Expression and characterization of six clinically relevant uroporphyrinogen decarboxylase gene mutations

The functional consequence of six uroporphyrinogen decarboxylase (UROD) gene mutations found in Danish patients with familial porphyria cutanea tarda was investigated. Wild-type UROD and the 6 mutants (3 missense, 1 nonsense and 2 frameshift mutants) were cloned and expressed using the prokaryotic gGEX-6P system, in which the protein is produced in fusion with glutathione S-transferase (GST). Enzymatic activity of the purified recombinant mutant fusion proteins ranged from undetectable to less than 12% of the recombinant wild-type protein. Mutant proteins cleaved from the GST part did not retain any catalytic activity. These observations can be ascribed to the structure/function relationships of the enzyme, and the fact that the enzyme is a dimer in its active form. Although the clinical manifestation of familial porphyria cutanea tarda is complex, the findings support the notion that different mutations may affect individuals differently.

Characterization of two isoalleles and three mutations in both isoforms of purified recombinant human porphobilinogen deaminase

Defects in the enzyme porphobilinogen deaminase (PBG-D) are associated with acute intermittent porphyria (AIP). Human PBG-D is transcribed into a housekeeping or an erythroid form as a result of differential promoter usage and splicing. In addition, three pairs of isoallelic forms have been described. However, whether the enzymatic properties of housekeeping and erythroid forms differ is unknown. In this study the two isoallelic forms, K210 and E210, were cloned and expressed in Escherichia coli together with three mutations associated with a clinical AIP phenotype. The mutations were introduced in the K210 isoallelic background and expressed as both the housekeeping and the erythroid form. The proteins were expressed as GST fusions and purified to homogeneity. Initial experiments revealed that the GST-PBG-D fusions and the purified PBG-D obtained by proteolytic removal of the GST moiety had enzymatic properties that were indistinguishable. Consequently, all analyses with mutant PBG-D were performed on the GST-fusion proteins. Comparison of the wild-type proteins revealed a significant difference in Km between isoalleles with a Km of 9 microM for K210 and 7 microM for E210, whereas no significant difference in activity or kinetics between the housekeeping and the erythroid isoforms was observed. The mutant proteins showed 0.3-1.0% wild-type activity, depending on mutation. There was a clear correlation between yield of recombinant protein and CRIM status of patients. Furthermore, co-expression of the mutant proteins with the bacterial chaperone GroESL did not affect protein yield or function to any significant extent, supporting the view that the investigated mutations primarily influence structure and function and not folding of the proteins.

Association of mutations in the hemochromatosis gene with shorter life expectancy

BACKGROUND

To investigate whether the frequency of carriers of mutations in the HFE gene associated with hereditary hemochromatosis diminishes with age as an indication that HFE mutations are associated with increased mortality. It is of value in the debate concerning screening for hereditary hemochromatosis to determine the significance of heterozygosity.

METHODS

Genotyping for mutations in exons 2 and 4 of the HFE gene using denaturing gradient gel electrophoresis in 1784 participants aged 45 to 100 years from 4 population-based studies: all 183 centenarians from the Danish Centenarian Study, 601 people aged 92 to 93 years from the Danish 1905 Cohort, 400 aged 70 to 94 years from the Longitudinal Study of Aging Danish Twins, and 600 aged 45 to 67 years from a study of middle-aged Danish twins.

RESULTS

All participants (N=1784) were screened for mutations in exon 4, and a trend toward fewer heterozygotes for the C282Y mutation-the mutation most often associated with hereditary hemochromatosis-was found. This was significant for the whole population (P=.005) and for women (P=.004) but not for men (P=.26). A group of 599 participants was screened for mutations in exon 2, and there was no variation in the distribution of mutations in exon 2 in the different age groups.

CONCLUSIONS

In a high-carrier frequency population like Denmark, mutations in HFE show an age-related reduction in the frequency of heterozygotes for C282Y, which suggests that carrier status is associated with shorter life expectancy.

Association between CYP1A2 polymorphism and susceptibility to porphyria cutanea tarda

Individuals with the most common form of the porphyrias, porphyria cutanea tarda (PCT), are believed to be genetically predisposed to development of clinically overt disease through mutations and polymorphisms in genes associated with known precipitating factors. In this study, we have examined a group of Danish patients with PCT for the presence of the C/A polymorphism in intron 1 of CYP1A2. The results demonstrate that the frequency of the highly inducible A/A genotype is increased in both familial and sporadic PCT. This suggests that inheritance of this genotype is a susceptibility factor in development of PCT.

