Diagnostic Yield and Clinical Utility of Sequencing Familial Hypercholesterolemia Genes in Patients With Severe Hypercholesterolemia

Abstract

Background: Approximately 7% of American adults have severe hypercholesterolemia (untreated low-density lipoprotein [LDL] cholesterol ≥190 mg/dl), which may be due to familial hypercholesterolemia (FH). Lifelong LDL cholesterol elevations in FH mutation carriers may confer coronary artery disease (CAD) risk beyond that captured by a single LDL cholesterol measurement.

Objectives: This study assessed the prevalence of an FH mutation among those with severe hypercholesterolemia and determined whether CAD risk varies according to mutation status beyond the observed LDL cholesterol level.

Methods: Three genes causative for FH (LDLR, APOB, and PCSK9) were sequenced in 26,025 participants from 7 case-control studies (5,540 CAD case subjects, 8,577 CAD-free control subjects) and 5 prospective cohort studies (11,908 participants). FH mutations included loss-of-function variants in LDLR, missense mutations in LDLR predicted to be damaging, and variants linked to FH in ClinVar, a clinical genetics database.

Results: Among 20,485 CAD-free control and prospective cohort participants, 1,386 (6.7%) had LDL cholesterol ≥190 mg/dl; of these, only 24 (1.7%) carried an FH mutation. Within any stratum of observed LDL cholesterol, risk of CAD was higher among FH mutation carriers than noncarriers. Compared with a reference group with LDL cholesterol <130 mg/dl and no mutation, participants with LDL cholesterol ≥190 mg/dl and no FH mutation had a 6-fold higher risk for CAD (odds ratio: 6.0; 95% confidence interval: 5.2 to 6.9), whereas those with both LDL cholesterol ≥190 mg/dl and an FH mutation demonstrated a 22-fold increased risk (odds ratio: 22.3; 95% confidence interval: 10.7 to 53.2). In an analysis of participants with serial lipid measurements over many years, FH mutation carriers had higher cumulative exposure to LDL cholesterol than noncarriers.

Conclusions: Among participants with LDL cholesterol ≥190 mg/dl, gene sequencing identified an FH mutation in <2%. However, for any observed LDL cholesterol, FH mutation carriers had substantially increased risk for CAD.

Keywords: coronary artery disease; gene sequencing; genetics; low-density lipoprotein cholesterol.

Figure 1. Impact of Familial Hypercholesterolemia, Rare Missense, and Rare Synonymous Mutations on LDL Cholesterol and Coronary Artery Disease

For each class of variants, the number of individuals within the 14,117 participants of the Myocardial Infarction Genetics Consortium case-control studies and % of CAD cases and CAD-free controls is provided. Number of individuals within each mutation category sum to more than the overall familial hypercholesterolemia mutation numbers due to overlap across variant classification. Increase in LDL cholesterol values determined via linear regression with adjustment for age, age², gender, cohort, and principal components of ancestry. Odds ratios for CAD were calculated via logistic regression with adjustment for gender, cohort, and principal components of ancestry.

Figure 2. LDL Cholesterol Values According to Familial Hypercholesterolemia Mutation Status

The distribution of low-density lipoprotein (LDL) cholesterol values according to familial hypercholesterolemia (FH mutation status) among the Myocardial Infarction Genetics Consortium studies is displayed. LDL cholesterol values were higher in FH mutation carriers (N = 164) as compared to noncarriers (N=13,954), p < 0.001.

Figure 3. Cumulative LDL cholesterol Exposure in Familial Hypercholesterolemia Mutation Carriers Compared on Non-carriers Matched on LDL cholesterol at Ascertainment

Hypercholesterolemic [low-density lipoprotein (LDL) cholesterol ≥ 130 mg/dl] carriers of a familial hypercholesterolemia (FH) mutation were identified in the Atherosclerosis Risk in Communities (ARIC) and Framingham Heart Study (FHS) Offspring cohorts and matched 1:1 to a FH mutation non-carriers according to age, gender, statin use, and LDL cholesterol at time of ascertainment. Mean ± standard error (SE) LDL cholesterol values at each study visit are displayed in each cohort according to mutation status. A matched pairs t-test demonstrated higher cumulative exposure to LDL cholesterol in FH mutation carriers versus non-carriers.

Central Illustration

A. Prevalence of a FH mutation amongst severely hypercholesterolemic individuals. B. Risk of coronary artery disease across LDL cholesterol and familial hypercholesterolemia mutation status categories. Odds ratios for CAD were calculated via logistic regression with adjustment for gender, cohort, and principal components of ancestry relative to a reference category of LDL cholesterol <130 mg/dl without a familial hypercholesterolemia (FH) mutation. Counts of CAD-free controls vs. CAD cases in each category are provided in Supplementary Table 6. P-value for mutation carriers vs. noncarriers across strata of LDL cholesterol < 0.0001. P-interaction between LDL cholesterol category and mutation status = 0.51