Molecular genetics of type 1 glycogen storage disease

Glycogen storage disease type 1 (GSD 1) comprises a group of autosomal recessive inherited metabolic disorders caused by deficiency of the microsomal multicomponent glucose-6-phosphatase system. Of the two known transmembrane proteins of the system, malfunction of the catalytic subunit (G6Pase) characterizes GSD 1a. GSD 1 non-a is characterized by defective microsomal glucose-6-phosphate or pyrophosphate/phosphate transport due to mutations in G6PT (glucose-6-phosphate translocase gene) encoding a microsomal transporter protein. Mutations in G6Pase and G6PT account for approximately 80 and approximately 20% of GSD 1 cases, respectively. G6Pase and G6PT work in concert to maintain glucose homeostasis in gluconeogenic organs. Whereas G6Pase is exclusively expressed in gluconeogenic cells, G6PT is ubiquitously expressed and its deficiency generally causes a more severe phenotype. Rapid confirmation of clinically suspected diagnosis of GSD 1, reliable carrier testing, and prenatal diagnosis are facilitated by mutation analyses of the chromosome 11-bound G6PT gene as well as the chromosome 17-bound G6Pase gene.

Protein kinase C isoenzyme: selective expression pattern of protein kinase C-θ during mouse development

Protein kinase C (PKC)-θ, a serine/threonine protein kinase and novel PKC subfamily member, has been recently identified as an essential component of the T cell synapse which activates the NF-kB signaling cascade leading to expression of the IL-2 gene during T cell activation. By RNA in situ hybridization to whole-body embryo sections it is shown that the murine PKCθ is specifically expressed in tissues with hematopoietic and lymphopoietic activity. Expression is also evident in skeletal muscle. A further highly specific expression was observed in the peripheral and central nervous system which is described in detail. Expression in the brain persists up to adult stages.

Single nucleotide polymorphisms in exons of the apo(a) kringles IV types 6 to 10 domain affect Lp(a) plasma concentrations and have different patterns in Africans and Caucasians

Lipoprotein(a) [Lp(a)] is a complex of apolipoprotein(a) [apo(a)] and low-density lipoprotein which is associated with atherothrombotic disease. Lp(a) plasma levels are controlled to a large extent by the apo(a) gene locus. Known polymorphisms in the apo(a) gene, including the kringle (K) IV-2 variable number of tandem repeats, explain only part of the large interindividual variability and do not explain the differences in Lp(a) concentrations between major human ethnic groups. Here we performed screening for single nucleotide polymorphisms (SNPs) in exons and flanking intron sequences of the apo(a) K IV types 6, 8, 9 and 10 which represent 1.3 kb of coding sequence in two African (Khoi San, Black South Africans) and one Caucasian (Tyroleans) populations and investigated whether they affect Lp(a) levels. Together, 768 alleles were analyzed. We identified 14 SNPs, including 11 non-synonymous SNPs (eight of which involved conserved residues), one splice site and two synonymous base changes. No sequence variants common to Africans and Caucasians were found. Several of the newly identified SNPs showed significant effects on Lp(a) plasma concentrations. The substitutions S37F in K IV-6 and G17R in K IV-8 were associated with Lp(a) levels significantly below average in Africans. In contrast, the R18W substitution in K IV-9, which occurred with a frequency of 8% in Khoi San, resulted in a significantly increased Lp(a) concentration. Together, our data suggest that several SNPs in the coding sequence of apo(a) affect Lp(a) levels. This indicates that many SNPs may have subtle effects on the gene product.

De novo mutation of the connexin 26 gene associated with dominant non-syndromic sensorineural hearing loss

Mutations of the connexin 26 (Cx26) gene cause isolated recessive or dominant hearing loss or both sensorineural hearing impairment and keratoderma. We have identified the first de novo mutation of the Cx26 gene, R75 W, in a sporadic case of isolated profound hearing loss. R75 W has been previously observed in association with hearing impairment and keratoderma in one family and is thus thought to cause both syndromic and non-syndromic hearing loss. This case illustrates the risk of a possible erroneous diagnosis of autosomal recessive hearing loss in a sporadic case.

