Genetics of Familial Combined Hyperlipidemia (FCHL) Disorder: An Update.

Familial combined hyperlipidemia (FCHL) is one of the most common familial lipoprotein disorders of the lipoproteins, with a prevalence of 0.5% to 2% in different populations. About 10% of these patients suffer from cardiovascular disease and this number is increased by up to 11.3% in the young survivors of myocardial infarction and by 40% among all the survivors of myocardial infarction. Although initially thought to be that FCHL has an inheritance pattern of monogenic, the disease's etiology is still not fully understood and it appears that FCHL has a complex pattern related to genetic variants, environmental factors, and lifestyles. Two strategies have been used to identify its complex genetic background: candidate gene and the linkage approach, which have yielded an extensive list of genes associated with FCHL with a variable degree of scientific evidence. Until now, more than 30 different genetic variants have been identified related to FCHL. In this study, we aimed to review the individual genes that have been described in FCHL and how these genes and variants can be related to the current concept of metabolic pathways resulting in familial combined hyperlipidemia.

Familial Hypercholesterolemia, Familial Combined Hyperlipidemia, and Elevated Lipoprotein(a) in Patients With Premature Coronary Artery Disease.

BACKGROUND: Familial hypercholesterolemia (FH), familial combined hyperlipidemia (FCHL), and elevated lipoprotein (a) (Lp[a]) increase risk of premature coronary artery disease (CAD). The objective of this study was to assess the prevalence of FH, FCHL, elevated Lp(a) and their impact on management in patients with premature CAD. METHODS: We prospectively recruited men ≤ 50 years and women ≤ 55 with obstructive CAD. FH was defined as Dutch Lipid Clinic Network scores ≥ 6. FCHL was defined as apolipoprotein B > 1.2 g/L, triglyceride and total cholesterol > 90th population percentile, and family history of premature cardiovascular disease. Lp(a) ≥ 50 mg/dL was considered to be elevated. RESULTS: Among 263 participants, 9.1% met criteria for FH, 12.5% for FCHL, and 19.4% had elevated Lp(a). Among patients with FH, 37.5% had FH-causing DNA variants. Patients with FH, but not other dyslipidemias, were more likely than nondyslipidemic patients to have received lipid-lowering therapy before presenting with CAD (33.3% vs 12.3%, P = 0.04) and combined lipid-lowering therapy after the presentation (41.7% vs 7.7%, P < 0.001). One year after presentation, 58.3%, 54.5%, and 58.8% of patients with FH, FCHL, and elevated Lp(a) had low-density lipoprotein cholesterol (LDL-C) < 1.8 mmol/L, respectively, compared with 68.0 % in reference group. Patients with FCHL were more likely to have non-high-density lipoprotein (HDL) and apolipoprotein B above recommended lipid goals (70.0% and 87.9%, respectively). CONCLUSIONS: FH, FCHL, and elevated Lp(a) are common in patients with premature CAD and have differing impact on treatment and achievement of lipid targets. Assessment for these conditions in patients with premature CAD provides valuable information for individualized management.

Incidence of type 2 diabetes in familial combined hyperlipidemia.

