3259Next-generation sequencing to confirm clinical FH in The Netherlands

Abstract

Abstract Background Pathogenic variants in the genes encoding the low-density lipoprotein receptor (LDLR), apolipoprotein B100 (APOB) and proprotein convertase subtilisin/kexin type 9 (PCSK9)) are known to cause familial hypercholesterolemia (FH), a disease characterized by high LDL-C levels. We set out to investigate which proportion of patients with extremely elevated LDL-C levels, who were referred for molecular analysis, carry a mutation in any of the three FH genes or other, putative FH genes. Methods Targeted next-generation sequencing of 28 genes involved in lipid metabolism was performed in 1475 clinical FH patients with LDL-C levels >5mmol/L (corresponding with possible, probable and definite FH score according to the Dutch Lipid Clinic Network criteria) and triglyceride levels <4.5 mmol/L. Genetic variants and copy number variants were curated consecutively using specialist analysis software. (Likely) pathogenic variants in LDLR, APOB, or PCSK9 were annotated as FH-causing variants. Results 14.3% of the 1475 patients with clinical FH were heterozygous carriers of a mutation in LDLR, APOB, or PCSK9. This number ranged from 8% in the lowest LDL-C group (5–5.99 mmol/L) to 56% in patients with the highest LDL-C levels (>8 mmol/L). Patients with LDLR, APOB, or PCSK9 variants had median LDL-C levels of 6.8 [5.7–7.9], 6.2 [5.1–7.0], and 6.4 [5.7–6.8] mmol/L [interquartile range], respectively. Mutation-negative FH patients had median LDL-C levels of 5.8 [5.2–6.5] mmol/L. Of the FH mutation-negative patients 7.4% had a (likely) pathogenic variant in the gene encoding lipoprotein lipase (LPL) and 1.3% in the apolipoprotein E (APOE) gene. The proportion of FH mutation-negative patients carrying an APOE variant increased from 1.2% in the lowest LDL-C group to 7.5% in patients with LDL-C >8 mmol/L. Mutation-positive FH patients were significantly younger (41.61±17.53 years vs 52.62±13.28 years P<0.001) and had a significant lower BMI (25.86±4.87 vs 26.55±4.07kg/m2, P=0.02) compared to mutation negative patients. Figure 1 Conclusions A genetic defect in LDLR, APOB or PCSK9 is identified in only 14.3% of the patients with a clinical FH phenotype (defined as LDL-C >5 mmol/L) referred for molecular testing in the Netherlands. Mutations in LPL and APOE were found in a minor proportion of the FH mutation-negative patients. Our finding that a mutation is only found 56% of patients who present with LDL-C levels above 8 mmol/L indicates that either misclassification of FH and/or other genetic defects may be present in this group. Acknowledgement/Funding Grant [016.156.445] from The Netherlands Organisation for Scientific Research (NWO)