Sensorineural hearing loss and the incidence of Cx26 mutations in Austria

A clinical evaluation and Cx26 mutation analysis was performed in 92 consecutive patients with sensorineural hearing loss in order to delineate the spectrum of genetically caused hearing loss. Among patients of Austrian origin, 53% were classified with hereditary hearing loss. Cx26 mutations were found in 26% of NSHL patients (40% of familial vs 18% of sporadic cases). The mutation 35delG accounted for 52.8% of all presumed GJB2 disease alleles. The second most frequent mutation was L90P (16.7%) having been reported with a prevalence of 0.7-3.5% in other populations. Three novel mutations were found. The novel mutation, R143Q, was associated with dominant high-frequency hearing loss. Pseudodominant transmission of NSHL was seen in four families with Cx26 mutations. A mutation 35delG carrier rate of 0.9% was observed among 672 controls from West-Austria. Cx26 mutations were found associated with mild to profound, and with asymmetric hearing impairment.

Mutations in the human DHCR7 gene

The Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive metabolic disorder characterized by variable congenital malformations, facial dysmorphism, and mental retardation. Mutations in the DHCR7 gene have been identified in SLOS patients. This gene encodes for the enzyme Delta7-sterol reductase which catalyses the last step of cholesterol biosynthesis. Among the 73 different mutations observed so far, including 10 novel mutations reported in this review, the majority are missense mutations (65) which cluster in three domains of the protein: in the transmembrane domain (TM mutations), in the fourth cytoplasmic loop (4L mutations), and at the C-terminus (CT mutations). Two nonsense mutations, one splice site mutation, two single nucleotide insertions, and three deletions which likely all represent null mutations were also described. Expression studies have demonstrated a decreased protein stability for all analyzed missense mutations. By comparing clinical severity scores, biochemical data, and mutations in SLOS patients a genotype-phenotype correlation has been established. The null and 4L mutations are associated with a severe clinical phenotype, and TM and CT mutations are associated with a mild clinical phenotype. DHCR7 mutational spectra in SLOS patients of British, German, Italian, and Polish origin demonstrate significant geographic frequency differences of common DHCR7 mutations.

Frequency gradients of DHCR7 mutations in patients with Smith-Lemli-Opitz syndrome in Europe: evidence for different origins of common mutations

Smith-Lemli-Opitz syndrome/RSH (SLOS) is a multiple congenital anomaly syndrome caused by mutations in the gene for Delta7-sterol reductase (DHCR7) which catalyses the last step in the biosynthesis of cholesterol. SLOS is among the common recessive disorders in Europeans but almost absent in most other populations. More than 40 mutations in the DHCR7 gene some of which are frequent have been described in SLOS patients of various origins. Here we report mutation analysis of the DHCR7 gene in SLOS patients from Poland (n = 15), Germany/Austria (n = 22) and Great Britain (n = 22). Altogether 35 different mutations were identified and the two null mutations IVS8-1G > C and W151X were the most frequent in the total sample. In all three populations three mutations accounted for >0.5 of SLOS chromosomes. The mutational spectra were, however, significantly different across these populations with each of the common mutations showing an east-west gradient (W151X, V326L) or vice versa (IVS8-1G > C). W151X is the most frequent (0.33) mutation in Polish SLOS patients. It has an intermediate frequency in German/Austrian patients (0.18) and is rare among British patients (0.02). V326L shows the same distribution pattern (Poland 0.23, Germany/Austria 0.18, Britain 0.02). In contrast IVS8-1G > C is most frequent in Britain (0.34) intermediate in Germany/Austria (0.20) and rare in Poland (0.03). All analysed IVS8-1G > C and V326L alleles shared the same DHCR7 haplotype, whereas the W151X mutation occurred on different haplotypes. There is evidence for both recurrent mutations and founder effects. Together this suggests that the common SLOS mutations in Europe have different geographic and historic origins and spread across the continent in opposite directions.