OBJECTIVE: Familial combined hyperlipidemia (FCHL) is common among survivors of a premature myocardial infarction. FCHL patients are characterized by visceral obesity, fatty liver, and insulin resistance. The aim of the present study was to determine the incidence and determinants of type 2 diabetes (T2D) in a longitudinal cohort of FCHL pedigrees. RESEARCH DESIGN AND METHODS: FCHL patients, their unaffected relatives and spouses included in our baseline cohort in 1998-2005 (n=596) were re-invited to determine the incidence of self-reported T2D (that was confirmed by medical records), used as the primary outcome measure. The Fatty Liver Index (FLI) and Homeostasis Model Assessment Insulin Resistance (HOMA2-IR) were used as markers of fatty liver and insulin resistance, respectively. A subset of the original cohort underwent ultrasound of the liver, and subcutaneous and visceral fat in 2002-2005 (n=275; 'ultrasound subcohort'). RESULTS: Follow-up data (median: 15 years) was acquired for 76%. The incidence rate of T2D was significantly higher in FCHL patients compared with spouses (19.2 per 1000 person-years vs 2.8 per 1000 person-years; HR : 6.3, 95% CI: 2.4 to 16.8), whereas no differences were observed between unaffected relatives and spouses (HR: 0.9, 95% CI: 0.3 to 2.6). Cox's proportional hazard regression analyses showed that baseline HOMA2-IR and FLI≥60, but not waist circumference, BMI, or the FCHL affected state, were independently associated with incident T2D. Similar results were obtained in the ultrasound subcohort (median follow-up: 11 years), in which baseline HOMA2-IR and fatty liver (assessed by ultrasound) were independently associated with incident T2D. CONCLUSION: This study further corroborates the suggestion that the liver plays a central role in the pathogenesis of cardiometabolic complications in FCHL. It supports periodical screening for T2D in this high-risk population.

Incidence of cardiovascular disease in familial combined hyperlipidemia: A 15-year follow-up study.

BACKGROUND AND AIMS: Familial combined hyperlipidemia (FCHL) is a complex dyslipidemia associated with premature cardiovascular disease (CVD). The present study was conducted to 1) determine the incidence of CVD in FCHL in this era of protocolled, primary prevention; and 2) examine whether cardiovascular risk estimation based on the Systemic Coronary Risk Estimation (SCORE) chart, as proposed in the 2016 ESC/EAS guidelines for the management of dyslipidemia, is justified in FCHL. METHODS: FCHL patients, their normolipidemic (NL) relatives and spouses originally included in our baseline cohort in 1998-2005 (n = 596) were invited for a follow-up visit to determine the incidence of CVD, defined as (non-)fatal coronary artery disease, ischemic stroke and peripheral artery disease requiring invasive treatment. RESULTS: Follow-up data (median: 15 years) was acquired for 85% of the original cohort. The cumulative incidence of CVD was significantly higher in FCHL patients than in spouses (23.6% versus 4.7%; hazard ratio (HR): 5.4, 95%CI: 2.0-14.6; HR after adjustment for risk factors included in SCORE: 4.7, 95%CI: 1.6-13.8), but not in NL relatives compared to spouses (5.8% versus 4.7%). The SCORE chart tended to overestimate CVD risk in the spouses (observed [O]/expected [E] ratio:0.2, p = 0.01), but not in FCHL patients (O/E:1.3, p = 0.50). CONCLUSIONS: Risk of primary CVD is still substantially increased in FCHL patients, despite preventive measures. The overestimation of CVD risk by the SCORE chart - a nowadays frequently observed phenomenon thanks to improved primary prevention - was not seen in FCHL. These results suggest that more aggressive treatment is justified to avoid excessive CVD in FCHL.

Molecular mechanisms, prevalence, and molecular methods for familial combined hyperlipidemia disease: A review.

Familial combined hyperlipidemia (FCHL) is the most common genetic dyslipidemia disorder which is accompanied by increasing of triglyceride and cholesterol. This disorder is a complex genetic disease although it also has monogenic forms. The familial form has several criteria for diagnosis that can be distinguished of nonfamilial position. It has been shown that a variety of internal and external risk factors are involved in the pathogenesis of FCHL. Environmental factors and the genetic background also play an important role in the FCHL pathogenesis. Many mechanisms and pathways are involved in lipid metabolism (ie, dysfunctional adipose tissue, hepatic fat and very low-density lipoprotein overproduction, triglyceride-rich lipoproteins, and clearance of low-density lipoprotein particles) that could lead to FCHL. Individuals with a positive family history like those who have a positive family history of cardiovascular diseases are more predispositions for this disorder. To date several methods have been used to identify the genetic background of the FCHL. In the current review, we summarized the prevalence and the molecular mechanisms involved in the FCHL disease. Moreover, we highlighted the used molecular methods for determining the genes involved in the FCHL.

