Prevalence of familial hypercholesterolemia among young north Karelian patients with coronary heart disease: a study based on diagnosis by polymerase chain reaction

Genetic testing for familial hypercholesterolemia in a Finnish cohort of patients with premature coronary artery disease and elevated LDL-C levels

Background

Based on Finnish LDLR-founder variations, the prevalence of familial hypercholesterolemia (FH) in Finland is estimated to be at least 1:600. Patients with FH have increased risk of premature coronary artery disease (CAD) and thus the prevalence of FH is expected to be higher in this subgroup.

Objective

To assess the prevalence of monogenic FH in a Finnish cohort of patients with premature CAD and elevated low-density lipoprotein cholesterol (LDL-C) levels.

Methods

Among 28,295 patients undergoing angiography at Heart Hospital at Tampere University Hospital between 2007 and 2017, we identified 162 patients diagnosed with premature CAD (men aged <55 years and women aged <60 years) and history of high LDL-C (≥5 mmol/L) levels without secondary causes of hypercholesterolemia. Clinical probability of FH was estimated, and genetic testing of FH was carried out in 80 patients with informed consent.

Results

Of the 80 patients with premature CAD and history of high LDL-C levels, 70% were men; the age at diagnosis of CAD for male and female patients was 48 and 53 years, respectively. In total, 58 (73%) patients had probable (n = 54) or definite (n = 4) FH based on Dutch Lipid Clinic Network criteria. A pathogenic variant of FH was found in five (6%) patients. Prevalence of the genetically verified FH was 1:16. The FH variant was found in 75% of patients with definite FH.

Conclusions

The prevalence of genetically verified FH was 1:16 among patients with premature CAD and elevated LDL-C level, which is 38 times higher than the estimated prevalence of 1:600 in the general Finnish population.

Familial Hypercholesterolemia in Premature Acute Coronary Syndrome. Insights from CholeSTEMI Registry

Familial hypercholesterolemia (FH) is an underdiagnosed genetic inherited condition that may lead to premature coronary artery disease (CAD). FH has an estimated prevalence in the general population of about 1:313. However, its prevalence in patients with premature STEMI (ST-elevation myocardial infarction) has not been widely studied. This study aimed to evaluate the prevalence of FH in patients with premature STEMI. Cardiovascular risk factors, LDLc (low-density lipoprotein cholesterol) evolution, and differences between genders were also evaluated. Consecutive patients were referred for cardiac catheterization to our center due to STEMI suspicion in 2018. From the 80 patients with confirmed premature CAD (men < 55 and women < 60 years old with confirmed CAD), 56 (48 men and eight women) accepted to be NGS sequenced for the main FH genes. Clinical information and DLCN (Dutch Lipid Clinic Network) score were analyzed. Only one male patient had probable FH (6-7 points) and no one reached a clinically definite diagnosis. Genetic testing confirmed that the only patient with a DLCN score ≥6 has HF (1.8%). Smoking and high BMI the most frequent cardiovascular risk factors (>80%). Despite high doses of statins being expected to reduce LDLc levels at STEMI to current dyslipidemia guidelines LDL targets (<55 mg/dL), LDLc control levels were out of range. Although still 5.4 times higher than in general population, the prevalence of FH in premature CAD is still low (1.8%). To improve the genetic yield, genetic screening may be considered among patients with probable or definite FH according to clinical criteria. The classical cardiovascular risk factors prevalence far exceeds FH prevalence in patients with premature STEMI. LDLc control levels after STEMI were out range, despite intensive hypolipemiant treatment. These findings reinforce the need for more aggressive preventive strategies in the young and for intensive lipid-lowering therapy in secondary prevention.

Prevalence of Familial Hypercholesterolemia Among the General Population and Patients With Atherosclerotic Cardiovascular Disease

Background:

Contemporary studies suggest that familial hypercholesterolemia (FH) is more frequent than previously reported and increasingly recognized as affecting individuals of all ethnicities and across many regions of the world. Precise estimation of its global prevalence and prevalence across World Health Organization regions is needed to inform policies aiming at early detection and atherosclerotic cardiovascular disease (ASCVD) prevention. The present study aims to provide a comprehensive assessment and more reliable estimation of the prevalence of FH than hitherto possible in the general population (GP) and among patients with ASCVD.

Methods:

We performed a systematic review and meta-analysis including studies reporting on the prevalence of heterozygous FH in the GP or among those with ASCVD. Studies reporting gene founder effects and focused on homozygous FH were excluded. The search was conducted through Medline, Embase, Cochrane, and Global Health, without time or language restrictions. A random-effects model was applied to estimate the overall pooled prevalence of FH in the general and ASCVD populations separately and by World Health Organization regions.

Results:

From 3225 articles, 42 studies from the GP and 20 from populations with ASCVD were eligible, reporting on 7 297 363 individuals/24 636 cases of FH and 48 158 patients/2827 cases of FH, respectively. More than 60% of the studies were from Europe. Use of the Dutch Lipid Clinic Network criteria was the commonest diagnostic method. Within the GP, the overall pooled prevalence of FH was 1:311 (95% CI, 1:250–1:397; similar between children [1:364] and adults [1:303], P =0.60; across World Health Organization regions where data were available, P =0.29; and between population-based and electronic health records–based studies, P =0.82). Studies with ≤10 000 participants reported a higher prevalence (1:200–289) compared with larger cohorts (1:365–407; P <0.001). The pooled prevalence among those with ASCVD was 18-fold higher than in the GP (1:17 [95% CI, 1:12–1:24]), driven mainly by coronary artery disease (1:16; [95% CI, 1:12–1:23]). Between-study heterogeneity was large ( I 2 >95%). Tests assessing bias were nonsignificant ( P >0.3).

Conclusions:

With an overall prevalence of 1:311, FH is among the commonest genetic disorders in the GP, similarly present across different regions of the world, and is more frequent among those with ASCVD. The present results support the advocacy for the institution of public health policies, including screening programs, to identify FH early and to prevent its global burden.

The Prevalence of Elevated Lipoprotein(a) in Patients Presenting With Coronary Artery Disease

BACKGROUND

Elevated lipoprotein(a) (Lp(a)) is an inherited lipid disorder and an independent risk factor for cardiovascular (CV) disease. Although its prevalence in the general population has been well-documented, the prevalence of elevated Lp(a) in patients with clinical coronary artery disease (CAD) is less clear. In this study, we hypothesised that there is an over-representation of elevated Lp(a) in patients with early-onset CAD compared to the general population.

METHODS

Between 6 February and 8 June 2018, we screened consecutive patients aged ≤70 years who presented to the Austin Hospital with any of the following criteria: (1) acute coronary syndrome (ACS); (2) percutaneous coronary intervention (PCI); or (3) coronary artery bypass grafting (CABG). Whilst examining a range of different Lp(a) levels, a dichotomous elevated Lp(a) was defined as concentrations ≥0.5 g/L. Other CV risk factors were documented including hypertension, type 2 diabetes mellitus, and familial hypercholesterolaemia (FH) using the Dutch Lipid Clinic Network Criteria (DLCNC), also incorporating family history and clinical examination.

