Decrease of Lp(a) during weight reduction in obese children is modified by the apo(a) kringle-IV copy number variation.

BACKGROUND: Lipoprotein(a) [Lp(a)] is considered an independent risk factor for cardiovascular disease. Its concentration is mainly determined by the kringle-IV repeat copy number variation (CNV) at the apolipoprotein(a) [apo(a)] locus. OBJECTIVE: We aimed to investigate the immediate effect of weight reduction on plasma Lp(a) levels and its dependency on the apo(a) CNV in obese children. DESIGN: We performed a prospective longitudinal intervention study of a low-fat hypocaloric diet conducted in a 3-week dietary camp for obese children. In all, 140 obese participants (54 boys and 86 girls) with a mean age of 12.5+/-1.6 years and a mean relative body mass index (BMI) before treatment of 165.6+/-24.7% were included. Body weight and plasma levels of Lp(a), lipids, apolipoproteins A-I and B, insulin, and C-reactive protein were determined before the onset and after the end of the intervention. In addition, the number of apo(a) kringle-IV repeats were determined using sodium dodecyl sulfate agarose gel electrophoresis. RESULTS: The mean loss of body weight was 5.0+/-1.3 kg (-6.6%), resulting in a mean decrease of the relative BMI of 6.6%. Blood chemistry revealed significant changes in all parameters, especially in Lp(a), with a decrease from 24.4+/-30.6 to 17.9+/-22.6 mg per 100 ml or -19% (P<0.001). The decrease of Lp(a) levels was higher in the group with low compared with high molecular weight apo(a) phenotypes (-23.9 vs -16.6%). CONCLUSIONS: Weight reduction in obese children is associated with significant changes in Lp(a) levels, especially in subjects with high pre-treatment Lp(a) concentrations. This effect is markedly influenced by the molecular phenotype at the copy-number variable apo(a) locus.

Sib-pair analysis detects elevated Lp(a) levels and large variation of Lp(a) concentration in subjects with familial defective ApoB.

Whether or not Lp(a) plasma levels are affected by the apoB R3500Q mutation, which causes Familial Defective apoB (FDB), is still a matter of debate. We have analyzed 300 family members of 13 unrelated Dutch index patients for the apoB mutation and the apolipoprotein(a) [apo(a)] genotype. Total cholesterol, LDL-cholesterol, and lipoprotein(a) [Lp(a)] concentrations were determined in 85 FDB heterozygotes and 106 non-FDB relatives. Mean LDL levels were significantly elevated in FDB subjects compared to non-FDB relatives (P < 0.001). Median Lp(a) levels were not different between FDB subjects and their non-FDB relatives. In contrast, sib-pair analysis demonstrated a significant effect of the FDB status on Lp(a) levels. In sib pairs identical by descent for apo(a) alleles but discordant for the FDB mutation (n = 11) each sib with FDB had a higher Lp(a) level than the corresponding non-FDB sib. Further, all possible sib pairs (n = 105) were grouped into three categories according to the absence/presence of the apoB R3500Q mutation in one or both subjects of a sib pair. The variability of differences in Lp(a) levels within the sib pairs increased with the number (0, 1, and 2) of FDB subjects present in the sib pair. This suggests that the FDB status increases Lp(a) level and variability, and that apoB may be a variability gene for Lp(a) levels in plasma.

A pentanucleotide repeat polymorphism in the 5' control region of the apolipoprotein(a) gene is associated with lipoprotein(a) plasma concentrations in Caucasians.