Mapping of a minimal apolipoprotein(a) interaction motif conserved in fibrin(ogen) beta - and gamma -chains

Lipoprotein(a) (Lp(a)) is a major independent risk factor for atherothrombotic disease in humans. The physiological function(s) of Lp(a) as well as the precise mechanism(s) by which high plasma levels of Lp(a) increase risk are unknown. Binding of apolipoprotein(a) (apo(a)) to fibrin(ogen) and other components of the blood clotting cascade has been demonstrated in vitro, but the domains in fibrin(ogen) critical for interaction are undefined. We used apo(a) kringle IV subtypes to screen a human liver cDNA library by the yeast GAL4 two-hybrid interaction trap system. Among positive clones that emerged from the screen, clones were identified as fibrinogen beta- and gamma-chains. Peptide-based pull-down experiments confirmed that the emerging peptide motif, conserved in the carboxyl-terminal globular domains of the fibrinogen beta and gamma modules specifically interacts with apo(a)/Lp(a) in human plasma as well as in cell culture supernatants of HepG2 and Chinese hamster ovary cells, ectopically expressing apo(a)/Lp(a). The influence of lysine in the fibrinogen peptides and of lysine binding sites in apo(a) for the interaction was evaluated by binding experiments with apo(a) mutants and a mutated fibrin(ogen) peptid. This confirmed the lysine binding sites in kringle IV type 10 of apo(a) as the major fibrin(ogen) binding site but also demonstrated lysine-independent interactions.

T cell expressed PKCtheta demonstrates cell-type selective function

T lymphocyte stimulation leading to interleukin-2 (IL-2) expression requires activation of protein kinase C (PKC); however, the relevant PKC isoform(s) have not yet been systematically defined. Here we examine seven major T cell expressed PKC isoforms (PKCalpha, delta, epsilon, zeta, nu, theta and iota) and identify PKCtheta to be essential for IL-2 expression (via the critical NF-AT and NF-kappaB enhancer) in Jurkat T cells. Employing a conditionally activated PKCtheta estrogen-receptor fusion mutant, a de novo synthesis-independent transactivation of JNK2 was established. Based on mRNA in situ hybridization to mouse whole body sections, PKCtheta was found to be highly expressed in lymphoid organs but also skeletal muscle and the nervous system. PKCtheta function appears to be cell-type specific, since its isoenzyme-selective function was not observed in ectopic expression studies, employing COS-1 or NIH3T3 cells. These results confirm PKCtheta to be the prime target for the activating effect of phorbol ester in T cell signaling and suggest that gene expression as well as gene function of PKCtheta is strictly controlled by the cell type.

Hypermetaphase and interphase fluorescence in situ hybridisation for monitoring of remission status in Philadelphia chromosome positive chronic myeloid leukaemia

Interferon (IFN) alone or in combination with cytostatic drugs, can induce major and durable cytogenetic remissions in chronic myelogenous leukaemia (CML) patients. Hypermetaphase (HMF) and interphase (IPF) fluorescence in situ hybridisation (FISH) have been described to be suitable for remission assessment. In the present study we applied HMF and IPF simultaneously to bone marrow (BM) probes from Ph-positive CML patients. As conventional cytogenetics (CC) is still deemed to be the <gold standard> for remission analysis we studied a group of patients analysed with this method as control. A mean of 50 metaphases was available for HMF analysis, whereas only an average of 18.7 metaphases could be analysed by CC. Remission assessment was frequently impossible by CC or HMF due to lack of metaphases, but always possible by applying IPF. Our results show that HMF should replace CC for routinely monitoring the remission status in Ph-positive CML patients and that in case of lack or insufficient number of metaphases in the majority of cases IPF is suitable for remission assessment.