RESULTS

One hundred and fifty-eight (158) patients were screened; 63 (39.9%) were under 60 years of age. Overall, elevated Lp(a) ≥0.5 g/L was identified in 57 patients (36.1%). Of these, nine patients (15.8%) also had probable or definite FH. General population data was obtained from the Copenhagen General Population Study which studied 6,000 men and women and showed that the estimated prevalence of Lp(a) ≥0.5 g/L in the general population was 20%.

CONCLUSIONS

Elevated Lp(a) is more prevalent in patients with relatively early-onset CAD compared to the general population and may contribute to previously unappreciated residual cardiovascular risk. Patients who present with early-onset CAD, should be routinely screened for elevated Lp(a).

Prognostic value of exercise tolerance test for predicting cardiovascular disease in asymptomatic individuals with heterozygous familiar hypercholesterolemia

Heterozygous familiar hypercholesterolemia (hFH) is an autosomal dominant inherited dyslipidemia, associated with premature cardiovascular disease (CVD). Aim of the study was to define prognostic factors for cardiovascular events (CVE) in asymptomatic individuals with hFH. All participants with recent diagnosis of hFH were recruited from the outpatient lipid clinic from 1987 to 2016, without any previous clinical evidence of CVD. A detailed clinical evaluation and laboratory investigation was obtained. Exercise tolerance test (ETT) was performed until maximum exercise capacity was achieved, without evidence of ischemia. Primary endpoint of the study was the first CVE. Four hundred fifty one participants were followed up for 10 ± 8 years, with 68 recorded cases of CVD (15%). Cumulative incidence of CVD was 15%, 24% and 32% for the 3 decades, respectively. In univariate analysis, male gender (p = 0.016), progression of age (p < 0.001), menopause (p = 0.030), waist-hip ratio (p = 0.043) and increased levels of Lp(α) (p = 0.014) were significantly associated with increased CVD incidence; whereas, exercise capacity (p = 0.025), low variation of heart rate (HR) during all stages of ETT compared to resting state (p = 0.020), maximum systolic (p = 0.014) and diastolic (p < 0.001) blood pressure were inversely associated with CVD. In multi-adjusted analysis, male gender (p < 0.001), duration of ETT (p = 0.023), estimated HR (p = 0.029), variation of HR during ETT compared to resting state (p < 0.05) and maximum diastolic pressure (p = 0.044) were significantly associated with CVD. Parameters of ETT in asymptomatic individuals with hFH, without any evidence of ischemia, may predict CVD in these high-risk patients after decades of observation.

Prevalence of familial hypercholesterolemia in patients with premature myocardial infarction

Background

Familial hypercholesterolemia (FH) is a genetic cause of premature myocardial infarction (PMI). Early diagnosis of FH is critical for prognosis.

Hypothesis

To investigate the prevalence of FH among a cohort of Chinese patients with PMI using genetic testing, and to evaluate different diagnostic criteria.

Methods

A total of 225 consecutive PMI patients were recruited. Low‐density lipoprotein receptor (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin‐kexin type 9 (PCSK9) and low‐density lipoprotein receptor adaptor protein 1 (LDLRAP1) genes were detected by Sanger sequencing. FH was diagnosed using the Dutch Lipid Clinic Network (DLCN) criteria and modified DLCN criteria, respectively. The prevalence and clinical features of FH were analyzed.

Results

In all PMI patients, pathogenic mutations of LDLR, APOB, PCSK9 and LDLRAP1 genes were found in 10 of 225 patients. Among all mutations, four mutations (LDLR c.129G>C, LDLR c.1867A>T, LDLRAP1 c.65G>C, and LDLRAP1 c.274G>A) were newly discovered. The prevalence of FH diagnosed by genetic testing was 4.4%. The prevalence of definite/probable FH diagnosed by DLCN and modified DLCN criteria reached 8.0% and 23.6%, respectively, and the mutation rates were 33.3% and 12.2%, respectively. The low‐density lipo‐protein cholesterol (LDL‐C) levels in PMI patients with FH were far from goal attainment. Only one of the FH patients had LDL‐C <2.5 mmol/L, and none of them had LDL‐C <1.8 mmol/L.

Conclusions

The prevalence of FH among Chinese patients with PMI appeared relatively common. Underdiagnosis and undertreatment of FH are still a big problem, which should arouse a widespread concern.

Application of expanded genetic analysis in the diagnosis of familial hypercholesterolemia in patients with very early-onset coronary artery disease

Background

Patients with monogenic familial hypercholesterolemia (FH) have high risk for coronary artery disease (CAD). A recent FH Expert Panel suggested that FH was underdiagnosed and undertreated which needs early diagnosis. Moreover, the proportion of DNA-confirmed FH patients hospitalized with very early-onset (≤ 35 years) CAD remains uncertain.

Methods

One hundred and five patients with age ≤ 35 years and LDL-C ≥ 3.4 mmol/L were tested for 9 genes (LDLR, APOB, PCSK9, APOE, STAP1, LIPA, LDLRAP1, ABCG5/8). Dutch Lipid Clinic Network (DLCN) and Simon Broome (SB) criteria for FH were also performed.

Results

The prevalence of genetically confirmed FH was 38.1% (n = 40) in 105 patients. DLCN categorized 26.7% patients to probable and definite FH while SB identified 17.1% of patients with possible to definite FH. Twenty-five (62.5%) and seventeen (42.5%) patients with pathogenic mutations were undiagnosed according to SB and DLCN criteria. FH variant carriers, especially homozygotes, had significantly higher plasma LDL-C levels. The best LDL-C threshold for genetically confirmed FH was 4.56 mmol/L in the present study.

Conclusions

FH is really a common cause for very young CAD patients (≤ 35 years) with a 38.1% of causative mutations in China and best LDL-C threshold for predicting mutations was 4.56 mmol/L. The underdiagnostic rate of clinical criteria was around 42.5–62.5%, suggesting that the expanded genetic testing could indeed promote the diagnosis of FH.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1737-7) contains supplementary material, which is available to authorized users.

Lipid profile and long-term outcome in premature myocardial infarction

BACKGROUND

Premature myocardial infarction (≤40 years) represents a rare disease with a distinct risk factor profile and a lipid phenotype that is characterized by a predominance of elevated triglyceride-rich lipoproteins. So far high-density and low-density lipoproteins remain the primary targets for risk stratification and treatment evaluation in coronary artery disease, but this strategy might be insensitive in patients with premature myocardial infarction.

AIM

Aim of this study was to investigate the predictive value of different lipid fractions on long-term cardiovascular outcome in patients with premature myocardial infarction.

METHODS

We prospectively enrolled 102 consecutive AMI survivors (≤40 years) in this prospective multicentre study and investigated the influence of the familial combined hypercholesterolaemia phenotype and a corresponding multimarker panel of different lipid fractions on cardiovascular outcome.

RESULTS

Total cholesterol, non-HDL cholesterol, remnant cholesterol and Apo B lipoprotein were significantly higher in patients experiencing MACE as compared to those who did not. The familial combined hypercholesterolaemia phenotype was associated with an unfavourable cardiovascular outcome even after adjustment for potential cofounders (adjusted HR 3.04,95% CI, 1.26-7.34, P = 0.013). Remnant cholesterol revealed the strongest association with MACE (adj.HR 1.94, 95%CI. 1.30-2.99, P = 0.001). Interestingly LDL and HDL revealed no significant impact on cardiovascular outcome in this study cohort.