The enormous interindividual variation in the plasma concentrations of the atherogenic lipoprotein(a) [Lp(a)] is almost entirely controlled by the apo(a) locus on chromosome 6q26-q27. A variable number of transcribed kringle4 repeats (K4-VNTR) in the gene explains a large fraction of this variation, whereas the rest is presently unexplained. We here have analyzed the effect of the K4-VNTR and of a pentanucleotide repeat polymorphism (TTTTA)n (n = 6-11) in the 5' control region of the apo(a) gene on plasma Lp(a) levels in unrelated healthy Tyroleans (n = 130), Danes (n = 154), and Black South Africans (n = 112). The K4-VNTR had a significant effect on plasma Lp(a) levels in Caucasians and explained 41 and 45% of the variation in Lp(a) plasma concentration in Tyroleans and Danes, respectively. Both, the pentanucleotide repeat (PNR) allele frequencies and their effects on Lp(a) concentrations were heterogeneous among populations. A significant negative correlation between the number of pentanucleotide repeats and the plasma Lp(a) concentration was observed in Tyroleans and Danes. The effect of the 5' PNRP on plasma Lp(a) concentrations was independent from the K4-VNTR and explained from 10 to 14% of the variation in Lp(a) concentrations in Caucasians. No significant effect of the PNRP was present in Black Africans. This suggests allelic association between PNR alleles and sequences affecting Lp(a) levels in Caucasians. Thus, in Caucasians but not in Blacks, concentrations of the atherogenic Lp(a) particle are strongly associated with two repeat polymorphisms in the apo(a) gene.

Control of ribosomal protein L1 synthesis in mesophilic and thermophilic archaea.

The mechanisms for the control of ribosomal protein synthesis have been characterized in detail in Eukarya and in Bacteria. In Archaea, only the regulation of the MvaL1 operon (encoding ribosomal proteins MvaL1, MvaL10, and MvaL12) of the mesophilic Methanococcus vannielii has been extensively investigated. As in Bacteria, regulation takes place at the level of translation. The regulator protein MvaL1 binds preferentially to its binding site on the 23S rRNA, and, when in excess, binds to the regulatory target site on its mRNA and thus inhibits translation of all three cistrons of the operon. The regulatory binding site on the mRNA, a structural mimic of the respective binding site on the 23S rRNA, is located within the structural gene about 30 nucleotides downstream of the ATG start codon. MvaL1 blocks a step before or at the formation of the first peptide bond of MvaL1. Here we demonstrate that a similar regulatory mechanism exists in the thermophilic M. thermolithotrophicus and M. jannaschii. The L1 gene is cotranscribed together with the L10 and L11 gene, in all genera of the Euryarchaeota branch of the Archaea studied so far. A potential regulatory L1 binding site located within the structural gene, as in Methanococcus, was found in Methanobacterium thermoautotrophicum and in Pyrococcus horikoshii. In contrast, in Archaeoglobus fulgidus a typical L1 binding site is located in the untranslated leader of the L1 gene as described for the halophilic Archaea. In Sulfolobus, a member of the Crenarchaeota, the L1 gene is part of a long transcript (encoding SecE, NusG, L11, L1, L10, L12). A previously suggested regulatory L1 target site located within the L11 structural gene could not be confirmed as an L1 binding site.

Concentrations of the atherogenic Lp(a) are elevated in FH.

Lipoprotein(a) (Lp(a)) is a complex in human plasma assembled from low-density lipoprotein (LDL) and apolipoprotein(a) (apo(a)). High plasma concentrations of Lp(a) are a risk factor for coronary heart disease (CHD) in particular in patients with concomitant elevation of LDL. We have analysed for elevated Lp(a) levels in patients with familial hypercholesterolaemia (FH), a condition caused by mutations in the LDL receptor (LDLR) gene and characterised by high LDL, xanthomatosis and premature CHD. To avoid possible confusion by the apo(a) gene which is the major quantitative trait locus controlling Lp(a) in the population at large, we used a sib pair approach based on genotype information for both the LDLR and the apo(a) gene. We analysed 367 family members of 30 South African and 30 French Canadian index patients with FH for LDLR mutations and for apo(a) genotype. Three lines of evidence showed a significant effect of FH on Lp(a) levels: (1) Lp(a) values were significantly higher in FH individuals compared to non-FH relatives (p < 0.001), although the distribution of apo(a) alleles was not different in the two groups; (2) comparison of Lp(a) concentrations in 28 sib pairs, identical by descent (i.b.d.) at the apo(a) locus but non-identical for LDLR status, extracted from this large sample demonstrated significantly elevated Lp(a) concentrations in sibs with FH (p < 0.001); (3) single i.b.d. apo(a) alleles were associated with significantly higher Lp(a) concentrations (p < 0.0001) in FH than non-FH family members. Variability in associated Lp(a) levels also depended on FH status and was highest when i.b.d. alleles were present in FH subjects and lowest when present in non-FH individuals. The study demonstrates that sib pair analysis makes it possible to detect the effect of a minor gene in the presence of the effect of a major gene. Given the interactive effect of elevated LDL and high Lp(a) on CHD risk our data suggest that elevated Lp(a) may add to the CHD risk in FH subjects.