Uroporphyrinogen decarboxylase gene mutations in Danish patients with porphyria cutanea tarda

Decreased uroporphyrinogen decarboxylase (UROD) activity is a characteristic feature of the most common of the porphyrias, porphyria cutanea tarda (PCT). A subgroup of the clinically overt PCT cases is associated with mutations in the gene encoding UROD and inherited as an autosomal-dominant trait. In this study, DNAs from 53 Danish PCT patients were subjected to genetic analysis for UROD mutations using denaturing gradient gel electrophoresis. Eleven genetic variations, seven of which are possible disease causing, were identified. All but one of these mutations were previously unknown, lending further support to the assumption that PCT is a heteroallelic disease. Only 11% of the examined patients were previously recognized as familial PCT cases. However, possible disease-related UROD mutations were identified in 24% of the examined patients, indicating that genetic analysis of PCT patients may improve differentiation between familial and sporadic PCT cases.

Porphyrins, porphyrin metabolism and porphyrias. II. Diagnosis and monitoring in the acute porphyrias

The acute porphyrias constitute a group of metabolic disorders engaging enzymes in the haem synthetic chain and generally following dominant inheritance patterns. Some gene carriers are vulnerable to a range of exogenous and endogenous factors, which may trigger neuropsychiatric symptoms. Early diagnosis is of prime importance since it makes way for counselling with the aim to block the development of acute, as well as late, disease. The medical and psycho-social consequences of a porphyria diagnosis are considerable and the freedom for maldiagnosis correspondingly small. The strain imposed upon the diagnostic process makes management in specialized laboratories necessary. Inadvertent handling of the diagnostic procedures in laboratories lacking in knowledge, experience and technical competence is repeatedly the reason for harmful underdiagnosis and overdiagnosis. Gene diagnosis of the carrier condition, principally within reach in all types of acute porphyria, is of incomparable versatility and accuracy. However, despite recent great achievements in the molecular biology of porphyric disease, genomic procedures cannot replace biochemical methods in monitoring the activity and progress of the disease, or the effects of therapy. The classical methods are also useful when it comes to screening for the associated disease states. In these tasks, professional handling of the methods and skillful interpretation of the results are of paramount importance. Knowledge of the limitations and pitfalls of the procedures is a guard against maldiagnosis, which may be fatal. In the article the main diagnostic challenges are discussed; the strategy for early detection of the gene carrier state, the recognition and surveillance of the acute porphyric crisis, the evaluation of subacute/subchronic symptoms, the differential diagnoses of the cutaneous porphyrias and the monitoring of late complications.

DGGE analysis of the coproporphyrinogen oxidase gene: two new mutations in DNA from Danish patients with hereditary coproporphyria

The knowledge of at least 21 different mutations and several polymorphisms in the coproporphyrinogen oxidase (CPO) gene demonstrates that the molecular basis of hereditary coproporphyria is heterogeneous. We developed a DGGE-based assay for the analysis of exons 2 to 7, including 14-96 nucleotides of the flanking intronic sequences of the CPO gene. To render it suitable for the clinical diagnostic laboratory, we designed the assay to allow use of identical PCR conditions and the same DGGE gel for analyses of all the regions. Using this assay, and subsequent sequencing of gene regions containing interallelic variations, two novel mutations in the CPO gene were identified: a missense mutation (607G-->A), leading to the substitution of an alanine with a threonine, and a nonsense mutation (1281G-->A), giving rise to a stop codon 28 codons upstream to the wild-type stop codon.

Role of acetaldehyde in the induction of heart left ventricular atrial natriuretic peptide gene expression in rats

We studied the effects of ethanol and acetaldehyde on myocardial gene expression of atrial natriuretic peptide (ANP) and growth of rats. Combined ethanol and calcium carbimide treatment increased blood-acetaldehyde levels and ANP mRNA levels by 40-60% in 2-8 day experiments, compared to the controls. The results suggest a role for acetaldehyde in the development of alcoholic heart dysfunction.

