Familial chylomicronemia caused by a novel type of mutation in the APOE-CI-CIV-CII gene cluster encompassing both the APOCII gene and the first APOCIV gene mutation: APOCII-CIV(Nijmegen)

Apolipoprotein CII (ApoCII) deficiency is a relatively rare cause of the chylomicronemia syndrome, a disorder characterized by severe fasting hypertriglyceridemia and massive accumulation of chylomicrons in plasma. Here we present a case which is the first example of apoCII deficiency caused by a major rearrangement in the APOCII gene. Southern blot analysis revealed an approximately 7.5-kb deletion disrupting the APOCII gene including the promotor region and first exon. Interestingly, the deletion also encompasses the APOCIV gene, a recently discovered novel gene upstream of APOCII. This deletion is the first mutation to be reported in the APOCIV gene.     

Genetic heterogeneity of Apo CII locus in north India

Apolipoprotein CII genotypes were determined in Brahmins, Banias, Jat Sikhs, Khatris, Ramgarhia, Ramdasia and Scheduled Castes of Punjab, North India (n = 930). The Apo CII exhibits three common polymorphic alleles CII*1, CII*2 and CII*3 with pooled frequencies 0.883, 0.114 and 0.003, respectively. CII*3 was absent in Brahmins. Distribution of Apo CII isoforms highlights a considerable variation among different ethnic groups across the world. The average heterozygosity of the Punjabi populations was 0.208. The gene diversity among these population groups was less than 0.1%.     

Crotonobetaine reductase from Escherichia coli consists of two proteins

Crotonobetaine reductase from Escherichia coli is composed of two proteins (component I (CI) and component II (CII)). CI has been purified to electrophoretic homogeneity from a cell-free extract of E. coli O44 K74. The purified protein shows l(-)-carnitine dehydratase activity and its N-terminal amino acid sequence is identical to the caiB gene product from E. coli O44 K74. The relative molecular mass of CI has been determined to be 86100. It is composed of two identical subunits with a molecular mass of 42600. The isoelectric point of CI was found to be 4.3. CII was purified from an overexpression strain in one step by ion exchange chromatography on Fractogel EMD TMAE 650(S). The N-terminal amino acid sequence of CII shows absolute identity with the N-terminal sequence of the caiA gene product, i.e. of the postulated crotonobetaine reductase. The relative molecular mass of the protein is 164400 and it is composed of four identical subunits of molecular mass 41500. The isoelectric point of CII is 5.6. CII contains non-covalently bound FAD in a molar ratio of 1:1. In the crotonobetaine reductase reaction one dimer of CI associates with one tetramer of CII. A still unknown low-molecular-mass effector described for the l(-)-carnitine dehydratase is also necessary for crotonobetaine reductase activity. Monoclonal antibodies were raised against the two components of crotonobetaine reductase.     

Familial apolipoprotein CII deficiency: A preliminary analysis of the gene defect in two independent families

Summary We have used a cDNA clone for human apolipoprotein CII (apo CII) to study the apo CII genes in two independent individuals with familial apo CII deficiency. With all the restriction enzymes so far used, gene fragments hybridising with apo CII cDNA are observed that are indistinguishable from normal samples. This demonstrates that in neither of these individuals is the defect due to a major deletion of DNA in or around the apo CII gene. We have used a common polymorphism of the apo CII gene detected with the enzyme TaqI to follow the inheritance of the gene in the families of these apo CII deficient individuals. The pattern of inheritance that we observe is consistent with the defect causing apo CII deficiency being in, or closely linked to the apo CII structural gene.     

Biotransformation of crotonobetaine to L(–)-carnitine in Proteus sp.

Two proteins, component I (CI) and component II (CII), catalyze the biotransformation of crotonobetaine to L(-)-carnitine in Proteus sp. CI was purified to electrophoretic homogeneity from cell-free extracts of Proteus sp. The N-terminal amino acid sequence of CI showed high similarity (80%) to the caiB gene product from Escherichia coli O44K74, which encodes the L(-)-carnitine dehydratase. CI alone was unable to convert crotonobetaine into L(-)-carnitine even in the presence of the cosubstrates crotonobetainyl-CoA or gamma-butyrobetainyl-CoA, which are essential for this biotransformation. The relative molecular mass of CI was determined to be 91.1 kDa. CI is composed of two identical subunits of molecular mass 43.6 kDa. The isoelectric point is 5.0. CII was purified to electrophoretic homogeneity from cell-free extracts of Proteus sp. and its N-terminal amino acid sequence showed high similarity (75%) to the caiD gene product of E. coli O44K74. The relative molecular mass of CII was shown to be 88.0 kDa, and CII is composed of three identical subunits of molecular mass 30.1 kDa. The isoelectric point of CII is 4.9. For the biotransformation of crotonobetaine to L(-)-carnitine, the presence of CI, CII, and a cosubstrate (crotonobetainyl-CoA or gamma-butyrobetainyl-CoA) were shown to be essential.     