Familial combined hyperlipidemia and hyperlipoprotein(a) as phenotypic mimics of familial hypercholesterolemia: Frequencies, associations and predictions.

BACKGROUND: A significant proportion of index cases presenting with phenotypic familial hypercholesterolemia (FH) are not found to have a pathogenic mutation and may have other inherited conditions. OBJECTIVES: Familial combined hyperlipidemia (FCHL) and elevated lipoprotein(a) [Lp(a)] may mimic FH, but the frequency and correlates of these disorders among mutation-negative FH patients have yet to be established. METHODS: The frequency of FCHL and elevated Lp(a) was investigated in 206 FH mutation-negative index cases attending a specialist lipid clinic. An FCHL diagnostic nomogram was applied to each index case; a positive diagnosis was made in patients with a probability score exceeding 90%. Plasma Lp(a) concentration was measured by immunoassay, with an elevated level defined as ≥0.5 g/L. Clinical characteristics, including coronary artery disease (CAD) events, were compared between those with and without FCHL and hyper-Lp(a). RESULTS: Of mutation-negative FH patients, 51.9% had probable FCHL. These patients were older (P = .002), had a higher BMI (P = .019) and systolic (P = .001) and diastolic blood pressures (P = .001) compared with those without FCHL. Elevated Lp(a) was observed in 44.7% of cases, and there were no significant differences in clinical characteristics with Lp(a) status. The presence of elevated Lp(a) (P = .002), but not FCHL, predicted CAD events. This association was independent of established CAD risk factors (P = .032). CONCLUSION: FCHL and elevated Lp(a) are common disorders in patients with mutation-negative FH. Among such patients, FCHL co-expresses with components of the metabolic syndrome, and elevated Lp(a) is the major contributor to increased CAD risk.

Clinical experience of scoring criteria for Familial Hypercholesterolaemia (FH) genetic testing in Wales.

BACKGROUND/OBJECTIVE: Familial Hypercholesterolaemia (FH) is caused by mutations in genes of the Low Density Lipoprotein (LDL) receptor pathway. A definitive diagnosis of FH can be made by the demonstration of a pathogenic mutation. The Wales FH service has developed scoring criteria to guide selection of patients for DNA testing, for those referred to clinics with hypercholesterolaemia. The criteria are based on a modification of the Dutch Lipid Clinic scoring criteria and utilise a combination of lipid values, physical signs, personal and family history of premature cardiovascular disease. They are intended to provide clinical guidance and enable resources to be targeted in a cost effective manner. METHODS: 623 patients who presented to lipid clinics across Wales had DNA testing following application of these criteria. RESULTS: The proportion of patients with a pathogenic mutation ranged from 4% in those scoring 5 or less up to 85% in those scoring 15 or more. LDL-cholesterol was the strongest discriminatory factor. Scores gained from physical signs, family history, coronary heart disease, and triglycerides also showed a gradient in mutation pick-up rate according to the score. CONCLUSION: These criteria provide a useful tool to guide selection of patients for DNA testing when applied by health professionals who have clinical experience of FH.

Factors associated with postprandial lipemia and apolipoprotein A-V levels in individuals with familial combined hyperlipidemia.