Diagnostic strategy, genetic diagnosis and identification of new mutations in intermittent porphyria by denaturing gradient gel electrophoresis

Acute intermittent porphyria (AIP) is an autosomal dominant inherited disease of heme metabolism caused by mutations in the hydroxymethylbilane synthase gene. Diagnosing AIP during an acute attack using traditional biochemical markers is unproblematic, but it can be difficult to obtain a definite diagnosis in asymptomatic carriers. These limitations may, however, be solved through a genetic approach for diagnosing AIP carrier status. A mutation screening assay based on the denaturing gradient gel electrophoresis (DGGE) principle was established in a setup that allows within 24 hr to pinpoint which of the 15 exons of the hydroxymethylbilane synthase gene carries the underlying mutation, and thereby reduces subsequent sequencing, needed to determine the specific mutation, to this particular gene region. To evaluate sensitivity and specificity of the DGGE assay, samples from 22 AIP patients with known mutations and six healthy controls were examined in a blinded design. Following unblinding, it was revealed that in all 22 AIP samples the correct mutation carrying region had been pointed out. In two samples containing a previously undescribed polymorphism, this additional region was also pointed out. All controls were correctly characterized as normal in the DGGE assay. Subsequently, to evaluate the assay in the clinical setting, samples from six previously uncharacterized Danish AIP probands were examined and the underlying mutation detected in all six. In conclusion, a simple and sensitive mutation screening assay based on the DGGE principle allows genetic diagnosis of AIP in a routine setting and may be used as an additional tool in genetic counseling of AIP families.

[Porphyria cutanea tarda]

Porphyria cutanea tarda (PCT), the most common porphyria disease, is characterized by blistering and skin fragility of sun-exposed skin. The symptoms are caused by lowered activity of uroporphyrinogen decarboxylase (URO-D) resulting in accumulation of water-soluble porphyrins in the skin. Most PCT cases are sporadic but can be familiar due to mutations in the URO-D gene located on chromosome number 1. The disease may be exacerbated by environmental factors. Iron accumulation is a characteristic finding and there is an association to hereditary haemochromatosis. Therapeutic venesection reduces the iron load and the uroporphyrins are mobilized by treatment with hydroxychloroquine. An increased risk of liver cirrhosis and hepatocellular carcinoma may presumably be reduced by early diagnosis and treatment.

Screening for mutations in the uroporphyrinogen decarboxylase gene using denaturing gradient gel electrophoresis. Identification and characterization of six novel mutations associated with familial PCT

The two porphyrias, familial porphyria cutanea tarda (fPCT) and hepatoerythropoietic porphyria (HEP), are associated with mutations in the gene encoding the enzyme uroporphyrinogen decarboxylase (UROD). Several mutations, most of which are private, have been identified in HEP and fPCT patients, confirming the heterogeneity of the underlying genetic defects of these diseases. We have established a denaturing gradient gel electrophoresis (DGGE) assay for mutation detection in the UROD gene, enabling the simultaneous screening for known and unknown mutations. The established assay has proved able to detect the underlying UROD mutation in 10 previously characterized DNA samples as well as a new mutation in each of six previously unexamined PCT patients. The six novel UROD mutations comprise three missense mutations (M01T, F229L, and M324T), two splice mutations (IVS3-2A-->T and IVS5-2A-->G) leading to exon skipping, and a 2-bp deletion (415-416delTA) resulting in a frameshift and the introduction of a premature stop codon. Heterologous expression and enzymatic studies of the mutant proteins demonstrate that the three mutations leading to shortening or truncation of the UROD protein have no residual catalytic activity, whereas the two missense mutants retained some residual activity. Furthermore, the missense mutants exhibited a considerable increase in thermolability. The six new mutations bring to a total of 29 the number of disease-related mutations in the UROD gene. The DGGE assay presented greatly improves the genetic diagnosis of fPCT and HEP, thereby facilitating the detection of familial UROD deficient patients as well as the discrimination between familial and sporadic PCT cases.

An improved PCR-based method for site directed mutagenesis using megaprimers

An improved protocol for site-directed mutagenesis based on the two-step polymerase chain reaction (PCR) megaprimer method is described. Compared to previously published protocols, the protocol described in this article ensures consistently a success rate of at least 85% with essentially no introduction of unwanted secondary mutations. The essential features of this protocol include an optimization of the template-primer amounts and ratio that allows the use of a reduced number of PCR cycles and the use of proof-reading thermostable DNA polymerases.

