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.

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.

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%.

Association of seropositivity for Chlamydia pneumoniae and coronary artery disease in heterozygous familial hypercholesterolaemia

In patients with familial hypercholesterolaemia heterozygous for the North Karelia (Finland) mutation, the presence of unequivocal coronary heart disease was significantly associated with high titres of IgG and IgA antibodies to Chlamydia pneumoniae.

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.

A novel point mutation (Pro84-->Ser) of the low density lipoprotein receptor gene in a family with moderate hypercholesterolemia

To obtain insight into the possibility that genetic variation of the structure of the low density lipoprotein (LDL) receptor protein could result in subtle changes of serum cholesterol levels, we used single-strand conformation polymorphism (SSCP) to screen all 18 exons of the LDL receptor gene in a panel of subjects with moderate hypercholesterolemia. One novel mutation, replacing C to T at nucleotide 313 and predicted to cause a substitution of serine for proline at codon 84, was identified in a single proband. A convenient PCR assay based on the use of primer-introduced restriction fragment length polymorphism was set up for the detection of this mutation. However, the pathophysiologic significance of the Pro84-->Ser replacement remains to be clarified, as serum LDL cholesterol levels were not significantly higher in mutation carriers vs. non-carriers in the affected family, and no other proband was identified, on screening of DNA samples from 350 Finns. The Pro84-->Ser mutation represents the second single-amino acid change of the LDL receptor protein so far reported which is not associated with the clinical phenotype of familial hypercholesterolemia.

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.

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.

Molecular genetics of familial hypercholesterolaemia: common and rare mutations of the low density lipoprotein receptor gene

Mutations of the low density lipoprotein (LDL) receptor gene give rise to familial hypercholesterolaemia (FH), one of the most common single-gene diseases in the world. Approximately 150 different LDL receptor gene mutations have been reported until now and the list seems to be continuously growing. Although hampering molecular genetic diagnosis of FH, this wide variability at the DNA level provides a useful tool to population genetics and may ultimately lead to better understanding of the variation in disease manifestations from family to family. The Finns are among the few populations in which one or two mutant LDL receptor genes explain the majority of FH cases. Either of the two 'Finnish-type' LDL receptor gene deletions, FH-Helsinki or FH-North Karelia, is present in more than 60% of the Finnish FH patients; there are no reports on their existence in other ethnic groups. Assays for these mutations were shown to markedly complement clinical diagnosis of FH in Finland.

The familial hypercholesterolemia (FH)-North Karelia mutation of the low density lipoprotein receptor gene deletes seven nucleotides of exon 6 and is a common cause of FH in Finland

A mutation of the LDL receptor gene very common among Finnish patients with heterozygous familial hypercholesterolemia (FH) was identified. This mutation, designated as FH-North Karelia, deletes seven nucleotides from exon 6 of the LDL receptor gene, causes a translational frameshift, and is predicted to result in a truncated receptor protein. Only minute quantities of mRNA corresponding to the deleted gene were detected. Functional studies using cultured fibroblasts from the patients revealed that the FH-North Karelia gene is associated with a receptor-negative (or binding-defective) phenotype of FH. Carriers of the FH-North Karelia gene showed a typical xanthomatous form of FH, with mean serum total and LDL cholesterol levels of 12 and 10 mmol/liter, respectively. This mutation was found in 69 (34%) out of 201 nonrelated Finnish FH patients and was especially abundant (prevalence 79%) in patients from the eastern Finland. These results, combined with our earlier data on another LDL receptor gene deletion (FH-Helsinki), demonstrate that two "Finnish-type" mutant LDL receptor genes make up about two thirds of FH mutations in this country, reflecting a founder gene effect. This background provides good possibilities to examine whether genetic heterogeneity affects the clinical presentation or responsiveness to therapeutic interventions in FH.

Lathosterol and other noncholesterol sterols during treatment of hypercholesterolemia with lovastatin alone and with cholestyramine or guar gum

Sixty-two patients aged 19-64 years with primary hypercholesterolemia (mean level of total cholesterol, 10.8 mmol/l) were treated with 80 mg/day lovastatin (L) alone for 18 weeks and, after randomization to either L + 20 g/day guar gum (L + GG) or L + 16 g/day cholestyramine (L + C) treatments, for an additional 18 weeks. The total cholesterol level declined from baseline by 34% during L and by 44% and 48% during L + GG and L + C, respectively. In terms of micromoles per millimole of cholesterol, serum levels of the cholesterol synthesis precursors cholestenol, desmosterol, and lathosterol were decreased and those of the plant sterols campesterol and sitosterol were increased by treatment with L. The serum contents of cholesterol precursors were increased markedly after the combination of either GG or C with L, but the increase was greater after the addition of C (e.g., the lathosterol to cholesterol ratio was 51% versus 212% for L + GG and L + C, respectively; p less than 0.001). Thus, a higher rate of removal of bile acids by C than by GG reduced more effectively the low density lipoprotein cholesterol level but simultaneously stimulated cholesterol synthesis compensatorily to a higher level even under concurrent treatment with L. The serum sitosterol to cholesterol ratio declined by 13% during L + GG but increased by 49% during L + C compared with the value under L alone, suggesting different effects of GG and C on the metabolism of plant sterols.

