Development of a high-resolution melting method for mutation detection in familial hypercholesterolaemia patients

Aims

Current screening methods, such as single strand conformational polymorphism (SSCP) and denaturing high performance liquid chromatography (dHPLC) that are used for detecting mutations in familial hypercholesterolaemia (FH) subjects are time consuming, costly and only 80–90% sensitive. Here we have tested high-resolution melt (HRM) analysis for mutation detection using the Rotor-Gene6000 realtime rotary analyser.

Methods and subjects

Polymerase chain reaction and melt conditions (HRM) for 23 fragments of the LDL-receptor gene, a region of exon 26 in the APOB gene (including p.R3527Q) and exon 7 of the PCSK9 gene (including p.D374Y) were optimized. Two double stranded DNA saturating dyes, LC-Green and Syto9, were compared for sensitivity. Eighty-two samples with known mutations were used as positive controls. Twenty-eight Greek FH heterozygous patients and two homozygous patients from the UK and Croatia were screened.

Results

HRM was able to identify all the positive control mutations tested, with similar results with either dye. Eight different variations were found in 17 of the 28 Greek FH patients for an overall detection rate of 61%: c.41delT (1), p.W165X (1), p.C173R (3), p.S286R (2), p.V429M (4), p.G549D (4), p.V613I (1), and a previously unreported mutation p.F694V (1) which is predicted to be FH-causing by functional algorithms. Mutations were found in both the homozygous patients; p.Q92X (Croatia) and p.Y489C (UK); both patients were homozygous for their respective mutations.

Conclusions

HRM is a sensitive, robust technique that could significantly reduce the time and cost of screening for mutations in a clinical setting.

Inhibition of human immunodeficiency virus-1 (HIV-1) by beta-chemokine analogues in mononuclear cells from HIV-1-infected patients with active tuberculosis

Tuberculosis (TB) enhances human immunodeficiency virus-1 (HIV-1) activity in patients with dual HIV-1/TB infection. Therapies that control augmentations of HIV-1 activity at sites of Mycobacterium tuberculosis (MTB) infection may be useful in inhibition of viral expansion. Regulated upon activation, normal T-cell expressed and secreted (RANTES) analogues (AOP and NNY) are potent in inhibiting the entry of primary HIV-1 isolates into host mononuclear cells. These analogues were used to inhibit MTB-induced HIV-1 entry in blood monunuclear cells (PBMC) from patients with pulmonary TB, and pleural fluid mononuclear cells (PFMC) from patients with pleural TB. PBMC or PFMC were cultured with and without MTB in presence and absence of RANTES analogues. HIV-1 strong stop DNA was assessed by real-time polymerase chain reaction (PCR) as a measure of infection. CCR5 mRNA was assessed by real-time reverse transcription (RT)-PCR and by immunostaining and FACS analysis. HIV-1 infection was induced by MTB in vitro in PBMC from the majority (14 of 20) of HIV-1/TB subjects, and new infection was inhibited by AOP- or NNY-RANTES. HIV-1 infection was also inhibited by these reagents in MTB-induced PFMC from three of three patients with pleural TB. Expression of CCR5 mRNA was significantly induced by MTB in PBMC from patients with pulmonary TB. Further, expression of CCR5 was higher in PFMC compared to PBMC from patients with pleural TB. Also, CCR5 was fourfold higher on CD14(+) pleural mononuclear cells than on CD4(+) lymphocytes. Blocking new HIV-1 infection of mononuclear cells may be useful in control of HIV-1 during dual HIV-1/TB infection.