Evaluation of a clinically applicable mutation screening technique for genetic diagnosis of familial hypercholesterolemia and familial defective apolipoprotein B

We have recently developed a simple mutation screening assay based on the denaturing gradient gel electrophoresis (DGGE) technique for detection of mutations in the coding and regulatory regions of the low density lipoprotein receptor (LDLR) gene and the codon 3500 region of the apolipoprotein (apo) B-100 gene leading to familial hypercholesterolemia (FH) and familial defective apo B-100 (FDB), respectively. To evaluate the assay, 14 Danish families suspected of FH were studied. In ten families, the DGGE assay detected seven different point mutations, including mutations undescribed prior to establishing the assay. In addition, in one of these ten families and in one of the remaining four families, Southern blotting detected the FH-DK3 exon 5 deletion. Based on segregation analysis and clinical data, the FH diagnosis was dubious in the remaining three families without DGGE or Southern blotting detectable mutations. In conclusion, a simple DGGE based mutation screening assay may detect underlying mutations in most FH/FDB families, thus allowing its routine use in genetic counselling of FH-families.

Three splicing defects, an insertion, and two missense mutations responsible for acute intermittent porphyria

Three splicing defects (IVS1+3G-->T, 86A-->T, IVS13-2A-->G), an insertion (416insCA), and two missense mutations (664G-->A and 833T-->G) in the porphobilinogen deaminase (PBGD) gene were identified in six unrelated Finnish patients with acute intermittent porphyria (AIP). The IVS1+3G-->T substitution resulted in activation of a cryptic splice site in intron 1 and retention of a 67-bp fragment in the mutant transcript. The 86A-->T mutation at the end of exon 3 was predicted to cause an amino acid substitution (E29L). However, sequencing of the cDNA sample of the proband revealed exon 3 skipping from the mutant transcript. The IVS13-2A-->G substitution caused retention of intron 13 in the mutant transcript. In exon 8, 416insCA resulted in a frameshift. All three splicing defects and the CA insertion resulted in a truncated protein and thus, probably the loss of PBGD activity. The two novel missense mutations, 664G-->A in exon 12 and 833T-->C in exon 14 caused a single amino acid substitution (V222M and L278P). So far 25 different mutations have been characterized from 37 (93%) of a total of 40 unrelated Finnish AIP families, confirming the genetic heterogeneity of the disease even in a previously isolated area of Finland.

Myosin heavy chain mRNA transform to faster isoforms in immobilized skeletal muscle: a quantitative PCR study

A quantitative polymerase chain reaction (PCR) method was used to measure the quantities of type I, IIa, IIx, and IIb myosin heavy chain (MHC) mRNA in total RNA preparations of the soleus, gastrocnemius, and plantaris muscles of normal and hindlimb-immobilized rats. Type IIx and even type IIb MHC mRNA were demonstrated at extremely low levels in normal soleus, 2.1 +/- 0.4 x 10(5) and 5.0 +/- 0.2 x 10(5) molecules of mRNA per microgram total RNA, respectively. Immobilization for 1 wk significantly altered the gene expression of MHC isoforms. In soleus, both type IIx and IIb MHC genes became significantly upregulated, 24-fold (P < 0.005) and 2.6-fold (P < 0.05), respectively. In gastrocnemius, the level of type IIa MHC mRNA decreased by 51% (P < 0.01) and the level of type IIx MHC mRNA increased by 140% (P < 0.05). In plantaris, the level of type IIa MHC mRNA decreased by 58% (P < 0.005). In conclusion, immobilization changed the MHC mRNA profile in three different types of skeletal muscle toward faster isoforms. The quantitative results permit reliable evaluation of changes in mRNA levels.

Detection and characterization of a novel splice mutation in the LDL receptor intron 12 resulting in two different mutant mRNA variants

Using a simple, standardized denaturing gradient gel electrophoresis (DGGE) based mutation screening technique, a novel G-to-A mutation in the last base of the intron 12 splice acceptor site of the LDL receptor gene was found in 2 Danish families with familial hypercholesterolemia (FH). The mutation is shown to result in 2 mRNA splice variants, both leading to truncated LDLR proteins, containing only the first 594 of the normal 839 amino acids. In one of the FH-families harbouring the mutation, a striking difference in the clinical picture amongst biochemically diagnosed FH patients was clarified when genetic analysis showed that 2 hypercholesterolemic family members, who despite advanced age had no atherosclerotic disease, had not inherited the family LDLR mutation. DGGE analyses of the LDLR exons, LDLR promoter, and apolipoprotein B codon 3456-3553 as well as Southern blotting of the LDLR gene were without signs of other mutations in the non-atherosclerotic hypercholesterolemics of the family. Availability of the clinically applicable mutation screening assay for FH may thus aid in defining reasons for phenotypic differences in FH families and potentially supply information allowing a more differentiated therapeutic approach to individual members of FH families.