Genetic control of lipoprotein(a) concentrations is different in Africans and Caucasians.

Lipoprotein(a) (Lp(a)) represents a quantitative trait in human plasma associated with atherothrombotic disease. Large variation in the distribution of Lp(a) concentrations exists across populations which is at present unexplained. Sib-pair linkage analysis has suggested that the apo(a) gene on chromosome 6q27 is the major determinant of Lp(a) levels in Caucasians. We have here dissected the genetic architecture of the Lp(a) trait in Africans (Khoi San, South African Blacks) and Caucasians (Austrians) by family/sib-pair analysis. Heritability estimates ranged from h2 = 51% in Blacks, h2 = 61% in Khoi San, to h2 = 71% in Caucasians. Analysis by a variance components model also demonstrated that the proportion of the total phenotypic variance explained by genetic factors is smaller in Africans (65%) than in Caucasians (74%). Importantly the sib-pair analysis clearly identified the apo(a) gene as the major locus in Caucasians which explained the total genetic variance. In the African samples the apo(a) gene accounted for only half the genetic variance. Together with previous results from population studies our data indicate that genetic control of Lp(a) levels seems to be distinctly different between Africans and Caucasians. In the former genetic factors distinct from the apo(a) locus and also non-genetic factors may play a major role.

Frequency distributions of apolipoprotein(a) kringle IV repeat alleles and their effects on lipoprotein(a) levels in Caucasian, Asian, and African populations: the distribution of null alleles is non-random.

A size polymorphism (K IV VNTR) and largely unknown sequence variation in the apolipoprotein(a) [apo(a)] gene on chromosome 6q26-q27 together determine most of the extreme variation in apo(a) glycoprotein expression and lipoprotein(a) [Lp(a)] plasma concentration in Caucasians. We have determined Lp(a) plasma concentrations, the number of kringle IV (K IV) repeats in the apo(a) gene and the expression of the apo(a) glycoprotein in four ethnic groups (Khoi San, South African Blacks, Hong Kong Chinese and Caucasians from the Tyrol, total n = 788). The distributions of Lp(a) concentrations, the frequencies of expressed and non-expressed apo(a) K IV alleles, and the impact of the size polymorphism on Lp(a) concentrations were all heterogeneous across populations. In contrast, the effect of the K IV repeat alleles appeared homogeneous. Lp(a) concentrations were higher in Africans and Chinese than in Caucasians, but this was not explained by differences in K IV repeat allele frequencies among populations. Lp(a) concentrations were highest in Khoi San, suggesting that high Lp(a) is an old African trait. When expressed as Spearman rank correlations the impact of the size polymorphism was smallest in African Blacks (R = -0.386) and largest in the Chinese (R = -0.692). In all four populations, the distribution of non-expressed apo(a) alleles was non-random. Rather they were significantly associated with distinct size alleles and overall positively with high K IV repeat numbers. The negative correlation of K IV repeat length with Lp(a) concentration was non-linear in Khoi San and the average apo(a)-size-allele-associated Lp(a) concentrations were markedly different between all populations. We conclude that besides the apo(a) size variation, other factors affect Lp(a) concentrations to different degrees in the study populations. Most likely, this is sequence variation in apo(a) which is not the same in the different ethnic groups.

The relative electrophoretic mobility of apo(a) isoforms depends on the gel system: proposal of a nomenclature for apo(a) phenotypes.