Inhibition of tau polymerization by its carboxy-terminal caspase cleavage fragment

Abnormal aggregation of the microtubule-associated protein, tau, occurs in many neurodegenerative diseases, making it important to understand the mechanisms of tau polymerization. Previous work has indicated that the C-terminal region of tau inhibits polymerization in vitro, and a growing body of evidence implicates caspase cleavage of tau at Asp 421 in the C-terminus as an important inducer of tau polymerization in Alzheimer's disease. In the present study, we provide evidence that the C-terminal peptide fragment produced by caspase cleavage inhibits tau polymerization, suggesting that caspase cleavage of tau enhances its polymerization by removing the inhibitory control element. Moreover, we provide evidence that the peptide assumes an alpha-helical configuration and inhibits tau assembly by interacting with residues 321-375 in the microtubule binding repeat region. These findings indicate that formation of the fibrillar pathologies during the course of Alzheimer's disease may be driven or sustained by apoptotic events leading to caspase activation.

Functional characterization of chimeric reverse transcriptases with polypeptide subunits of highly divergent HIV-1 group M and O strains

Human immunodeficiency virus (HIV)-1 strains have been divided into three groups: main (M), outlier (O), and non-M non-O (N). Biochemical analyses of HIV-1 reverse transcriptase (RT) have been performed predominantly with enzymes derived from HIV-1 group M:subtype B laboratory strains. This study was designed to optimize the expression and to characterize the enzymatic properties of HIV-1 group O RTs as well as chimeric RTs composed of group M and O p66 and p51 subunits. The DNA-dependent DNA polymerase activity on a short heteropolymeric template-primer was similar with all enzymes, i.e. the HIV-1 group O and M and chimeric RTs. Our data revealed that the 51-kDa subunit in the chimeric heterodimer p66(M:B)/p51(O) confers increased heterodimer stability and partial resistance to non-nucleoside RT inhibitors. Chimeric RTs (p66(M:B)/p51(O) and p66(O)/p51(M:B)) were unable to initiate reverse transcription from tRNA(3)(Lys) using HIV-1 group O or group M:subtype B RNA templates. In contrast, HIV-1 group O and M RTs supported (-)-strand DNA synthesis from tRNA(3)(Lys) hybridized to any of their corresponding HIV-1 RNA templates. HIV-2 RT could not initiate reverse transcription on tRNA(3)(Lys)-primed HIV-1 genomic RNA. These findings suggest that the initiation event is conserved between HIV-1 groups, but not HIV types.

C-terminal inhibition of tau assembly in vitro and in Alzheimer's disease

Alzheimer's disease (AD) is, in part, defined by the polymerization of tau into paired helical and straight filaments (PHF/SFs) which together comprise the fibrillar pathology in degenerating brain regions. Much of the tau in these filaments is modified by phosphorylation. Additionally, a subset also appears to be proteolytically truncated, resulting in the removal of its C terminus. Antibodies that recognize tau phosphorylated at S(396/404)or truncated at E(391) do not stain control brains but do stain brain sections very early in the disease process. We modeled these phosphorylation and truncation events by creating pseudo-phosphorylation and deletion mutants derived from a full-length recombinant human tau protein isoform (ht40) that contains N-terminal exons 2 and 3 and all four microtubule-binding repeats. In vitro assembly experiments demonstrate that both modifications greatly enhance the rates of tau filament formation and that truncation increases the mass of polymer formed, as well. Removal of as few as 12 or as many as 121 amino acids from the C terminus of tau greatly increases the rate and extent of tau polymerization. However, deletion of an additional 7 amino acids, (314)DLSKVTS(320), from the third microtubule-binding repeat results in the loss of tau's ability to form filaments in vitro. These results suggest that only part of the microtubule-binding domain (repeats 1, 2 and a small portion of 3) is crucial for tau polymerization. Moreover, the C terminus of tau clearly inhibits the assembly process; this inhibition can be partially reversed by site-specific phosphorylation and completely removed by truncation events at various sites from S(320) to the end of the molecule.

Glycaemic control and familial factors determine hyperlipidaemia in early childhood diabetes. Oxford Regional Prospective Study of Childhood Diabetes

AIMS

To determine whether abnormal lipid levels in children with Type 1 diabetes mellitus are the result of poor metabolic control or may in part be determined by genetic factors.