CONCLUSION

Non-HDL and remnant cholesterol are strongly associated with an unfavourable outcome in patients with premature myocardial infarction and might be the preferred treatment target for lipid-lowering therapy.

The cost-effectiveness of screening strategies for familial hypercholesterolaemia in Poland

BACKGROUND AND AIMS

Familial hypercholesterolaemia (FH) elevates the cholesterol level and increases the risk of coronary events and death. Early detection and treatment reduce this risk. We aimed to determine the cost-effectiveness of FH screening in Poland in children, first job takers, and after an acute coronary syndrome (ACS) event, each followed by a cascade screening in the relatives of the positively-diagnosed subjects.

METHODS

A decision tree was constructed to model the diagnosis process. We considered scenarios with and without genetic testing. A life-time Markov was built to investigate the effectiveness (life years gained, LYG; and quality-adjusted life years, QALY) and cost (public payer perspective) of treatment in FH-affected subjects. The clinical benefits result from early treatment reducing the risk of coronary heart disease (and death, in result). Model parameters were based on published data and experts' opinions. The costs (patients visits, tests, drugs) were estimated from the National Health Fund data and other publicly-available sources.

RESULTS

Screening ACS patients below 55/65 years of age in men/women is the most cost-effective strategy: the cost of one LYG (QALY) amounts to 100 EUR (110 EUR). Removing the age limit or using genetic tests reduced cost-effectiveness; nonetheless, all strategies remained cost effective: the cost of one LYG or QALY was <5040 EUR, much lower than the official threshold of ca. 29,800 EUR/QALY.

CONCLUSIONS

Screening for FH is highly cost-effective in Poland. The strategies are complementary, and using a combination thereof is recommended.

Prevalence of DNA-confirmed familial hypercholesterolaemia in young patients with myocardial infarction

PURPOSE

To report the prevalence of DNA-confirmed Familial Hypercholesterolaemia (FH) in young patients with acute myocardial infarction, the relative contribution of smoking and diabetes and to compare these rates with those in the general population.

METHODS

A pilot clinical service was established to diagnose FH in young patients (≤50 years) with myocardial infarction at a London hospital. Over 23 months, 231 such patients, underwent testing for 48 common FH-mutations and whole exon LDLR gene deletions and duplications. Patients with total cholesterol levels ≥7.0 mmol/L, additionally, underwent full sequencing of the LDLR gene. Smoking and diabetes history were recorded. The prevalence of FH, smoking and diabetes were determined and compared with the prevalence in age and sex matched controls from published surveys.

RESULTS

The prevalence of DNA-confirmed FH was 1.3% (95% confidence interval 0.3%-3.8%) compared with 0.2% (0.17%-0.23%) in the general population (p=0.012). Observed prevalence rates for smoking and diabetes were 57% (50.3%-63.6%) and 13.4% (9.2%-18.6%) respectively in patients, compared with expected rates of 25% (23.9%-26.2%) and 4.6% (4.1%-5.2%) in the general population (p<0.001 for both comparisons).

CONCLUSION

FH is an important cause of premature myocardial infarction but it accounts for only a small proportion of all such events. The endemic risk factors, smoking and diabetes, far exceed FH in patients with acute myocardial infarction aged 50 or less. Consideration should be given to extending the use of statins and blood pressure drugs to a younger group of smokers and diabetics, who are excluded from treatment by conventional prevention strategies.

Subjects with molecularly defined familial hypercholesterolemia or familial defective apoB-100 are not being adequately treated

OBJECTIVES

To study whether subjects with a molecular genetic diagnosis of familial hypercholesterolemia (FH) or familial defective apoB-100 (FDB) are being adequately treated.

DESIGN

A questionnaire regarding medical history was sent to 2611 subjects who had been provided with a molecular genetic diagnosis of FH or FDB, and a blood sample was obtained for lipid measurements.

RESULTS

956 (36.6%) of the 2611 subjects participated. The mean age for starting lipid-lowering therapy was 33.4 (±12.1) years. Among those below 18 years of age, only 20.4% were on lipid-lowering drugs, whereas 89.1% of those aged 18 and above were on lipid-lowering drugs. The mean levels of total serum cholesterol and LDL-cholesterol were 5.7 (±1.5) mmol/l and 3.9 (±1.3) mmol/l, respectively. Among those who were on lipid-lowering drugs, 29.0% and 12.2% had levels of LDL cholesterol below 3.0 mmol/l and 2.6 mmol/l, respectively. Only 47.3% of the 956 subjects were considered as being adequately treated largely due to a failure to titrate their drug regimens. From the use of cholesterol-years score, lipid-lowering therapy must start before the age of 20 in order to prevent the subjects from contracting premature coronary heart disease.

CONCLUSION

The majority of FH/FDB subjects are being diagnosed late in life and are not being adequately treated. In order to prevent them from contracting premature coronary heart disease, it is key that levels of LDL cholesterol are normalized from a young age and that sufficient doses of lipid-lowering drugs are being used.

Non-high density lipoprotein cholesterol is the best discriminator of myocardial infarction in young individuals

BACKGROUND

Several studies have shown that non-high density lipoprotein (HDL) cholesterol is a strong and independent predictor of cardiovascular events. We investigated whether non-HDL cholesterol can discriminate young individuals with myocardial infarction (MI) from age- and sex-matched controls.

METHODS

We conducted a case-control study which included 100 consecutive patients who had survived their first MI before the age of 36 years and 100 age- and sex-matched healthy controls without a history of cardiovascular disease. Cardiovascular risk factors were reported and fasting lipids and apolipoproteins were measured.

RESULTS

Patients with premature MI had significantly higher levels of total cholesterol, low density lipoprotein cholesterol, triglycerides, apolipoprotein B, lipoprotein (a) and non-HDL cholesterol and significantly lower levels of HDL cholesterol and apolipoprotein A. Multivariate logistic regression analysis showed that for every 10mg/dl increase in non-HDL cholesterol levels, the odds of having a MI were increased by 34% after controlling for age, sex, body mass index, presence of hypertension, diabetes and smoking habits. Moreover, participants in the highest tertile of non-HDL cholesterol levels had 28-fold higher odds for having a MI (95% confidence interval, 7.5-104.1), compared to those in the lowest tertile. Finally, discriminant analysis showed that non-HDL cholesterol (lambda-Wilks=0.68) was the strongest discriminator for MI among all studied risk factors while smoking (lambda-Wilks=0.80) was the strongest discriminator for MI among the non-lipid risk factors.

CONCLUSIONS

Our study suggests that among conventional lipid and non-lipid risk factors non-HDL cholesterol is the best discriminator to predict the presence of MI in individuals under the age of 36 years.

Guidelines for the diagnosis and management of heterozygous familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a genetic disorder of lipoprotein metabolism characterized by very high plasma concentrations of low density lipoprotein cholesterol (LDLc), tendon xanthomas and increased risk of premature coronary heart disease (CHD). FH is a public health problem throughout the world. There are 10,000,000 people with FH worldwide, mainly heterozygotes, and approximately 85% of males and 50% of females with FH will suffer a coronary event before 65 years old if appropriate preventive efforts are not implemented. Early identification of persons with FH and their relatives, and the early start of treatment are essential issues in the prevention of premature cardiovascular disease (CVD) and death in this population. However, guidelines for the general population formally exclude FH from their diagnostic and treatment recommendations. These guidelines have been elaborated by a group of international experts with the intention to answer the main questions about heterozygous FH (heFH) subjects that physicians worldwide face in the diagnosis and management of these patients.