Homozygosity for the W151X stop mutation in the delta7-sterol reductase gene (DHCR7) causing a lethal form of Smith-Lemli-Opitz syndrome: retrospective molecular diagnosis

Smith-Lemli-Opitz syndrome (SLOS) is a multiple congenital anomalies syndrome caused by an abnormality in cholesterol metabolism. The clinical severity may vary from very mild to lethality in utero, making diagnosis difficult at both ends of the spectrum. Patients with severe SLOS might often escape diagnosis because they die before the correct diagnosis is made. We describe an Austrian family whose first child died neonatally with multiple congenital anomalies. The second pregnancy was terminated because the fetus showed similar severe anomalies ultrasonographically. A further pregnancy ended in a spontaneous first trimester abortion. Clinical diagnosis of SLOS was not considered until the autopsy of the fetus of the terminated pregnancy. Because no material for biochemical testing was available we performed mutational analysis of the DHCR7 gene from paraffin-embedded tissue and a Guthrie card focusing on mutations known to cause a severe SLOS phenotype. This demonstrated homozygosity for the mutation W151X, which has been demonstrated to be a functional null mutation. Our data confirm the concept that homozygosity for functional null alleles of the DHCR7 locus results in intrauterine or perinatal lethality. Furthermore, our findings suggest the usefulness of molecular studies of stored material in similarly affected cases where no material for biochemical analysis is available.

Mutation analysis in glycogen storage disease type 1 non-a

We report molecular and clinical findings in 13 patients with rare types of glycogen storage disease 1 (GSD1 non-a). Analysis of G6PT encoding a microsomal transporter protein has revealed mutations on both chromosomes in each case, four of which are novel. Diagnosis has been confirmed in three patients suspected of having GSD1 non-a without enzymatic studies involving liver biopsy, thus emphasising the advantage of G6PT mutation analysis for all GSD1 non-a patients.

Mental and psychomotoric retardation in two brothers with pure partial trisomy 7q32-q34 due to a maternal insertion (14;7)

We present two brothers with mental retardation, seizures disorder, generalized muscular hypertonia, kyphoscoliosis, minor anomalies and a prominent midface. GTG-banded chromosome analysis showed a derivative chromosome 14 without clues toward the origin of the rearrangement. Microdissection of the derivative chromosome 14 and subsequent reverse painting demonstrated partial trisomy 7q32-q34 as the unbalanced product of a maternal insertion (14;7). Thus, we identified two cases with pure trisomy 7q32-q34 that allowed further delineation of this aneusomy syndrome.

Lipoprotein(a) determination and risk of cardiovascular disease in South African patients with familial hypercholesterolaemia

OBJECTIVE

A raised plasma level of lipoprotein(a) (Lp(a)) is an established genetic risk factor for coronary heart disease (CHD), particularly in patients with concomitant elevation of low-density lipoprotein (LDL) cholesterol. The current study focused on the comparison of two commercially available Lp(a) assay kits to determine whether differences observed in measured Lp(a) levels could be deemed negligible in CHD risk assessment in familial hypercholesterolaemic (FH) patients.

DESIGN

To compare results obtained on duplicate plasma samples using two commercially available Lp(a) measuring kits, the immunoradiometric assay (RIA) and the enzyme-linked immunoabsorbent assay (ELISA).

SETTING

Division of Human Genetics, Department of Obstetrics and Gynaecology, University of Stellenbosch, Tygerberg, South Africa and the Institute for Medical Biology and Human Genetics, University of Innsbruck, Austria.

SUBJECTS

Plasma samples were obtained from 146 family members of 65 molecularly characterised South African FH families for comparative analysis.

RESULTS

Using the RIA method, 34 samples (23%) considered to be in the normal range by the ELISA technique, were placed in the high-risk group (> 30 mg/dl). Only one sample, considered to have a normal Lp(a) level with the RIA method, was categorised by the ELISA technique as high risk.