METHODS

Non-fasting lipid levels were measured in 141 children with Type 1 diabetes (age range 7.7-19 years) 3 years after diagnosis, and in 192 of their parents. Glycosylated haemoglobin and the urinary albumin-creatinine ratio (three urine samples) were estimated in each child annually.

RESULTS

The children had a mean total cholesterol of 4.46 +/- 1.25 mmol/l (+/- SD) and a median triacylglycerol of 1.18 mmol/l (range 0.32-4.7). A total of 15.3% of the population had a total cholesterol > 5.2 mmol/l and 17.9% had a triacylglycerol > 1.7 mmol/l; in 5.6% both total cholesterol and triacylglycerol were greater than these cut-off points. Total cholesterol, triacylglycerol and very low density lipoprotein-cholesterol were significantly correlated to glycaemic control. However, total cholesterol was also significantly related to parental total cholesterol either as analysed separately or as mean parental total cholesterol (r = 0.37, P = 0.0001). In stepwise multiple regression analysis both mean parental total cholesterol (P = 0.001) and HbA1c (P = 0.015) were significant determinants of the child's total cholesterol. The children studied were being followed prospectively for the development of microalbuminuria and there was a weak association across tertiles of total cholesterol, linking higher levels to the development of microalbuminuria (P < 0.05).

CONCLUSIONS

We conclude that both glycaemic control and familial factors may be important determinants of lipid levels in young people with diabetes. Both may contribute to the subsequent risk of cardiovascular disease and possibly the development of incipient diabetic nephropathy.

Dermatology in southwestern Ethiopia: rationale for a community approach

BACKGROUND

Skin diseases represent one of the most frequent causes of morbidity in developing countries; however, little is known about the dermatologic needs of the population. The prevalence of skin disease in two different rural communities in southwestern Ethiopia was determined using descriptive epidemiologic techniques.

METHODS

A household survey, designed to ascertain demographic information and dermatologic needs, was given to all households in both communities (827). The point prevalence of skin diseases was determined after examination by dermatologists of 768 self-selected individuals (40% of individuals were invited to attend dermatologic examination, either those self-reporting skin disease or identified as positive cases during the household survey); an individual survey form was given to all of these patients.

RESULTS

Although 47% (S/UO) and 59% (Kishe) of the households in the two communities reported skin symptoms, the true dermatologic needs of these settlements were far greater than the expressed values, as examination by dermatologists of randomly selected households revealed that 67% of householders not reporting dermatoses had significant skin disease. During the point prevalence study, the commonest complaints were parasitic (scabies, pediculosis, and onchocerciasis) infestations (46% of diagnoses), followed by bacterial and fungal infections (33%); other conditions included endemic nonfilarial elephantiasis. Overcrowding was the main risk factor for infection. Thirty-two per cent (S/UO) and 39% (Kishe) of examined individuals had received previous treatments, which were ineffective in 74% and 63% respectively.

CONCLUSIONS

Subsistence farmers spend a high proportion of their limited cash income on ineffective treatment. Simple schemes of management for the most common dermatoses, which local health workers could be trained to recognize and manage, could do much to redress the burden of skin disease in this population.

Acute effect of fructose on postprandial lipaemia in diabetic and non-diabetic subjects

We investigated whether the potentiation of postprandial lipaemia by fructose occurs in both non-diabetic subjects and those with non-insulin-dependent diabetes mellitus. Six non-diabetic and six diabetic subjects were studied on two occasions. They were given a meal containing 1 g fat/kg body weight with, on one occasion, 0.75 g fructose/kg body weight, on the other occasion 0.75 g starch/kg body weight. In both groups, plasma glucose and insulin concentrations rose more after starch than after fructose. At 1-2 h after the meal, plasma non-esterified fatty acid concentrations were suppressed more after fructose than after starch, but later they rose more after fructose than after starch. Plasma triacylglycerol concentrations rose more slowly after fructose, but were considerably higher than those after starch from 4-6 h after the meal. There were no differences in post-heparin plasma lipoprotein lipase (EC 3.1.1.34) activity at the end of the test. The potentiation of postprandial lipaemia by fructose was positively related to the fasting plasma insulin concentration, suggesting that insulin-resistant subjects are more prone to this effect. We conclude that the potentiation of postprandial lipaemia by fructose is seen in both diabetic and non-diabetic subjects. Our results suggest that alterations in the dynamics of plasma non-esterified fatty acids might underlie the effects of fructose on triacylglycerol metabolism.