Squalene and noncholesterol sterols in serum and lipoproteins of children with and without familial hypercholesterolemia

Squalene and noncholesterol sterols, e.g. lathosterol and plant sterols, the respective markers of cholesterol synthesis and absorption, are transported with cholesterol in serum lipoproteins. Their concentrations and ratios to cholesterol in serum and lipoproteins have not been carefully compared, especially in children and in marked hypercholesterolemia. Thus, we measured these variables with gas-liquid chromatography in 18 children with and 29 without familial hypercholesterolemia, all aged 5-17 y. Concentrations of most noncholesterol sterols were higher in serum, LDL, and intermediate density lipoprotein in the children with than those without familial hypercholesterolemia. Despite accumulation of noncholesterol sterols mainly in LDL (75% in familial hypercholesterolemia and 55% in non-familial hypercholesterolemia, p < 0.001), their ratios were mostly similar in serum and lipoproteins of the two groups. The ratios of squalene and lathosterol were higher in VLDL and intermediate density lipoprotein, whereas in LDL that of lathosterol was lower than the respective serum values in both groups. Absorption marker sterol ratios were highest in HDL in both groups. Thus, even though the ratios of noncholesterol sterols to cholesterol in serum reflect, in general, synthesis and absorption of cholesterol, their ratios in different lipoproteins could give additional information of cholesterol metabolism.

Cholesterol metabolism in normal and heterozygous familial hypercholesterolemic newborns

In heterozygous familial hypercholesterolemia (FH), serum low-density lipoprotein (LDL) cholesterol levels are frequently increased in utero. A unique Finnish FH population, FH-North Karelia (FH-NK), has been identified, providing an excellent opportunity to study the diagnostic significance of cholesterol metabolism in FH. For that purpose, we investigated lipoprotein lipids, cholesterol precursors (squalene, methyl, and demethyl sterols), cholestanol, and plant sterols in FH-NK newborns (n = 5), non-FH siblings (n = 7), and controls (n = 20) at birth and after 1-year follow-up in 8 FH-NK and 5 non-FH children. The sum of concentrations (micrograms per deciliter) of methyl sterol (8-monomethylsterol, methostenol, 8-dimethylsterol, 8,24-dimethylsterol, and lanosterol) and squalene was higher in FH newborns than in non-FH siblings but overlapped with one control case. Cord-blood total or LDL cholesterol values could not be used for diagnostic purposes, whereas 1-year LDL cholesterol values were highly superior to those measured at birth. The methyl sterol ratio in cord blood was 29 to 193 10(2) mmol/mol cholesterol and was undetectable in serum at the age of 1 year; those of the demethyl precursor sterols were 1.5 to 8 times higher in cord blood than in serum at the age of 1 year, suggesting that cholesterol synthesis was markedly increased at birth. Plant sterols, not synthesized in human beings, were already present in serum of all the groups at birth, indicating their transfer, apparently with cholesterol, from mother to fetus. Babies born to FH mothers showed a greater tendency toward accelerated cholesterol synthesis than did those born to FH fathers. Despite signs of markedly high but similar synthesis of cholesterol at birth in FH and non-FH newborns, the diagnosis of FH was questionable by measurement of cholesterol precursors or LDL cholesterol in cord blood. The latter measurement, at the 1-year mark, is superior for diagnostic purposes.

A major gene effect on fasting insulin and insulin sensitivity in familial combined hyperlipidemia

The most common inherited dyslipidemia, familial combined hyperlipidemia (FCHL), is associated with insulin resistance. Whether insulin sensitivity in these families is inherited is not known. Therefore, we investigated the inheritance of insulin sensitivity in 352 nondiabetic family members from 37 families with FCHL, 105 of whom had undergone testing using the hyperinsulinemic-euglycemic clamp technique for the measurement of insulin sensitivity. First, complex segregation analysis of fasting insulin levels (both unadjusted and age-, age(2)-, and BMI-adjusted) was used for modeling of the variance in fasting insulin levels. In these analyses, Mendelian codominant inheritance (P = 0.320 for unadjusted and P = 0.295 for adjusted insulin values) was not rejected over the most general model and fit the data significantly better than the sporadic model (P < 0.001). Polygenic and environmental models were rejected (P < 0.001). The Mendelian codominant model explained 44 and 45% of the variance in unadjusted and adjusted fasting insulin levels, respectively. The proposed genotypes of this locus, based on segregation analysis, were associated with directly measured insulin sensitivity in 105 FCHL family members who underwent the hyperinsulinemic-euglycemic clamp (P < 0.001). These results provide evidence for a major gene regulating insulin sensitivity in FCHL families. Possible pleiotropic effects of this insulin sensitivity locus on dyslipidemias in FCHL remain to be elucidated.

Familial hypercholesterolaemia in Finland: common, rare and mild mutations of the LDL receptor and their clinical consequences. Finnish FH-group

Familial hypercholesterolaemia (FH) is an autosomal co-dominantly inherited condition resulting from mutations of the low-density lipoprotein (LDL) receptor which occur in heterozygous form in approximately one in 500 individuals. Clinically, FH is characterized by 2-3-fold elevation of serum LDL cholesterol levels, accelerated development of atherosclerotic vascular disease, and, if untreated, shortened lifespan. The Finnish population, which represents a genetic isolate, offers exceptional possibilities for genetic-epidemiological studies on FH, as a handful of founder gene mutations account for the majority of FH cases in Finland. This review summarizes data from our FH studies carried out since 1985. We wish to emphasize the continuum of genotype-phenotype relationships, the importance of molecular diagnosis, the detection of novel risk factors of vascular disease, and innovations inhibiting cholesterol absorption for the modern treatment of FH.

Cardiovascular risk factors associated with insulin resistance cluster in families with early-onset coronary heart disease

Coronary heart disease (CHD) is a multifactorial disease caused by environmental and genetic factors. CHD clusters in families, but it is not known whether susceptibility to early-onset CHD is associated with the clustering of cardiovascular risk factors. Therefore, we determined the levels of cardiovascular risk factors among siblings with and without severe early-onset CHD drawn from 101 Finnish families. Probands with CHD, compared with their siblings without CHD, had, respectively, higher 2-hour insulin levels (475.7 versus 331.8 pmol/L, P=0.011) and 2-hour insulin areas (796.2 versus 640.4 pmol/L per hour, P=0.031) in an oral glucose tolerance test, lower high density lipoprotein cholesterol levels (1.22 versus 1.42 mmol/L, P=0.001), higher total triglyceride levels (1.91 versus 1.68 mmol/L, P=0.018), higher very low density lipoprotein triglyceride levels (1.25 versus 1.06 mmol/L, P=0.011), and higher fibrinogen levels (3.8 versus 3.4 g/L, P= 0.008). No significant differences were found in cardiovascular risk factors between affected siblings and probands with CHD. Environmental or lifestyle factors did not differ between siblings with or without early-onset CHD. We conclude that cardiovascular risk factors associated with the insulin resistance syndrome (hyperinsulinemia, low high density lipoprotein cholesterol, high total and very low density lipoprotein triglycerides, and high fibrinogen) are likely to contribute indirectly to early-onset CHD.