Phenotypic presentation of the FH-Cincinnati type 5 low density lipoprotein receptor mutation

Familial hypercholesterolaemia (FH) is an autosomal dominant hereditary disease of lipid metabolism that in most families is caused by mutations in the low density lipoprotein receptor (LDLR) gene. Though more than 150 mutations are known, the clinical picture associated with most of these is not known. Genetic FH diagnosis may soon become routine in the setting of genetic counselling, and therefore thorough information on the phenotype-genotype relationship of different mutations is now important. In this study, index patients from each of 14 Danish FH families were screened for mutations in exon 2 of the LDLR gene using a denaturing gradient gel electrophoresis (DGGE)-based mutation screening assay. A deviating DGGE pattern identified two index patients, where subsequent sequencing revealed heterozygosity for the FH Cincinnati type 5 Trp23-to-Stop LDLR mutation. Data from three generations of the families allowed the first clinical and biochemical description of this mutation. Evidence that genetic analysis adds independent diagnostic information compared to traditional clinical/biochemical FH diagnosis was documented by demonstrating the presence of the FH Cincinnati mutation in a family member with a completely normal lipid profile. By comparison to non-FH family members, it was documented that carrier status for the FH Cincinnati mutation is associated with a significant risk of cardiovascular disease. Thus, genetic analysis may improve diagnostic precision and help to define more precisely which of the members of FH families are in need of preventive interventions and may aid in establishing phenotype-genotype relationships allowing more refined genetic counselling in FH.

Clinically applicable mutation screening in familial hypercholesterolemia

Mutations in the LDL receptor (LDLR) gene and the codon 3500 region of the apolipoprotein (apo) B-100 gene result in the clinically indistinguishable phenotypes designated familial hypercholesterolemia (FH) and familial defective apo B-100 (FDB), respectively. Introduction of genetic diagnosis in phenotypic FH families may remove the diagnostic inaccuracies known from traditional clinical/biochemical FH diagnosis and allow more differentiated prognostic evaluations and genetic counseling of FH/FDB families. Previous genetic screening methods for FH have, however, been too cumbersome for routine use, however. To overcome these problems, we designed a mutation screening assay based on the highly sensitive denaturing gradient gel electrophoresis (DGGE) technique. The setup allows within 24 hr to pinpoint if and where a potential mutation is located in the LDLR promoter, the 18 LDLR gene exons and corresponding intronic splice site sequences, or in the codon 3500 region of apo B-100. The pinpointed region is subsequently sequenced. As an evaluation of the sensitivity, we demonstrated the ability of the assay to detect 27 different mutations or polymorphisms covering all the examined regions, except LDLR exon 16. In conclusion, a simple, but sensitive, clinically applicable mutation screening assay based on the DGGE principle may reveal the underlying mutation in most FH/FDB families and offer a tool for a more differentiated prognostic and therapeutic evaluation in FH/FDB.

Improved RNase protection assay for quantifying LDL-receptor mRNA; estimation of analytical imprecision and biological variance in peripheral blood mononuclear cells

We have improved the protocol for RNA quantification by using RNase protection. Instead of precipitation and extraction with phenol and chloroform, we use a faster and more reliable precipitation based on guanidinium thiocyanate (GdSCN). The internal standard is produced by in vitro transcription of a DNA template constructed so as to allow simultaneous detection of the in vitro transcript and the low-density lipoprotein receptor (LDLR) mRNA by use of the same probe and hybridization. Addition of this internal standard at the step for RNA isolation reduced the analytical imprecision from 40.8% to 19.3%. Estimates of the within- and between-subject biological variations of the LDLR mRNA content in peripheral blood mononuclear cells (PBMCs) isolated from healthy volunteers were 21.5% and 13.6%, respectively, and the analytical imprecision was 22.6%. The mean content of LDLR mRNA in PBMCs from healthy individuals was 0.78 copies per cell.