BACKGROUND: Alterations in postprandial metabolism have been described in familial combined hyperlipidemia (FCH); however, their underlying mechanisms are not well characterized. We aimed to identify factors related to the magnitude of postprandial lipemia and apolipoprotein (apo) A-V levels in subjects with FCH. METHODS: FCH cases (n = 99) were studied using a standardized meal test. Abdominal obesity was assessed using the waist to hip ratio (WHR). A linear regression model was performed to investigate the variables associated with the triglycerides incremental area under the curve (iAUC). Independent associations between metabolic variables and apo A-V iAUC were also investigated in a randomly selected subgroup (n = 44). The study sample was classified according to the presence of fasting hypertriglyceridemia (≥150 mg/dL) and abdominal obesity (WHR ≥0.92 in men and ≥0.85 in women) to explore differences in parameters. RESULTS: The fasting apo B-48 levels (r = 0.404), and the WHR (r = 0.359) were independent factors contributing to the triglycerides iAUC (r2 = 0.29, P < 0.001). The triglycerides iAUC was independently associated with the apo A-V iAUC (r2 = 0.54, P < 0.01). Patients with both hypertriglyceridemia and abdominal obesity showed the most robust triglycerides and apo A-V postprandial responses. CONCLUSIONS: In patients with FCH the fasting apo B-48 level is the main factor associated with postprandial lipemia. Abdominal obesity also contributes to the magnitude of the postprandial response.The triglycerides postprandial increment is the principal factor associated with the apo A-V postprandial response.

Hiperlipidemia familiar combinada: documento de consenso / Familial combined hyperlipidemia: consensus document

La hiperlipidemia familiar combinada (HFC) es un trastorno muy frecuente asociado a enfermedad coronaria prematura. Se transmite de forma autosómica dominante, aunque no existe un gen único asociado al trastorno. El diagnóstico se realiza mediante criterios clínicos, y son importantes la variabilidad del fenotipo lipídico y la historia familiar de hiperlipidemia. Es frecuente la asociación con diabetes mellitus tipo 2, hipertensión arterial y obesidad central. Los pacientes con HFC se consideran de riesgo cardiovascular alto y el objetivo terapéutico es un colesterol-LDL < 100 mg/dl, y < 70 mg/dl en presencia de enfermedad cardiovascular establecida o diabetes mellitus. Los pacientes con HFC requieren tratamiento con estatinas potentes y, a veces, tratamiento combinado. La identificación y el manejo de otros factores de riesgo cardiovascular, como la diabetes y la hipertensión, son fundamentales para reducir la carga de enfermedad cardiovascular. Este documento proporciona recomendaciones para el diagnóstico y el tratamiento integral de los pacientes con HFC especialmente dirigidas a médicos de atención primaria (AU)

Familial combined hyperlipidemia (FCH) is a frequent disorder associated with premature coronary artery disease. It is transmitted in an autosomal dominant manner, although there is not a unique gene involved. The diagnosis is performed using clinical criteria, and variability in lipid phenotype and family history of hyperlipidemia are necessaries. Frequently, the disorder is associated with type 2 diabetes mellitus, arterial hypertension and central obesity. Patients with FCH are considered as high cardiovascular risk and the lipid target is an LDL-cholesterol < 100 mg/dL, and < 70 mg/dL if cardiovascular disease or type 2 diabetes are present. Patients with FCH require lipid lowering treatment using potent statins and sometimes, combined lipid-lowering treatment. Identification and management of other cardiovascular risk factors as type 2 diabetes and hypertension are fundamental to reduce cardiovascular disease burden. This document gives recommendations for the diagnosis and global treatment of patients with FCH directed to specialists and general practitioners (AU)

The genetics of familial combined hyperlipidaemia.

Almost 40 years after the first description of familial combined hyperlipidaemia (FCHL) as a discrete entity, the genetic and metabolic basis of this prevalent disease has yet to be fully unveiled. In general, two strategies have been applied to elucidate its complex genetic background, the candidate-gene and the linkage approach, which have yielded an extensive list of genes associated with FCHL or its related traits, with a variable degree of scientific evidence. Some genes influence the FCHL phenotype in many pedigrees, whereas others are responsible for the affected state in only one kindred, thereby adding to the genetic and phenotypic heterogeneity of FCHL. This Review outlines the individual genes that have been described in FCHL and how these genes can be incorporated into the current concept of metabolic pathways resulting in FCHL: adipose tissue dysfunction, hepatic fat accumulation and overproduction, disturbed metabolism and delayed clearance of apolipoprotein-B-containing particles. Genes that affect metabolism and clearance of plasma lipoprotein particles have been most thoroughly studied. The adoption of new traits, in addition to the classic plasma lipid traits, could aid in the identification of new genes implicated in other pathways in FCHL. Moreover, systems genetic analysis, which integrates genetic polymorphisms with data on gene expression levels, lipidomics or metabolomics, will attribute functions to genetic variants in addition to revealing new genes.