The hormone sensitive lipase gene in familial combined hyperlipidemia and insulin resistance

BACKGROUND

Insulin resistance in the most common familial dyslipidemia, familial combined hyperlipidemia (FCHL), could be due to variations in the hormone sensitive lipase (HSL) gene.

MATERIALS AND METHODS

The coding region of the HSL gene was screened with the single strand conformation polymorphism analysis in probands of 27 FCHL families with 228 members. In addition, the C-60G promoter substitution of the HSL gene was determined by the restriction fragment length polymorphism analysis in these subjects.

RESULTS

No variants in the coding region of the HSL gene were found and the allele frequencies of the C-60G promoter substitution and the silent variant (G3138A) in the 3' untranslated region did not differ between 110 control subjects and 27 probands with FCHL. However, in control women the C-60G substitution was associated with high body mass index [30.6 +/- 0.9 kg m(-2) (mean +/- SD) in subjects with the C/G genotype and 24.8 +/- 4.6 in subjects with the C/C genotype, P = 0.012], and in control men with high rates of insulin-stimulated whole body glucose uptake (70.1 +/- 14.7 vs. 56.7 +/- 14.2 micromol kg(-1) min(-1), P = 0.014). In 228 FCHL family members this substitution was associated with high low-density lipoprotein cholesterol levels in men (4.51 +/- 1.12 vs. 5.17 +/- 1.28 mmol L(-1), P = 0.049), but not in women.

CONCLUSIONS

The HSL gene is not a major gene for FCHL. However, the - 60G allele of this gene may affect body weight, insulin sensitivity and serum cholesterol levels.

G-250A substitution in promoter of hepatic lipase gene is associated with dyslipidemia and insulin resistance in healthy control subjects and in members of families with familial combined hyperlipidemia

Low activity of hepatic lipase (HL) has been associated with high levels of triglycerides and high density lipoproteins, but the association of the HL promoter variants with insulin sensitivity has not been investigated. Therefore, in this study, the relationship of the G-250A promoter variant of the HL gene to the rates of insulin-stimulated glucose uptake measured by the hyperinsulinemic euglycemic clamp was investigated in 110 control subjects (82 men and 28 women, aged 50.7+/-7.6 [mean+/-SD] years, body mass index 26. 1+/-3.6 kg/m(2)) and in 105 first-degree relatives (65 men and 40 women, aged 47.8+/-16.0 years, body mass index 26.9+/-5.3 kg/m(2)) of 34 families with familial combined hyperlipidemia (FCHL). The A-250 allele of the HL promoter was associated with low rates of insulin-stimulated whole-body nonoxidative glucose disposal in control subjects (41.1+/-12.7 micromol. kg(-1). min(-1) in subjects with the G-250G genotype, 36.9+/-13.1 micromol. kg(-1). min(-1) in subjects with the G-250A genotype, and 29.9+/-13.5 micromol. kg(-1). min(-1) in subjects with the A-250A genotype; P=0.012 adjusted for age and sex) and with low rates of insulin-stimulated whole-body glucose oxidation in FCHL family members (16.7+/-4.2 versus 15.0+/-4. 4 versus 14.1+/-4.4 micromol. kg(-1). min(-1), P=0.024). In addition, the A-250 allele was associated with high levels of fasting insulin (P=0.047), very low density lipoprotein cholesterol (P=0.007), and total (P=0.009) and very low density lipoprotein (P=0.005) triglycerides in control subjects and with high levels of low density lipoprotein triglycerides (P=0.001) in FCHL family members (n=340). We conclude that the G-250A promoter variant of the HL gene is associated with dyslipidemia and insulin resistance. Mechanisms via which this polymorphism could affect insulin sensitivity remain to be elucidated.

Common founder mutation in the LDL receptor gene causing familial hypercholesterolaemia in the Icelandic population

Haplotype analysis in 18 apparently unrelated families with familial hypercholesterolaemia (FH) in Iceland has identified at least five different chromosomes cosegregating with hypercholesterolaemia. The most common haplotype was identified in 11 of the 18 families, indicating a responsible for FH in the Icelandic population. By using single-strand conformation polymorphism (SSCP) and direct sequencing of amplified DNA, we identified a novel mutation (a T to a C) in the second nucleotide in the 5' part of intron 4 in the LDL receptor gene. This mutation was present in approximately 60% of the FH families (10/18), supporting the prediction of a common founder. These families could be traced to a common ancestor in half of the cases by going back no further than the eighteenth century. The mutation was predicted to affect correct splicing of exon 4, and analysis at the cellular level demonstrated an abnormal mRNA containing intron 4 sequence in lymphoblastoid cells from a patient carrying this mutation. Translation of the mRNA would lead to a premature stop codon and a truncated nonfunctional protein of 285 amino acids. The novel sequence change created a new restriction site for the restriction endonuclease NlaIII, and using this assay, 29 unrelated individuals with possible FH attending a lipid clinic for treatment were examined for this mutation. Two individuals in this group of patients were found to be carriers of this mutation, supporting the suggestion of a founder mutation. Using this assay for the detection of FH in the Icelandic population should identify > 60% of these individuals.

Stanol ester margarine alone and with simvastatin lowers serum cholesterol in families with familial hypercholesterolemia caused by the FH-North Karelia mutation

In heterozygous familial hypercholesterolemia (FH), serum low density lipoprotein (LDL) cholesterol levels are already elevated at birth. Premature coronary heart disease occurs in approximately 30% of heterozygous untreated adult patients. Accordingly, to retard development of atherosclerosis, preventive measures for lowering cholesterol should be started even in childhood. To this end, 19 FH families consumed dietary stanol ester for 3 months. Stanol ester margarine lowers the serum cholesterol level by inhibiting cholesterol absorption. Each individual in the study replaced part of his or her daily dietary fat with 25 g of 80% rapeseed oil margarine containing stanol esters (2.24 g/d stanols, mainly sitostanol). The families who consumed this margarine for 12 weeks included 24 children, aged 3 to 13 years, with the North Karelia variant of FH (FH-NK), 4 FH-NK parents, and 16 healthy family members, and a separate group of 12 FH-NK adults who consumed the margarine for 6 weeks and who were on simvastatin therapy (20 or 40 mg/d). Fat-soluble vitamins were measured by high-pressure liquid chromatography, and cholesterol precursor sterols (indexes of cholesterol synthesis) and cholestanol and plant sterols (indexes of cholesterol absorption efficiency) were assayed by gas-liquid chromatography. No side effects occurred. Serum LDL cholesterol levels were reduced by 18% (P<0.001), 11%, 12% (P<0.001), and 20% (P<0.001) in the 4 groups, respectively. The serum campesterol-to-cholesterol ratios fell by 31% (P<0.001), 29%, 23% (P<0.001), and 36% (P<0.001), respectively, suggesting that cholesterol absorption efficiency was inhibited. Serum lathosterol ratios were elevated by 38% (P<0.001), 11%, 15% (P<0.001), and 19% (P<0.001), respectively, suggesting that cholesterol synthesis was compensatorily upregulated. The FH-NK children increased their serum lathosterol ratio more than did the FH-NK adults treated with stanol ester margarine and simvastatin (P<0.01). In the FH-NK children, serum retinol concentration and alpha-tocopherol-to-cholesterol ratios were unchanged by stanol ester margarine, but alpha- and beta-carotene concentrations and ratios were decreased. As assayed in a genetically defined population of FH patients, a dietary regimen with stanol ester margarine proved to be a safe and effective hypolipidemic treatment for children and adults. In FH-NK adults on simvastatin therapy, serum LDL cholesterol levels could be reduced even further by including a stanol ester margarine in the regimen.