Improved RNase protection assay for quantifying LDL-receptor mRNA; estimation of analytical imprecision and biological variance in peripheral blood mononuclear cells

We have improved the protocol for RNA quantification by using RNase protection. Instead of precipitation and extraction with phenol and chloroform, we use a faster and more reliable precipitation based on guanidinium thiocyanate (GdSCN). The internal standard is produced by in vitro transcription of a DNA template constructed so as to allow simultaneous detection of the in vitro transcript and the low-density lipoprotein receptor (LDLR) mRNA by use of the same probe and hybridization. Addition of this internal standard at the step for RNA isolation reduced the analytical imprecision from 40.8% to 19.3%. Estimates of the within- and between-subject biological variations of the LDLR mRNA content in peripheral blood mononuclear cells (PBMCs) isolated from healthy volunteers were 21.5% and 13.6%, respectively, and the analytical imprecision was 22.6%. The mean content of LDLR mRNA in PBMCs from healthy individuals was 0.78 copies per cell.

Genetic diagnosis with the denaturing gradient gel electrophoresis technique improves diagnostic precision in familial hypercholesterolemia

BACKGROUND

Familial hypercholesterolemia (FH) is an autosomal dominant inherited disorder of lipid metabolism caused by mutations in the LDL receptor gene. FH is characterized clinically by elevated LDL cholesterol level and premature coronary disease. Diagnosing FH on clinical grounds may be difficult, and previous genetic methods are too cumbersome for routine use except in the few populations with FH-founder mutations. A simple mutation screening technique based on denaturing gradient gel electrophoresis (DGGE) has been highly useful in detecting mutations in other genes, and in the present study we evaluated the diagnostic potential of this method for the diagnosis of FH.

METHODS AND RESULTS

Conditions for screening exon 3 of the LDL receptor gene using the DGGE technique were established and 14 Danish FH families were examined. An index patient from 1 family had an abnormal DGGE pattern; consequently, an examination of exon 3 of the LDL receptor gene in 21 members of this patient's family was done. The DGGE pattern was seen only in patients with a definite clinical diagnosis of FH. Subsequent sequencing of exon 3 of the LDL receptor gene in these individuals revealed the presence of the French-Canadian type 4 Trp66-Gly mutation. However, in 4 of 11 cases in which a definite clinical diagnosis of FH had been made, the inheritance of the French-Canadian type 4 mutation could be rejected on the basis of genetic analysis.

CONCLUSIONS

Introduction of a simple genetic analysis based on DGGE may improve the precision of diagnosis in FH families.

Robust nonradioactive oligonucleotide ligation assay to detect a common point mutation in the CYP2D6 gene causing abnormal drug metabolism

A new nonradioactive oligonucleotide ligation assay for the detection of a common point mutation in the CYP2D6 gene is presented. The assay takes advantage of simultaneous time-resolved fluorescence measurements of lanthanide-labeled probes and the specificity of T4-DNA ligase in combination with the polymerase chain reaction. This strategy makes it possible to perform the assay using both the wild-type-specific and mutant-specific probes simultaneously, securing an internal control in each reaction. We show that the allele-specific ligation part of the assay can be performed with great accuracy over a wide range of temperatures, salt concentrations, and T4-DNA ligase concentrations. This eliminates the risk of false-positive or false-negative reactions due to variations in these factors. Because the assay is simple to perform, is very reliable, and can be partly automated, we conclude that it is well-suited for analysis in a routine laboratory.

Robust nonradioactive oligonucleotide ligation assay to detect a common point mutation in the CYP2D6 gene causing abnormal drug metabolism

A new nonradioactive oligonucleotide ligation assay for the detection of a common point mutation in the CYP2D6 gene is presented. The assay takes advantage of simultaneous time-resolved fluorescence measurements of lanthanide-labeled probes and the specificity of T4-DNA ligase in combination with the polymerase chain reaction. This strategy makes it possible to perform the assay using both the wild-type-specific and mutant-specific probes simultaneously, securing an internal control in each reaction. We show that the allele-specific ligation part of the assay can be performed with great accuracy over a wide range of temperatures, salt concentrations, and T4-DNA ligase concentrations. This eliminates the risk of false-positive or false-negative reactions due to variations in these factors. Because the assay is simple to perform, is very reliable, and can be partly automated, we conclude that it is well-suited for analysis in a routine laboratory.