Preparative isoelectric focussing of apolipoproteins C and E from human very low density lipoproteins.

The application of isoelectric focussing on a gel-stabilized layer for the separation of the Tris-urea-soluble apolipoproteins of very low density lipoproteins has been described. This method in one step, allows the separation of most apolipoproteins, which were then analyzed and characterized. Apolipoproteins CII and CI were isolated as single protein bands with apparent pI of 5.0 and 6.5, respectively. Apolipoprotein CII was biologically active and could activate lipoprotein lipase. Apolipoprotein CIII was separated into several protein bands with pI ranging from 4.7 to 5.1 as a function of their number of sialic acid residues. Apolipoprotein E was isolated and characterized into five polymorphic bands with pI of 5.7, 5.8, 5.9, 6.0, and 6.2, respectively.     

Apolipoprotein CII (apo CII) gene expression defect in an individual with familial apo CII deficiency

We have examined the expression of the apolipoprotein CII (apo CII) gene in an individual with familial apo CII (apo CII) deficiency. Total RNA was prepared from this patient's liver tissue and analysed in Slot Blot and Northern Blot experiments using a cloned apo CII cDNA as a probe. In this patient, there is at least a four-fold decrease in the level of apo CII mRNA, when compared to liver tissue from a control individual. The residual apo CII mRNA detected in this patient is of normal length. These results suggest that the failure to detect apo CII protein in this patient's serum is not due to a failure to transcribe or process apo CII mRNA, but probably to a defect in the translation of the apo CII message. This defect results in partial degradation of the apo CII message leading to the much reduced levels which we have observed.     

The gene causing familial hypoalphalipoproteinemia is not caused by a defect in the apo AI-CIII-AIV gene cluster in a Spanish family

Summary High-density lipoprotein (HDL) cholesterol levels have an inverse relationship with the frequency of coronary and cerebrovascular disease. Most commonly HDL deficiency is environmentally modulated. Familial hypoalphalipoproteinemia (FHA) is a genetically determined HDL deficiency disease, in all likelihood transmitted as an autosomal dominant trait and associated with premature atherosclerosis. Apolipoprotein AI (apo AI) is the major apoprotein in the HDL particle, and defects in this protein have been suggested as the cause of FHA. We have identified a large family of Spanish descent with FHA and performed genetic linkage analysis using restriction fragment length polymorphisms in the Apo AI-CIII-AIV gene cluster to test this hypothesis. Results in this family formally exclude the apo AI-CIII-AIV gene cluster as the site for the mutation underlying FHA.     

A deletion mutation in the ApoC-II gene (ApoC-II Nijmegen) of a patient with a deficiency of apolipoprotein C-II

The apolipoprotein C-II gene from a patient with a deficiency of apoC-II was cloned and sequenced. A single base deletion of a guanosine at position 2943 in exon three of the gene of the proband was identified by sequence analysis. This point mutation results in a shift of the reading frame and introduces a premature termination codon (TGA) at a position in the gene immediately following amino acid 17 of the mature C-II apolipoprotein. This single base deletion results in the loss of a normally occurring HphI restriction enzyme site in the apoC-II gene. Amplification of the mutant DNA sequence by the polymerase chain reaction and restriction enzyme digestion with HphI established that the patient is a homozygote for the base deletion. No apoC-II was detectable in the patient's plasma by two-dimensional gel electrophoresis and immunoblotting. We propose that the guanosine deletion is the primary genetic defect in this kindred leading to premature termination and formation of a nonfunctional truncated 17-amino acid C-II apolipoprotein which ultimately results in apoC-II deficiency.     

Point mutations and polymorphisms in the human dystrophin gene identified in genomic DNA sequences amplified by multiplex PCR

Summary About one third of Duchenne muscular dystrophy (DMD) patients have no gross DNA rearrangements in the dystrophin gene detectable by Southern blot analysis or multiplex exon amplification. Presumably, in these cases, the deficiency is caused by minor structural lesions of the dystrophin gene. However, to date, only a single human DMD case has been described where a point mutation, producing a stop codon, accounts for the DMD phenotype. To screen for microheterogeneities in the dystrophin gene, we applied analysis by chemical mismatch cleavage to thirteen exons amplified in multiplex sets by the polymerase chain reaction. This analysis covers approximately 20% of the dystrophin-coding sequence. Sixty DMD patients without detectable deletions or duplications were investigated, leading to the identification of two point mutations and four polymorphisms with a frequency higher than 5%. Both point mutations are frameshift mutations in exons 12 and 48, respectively, and are closely followed by stop codons, thus explaining the functional deficiency of the dystrophin gene products in both patients.     