Impaired free fatty acid suppression during hyperinsulinemia is a characteristic finding in familial combined hyperlipidemia, but insulin resistance is observed only in hypertriglyceridemic patients

Insulin resistance has been associated with hypertriglyceridemia, combined hyperlipidemia, and familial combined hyperlipidemia (FCHL). Whether all FCHL patients with different types of dyslipidemia have low insulin sensitivity has not been evaluated. We measured insulin sensitivity by the hyperinsulinemic euglycemic clamp with indirect calorimetry in 110 healthy controls and in 105 nondiabetic, FCHL family members: in 50 without dyslipidemia, in 19 with hypercholesterolemia (total cholesterol >/=7.7 mmol/L), in 22 with hypertriglyceridemia (total triglycerides >/=2.4 mmol/L in men 2.4 mmol/L in women), and in 14 with combined hyperlipidemia. During the hyperinsulinemic clamp, FCHL family members had higher free fatty acid levels than did controls (0.06+/-0.06 [mean+/-SD] in controls versus 0.16+/-0.11 in relatives without dyslipidemia versus 0.15+/-0. 07 in hypercholesterolemic patients versus 0.29+/-0.14 in hypertriglyceridemic patients versus 0.27+/-0.17 mmol/L in patients with combined hyperlipidemia; P<0.001 after adjustment for age, sex, and body mass index). Relatives without dyslipidemia (16.4+/-4.4 micromol. kg(-1). min(-1), P=0.001) and patients with hypertriglyceridemia (12.8+/-3.8 micromol. kg(-1). min(-1), P<0.001) and with combined hyperlipidemia (13.7+/-3.1 micromol. kg(-1). min(-1), P<0.001) had lower rates of insulin-stimulated glucose oxidation than did controls (19.4+/-4.7 micromol. kg(-1). min(-1)). Also, the rates of nonoxidative glucose disposal were lower in patients with hypertriglyceridemia (P=0.001) and combined hyperlipidemia (P=0.011) than in controls. In contrast, subjects with hypercholesterolemia and control subjects had similar rates of insulin-stimulated glucose uptake. We conclude that a defect in free fatty acid suppression during hyperinsulinemia, probably located in adipose tissue, is characteristic for all FCHL patients with varying types of dyslipidemia, whereas insulin resistance in skeletal muscle is observed only in FCHL patients with elevated triglyceride levels.

Post mortem molecularly defined familial hypercholesterolemia and sudden cardiac death of young men

Familial hypercholesterolemia (FH) is among the most common single-gene diseases and is due to mutations of the low-density lipoprotein (LDL) receptor gene. In heterozygous FH, serum LDL-cholesterol level is elevated two- to threefold compared to unaffected individuals, men in particular are prone to premature atherosclerosis and early cardiac deaths. However, very little data are available concerning the incidence of premature deaths in FH patients. In Finland two LDL receptor founder mutations cover two-thirds of FH cases, offering a unique possibility to study the potential role of FH in unexpected early cardiac deaths. We studied a total of 149 deceased who had suffered early (< or = 50 years) unexpected cardiac death due to coronary heart disease (CHD). Three individuals (2%) had molecularly defined heterozygous FH, and heterozygous FH was present in two (3%) of the 67 subjects who had demonstrable acute myocardial infarction (AMI). Considering that the two FH mutations cover two-thirds of FH cases in Finland, the overall prevalence of FH underlying early cardiac deaths caused by AMI may be estimated to be in the range 3 to 5%.

An overview of genetic factors influencing plasma lipid levels and coronary artery disease risk

BACKGROUND

Coronary artery disease (CAD) is a major cause of morbidity and mortality in most Western countries and its origin involves a significant genetic component.

METHODS

Genetic and epidemiologic studies have been performed to identify factors that influence the CAD risk in the population.

RESULTS

The primary loci that have been demonstrated to be associated with increased CAD risk owing to genetic mutations include the low-density lipoprotein receptor, apolipoprotein B-100, and lipoprotein(a). Additional implicated loci include lipoprotein lipase, apolipoprotein CII, cholesteryl ester transfer protein, apolipoprotein AI, and lecithin-cholesterol acyl transferase.

CONCLUSIONS

Numerous mutations in known genes exert a major effect on CAD risk in some patients. However, in most patients with CAD, the genetic component is believed to be attributable to the aggregate effect of loci that, individually, exert only a minor influence on lipoprotein levels.

Inheritance of two different alleles of the low-density lipoprotein (LDL)-receptor gene carrying the recurrent Pro664Leu mutation in a patient with homozygous familial hypercholesterolaemia

Familial hypercholesterolaemia (FH) is caused by mutations in the low-density lipoprotein (LDL)-receptor gene that result in impaired clearance of plasma LDL and increased risk of coronary heart disease. Numerous different mutations have been found in FH patients worldwide, the majority of which are infrequent in out-bred populations and account for 2% or less of patients with the disorder in large cohorts. Thus, it was surprising to find that two homozygous FH patients referred to a single hospital in the UK were both apparently homozygous for the Pro664Leu mutation. One, an Asian patient, was a true homozygote. The other, of English origin, had inherited two different alleles of the LDL-receptor gene with the same mutation from unrelated parents, as inferred from the haplotype of polymorphic markers. A third, clinically homozygous FH patient, despite being the offspring of first cousins, had inherited one 'Asian' Pro664Leu allele, but an allele with a 1-bp deletion in exon 5 from the other parent. The Pro664Leu mutation in the LDL-receptor gene has now been described in heterozygous patients of very different ethnic origin and is associated with different haplotypes, suggesting that the same base change at a CpG may have recurred as many as six times.

Fine mapping of low-density lipoprotein receptor gene by genetic linkage on chromosome 19p13.1-p13.3 and study of the founder effect of four French Canadian low-density lipoprotein receptor gene mutations

Familial hypercholesterolemia (FH) is one of the most common autosomal codominant diseases. FH is caused by mutations in the low-density lipoprotein receptor (LDLR) gene and is characterized by raised plasma LDL-cholesterol, tendon xanthomas, and premature coronary heart disease. The frequency of FH among French Canadians in northeastern Quebec is higher than in most other populations, 1:154 vs. 1:500 due to high prevalence of few recurrent mutations in the LDLR gene. In the French Canadian population, 11 mutations in the LDLR gene have been found to occur in geographically diverse areas and account for > 90% of cases. We have first constructed a high-resolution genetic map to locate several highly polymorphic markers close to LDLR locus, thus providing the necessary tools to study the origin of the four most common mutations which account for approximately 80% of our FH patients. We have then genotyped five markers (D19S413, D19S865, D19S221, D19S914, D19S586) in 102 heterozygotes (38 del > 15kb; 36 W66G; 16 C646Y; 12 E207K), two compound heterozygotes (del > 15kb/W66G; del > 15kb/C646Y) and seven homozygotes (three del > 15 kb; three W66G: one E207K) with FH unrelated to the first and second degree. We have found that patients bearing the same LDLR gene mutation carry a common haplotype at the LDLR locus although there is evidence for the early occurrence of a recombinational event between the LDLR and the D19S221 locus in the French Canadian patients bearing the W66G mutation. The fine mapping of LDLR gene close to several highly informative microsatellite markers provide fine mapping details of the LDLR region and additional tools for studies of association between plasma lipoprotein levels and LDLR gene.