Non-cholesterol sterols in different forms of primary hyperlipemias.

BACKGROUND AND AIMS: We investigated the behaviour of non-cholesterol sterols, surrogate markers of cholesterol absorption (campesterol and sitosterol) and synthesis (lathosterol), in primary hyperlipemias. METHODS AND RESULTS: We studied 53 patients with polygenic hypercholesterolemia (PH), 38 patients with familial combined hyperlipemia (FCH), and 19 age- and sex-matched healthy control subjects. In all participants, plasma sitosterol, campesterol and lathosterol were determined by gas chromatography coupled to mass spectrometry. To correct for the effect of plasma lipid levels, non-cholesterol sterol concentrations were adjusted for plasma cholesterol (10² µmol/mmol cholesterol). Patients with FCH were more frequently men, and had higher body mass index (BMI), fasting glucose, insulin and HOMA-IR. Lathosterol was higher in FCH than in pH or controls (p < 0.05). Campesterol was significantly lower in FCH (p < 0.05), while no differences were found between pH and controls. Sitosterol displayed higher values in pH compared to FCH (p < 0.001) and controls (p < 0.05). Spearman's rank correlations showed positive correlations of lathosterol with BMI, waist circumference, HOMA-IR, triglycerides, apoprotein B, and a negative one with HDL-cholesterol. Sitosterol had a negative correlation with BMI, waist circumference, HOMA-IR, triglycerides, and a positive one with HDL-cholesterol and apoprotein AI. Multivariate regression analyses showed that cholesterol absorption markers predicted higher HDL-cholesterol levels, while HOMA-IR was a negative predictor of sitosterol and BMI a positive predictor of lathosterol. CONCLUSIONS: Our findings suggest the occurrence of an increased cholesterol synthesis in FCH, and an increased cholesterol absorption in pH. Markers of cholesterol synthesis cluster with clinical and laboratory markers of obesity and insulin resistance.

Fibromuscular dysplasia as a cause of stroke in a 9-year-old girl.

Fibromuscular dysplasia is a rare, idiopathic and nonatheromatous disease. It is rarely encountered as a cause of stroke in children. We report a nine-year-old girl with stroke in whom extensive fibromuscular dysplasia of intracranial vessels was established. She also had familial combined hyperlipidemia as an additional risk factor. This case suggests that additional risk factors like hyperlipidemia in cases with fibromuscular dystrophy may facilitate the occurrence of stroke at early ages.

FABP4 plasma levels are increased in familial combined hyperlipidemia.

The lipid profile of familial combined hyperlipidemia (FCHL) shares some characteristics with atherogenic dyslipidemia seen in diabetes, metabolic syndrome, and obesity. Adipocyte fatty acid-binding protein 4 (FABP4) appears to be a determinant of atherogenic dyslipidemia. We examined relationships between FABP4 plasma concentrations, dyslipidemia, and metabolic variables in patients with FCHL. We studied 273 unrelated FCHL patients and 118 control subjects. FABP4 was higher in FCHL than controls, with mean levels of 21.8 (10.1) microg/l and 19.2 (9.2) microg/l, respectively (adjusted P= 0.012). In FCHL, FABP4 correlated to body mass index (BMI), waist circumference, insulin levels, and homeostasis model assessment (HOMA) index (all P< 0.05), but not to lipid levels, whereas in obese patients, FABP4 correlated to triglyceride levels (r = 0.303, P= 0.014) and very low density lipoprotein size (r = 0.502, P = 0.001), as determined by nuclear magnetic resonance. Associations of FABP4 with BMI and waist circumference, but not with insulin levels, persisted in this subgroup. Plasma FABP4 does not influence the lipid phenotype of FCHL. In a small subgroup of obese FCHL, FABP4 levels were associated with triglyceride-rich lipoproteins independent of insulin resistance. These results support a hyperlipidemic mechanism of FCHL different from similar metabolic conditions where fat mass is strongly related to FABP4 and hypertriglyceridemia.

