelines more aggressive (from age 6–8); concerns about very long-term statin safety in children vs magnitude of cumulative LDL-C benefit
- Whether genetic vs phenotypic FH diagnosis changes management beyond risk stratification: genetics identifies higher-risk subset within LDL-C ≥190 mg/dL group, but treatment goals are identical in most cases
- HoFH: emerging RNA-based therapies (siRNA targeting PCSK9, ANGPTL3, or APOB) and ANGPTL3 gene editing (CTX310, VERVE-201) may eventually replace current complex regimens — not yet guideline-incorporated; ARO-ANG3 siRNA Phase 2b (ARCHES-2) ongoing in HoFH (sources/angptl3-inhibition-tcm-2024 — high)
- Evinacumab COR discordance (HoFH): ESC 2025 COR IIa B (consider in HoFH ≥5 y not at LDL-C goal on max therapy) vs ACC/AHA 2026 COR 2b (weaker — HoFH with LDL-C ≥100 mg/dL on max statin + ezetimibe + PCSK9 mAb). ESC also extends indication to paediatric patients ≥5 years explicitly sources/lipid-esc-2025 sources/lipid-aha-2026 (both very high)
Connections
- Related to concepts/Dyslipidemia-Management — FH is the most severe LDL-C disorder requiring most intensive treatment
- Related to concepts/ASCVD-Risk-Assessment — PREVENT equations specifically contraindicated in FH
- Related to concepts/Lipoprotein-a — elevated Lp(a) common in FH; multiplicative risk if both present
- Related to concepts/DTC-Genetic-Testing — LDLR/APOB/PCSK9 in DTC panels; gene-first FH screening cost-effectiveness
- Related to concepts/ANGPTL3-Inhibition — evinacumab LDLR-independent mechanism; key HoFH treatment option; siRNA and gene editing in development
- Related to entities/Evinacumab — anti-ANGPTL3 mAb; FDA/EMA approved HoFH
- Related to sources/genetic-test-aha-2020 — FH genetic testing criteria Table 4; cascade screening recommendations
- Related to concepts/PCSK9-Inhibitors — PCSK9 GoF mutations cause FH; mAb genotype-specific response in HoFH; evolocumab FOURIER; alirocumab ODYSSEY
- Related to entities/Evolocumab — genotype-specific HoFH dosing table; FOURIER CVOT
- Related to entities/Alirocumab — ODYSSEY Outcomes CVOT
Sources
- sources/consumer-genetictest-aha-2025
- sources/genetic-test-aha-2020
- sources/inherited-basis-cad-nejm-2026
- sources/lipid-aha-2026
- sources/lipid-esc-2025
- sources/obicetrapib-broadway-nejm-2025 — BROADWAY RCT; 17% HeFH; obicetrapib −32.6 pp LDL-C add-on; Lp(a) −33.5%
- sources/angptl3-inhibition-tcm-2024 — evinacumab clinical trial data (Raal Phase 3; Rosenson Phase 2); LDLR-independent mechanism; siRNA/ASO/gene editing review
- sources/pcsk9-inhibitors-nrc-2018 — PCSK9 GoF FH genetics; evolocumab HoFH genotype-specific response; FOURIER CVOT; LDL-C cumulative burden concept
- sources/verve102-pcsk9-nejm-2026 — VERVE-102 Heart-2 Phase 1 NEJM 2026; PCSK9 base editing in HeFH/premature CAD; safety and dose-response data (high)