Genetics of lipoprotein disorders

The study of lipoprotein metabolism has led to major breakthroughs in the fields of cellular physiology, molecular genetics, and protein chemistry. These advances in basic science are reflected in medicine in the form of improved diagnostic methods and better therapeutic tools. Perhaps the greatest benefit is the improved ability to identify at an early stage patients who are at high risk for atherosclerosis, providing clinicians the opportunity to proceed swiftly with intensive lipid-lowering therapy for the prevention of cardiovascular complications. Recent clinical trials have shown that such an approach is not only cost-effective but saves lives while improving the quality of life. They also emphasize the important role physicians can have in prevention. More than half of patients with premature CAD have a familial form of dyslipoproteinemia. This review of the genetics of atherogenic lipoprotein disorders underscores the importance of identifying major genetic defects. It also stresses the need to take into account multifactorial etiologies and clustering of risk factors, as well as gene-gene and gene-environment interactions in assessing the atherogenic potential of a lipid transport disorder. Table 2 summarizes the key points in the diagnosis, clinical implications, and treatment of the major inherited atherogenic dyslipidemias.

Relative contribution of low-density lipoprotein receptor and lipoprotein lipase gene mutations to angiographically assessed coronary artery disease among French Canadians

Men with low-density lipoprotein receptor gene mutations causing familial hypercholesterolemia (FH) are at high risk of premature coronary artery disease (CAD). The dyslipidemic state found among patients who are heterozygous for mutations in the lipoprotein lipase (LPL) gene may also increase the risk of CAD. In the present study, the association of the heterozygous forms of low-density lipoprotein receptor gene mutations causing FH as well as of LPL gene mutations causing (P207L and G188E) or not causing (D9N and N291S) complete loss of LPL activity with angiographically assessed CAD was estimated in a cohort of 412 French Canadian men aged <60 years who consecutively underwent coronary angiography for the investigation of retrosternal pain. The frequency of FH as well as of LPL gene mutations tended to increase with the number of narrowed coronary arteries. However, CAD occurred earlier in FH patients than in partly LPL-deficient patients. Indeed, the proportion of men affected by FH was of 16.4% in those <45 years of age, and solely 4.3% among those between 56 and 60 years of age (p <0.0001). In contrast, the LPL gene defect was found in only 4.0% of men aged <45 years, whereas this prevalence reached 8.3% among those aged 56 to 60 years. In multivariate analyses, the association of LPL with CAD was not independent of age, high-density lipoprotein cholesterol concentrations, and other covariates included at baseline, and was not affected by the type of mutation in the LPL gene. In contrast, FH was associated with CAD with minimal contribution of other cardiovascular risk factors. However, the relation between FH and CAD was at least partly dependent on plasma apolipoprotein B concentrations. In the different regression models, fasting insulin and plasma high-density lipoprotein cholesterol concentrations were important covariates of CAD, whether or not patients were affected by FH or LPL deficiency. In conclusion, the association of LPL gene mutations with CAD was delayed compared with FH, appeared to be markedly exacerbated by the presence of additional risk factors, and was not affected by the type of mutation in the LPL gene.

Neonatal diagnosis of familial hypercholesterolemia in newborns born to a parent with a molecularly defined heterozygous familial hypercholesterolemia

This study was designed to compare blood lipid levels in newborn individuals with molecularly defined heterozygous familial hypercholesterolemia [FH] to those in non-affected babies and to clarify the value of lipid determinations in assessment of diagnosis of FH at birth and 1 year of age. Twenty-five babies were born to 21 parents with DNA-documented heterozygous FH. Analysis of their cord blood samples revealed 11 newborns with the FH-North Karelia [FH-NK] mutation, 3 newborns with the FH-Helsinki [FH-HKI] mutation, and 11 nonaffected newborns. Cord serum total [TC] and LDL cholesterol [LDL-C] levels (mean +/- SD) in affected newborns (2.60 +/- 0.70 and 1.77 +/- 0.56, respectively) were significantly (P < .001) higher than those in nonaffected ones (1.54 +/- 0.23 and 0.78 +/- 0.15, respectively) and another cohort of 30 randomly selected control samples from apparently healthy newborns (1.84 +/- 0.46 and 1.03 +/- 0.30, respectively). However, there was overlapping of individual lipid levels in these three groups precluding the use of TC or LDL-C determinations in neonatal diagnosis of FH. In contrast, 1 year follow-up samples from 10 affected and 7 nonaffected individuals, as well as additional samples collected from another group of 8 affected and 9 nonaffected individuals, indicated that serum cholesterol levels showed much greater increment in children with FH. Thus, at the age of 1 year the mean serum TC and LDL-C levels in the affected infants (8.38 +/- 1.18 and 7.02 +/- 1.07, respectively) were much higher (P < .001) than the corresponding levels (4.40 +/- 0.66 and 2.89 +/- 0.68, respectively) in the nonaffected infants, and the individual ranges of TC and LDL-C levels were nonoverlapping in these two groups. Serum HDL cholesterol [HDL-C] levels in 1-year-old children with FH (0.95 +/- 0.14) were approximately 20% lower than those of their similar at birth. In conclusion, phenotypic expression of heterozygous FH, as defined by molecular analysis of genomic DNA, is evident in serum LDL-C (but not HDL-C) levels already at birth, but for diagnostic purposes blood lipid determinations carried out at the age of 1 year are highly superior to those performed at birth.

Familial hypercholesterolemia in the Finnish north Karelia. A molecular, clinical, and genealogical study

A specific mutation termed FH-North Karelia [FH-NK] accounts for almost 90% of familial hypercholesterolemia [FH] cases in the Finnish North Karelia, with a population of about 180,000. Extensive search for its presence in the entire North Karelia province revealed 340 carriers of this mutation. Other mutations of the LDL receptor [LDLR] gene accounted for 67 cases of heterozygous FH. This gives a minimum FH prevalence of 1 in 441 inhabitants in North Karelia, with the highest density of patients in the Polvijärvi commune (1 in 143 inhabitants). Old parish records, confirmation records, and tax records were used to track a common ancestor for most of the present-day North Karelian FH-NK patients in the village of Puso, located within an area where the FH prevalence today is the highest. DNA analysis indicated that 2% of the subjects aged 1 to 25 years would have been diagnosed as false-negative and 7% as false-positive FH patients on the basis of LDL cholesterol [LDL-C] determinations alone. Common genetic variations of apolipoprotein E [apoE], XbaI, polymorphism of apolipoprotein B [apoB], and PvuII polymorphism of the intact LDLR allele contributed little to serum lipid variation in established carriers of the FH-NK allele, although apoE2/4 genotype and the presence of the PvuII restriction site tended to be associated with relatively low LDL-C levels. Coronary heart disease (CHD) was present in 65 (30%) out of the 179 FH gene carriers aged > or = 25 years, and 19 individuals had a previous history of acute myocardial infarction (AMI). The average age (mean +/- SD) at onset of CHD was 42 +/- 7 years for males and 48 +/- 11 years for females (P < .05). In stepwise logistic regression analysis carried out in carriers of the FH-NK allele, age, gender, smoking, and apoE allele E2 all emerged as independent determinants of risk of CHD or AMI. It may be concluded that the relatively high prevalence of FH patients in North Karelia province provides a unique founder population in which genetic and nongenetic factors modifying the course of FH can be effectively investigated.