CONCLUSION

Our data demonstrate that measurements of Lp(a) using the RIA method (the only assay available in South Africa at the time of this study) differ significantly from those obtained by the reference ELISA technique, suggesting that misclassification could lead to inaccurate CHD risk assessment. This is an important consideration in Afrikaner FH families, where plasma levels of Lp(a) have been shown to be elevated significantly in FH patients compared with non-FH individuals.

Mutational spectrum in the Delta7-sterol reductase gene and genotype-phenotype correlation in 84 patients with Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS), an autosomal recessive malformation syndrome, ranges in clinical severity from mild dysmorphism and moderate mental retardation to severe congenital malformation and intrauterine lethality. Mutations in the gene for Delta7-sterol reductase (DHCR7), which catalyzes the final step in cholesterol biosynthesis in the endoplasmic reticulum (ER), cause SLOS. We have determined, in 84 patients with clinically and biochemically characterized SLOS (detection rate 96%), the mutational spectrum in the DHCR7 gene. Forty different SLOS mutations, some frequent, were identified. On the basis of mutation type and expression studies in the HEK293-derived cell line tsA-201, we grouped mutations into four classes: nonsense and splice-site mutations resulting in putative null alleles, missense mutations in the transmembrane domains (TM), mutations in the 4th cytoplasmic loop (4L), and mutations in the C-terminal ER domain (CT). All but one of the tested missense mutations reduced protein stability. Concentrations of the cholesterol precursor 7-dehydrocholesterol and clinical severity scores correlated with mutation classes. The mildest clinical phenotypes were associated with TM and CT mutations, and the most severe types were associated with 0 and 4L mutations. Most homozygotes for null alleles had severe SLOS; one patient had a moderate phenotype. Homozygosity for 0 mutations in DHCR7 appears compatible with life, suggesting that cholesterol may be synthesized in the absence of this enzyme or that exogenous sources of cholesterol can be used.

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.

Molecular basis of congenital lp(a) deficiency: a frequent apo(a) 'null' mutation in caucasians

High plasma concentrations of lipoprotein(a) [Lp(a)], a covalent low-density lipoprotein-apolipoprotein(a) [apo(a)] complex, are associated with coronary heart disease and stroke. Heritability of Lp(a) levels is high and the major locus determining Lp(a) concentrations is the apo(a) gene. We here demonstrate that a G-->A substitution at the +1 donor splice site of the apo(a) kringle (K) IV type 8 intron occurs with a high frequency ( approximately 6%) in Caucasians but not in Africans and is associated with congenital deficiency of Lp(a) in plasma. This mutation alone accounts for a quarter of all 'null' apo(a) alleles in Caucasians. RT-PCR analysis based on apo(a) illegitimate transcription in lympho- blastoid cells demonstrated that the donor splice site mutation results in an alternative splicing of the K IV type 8 intron and encodes a truncated form of apo(a). Expression of the alternatively spliced cDNA analogue in HepG2 cells showed that the truncated apo(a) form is secreted but is unable to form the covalent Lp(a) complex. Immunoprecipitated plasma apo(a) from homozygotes for the mutation was almost completely fragmented. Taken together, our data indicate that a failure in complex formation followed by fast degradation in plasma of the truncated free apo(a) is one mechanism which underlies the null Lp(a) type associated with the donor splice site mutation.

Role of lipoprotein(a) and apolipoprotein(a) phenotype in atherogenesis: prospective results from the Bruneck study

BACKGROUND

Experimental studies have suggested both atherogenic and thrombogenic properties of lipoprotein(a) [Lp(a)], depending on Lp(a) plasma concentrations and varying antifibrinolytic capacity of apolipoprotein(a) [apo(a)] isoforms. Epidemiological studies may contribute to assessment of the relevance of these findings in the general population.