Five-year incidence of type 2 diabetes mellitus in patients with familial combined hyperlipidaemia.

BACKGROUND: The current study was conducted to investigate whether patients with familial combined hyperlipidaemia (FCHL ) are predisposed to the development of type 2 diabetes mellitus (T2DM). METHODS: A cohort of 56 FCHL patients and 54 spouses was followed over time with a five-year interval. Diagnosis of T2DM was based on fasting glucose levels or use of antidiabetic medication. Baseline body mass index, waist circumference, blood pressure, use of antihypertensive and lipid-lowering medication, plasma cholesterol, triglycerides, apolipoprotein B, glucose, insulin and alanine aminontransferase (ALAT) levels were determined as potential predictors of new onset T2DM. RESULTS: Baseline prevalence of T2DM was 2% in spouses and 9% in FCHL patients, and 4 and 20%, respectively, after five-year follow-up. The incidence of T2DM was significantly higher in FCHL patients (2 vs 14%; OR 9.1; 95% CI 1.0 to 81.4; p=0.04; age and sex adjusted). Of all baseline variables, only plasma insulin levels (not glucose) significantly predicted the development of T2DM (p=0.04). CONCLUSION: The present study is the first to present incidence numbers of T2DM in FCHL and demonstrates that FCHL patients, as compared with healthy controls, are predisposed to the development of T2DM. This is - at least in part - accounted for by an increased insulin resistance.

Taq1B polymorphism of cholesteryl ester transfer protein (CETP) gene in primary combined hyperlipidaemia.

BACKGROUND & OBJECTIVE: Cholesteryl ester transfer protein (CETP) gene polymorphism is known to be associated with changes in lipid profiles. Primary hyperlipidaemia is considered to be a major risk factor for pancreatitis, atherosclerosis and coronary heart disease. We investigated the association of one common polymorphism in the CETP gene (Taq1B) with plasma lipid levels and CETP activity in Iranian subjects with and without primary combined hyperlipidaemia. METHODS: The study included 102 patients with primary combined hyperlipidaemia and 214 health individuals. Polymerase chain reaction and restriction fragment length polymorphisms were used for genotype detection. To determine the relationship between Taq1B polymorphism and lipid levels, lipids and CETP activity were measured in primary combined hyperlipidaemic and normolipidaemic subjects, with and without Taq1B polymorphism. RESULTS: Plasma CETP activity was significantly (P<0.001) higher in primary combined hyperlipidaemic individuals than in controls. Plasma HDL-C was higher in both groups, in the B(2)B(2) genotype than in the B(1)B(1) and B(1)B(2) genotypes, whereas the serum TG concentrations and CETP activity were lower in B(2)B(2) genotype compared with other genotypes (B(1)B(1) and B(1)B(2)). The genotype and allelic frequencies for this polymorphism differed significantly between hyperlipidaemic and nonmolipidaemic individuals (P<0.05). In both groups, CETP Taq 1B polymorphism (presence of B(2) allele) correlated significantly with HDL-cholesterol (HDL-C) (r=0.201 and r=0.452 in control and patient groups respectively) and CETP activity (r= -0.123 for controls and r= -0.192 for patients). INTERPRETATION & CONCLUSION: The results showed that Taq 1B polymorphism of CETP gene was associated with changes in lipids profile and plasma CETP activity in the selected population and might have a role in contributing to genetic risk of developing coronary artery disease.

Small and dense LDL in familial combined hyperlipidemia and N291S polymorphism of the lipoprotein lipase gene.