Comparison between lovastatin and cholestyramine in the treatment of moderate to severe primary hypercholesterolaemia

120 patients (64 men, 56 women) aged 19-66 years with primary hypercholesterolaemia (mean serum total cholesterol 10.1 mmol/l, range 6.5-16.3 mmol/l) with normal or moderately raised concentrations of serum triglycerides were randomised after four weeks' diet and four weeks' diet+placebo phase either to cholestyramine (40 patients) or lovastatin (80 patients) treatments for the succeeding 12 weeks. The maximal daily doses were 24 g of cholestyramine and 80 mg of lovastatin. The baseline data of the treatment groups were comparable with the exception of HDL-cholesterol concentrations, which were lower in the lovastatin group. The mean reductions in total serum cholesterol concentrations were 24.3% for cholestyramine (P less than or equal to 0.01) and 33.4% for lovastatin (P less than or equal to 0.01) (P less than or equal to 0.01 between the treatment groups), in LDL-cholesterol 32.1% (P less than or equal to 0.01) and 40.7% (P less than or equal to 0.01) (P less than or equal to 0.05 between the treatment groups) and in apolipoprotein B 23.3% (P less than or equal to 0.01) and 33.3% (P less than or equal to 0.01) (P less than or equal to 0.01 between the treatment groups), respectively. Lovastatin was the only drug to reduce serum triglyceride concentrations, it did so by 26.0%. HDL-cholesterol increased by 7.7% (P = NS) when cholestyramine was taken and by 13.5% (P less than or equal to 0.05) with lovastatin (P = NS between the treatment groups). Apolipoprotein A1 remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence and geographical distribution of major LDL receptor gene rearrangements in Finland

In order to determine the prevalence of major rearrangements of the low density lipoprotein (LDL) receptor gene in Finland, DNA samples of 199 unrelated Finnish patients with the heterozygous form of familial hypercholesterolaemia (FH) were examined by Southern blot analysis. The FH-Helsinki mutation, characterized by a 9.5-kb deletion in the 3'-end of the LDL receptor gene, was found in 75 (38%) of the patients. The prevalence of this mutation ranged from 26-58% in different areas of Finland. A striking exception was the North Karelia region, where only one out of 26 (4%) FH patients was found to carry the FH-Helsinki allele. Two patients were found to carry other types of large nucleotide rearrangements of the LDL receptor gene. One mutation was a 7.5-kb deletion eliminating exons 7 to 10, and the other was a 13-kb deletion covering exons 11 to 16 of the LDL receptor gene. Serum lipoprotein levels were very similar in each category of mutation, i.e. in patients with the FH-Helsinki gene, those with the two other types of deletion, and the remaining patients with as yet unknown types of LDL receptor gene defects. These results show that, even in genetically uniform populations, FH may be heterogeneous at the DNA level. DNA techniques enable an unequivocal diagnosis for almost 40% of the Finnish patients with the heterozygous form of FH.

Combination therapy with lovastatin and guar gum versus lovastatin and cholestyramine in treatment of hypercholesterolemia

Sixty-two patients (34 men and 28 women) aged 19-64 years, half of whom had familial hypercholesterolemia, treated initially for 18 weeks with lovastatin alone were randomly allocated either to lovastatin (L) and cholestyramine (16 g/day) or lovastatin and guar gum (L + GG 20 g/day) treatment for 18 additional weeks to compare the hypocholesterolemic effects of these two combination therapies. The patients were selected for this study from a larger study of patients (n = 120) with severe hypercholesterolemia [serum total cholesterol (serum Chol) 6.5-16.3 mM before treatment], and only those patients in whom serum Chol after lovastatin alone (dose 80 mg/day) remained greater than or equal to 5.2 mM were eligible for evaluation of combination therapies. Serum Chol decreased from 10.6 +/- 1.6 to 5.9 +/- 1.3 mM (mean +/- SD) (p less than 0.001) and low-density lipoprotein cholesterol (LDL Chol) from 8.5 +/- 1.8 to 4.1 +/- 1 mM (p less than 0.001) in patients treated with L + GG (values before the beginning of lovastatin and at the end of the combination therapy). The respective changes were from 10.9 +/- 2.2 to 5.5 +/- 1.2 mM (p less than 0.001) and from 8.7 +/- 2.3 to 3.5 +/- 1.2 mM (p less than 0.001) in patients treated with lovastatin and cholestyramine (L + C). At the end of the study, both serum Chol (p less than 0.005) and LDL Chol (p less than 0.01) were significantly lower with L + C than with L + GG.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic polymorphism of the apolipoprotein B gene locus influences serum LDL cholesterol level in familial hypercholesterolemia

An XbaI restriction fragment length polymorphism (RFLP) within the coding region of the apolipoprotein B (apoB) gene has been found to be associated with serum cholesterol and triglyceride levels in several populations. Mutations in another genetic locus, the low density lipoprotein (LDL) receptor gene, give rise to familial hypercholesterolemia (FH), a disease characterized by hypercholesterolemia, tendon xanthomas and atherosclerosis. We determined the XbaI genotypes and serum lipoprotein levels of 120 unrelated patients with the heterozygous form of FH. A non-parametric analysis of variance showed a significant association between elevated serum total cholesterol concentration (P less than 0.05), serum LDL-cholesterol concentration (P less than 0.025) and the presence of the XbaI restriction site (X2 allele). Thus, patients homozygous for the presence of the XbaI restriction site (genotype X2X2, n = 28) had on average a 14% higher serum total cholesterol level and a 21% higher serum LDL-cholesterol level than those homozygous for the absence of this site (genotype X1X1, n = 29); patients heterozygous for the XbaI restriction site (genotype X1X2, n = 63) had intermediate serum total and LDL-cholesterol levels. No significant differences were seen in serum triglyceride or high-density lipoprotein (HDL)-cholesterol values between these patient groups. These data demonstrate that genetic polymorphism of the principal ligand for the LDL receptor, apoB, may contribute to serum cholesterol regulation, even in patients with grossly distorted cholesterol homeostasis.