Minisequencing: a specific tool for DNA analysis and diagnostics on oligonucleotide arrays

We describe a method for multiplex detection of mutations in which the solid-phase minisequencing principle is applied to an oligonucleotide array format. The mutations are detected by extending immobilized primers that anneal to their template sequences immediately adjacent to the mutant nucleotide positions with single labeled dideoxynucleoside triphosphates using a DNA polymerase. The arrays were prepared by coupling one primer per mutation to be detected on a small glass area. Genomic fragments spanning nine disease mutations, which were selected as targets for the assay, were amplified in multiplex PCR reactions and used as templates for the minisequencing reactions on the primer array. The genotypes of homozygous and heterozygous genomic DNA samples were unequivocally defined at each analyzed nucleotide position by the highly specific primer extension reaction. In a comparison to hybridization with immobilized allele-specific probes in the same assay format, the power of discrimination between homozygous and heterozygous genotypes was one order of magnitude higher using the minisequencing method. Therefore, single-nucleotide primer extension is a promising principle for future high-throughput mutation detection and genotyping using high density DNA-chip technology.

Deletions of the low density lipoprotein receptor gene underlying familial hypercholesterolaemia: screening by polymerase chain reaction using pooled DNA and blood samples

We evaluated the feasibility of methods based on the polymerase chain reaction (PCR) and non-automated or automated gel electrophoresis to detect clinically important DNA deletions in pooled DNA and blood samples. Two common low density lipoprotein (LDL) receptor mutations causing familial hypercholesterolaemia (FH) in the Finnish population were easily identified in pools corresponding to 20 individuals. One of these mutations (FH-North Karelia) deletes seven nucleotides from exon 6 of the LDL receptor gene. PCR amplification of DNA samples from the heterozygous patients with the FH-North Karelia gene results in the formation of DNA heteroduplexes, which markedly improves mutation detection. These studies show the applicability of semi-automated PCR techniques in the screening of DNA deletions and demonstrate the clinical diagnostic usefulness of heteroduplex formation.

Differences in the phenotypic characteristics of subjects with familial defective apolipoprotein B-100 and familial hypercholesterolemia

Familial defective apolipoprotein B-100 (FDB) is a recently identified autosomal-dominantly inherited disorder caused by a point mutation in the apolipoprotein (apo) B gene. To determine whether the phenotypic characteristics in FDB subjects are similar to those in subjects with familial hypercholesterolemia (FH), 76 kindreds fulfilling the clinical criteria for heterozygous FH/FDB were characterized using molecular biological techniques. Allele-specific polymerase chain reaction (PCR) at the apoB locus was used for diagnosis or exclusion of FDB. PCR-based methods for detection of two point mutations (V408M and P664L) at the LDL receptor (LDLR) locus, cosegregation analysis using eight restriction fragment length polymorphisms (RFLPs) at the LDLR locus, or the exclusion of FDB confirmed the clinical diagnosis of FH. Three kindreds were not included because of a missing cosegregation between a particular haplotype and the FH phenotype. We predicted that a similar number of kindreds would be detected in the two groups, assuming comparable prevalences of the diseases in our population and similar phenotypic characteristics. However, only nine kindreds were identified with the FDB mutation compared with 64 kindreds with FH (P < .0001). From these 73 kindreds, 28 FDB heterozygotes and 129 FH heterozygotes were compared using multivariate analysis. There were no differences between these two groups with respect to age, sex, and apoE genotype distribution, lipoprotein(a) concentrations, body mass index, blood pressure, and smoking habits. However, FDB subjects demonstrated significantly lower concentrations of total cholesterol (8.1 versus 10.2 mmol/L, P < .001), LDL cholesterol (6.3 versus 8.2 mmol/L, P < .001), and triglycerides (1.3 versus 1.8 mmol/L, P = .025) and higher concentrations of HDL cholesterol (1.4 versus 1.2 mmol/L, P = .015) than subjects with FH. In contrast to FH, female FDB subjects tended to have higher concentrations of total cholesterol (8.9 versus 7.5 mmol/L, P = .032) and LDL cholesterol (7.1 versus 5.7 mmol/L, P = .026) than FDB males. The same results regarding total and LDL cholesterol and sex differences were observed when individual data of 238 FDB and 415 FH subjects from the literature were compared. In addition, FDB subjects showed much larger total cholesterol fluctuations than FH subjects (median of intraindividual coefficients of variation: FDB, 14.5%; FH, 5.3%; P < .001). In summary, these results demonstrate that FDB subjects tend to have a milder form of hyperlipoproteinemia than FH subjects and that only a part of the subjects with FDB fulfill the established criteria for identifying FH.

Heterozygous familial hypercholesterolaemia: the influence of the mutation type of the low-density-lipoprotein receptor gene and PvuII polymorphism of the normal allele on serum lipid levels and response to lovastatin treatment

OBJECTIVES

To study whether (i) the low-density-lipoprotein (LDL)-receptor gene mutation type itself or (ii) the PvuII restriction-fragment-length polymorphism (RFLP) of the intact LDL-receptor gene affects serum lipid levels and their responses to lovastatin treatment in heterozygous familial hypercholesterolaemia (FH).

DESIGN

Comparison of serum lipid levels in 149 heterozygous FH patients, including 79 patients with the FH Helsinki gene and 70 patients with the FH North Karelia gene, grouped according to the PvuII RFLP status of their nonmutated LDL-receptor allele; studies of lovastatin responses in 23 FH patients with different mutation types.

SUBJECTS

Molecularly defined heterozygous FH patients.

INTERVENTIONS

DNA analysis by polymerase chain-reaction assay (PCR) and Southern blotting, fasting serum lipid measurements in all patients, and administration of lovastatin 40-80 mg daily to 16 FH Helsinki patients and seven FH North Karelia patients.

MAIN OUTCOME MEASURES

Baseline and post-treatment serum cholesterol. LDL cholesterol, high-density-lipoprotein (HDL) cholesterol and triglyceride levels.

RESULTS

There were no significant differences in serum total or LDL-cholesterol levels in FH patients with the FH Helsinki gene compared with those carrying the FH North Karelia gene. Regardless of the mutation type, patients without the PvuII site in the normal LDL-receptor gene (P--subjects) tended to have 6-8% higher serum and LDL-cholesterol levels than patients possessing this restriction site (P+ subjects). Although not statistically significant, this difference is qualitatively and quantitatively similar to that reported in three different non-FH populations. Treatment with lovastatin brought about similar hypolipidaemic responses in FH patients with either mutation type (FH Helsinki or FH North Karelia) or PvuII RFLP status (P+ or P-).

CONCLUSIONS

Two LDL-receptor gene mutations with dissimilar phenotypic characteristics are associated with similar serum lipid levels and response to statin treatment. Our data also support the previous assumption that the PvuII RFLP of the LDL-receptor gene locus is associated with variation of serum cholesterol levels.