There is a predominance of small and dense LDL cholesterol particles in familial combined hyperlipidemia (FCH). The lipoprotein lipase gene could exert an influence in these circumstances.To study the relationship of pattern B LDL and lipids with N291S polymorphism of lipoprotein lipase (LPL) in FCH patients.Lipid profile, apolipoproteins, diameter of LDL and N291S polymorphism were determined in 93 patients with FCH and 286 individuals from the general population.FCH patients with N291S polymorphism showed a lower mean diameter of LDL. FCH patients with pattern B LDL showed higher concentrations of triglycerides, VLDLc, non-HDLc and apo B100 and lower levels of HDLc than those with pattern A. Of FCH patients with polymorphism 87.5% presented pattern B and 12.5% pattern A, while patients without polymorphism presented pattern A in 69.2% cases and pattern B in 30.8% cases, with differences being statistically significant (p < 0.004). The prevalence of this mutation in our FCH patients was 9.7%.The prevalence of N291S mutation in our FCH patients was similar to the 9.3% described in Dutch FCHL patients but clearly higher than the 2-5% described for other Caucasian populations. No polymorphism was found in our general population sample. FCH patients with phenotype B of LDL possessed an atherogenic lipid profile. The relationship between small and dense LDL and the presence of the N291S mutation may identify patients with high cardiovascular risk.

Familial combined hyperlipidaemia: under - defined and under - diagnosed?

Familial combined hyperlipidaemia (FCH) was identified in early genetic studies of populations as a dominant condition associated with mixed hyperlipidaemia and early onset coronary heart disease. Later studies extended the phenotype and noted that this genetic hyperlipidaemia was sensitive to environmental effects. This article reviews the definitions, animal models and genetics of FCH. In contrast to familial hypercholesterolaemia, which is caused by mutations in a limited number of affected genes, the genetics of FCH have remained obscure and very few definite candidate genes have been identified. A strong role for the apoA-I, A-IV, A-V, C-III cluster on chromosome 11 was identified early on and multiple associations have been found to hyperlipidaemia in this region and more strongly to adjacent sections of the chromosome. More recently quantitative trait mapping has identified a number of candidate genes including upstream transcription factor -1 (USF-1) on 1 q21 and CD-36 on chromosome 4. Of these the strongest evidence, based on 4 analyses, links the lipid components of FCH to intronic variants in the USF-1 gene on chromosome 1q21-23. Unfortunately USF-1 yet fails to show clear associations with diabetes and the metabolic syndrome which co-map to this region and are also associated with mixed hyperlipidaemia. Large scale validation of USF-1 variants in other populations is still awaited. It is likely that FCH is a heterogeneous condition, that is subject to wide-scale environmental confounding from common traits such as obesity and the metabolic syndrome, and that the resolution of its genetics is going to prove a severe challenge.

Paraoxonase (PON1) is associated with familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCH) is a common genetic lipid disorder of which the molecular basis still remains to be elucidated. Since the HDL-associated enzyme serum paraoxonase (PON1) is associated with variation in serum lipids and lipoproteins, we determined whether variation in PON1 also contributes to the FCH phenotype. The study population consisted of 32 well-defined families with FCH, including 103 FCH patients and 240 normolipidemic relatives (NLR). In addition to plasma lipids and lipoproteins we determined PON1 activity (arylesterase- and paraoxonase activity) as well as the common genetic variants -107C>T, 55L>M and 192Q>R in the PON1 gene. The arylesterase activity was significantly higher in FCH patients when compared to NLR (P<0.001). In the total population, the PON1 genetic variants associated with the highest arylesterase activity (-107CC and 55LL) also associated with higher levels of total cholesterol, apolipoprotein B, triglycerides and VLDL-cholesterol and decreased levels of HDL-cholesterol. In support, the combination of the -107CC with the 55LL genotype associated with a significant increased risk for FCH when compared to the -107TT/55MM genotype (odds ratio 5.0 (95% CI, 1.3-19.1, P=0.02)). In conclusion, in this population of subjects from well-defined families with FCH, PON1 is biochemically and genetically associated with FCH.