Familial dysbetalipoproteinemia: highly atherogenic and underdiagnosed disorder

Familial dysbetalipoproteinemia (FD) is a genetic, highly atherogenic disorder. The penetrance of FD depends on the patient’s lifestyle and concomitant diseases. Despite the fact that FD was described almost half a century ago, it is still insufficiently studied and is extremely rarely diagnosed. In actual clinical practice, physicians do not have clear understanding of clinical course and genetic basis of FD. The aim was to present the most complete, but at the same time a critical review with a modern view on FD. We analyzed Russian and foreign publications from following electronic databases: PubMed, eLIBRARY, Google Scholar. As a result, the phenotypic features and genetic variability of the disease were considered and the main issues of diagnosis and treatment of patients with FD were discussed. The data presented will help the clinician to timely suspect the FD, conduct a full range of investigations and prescribe evidence-based lipid-lowering therapy.

Risk factors for the presence and development of Familial Dysbetalipoproteinemia in subjects from the general population with an APOE2E2 genotype

Background Subjects who carry one or two ɛ2 alleles of the APOE gene are protected from cardiovascular disease due to low LDL-cholesterol levels. However, 10–18% of ɛ2 homozygotes (ɛ2ɛ2) develop Familial Dysbetalipoproteinemia (FD), which is characterized by extensive remnant lipoprotein accumulation, making it a good model to study the effect of remnants on atherosclerosis and cardiovascular disease. Important causal factors for FD, or an “FD like phenotype” in ɛ2 heterozygotes (ɛ2ɛ3), are thought to be adiposity and insulin resistance. However, to date this relation was only evaluated in cross-sectional studies. Purpose To evaluate the cross-sectional and longitudinal association of adiposity and insulin resistance on the presence and development of FD in ɛ2ɛ2 or an “FD-like” phenotype in ɛ2ɛ3 subjects. Methods For this study we included 18042 subjects with an APOE measurement from two Dutch population-based cohorts; the PREVEND cohort (follow-up 4.1 (interquartile range (IQR) 4.0–4.4) years) and the Rotterdam Study (follow-up 10.1 (IQR 5.6–10.8) years). Subjects with an ɛ3ɛ3 genotype (n=10391) and ɛ4 carriers were excluded (n=5265). FD and “FD like” phenotype were defined as triglyceride levels >3 mmol/l or use of lipid lowering medication. Logistic regression models were used to evaluate the effect of age, sex, BMI, waist circumference, type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) on FD lipid phenotype. Changes in adiposity measures and insulin resistance between baseline and follow-up were compared in subjects with and without development of FD at follow-up. Results In total, 2386 subjects were included of whom 118 participants had ɛ2ɛ2 and 2268 had ɛ2ɛ3 of whom 68% completed a follow-up visit. Subjects mean age was 59±14 years and 44% were male. In ɛ2ɛ2 subjects, 19% (n=23) had FD at baseline and 16% (n=11) developed FD during follow-up. In ɛ2ɛ3 subjects 13% (n=305) had an “FD like” phenotype at baseline and 11% (n=146) at follow-up. Cross-sectional determinants for the presence of an FD or “FD like” phenotype at baseline were male sex, BMI, waist circumference and non-lipid MetS criteria. In ɛ2ɛ2 subjects who developed FD during follow-up, markers of adiposity and insulin resistance did not change compared to baseline. However, these FD patients more often had adiposity (BMI, weight and waist circumference) and T2DM at baseline, compared to those and who did not developed FD. Conclusions These results show for the first time that adiposity and insulin resistance are important risk markers for future development of FD or “FD like” phenotype in ɛ2ɛ2- and ɛ2ɛ3 subjects. The increased susceptibility of ɛ2 carriers for development of an FD lipid phenotype by adiposity and insulin resistance might be due to impaired remnant clearance consequent to decreased binding affinity of APOɛ2 to the LDL-receptor in combination with degradation of the heparan sulfate receptor by insulin resistance (mediated by sulfatase 2 activation). Odds Ratios for FD lipid phenotype Funding Acknowledgement Type of funding source: Public hospital(s). Main funding source(s): UMC Utrecht; Erasmus MC; UMC Groningen

Severe Combined Dyslipidemia With a Complex Genetic Basis

Background. Familial dysbetalipoproteinemia (also known as type 3 hyperlipoproteinemia) is typically associated with homozygosity for the apolipoprotein E2 isoform, but also sometimes with dominant rare missense variants in the APOE gene. Patients present with roughly equimolar elevations of cholesterol and triglyceride (TG) due to pathologic accumulation of remnant lipoprotein particles. Clinical features include tuberoeruptive xanthomas, palmar xanthomas, and premature vascular disease. Case. A 48-year-old male presented with severe combined dyslipidemia: total cholesterol and TG were 11.5 and 21.4 mmol/L, respectively. He had dyslipidemia since his early 20s, with tuberous xanthomas on his elbows and knees. His body mass index was 42 kg/m2. He also had treated hypertension, mild renal impairment, and a history of gout. He had no history of cardiovascular disease, peripheral arterial disease, or pancreatitis. Multiple medications had been advised including rosuvastatin, ezetimibe, fenofibrate, and alirocumab, but his lipid levels were never adequately controlled. Genetic Analysis. Targeted next-generation sequencing identified (1) the APOE E2/E2 homozygous genotype classically described with familial dysbetalipoproteinemia; (2) in addition, one APOE E2 allele contained the rare heterozygous missense variant p.G145D, previously termed apo E-Bethesda; (3) a rare heterozygous APOC2 nonsense variant p.Q92X; and (4) a high polygenic risk score for TG levels (16 out of 28 TG-raising alleles) at the 82nd percentile for age and sex. Conclusion. The multiple genetic “hits” on top of the classical APOE E2/E2 genotype likely explain the more severe dyslipidemia and refractory clinical phenotype.