Genetic apo(a) isoforms were originally defined according to their relative mobility in SDS-PAGE compared to apoB-100 and were designated as F, B or S1-S4 isotypes. This widely accepted nomenclature does not accommodate the broad spectrum of apo(a) isoforms (> 30) detected by high resolution SDS-agarose gel electrophoresis. Moreover we here show that the relative mobilities of apo(a) isoforms depend on the SDS-gel system used. Comparison of the SDS-PAGE system originally used for phenotyping with SDS-agarose gel electrophoresis and two commercial SDS-PAGE systems (PhastGel, Pharmacia, Sweden and NOVEX, USA) demonstrated marked differences in resolving power and resulted in very different Rf values for identical isoforms. Hence phenotyping results from laboratories using different systems are not comparable. We therefore propose a nomenclature of apo(a) isoforms which reports the number of kringle IV repeats in the apo(a) allele (e.g. apo(a) K-IV20 would designate an isoform with 20 K-IV repeats). This is achieved by using standards in which the number of kringle IV repeats has been determined by pulsed field gel electrophoresis of genomic DNA. The proposed nomenclature (i) accounts for the increased resolution of apo(a) phenotyping methods: (ii) is flexible to the introduction of smaller or larger isoforms; (iii) allows to report data from systems with lower resolution as 'binned' isoform categories; (iv) allows the comparison of phenotyping results between different investigators; and (v) can be applied on DNA as well as on protein based apo(a) phenotyping.

Statin therapy in a kindred with both apolipoprotein B and low density lipoprotein receptor gene defects.

We studied an extended family of similar genetic and environmental background to determine whether there is a difference in response to statin therapy in those subjects with heterozygous familial hypercholesterolaemia (FH Afrikaner-1 (FH1) or FH Afrikaner-2 (FH2)) compared to those with familial defective apo B-100 (FDB), or both FH plus FDB. Fasting lipid profiles and Lp(a) levels were done on 18 members of the family and then repeated following 6 weeks of therapy with simvastatin 20 mg daily. Statin therapy reduced LDL-cholesterol (LDL-C) by 31% in those with FH (n = 7); 29.8% in FDB (n = 5) and 25.4% in those with both FDB and FH (n = 5). There was no response to statin therapy in the single subject with both FH1, FH2, as well as FDB. Lp(a) levels did not change significantly either within or between any of the groups following statin therapy (FH from 6.5 (1.2-72.3) to 5.3 (1.2-52.3), FDB from 6.1 (4.70-71) to 8.2 (5.7 79) and FDB plus FH from 4.5 (2.6-17.4) to 3.1 (1.9-24) mg/dl). Statins are equally effective in lowering LDL-C in related subjects with heterozygous FH, FDB or both FDB plus FH. The ability of statins to lower LDL-C in FDB is probably due to increased hepatic uptake of lipoprotein precursors of LDL that can bind via apo E receptors. Lp(a) concentration is not reduced by drugs that stimulate LDL receptor activity implying that LDL receptors do not contribute greatly to normal clearance of Lp(a) in hypercholesterolaemic subjects with defects in receptor-mediated endocytosis of LDL.

Corticotropin-induced reduction of plasma lipoprotein(a) concentrations in healthy individuals and hemodialysis patients: relation to apolipoprotein(a) size polymorphism.

Lipoprotein(a) [Lp(a)], a strong independent cardiovascular risk factor, consists of the unique apolipoprotein(a) [apo(a)] covalently linked to a low-density lipoprotein particle. Apo(a) contains a widely differing number of the plasminogen-like kringle IV, a size polymorphism that is codominantly inherited. In addition to powerful genetic control, renal failure is known to influence the plasma Lp(a) concentration. There is still a lot to be learned about the mode and site of catabolism of Lp(a), and there is no readily applicable Lp(a)-lowering treatment available. Therefore, it was of interest to study further the Lp(a)-lowering effect of corticotropin (ACTH) that has been demonstrated in small studies. The main purpose of the present study was to investigate the influence of ACTH on different apo(a) isoforms. Short-term treatment with ACTH decreased the plasma Lp(a) concentration in all 26 study participants. The two study groups (12 healthy individuals and 14 hemodialysis patients) responded similarly, with a median decrease in plasma Lp(a) of 39% and 49%, respectively. In subjects with two clearly separable apo(a) bands, apo(a) phenotyping and densitometric scanning of the bands before and after treatment with ACTH revealed a change in the proportion of apo(a) isoforms, ie, a shift toward the isoform with lower molecular weight. This was observed in seven of nine investigated subjects (four of five healthy individuals and three of four hemodialysis patients).

Decrease of plasma apolipoprotein A-IV during weight reduction in obese adolescents on a low fat diet.