METHODS AND RESULTS

This study prospectively investigated the association between Lp(a) plasma concentrations, apo(a) phenotypes, and the 5-year progression of carotid atherosclerosis assessed by high-resolution duplex ultrasound in a random sample population of 826 individuals. We differentiated early atherogenesis (incident nonstenotic atherosclerosis) from advanced (stenotic) stages in atherosclerosis that originate mainly from atherothrombotic mechanisms. Lp(a) plasma concentrations predicted the risk of early atherogenesis in a dose-dependent fashion, with this association being confined to subjects with LDL cholesterol levels above the population median (3.3 mmol/L). Apo(a) phenotypes were distributed similarly in subjects with and without early carotid atherosclerosis. In contrast, apo(a) phenotypes of low molecular weight emerged as one of the strongest risk predictors of advanced stenotic atherosclerosis, especially when associated with high Lp(a) plasma concentrations (odds ratio, 6.4; 95% CI, 2.8 to 14. 9).

CONCLUSIONS

Lp(a) is one of the few risk factors capable of promoting both early and advanced stages of atherogenesis. Lp(a) plasma concentrations predicted the risk of early atherogenesis synergistically with high LDL cholesterol. Low-molecular-weight apo(a) phenotypes with a putatively high antifibrinolytic capacity in turn emerged as one of the leading risk conditions of advanced stenotic stages of atherosclerosis.

Switch from antagonist to agonist of the androgen receptor bicalutamide is associated with prostate tumour progression in a new model system

Advanced prostate cancer is treated by androgen ablation and/or androgen receptor (AR) antagonists. In order to investigate the mechanisms relevant to the development of therapy-resistant tumours, we established a new tumour model which closely resembles the situation in patients who receive androgen ablation therapy. Androgen-sensitive LNCaP cells were kept in androgen-depleted medium for 87 passages. The new LNCaP cell subline established in this manner, LNCaP-abl, displayed a hypersensitive biphasic proliferative response to androgen until passage 75. Maximal proliferation of LNCaP-abl cells was achieved at 0.001 nM of the synthetic androgen methyltrienolone (R1881), whereas 0.01 nM of this compound induced the same effect in parental cells. At later passages (> 75), androgen exerted an inhibitory effect on growth of LNCaP-abl cells. The non-steroidal anti-androgen bicalutamide stimulated proliferation of LNCaP-abl cells. AR protein expression in LNCaP-abl cells increased approximately fourfold. The basal AR transcriptional activity was 30-fold higher in LNCaP-abl than in LNCaP cells. R1881 stimulated reporter gene activity in LNCaP-abl cells even at 0.01 nM, whereas 0.1 nM of R1881 was needed for induction of the same level of reporter gene activity in LNCaP cells. Bicalutamide that acts as a pure antagonist in parental LNCaP cells showed agonistic effects on AR transactivation activity in LNCaP-abl cells and was not able to block the effects of androgen in these cells. The non-steroidal AR blocker hydroxyflutamide exerted stimulatory effects on AR activity in both LNCaP and LNCaP-abl cells; however, the induction of reporter gene activity by hydroxyflutamide was 2.4- to 4-fold higher in the LNCaP-abl subline. The changes in AR activity were associated neither with a new alteration in AR cDNA sequence nor with amplification of the AR gene. Growth of LNCaP-abl xenografts in nude mice was stimulated by bicalutamide and repressed by testosterone. In conclusion, our results show for the first time that the nonsteroidal anti-androgen bicalutamide acquires agonistic properties during long-term androgen ablation. These findings may have repercussions on the natural course of prostate cancer with androgen deprivation and on strategies of therapeutic intervention.

Is apolipoprotein(a) a susceptibility gene for type I diabetes mellitus and related to long-term survival?

AIMS/HYPOTHESIS

High lipoprotein(a) [Lp(a)] plasma concentrations are a genetically determined risk factor for atherosclerotic complications. In healthy subjects Lp(a) concentrations are mostly controlled by the apolipoprotein(a) [apo(a)] gene locus which determines a size polymorphism with more than 30 alleles. Subjects with low molecular weight apo(a) phenotypes on average have higher Lp(a) concentrations than those with high molecular weight apo(a) phenotypes. There are many opinions about whether and why Lp(a) is raised in patients with Type I diabetes (insulin-dependent) mellitus.