Detection of a single base deletion in codon 424 of the low density lipoprotein receptor gene in a Danish family with familial hypercholesterolemia

We performed a screening of exon 9 of the low density lipoprotein receptor (LDLR) gene in 14 Danish families with familial hypercholesterolemia (FH) using the denaturing gradient gel electrophoresis (DGGE) technique. In one of the probands from these families an abnormal band pattern in the gradient gel was detected. Subsequent DGGE analysis of the family of this index patient revealed that the DGGE pattern cosegregated with the disease in this family. Sequencing of the exon showed a deletion of a C in codon 424 of the LDLR gene resulting in a frame shift with the introduction of a stop codon 5 codons further downstream. The mutation is referred to as FH-Odense. The predicted truncated receptor protein consists of the 428 amino terminal amino acids. Consequently, the cytosolic and membrane spanning parts of the mature LDL receptor, which normally secure the receptor in the plasma membrane, are missing. The FH-Odense mutation results in severe premature coronary atherosclerosis as shown by the clinical expression in 5 generations of the affected family.

Effect of simvastatin in patients with type I (insulin-dependent) diabetes mellitus and hypercholesterolemia

In 10 hypercholesterolemic patients with Type I (insulin-dependent) diabetes, simvastatin 10-40 mg/day was compared to placebo in a randomized, double-blind, cross-over study with treatment periods of 12 weeks. Between each treatment there was a wash-out period of 4 weeks. Compared to placebo, simvastatin reduced total cholesterol by 19% (p less than 0.001) and low density lipoprotein (LDL) cholesterol by 24% (p less than 0.001). Simvastatin therapy reduced plasma triglyceride by 8% and increased high density lipoprotein (HDL) cholesterol by 8%, but neither of these alterations was significant (p greater than 0.05). Diabetic control and daily requirement of insulin were not influenced by simvastatin. In six patients, all men, there were no alterations in the concentrations of dehydroepiandrosterone-sulphate, testosterone, estradiol, prolactin, luteinizing hormone or follicle-stimulating hormone, while sex hormone-binding globulin was significantly (19% (p less than 0.05)) reduced during therapy with simvastatin. Thus, in Type I (insulin-dependent) diabetic patients, simvastatin causes significant reductions in plasma total cholesterol and LDL cholesterol which are similar in magnitude to those observed in non-diabetics. This favourable effect can be obtained without any concomitant negative influence on glucose regulation or total gonadal steroid hormone concentrations.

Heterogeneity of C4d and C3d and their complex formation with serum albumin

High molecular weight (Mr around 175 KD) forms of C4d and C3d as well as free C4d and C3d (Mr about 40 KD) were demonstrable in normal human serum (NHS). Following in vitro C activation in NHS by delta IgG, the 40 KD C4d component increased markedly. By immunofixation it was shown that the high molecular forms of C4d and C3d reacted with biotinylated anti-human albumin IgG, whereas the 40 KD-free C4d and C3d fragments did not. Furthermore, the incorporation of anti-albumin IgG in the first dimensional gel in crossed immunoelectrophoresis caused retention of the 175 KD C4d component but not of free C4d. The 175 KD C4d had a distinctly higher electrophoretic migration velocity (post-albumin region) than the 40 KD C4d fragment. The C3d-, C4d-serum albumin complexes could not be dissociated by reducing agents (DTT, mercaptoethanol), a non-ionic detergent, or exposure to high and low ionic strength.

Preparation of antibodies against the fourth complement component (C4) and development of a direct electroimmunoassay for quantification of C4d

The specificity of several preparations of antihuman C4 antibodies were examined by crossed immunoelectrophoresis. Two antibody preparations with anti-C4c and anti-"total" C4 reactivity respectively were prepared by immunoadsorption procedures and defined by comparison with reference antibodies of known specificity. These two antibody preparations were used in the development of a rocket immunoelectrophoresis with an intermediate gel for specific and direct quantification of C4d. This method permits the selective quantification of activation of the classical complement pathway as opposed to the alternative pathway activation.

Immunoelectrophoretic analysis of C4 split products expressing D but not C epitopes: influence of storage, Ca2+ and Ca2+-chelating agents

Based on immunoelectrophoretic methods a heterogeneity in the electrophoretic mobility of C4d was observed. C4d was defined immunochemically as C4 molecules expressing D but lacking C epitopes. A beta-mobile form was observed when EDTA or heparin was not added to the sample prior to electrophoretic analysis. This component was generated during electrophoresis. Another C4d component migrating to the post-albumin region probably represented an in vivo generated split product. However, this C4d form was also produced during storage of serum or plasma at room temperature and its formation was enhanced in the presence of EDTA. Based on these findings standard conditions for collection and storage of clinical samples for quantification of C4d by electroimmunoassay are suggested.