OBJECTIVE: Apolipoprotein (apo) A-IV is an antiatherogenic apolipoprotein, which may be involved in the regulation of food intake. Plasma apoA-IV is elevated in human obesity and apoA-IV polymorphisms have been associated with the extent of obesity. Our aim was to determine the effects of weight loss on plasma apo-IV in obese adolescents and to examine the relation of apoA-IV with the degree of obesity. DESIGN: Longitudinal intervention study of a low fat hypocaloric diet conducted in a dietary camp. SUBJECTS: Two groups of obese adolescents (n=47 and n=29), age: 12.7+/-1.7 and 11.7+/-2.6 y, relative body mass index (RBMI): 168+/-24 and 175+/-34%, respectively. MEASUREMENTS: Plasma total apoA-IV, apoA-I, apoB, plasma distribution of apoA-IV, leptin, lipids, and lipoproteins before and after 3 weeks of weight reduction. RESULTS: Plasma apoA-IV decreased from 11.5+/-4.1 mg/dl before to 6.7+/-2.2 mg/dl after weight reduction in the first group (P<0.001) and to a similar extent in the second group. The relative amount of lipid-free apoA-IV and apoA-IV associated with apoA-I increased slightly, whereas apoA-IV associated with lipoproteins devoid of apoA-I decreased. ApoA-IV levels before and after weight reduction and the changes in plasma apoA-IV did not independently correlate with RBMI, weight loss, or plasma leptin. CONCLUSION: Plasma apoA-IV decreases markedly in overweight adolescents undergoing short-term weight reduction. The decrease is not directly related to the degree of weight loss and the mechanisms underlying this reduction remain to be clarified.

Lipoprotein(a) in homozygous familial hypercholesterolemia.

Lipoprotein(a) [Lp(a)] is a quantitative genetic trait that in the general population is largely controlled by 1 major locus-the locus for the apolipoprotein(a) [apo(a)] gene. Sibpair studies in families including familial defective apolipoprotein B or familial hypercholesterolemia (FH) heterozygotes have demonstrated that, in addition, mutations in apolipoprotein B and in the LDL receptor (LDL-R) gene may affect Lp(a) plasma concentrations, but this issue is controversial. Here, we have further investigated the influence of mutations in the LDL-R gene on Lp(a) levels by inclusion of FH homozygotes. Sixty-nine members of 22 families with FH were analyzed for mutations in the LDL-R as well as for apo(a) genotypes, apo(a) isoforms, and Lp(a) plasma levels. Twenty-six individuals were found to be homozygous for FH, and 43 were heterozygous for FH. As in our previous analysis, FH heterozygotes had significantly higher Lp(a) than did non-FH individuals from the same population. FH homozygotes with 2 nonfunctional LDL-R alleles had almost 2-fold higher Lp(a) levels than did FH heterozygotes. This increase was not explained by differences in apo(a) allele frequencies. Phenotyping of apo(a) and quantitative analysis of isoforms in family members allowed the assignment of Lp(a) levels to both isoforms in apo(a) heterozygous individuals. Thus, Lp(a) levels associated with apo(a) alleles that were identical by descent could be compared. In the resulting 40 allele pairs, significantly higher Lp(a) levels were detected in association with apo(a) alleles from individuals with 2 defective LDL-R alleles compared with those with only 1 defective allele. This difference of Lp(a) levels between allele pairs was present across the whole size range of apo(a) alleles. Hence, mutations in the LDL-R demonstrate a clear gene-dosage effect on Lp(a) plasma concentrations.

Sequence polymorphism in kringle IV 37 in linkage disequilibrium with the apolipoprotein (a) size polymorphism.