METHODS

We investigated Lp(a) plasma concentrations and apo(a) phenotypes in 327 patients with Type I diabetes mellitus (disease duration 1-61 years) and in 200 control subjects matched for age and sex.

RESULTS

Patients with a disease duration of up to 15 years had significantly higher Lp(a) concentrations (24.3 +/- 34.0 mg/dl vs 16.7 +/- 22.6 mg/dl, p = 0.014) compared with control subjects. This increase can be explained by a considerably higher frequency of low molecular weight apo(a) phenotypes (38.9% vs 23.5%, p < 0.005). The frequency of low molecular weight apo(a) phenotypes decreased continuously with disease duration from 41.7% in those with disease duration of up to 5 years to 18.2% in those with the disease lasting more than 35 years.

CONCLUSIONS/INTERPRETATION

Our data show that an increase of Lp(a) in Type I diabetic patients can only be observed in groups with short diabetes duration and that this elevation is genetically determined. Therefore, the apo(a) gene, located at 6q26-27, might be a susceptibility gene for Type I diabetes mellitus which is supported by recently published studies reporting evidence for linkage of this region (6q27) with Type I diabetes mellitus. Furthermore, the decreasing frequency of low molecular weight apo(a) phenotypes with disease duration suggests a survivor effect.

Lipoprotein(a) plasma concentrations after renal transplantation: a prospective evaluation after 4 years of follow-up

The highly atherogenic lipoprotein(a) [Lp(a)] is significantly elevated in patients with renal disease. It is discussed controversially whether Lp(a) concentrations decrease after renal transplantation and whether the mode of immunosuppressive therapy influences the Lp(a) concentrations. In a prospective study the Lp(a) concentrations before and on average 48 months after renal transplantation were measured in 145 patients. The determinants of the relative changes of Lp(a) concentrations were investigated in a multivariate analysis. Patients treated by CAPD showed a larger decrease of Lp(a) than hemodialysis patients, reflecting their markedly higher Lp(a) levels before transplantation. The relative decrease of Lp(a) was higher with increasing Lp(a) concentrations before transplantation in combination with an increasing molecular weight of apolipoprotein(a) [apo(a)]. That means that the relative decrease of Lp(a) is related to the Lp(a) concentration and the apo(a) size polymorphism. With increasing proteinuria and decreasing glomerular filtration rate, the relative decrease of Lp(a) became less pronounced. Neither prednisolone nor cyclosporine (CsA) had a significant impact on the Lp(a) concentration changes. Azathioprine (Aza) was the only immunosuppressive drug which had a dose-dependent influence on the relative decrease of Lp(a) levels. These data clearly demonstrate a decrease of Lp(a) following renal transplantation which is caused by the restoration of kidney function. The relative decrease is influenced by Aza but not by CsA or prednisolone.

The seventh myth of lipoprotein(a): where and how is it assembled?

Our understanding of the genetics, metabolism and pathophysiology of the atherogenic plasma lipoprotein Lp(a) has considerably increased over past years. Nevertheless, the precise mechanisms regulating the biosynthesis and assembly of Lp(a) are poorly understood and controversially discussed. Lp(a) plasma concentrations are determined by synthesis and not by degradation. Transcriptional and post-translational mechanisms have been identified as regulating Lp(a) production in primary hepatocytes and transfected cell lines. Assembly of Lp(a) occurs extracellularly from newly synthesized apolipoprotein(a) and circulating LDL. This view has recently been challenged by in-vivo kinetic studies in humans which are compatible with an intracellular assembly event. Lp(a) assembly is a complex two-step process of multiple non-covalent interactions between apolipoprotein(a) and apolipoprotein B-100 of LDL followed by covalent disulfide linkage of two free cysteine residues on both proteins.