DNA sequence duplication in Rhodobacter sphaeroides 2.4.1: evidence of an ancient partnership between chromosomes I and II

The complex genome of Rhodobacter sphaeroides 2.4.1, composed of chromosomes I (CI) and II (CII), has been sequenced and assembled. We present data demonstrating that the R. sphaeroides genome possesses an extensive amount of exact DNA sequence duplication, 111 kb or approximately 2.7% of the total chromosomal DNA. The chromosomal DNA sequence duplications were aligned to each other by using MUMmer. Frequency and size distribution analyses of the exact DNA duplications revealed that the interchromosomal duplications occurred prior to the intrachromosomal duplications. Most of the DNA sequence duplications in the R. sphaeroides genome occurred early in species history, whereas more recent sequence duplications are rarely found. To uncover the history of gene duplications in the R. sphaeroides genome, 44 gene duplications were sampled and then analyzed for DNA sequence similarity against orthologous DNA sequences. Phylogenetic analysis revealed that approximately 80% of the total gene duplications examined displayed type A phylogenetic relationships; i.e., one copy of each member of a duplicate pair was more similar to its orthologue, found in a species closely related to R. sphaeroides, than to its duplicate, counterpart allele. The data reported here demonstrate that a massive level of gene duplications occurred prior to the origin of the R. sphaeroides 2.4.1 lineage. These findings lead to the conclusion that there is an ancient partnership between CI and CII of R. sphaeroides 2.4.1.     

Molecular characterisation of two alpha-1-antitrypsin deficiency variants: proteinase inhibitor (Pi) NullNewport (Gly115→Ser) and (Pi) Z Wrexham (Ser−19→Leu)

Summary Two single point mutations in the alpha-1-antitrypsin gene, resulting in AAT deficiency, have been characterised in heterozygotes by DNA amplification and direct sequencing. The mutations result in amino acid substitutions, Gly¹¹⁵Ser and Ser^–19Leu, in the leader sequence, respectively, and have been designated Pi Null_Newport and Pi Z Wrexham. In the two families studied the mutations occur on chromosomes which also carry the common mutation causing Z deficiency. Individuals with such a deficiency are, therefore, compound heterozygotes. It is not known if these particular mutations would only cause a mild form of AAT deficiency in the absence of the Z mutation as they do not appear to cause predictable folding abnormalities. They do, however, result in severe deficiency when the Z mutation occurs in the same gene.     

Ornithine transcarbamylase deficiency: new sites with increased probability of mutation

Ornithine transcarbamylase (OTC) deficiency, the most common inborn error of the urea cycle, shows an X-linked inheritance with frequent new mutations. Investigations of patients with OTC deficiency have indicated an overproportionate share of mutations at CpG dinucleotides. These statistics may, however, be biased because of the easy detection of CpG mutations by screening for TaqI and MspI restriction sites. In the present study, we investigated 30 patients, with diagnosed OTC deficiency, for new sites with an increased probability of mutation by complete DNA sequence analysis of all ten exons of the OTC gene. In six patients, two codons in exons 2 and 5, respectively, contained novel recurrent mutations, all of them affecting CpG dinucleotides. They included C to T and G to A transitions in codon 40, changing an arginine to cysteine and histidine, respectively, and a C to T transition in codon 178 causing the substitution of threonine by methionine. The first two mutations were characterized by a mild clinical course with high risk of sudden death in late childhood or early adulthood, whereas the third mutation showed a more severe phenotypic expression. In addition to these novel mutations, we identified four patients with the known R277W mutation, making it the most common point mutation of the OTC gene.     

Mild hemophilia A associated with a cryptic donor splice site mutation in intron 4 of the factor VIII gene

Hemophilia A, an X-linked disease caused by deficiency of factor VIII, is characterized by variation in clinical severity and coagulation activity. This variation is though to reflect heterogeneity of mutations in the factor VIII gene. Here we describe a CG-to-CA mutation within a potential cryptic donor splice site in intron 4 of the factor VIII gene from a patient with mild disease. This mutation makes the cryptic sequence resemble more closely the consensus sequence for donor splice sites. We infer that the mutation activates the cryptic donor splice site, which in turn causes a defect in RNA processing.