Apolipoprotein(a) [apo(a)] contains a variable number of identical (K-IV A/B) or nearly identical (K-IV 1, K-IV 30-37) kringle repeats that are homologous to K-IV from plasminogen. The sizes of 414 apo(a) alleles were determined by pulsed-field gel electrophoresis (PFGE) of KpnI-digested DNA. Furthermore, sequence variation in the apo(a) K-IV 30-37 domain was analysed. Reverse transcription/polymerase chain reaction (RT-PCR) cloning of human liver poly A+ RNA followed by sequencing revealed a single nucleotide exchange in the ultimate K-IV (K-IV 37) of apo(a) (codon 4168); this results in an ATG (Met) to ACG (Thr) substitution. A PCR-based restriction assay of genomic DNA demonstrated that this substitution represents a common polymorphism. In 231 unrelated Tyroleans, the frequencies for the K-IV 37 Thr and K-IV 37 Met alleles were 0.66 and 0.34, respectively. The phase between the K-IV 37 Met/Thr and the KpnI size polymorphism was determined for 224 alleles. A significant linkage disequilibrium was detected between the sequence and size polymorphisms of apo(a). K-IV 37 Met was significantly associated with KpnI allele no. 18 (DAB = 0.0267 +/- 0.0101; chi 2 = 10.09, df = 1). The Met/Thr polymorphism was further used to test whether deletions or duplications of K-IV 37 occur frequently in the apo(a) gene. Some 40 apo(a) alleles, 22 of which were from subjects that appeared to be double heterozygotes for K-IV repeat number and the Met/Thr variation were separated by PFGE and analysed for the 4168 Met/Thr polymorphism. The Met and Thr sequences were always present on different size alleles and no evidence for a duplication or deletion of K-IV 37 was obtained. This suggests that the copy number of K-IV 37 is invariable, in contrast to the highly variable K-IV A/B domain of the gene. The 4168 Met/Thr polymorphism had no effect on Lp(a) concentration, neither did it influence the lysine-binding property of the Lp(a) particle.

Lp(a) levels and atherosclerotic vascular disease in a sample of patients with familial hypercholesterolemia sharing the same gene defect.

There is considerable variation in the severity of cardiovascular disease among patients with familial hypercholesterolemia (FH). Some reports have suggested that plasma lipoprotein(a) [Lp(a)] levels may explain such variation and that FH subjects deficient in LDL receptors, especially those with coronary heart disease, tend to have elevated Lp(a) levels. We have investigated the possible role of the LDL receptor in determining plasma Lp(a) levels in genetically homogeneous FH population and the contribution of Lp(a) to cardiovascular risk. A total of 98 FH subjects and 66 healthy first- and second-degree relatives from 30 families with FH due to the French-Canadian > 10-kilobase deletion of the LDL receptor gene were studied. A reference group of 392 normolipidemic French-Canadian participants in a Heart Health Survey was used for comparison. FH subjects were subdivided into subsets of 63 individuals free from atherosclerotic vascular disease (AVD) and 35 individuals with AVD. A complete cardiovascular evaluation was performed, and plasma lipid, lipoprotein, and Lp(a) levels were measured in all subjects in the absence of medication. Apolipoprotein (a) [apo(a)] phenotype was determined in 112 of FH and non-FH subjects. The log-transformed values for plasma Lp(a) were not significantly different among the three groups: 0.98 +/- 0.54 (mean +/- SD) in FH subjects with AVD, 0.89 +/- 0.51 in FH subjects without AVD, and 0.82 +/- 0.64 in their relatives. The distribution of the apo(a) phenotypes did not differ between the FH and non-FH groups. Comparison of two age- and sex-matched subgroups of FH subjects, with and without AVD, failed to show any differences in Lp(a) level. However, mean Lp(a) log values in the reference group (n = 392) were significantly lower than values obtained for the total FH group (0.79 +/- 0.57 versus 0.92 +/- 0.52, respectively; P < .05) but were not different from those of the unaffected family members. Thus, in our sample, the LDL receptor appears not to influence plasma Lp(a) levels; rather, these levels reflect shared apo(a) genes. The cardiovascular risk in this group of subjects with FH was related to age, male sex, total and LDL cholesterol, and higher apoB but not Lp(a) levels.

Renovascular arteriovenous differences in Lp[a] plasma concentrations suggest removal of Lp[a] from the renal circulation.

High plasma concentrations of lipoprotein[a] (Lp[a]) are considered a genetically determined risk factor for atherosclerosis. Lp[a] is produced by the liver. The site(s) and mechanism(s) of catabolism are presently unclear. Lp[a] is elevated secondary to end-stage renal disease which suggests a direct or indirect role of the kidney in the metabolism of Lp[a]. We therefore investigated, by a simple in vivo approach, whether Lp[a] is removed by the human kidney. Lp[a] plasma concentrations were measured simultaneously by various methods in the ascending aorta and renal vein of 100 patients undergoing coronary angiography or coronary angioplasty. Lp[a] levels differed significantly between the two vessels even after correcting for hemoconcentration (20.1 +/- 21.6 mg/dL versus 18.7 +/- 20.3 mg/dL, P < 0.001). This corresponds to a mean arteriovenous difference of -1.4 mg/ dL or -9% of the arterial concentration. No Lp[a] or intact apo[a] could be detected in urine from healthy probands. Although we cannot assign the kidney a regulatory role for Lp[a] plasma levels in humans with normal renal function, we conclude from our data that substantial amounts of this atherogenic lipoprotein are taken up by the kidney. The underlying mechanisms are unknown at the moment. This study therefore demonstrates for the first time that the human kidney plays an active role in the catabolism of Lp[a]. This may explain the elevated Lp[a] concentrations found in patients with chronic renal insufficiency.

Apolipoprotein(a) kringle IV repeat number predicts risk for coronary heart disease.

A high plasma concentration of lipoprotein(a) [Lp(a)] has been suggested as a risk factor for coronary heart disease (CHD), but some recent prospective studies have questioned the significance of Lp(a). Lp(a) concentrations are determined to a large extent by the hypervariable apo(a) gene locus on chromosome 6q2.7, which contains a variable number of identical tandemly arranged transcribed kringle IV type 2 repeats. The number of these repeats correlates inversely with plasma Lp(a) concentration. We analyzed whether apo(a) gene variation (kringle IV repeat number) is associated with CHD. Apo(a) genotypes were determined by pulsed-field gel electrophoresis/genomic blotting in CHD patients who had undergone angiography (n = 69) and control subjects matched for age, sex, and ethnicity (n = 69) and were related to Lp(a) concentration, apo(a) isoform in plasma, and disease status. Apo(a) alleles with a low kringle IV copy number ( < 22) and high Lp(a) concentration were significantly more frequent in the CHD group (P < .001), whereas large nonexpressed alleles were more frequent in control subjects. The odds ratio for CHD increased continuously with a decreasing number of kringle IV repeats and ranged from 0.3 in individuals with > 25 kringle IV repeats on both alleles to 4.6 in those with < 20 repeats on at least one allele. This provides direct genetic evidence that variation at the apo(a) gene locus, which determines Lp(a) levels, is also a determinant of CHD risk.

Comparative genomic hybridization reveals a partial de novo trisomy 6q23-qter in an infant with congenital malformations: delineation of the phenotype.

We report the use of comparative genomic hybridization (CGH) to define the origin of a small extra segment (unidentifiable by classical cytogenetics) present in a de novo add(13)q34 chromosome that we found in the karyotype of a newly born boy with congenital heart defects, brain anomalies and dysmorphic signs. Initial investigation with fluorescence in situ hybridization (FISH) and a chromosome-13-specific library revealed that the excess material was not derived from chromosome 13. To uncover the origin of the unknown chromosome material, CGH was carried out on DNA isolated from blood lymphocytes of the patient. By using a conventional fluorescence microscope with no digital imaging devices, a single distinct region with gain of fluorescent intensity was observed on distal chromosome 6q. Confirmation of this finding by FISH with a chromosome-6-specific paint and a subtelomeric yeast artificial chromosome clone from 6q26-q27, in combination with the band morphology of the small extra chromosomal segment, allowed us to diagnose the additional material as being derived from chromosome 6q23-qter. FISH with a telomere 13q probe detected a terminal deletion of 13q34-qter on the derivative chromosome 13, indicating that the der(13) was a result of a translocation event. Genotyping of the hypervariable apolipoprotein (a) gene, which lies within 6q26-q27, showed that the additional chromosome 6 material was inherited from the mother. The karyotype of the proposita is therefore: 46,XY,-13,+der(13)t(6;13)(q23;q34) de novo (mat). Our results confirm the usefulness of CGH as an attractive alternative method for the characterization of constitutional small genetic imbalances and contribute to the delineation of the trisomy 6q23-qter phenotype.