Tinea capitis in south-western Ethiopia: a study of risk factors for infection and carriage

BACKGROUND

Tinea capitis is a common dermatophyte infection which constitutes an important public health problem among children worldwide. The endemic nature of scalp ringworm in Africa is perpetuated mainly by the lack of knowledge about the prevalence and carrier status, and the absence of control measures.

METHODS

Two hundred and nineteen schoolchildren from urban and rural communities of the Illubabor district, south-western Ethiopia, were examined, and scalp samples were taken. Children were classified according to clinical signs and mycologic findings.

RESULTS

Physical examination revealed that 29% of the children had clinical lesions compatible with tinea capitis. Dermatophytes were isolated from 33% of the children's scalp samples; of these, 16% had clinical lesions and 17% were identified as carriers. Trichophyton violaceum was responsible for 97% of infections.

CONCLUSIONS

Tinea capitis was the second most prevalent cutaneous finding in these children, with a higher prevalence in the urban community; the predictive value of the clinical diagnosis was low and a high proportion of children were identified as carriers in these communities. No relationship between household overcrowding and scalp infection was found.

The prevalence of skin disease among school children in rural Ethiopia--a preliminary assessment of dermatologic needs

It is always assumed that the prevalence of skin diseases in developing countries is very high, and that infestations and skin infections are highly endemic in poor rural communities; however, very few epidemiologic reports verify these assumptions. As part of a continuing study of dermatologic needs in southwestern Ethiopia, and to estimate the prevalence of treatable skin disease in children, a school survey was undertaken in Shebe. In October 1992, 112 children were examined by a team of dermatologists and their conditions were recorded. Twenty-two children (19.6%) were considered healthy and 90 (80.4%) had one or more skin diseases. A total of 140 conditions were identified and considered treatable in 98% of children. Infestations were the most prevalent skin pathology, 81.2%, followed by fungal infections, 13.4%.

Inhibition of tumor cell proliferation by dexamethasone: 31P NMR studies of RIF-1 fibrosarcoma cells perfused in vitro

The impact on tumor cell metabolism of a substantial reduction in cell proliferation rate without acute cytotoxicity was examined in cultured RIF-1 tumor cells following treatment with an antiproliferative steroid, dexamethasone (DEX). After 48 h exposure to 4 mM DEX, acute cell viability was essentially unchanged: cells were 93 +/- 2% trypan blue excluding in both control and treated cultures (all values are mean +/- SD). The fraction of actively proliferating cells in the S phase (as indicated by incorporation of 5-bromodeoxyuridine) was only 4 +/- 3%, compared with 13 +/- 3% in age-matched control cultures (n =4, paired t-test: p < 0.004) and 23 +/- 7% at the beginning of the treatment. Three days of DEX treatment resulted in a limited increase in the level of apoptosis (programmed cell death): cells did not become rounded or detached, but the fraction expressing apoptotic DNA fragmentation (susceptible to nick end labeling by terminal deoxy-nucleotidyl transferase) was 15 +/- 7%, vs 2 +/- 1% in control cultures (p < 0.02). Despite a 75% inhibition of cell proliferation, DEX caused only a modest change in the 31P NMR spectra of RIF-1 cells in vitro. The ratio of phosphocreatine to nucleoside triphosphates (NTP) was 30% higher, on average, in treated than in control cells (n = 8, paired t-test, p < 0.02), even when both treated and control cell densities were low. The level of total phosphomonoester (relative to NTP) was lower at low cell density, but this was independent of whether cells were growing rapidly (control low density) or were growth inhibited by DEX. Neither the ratio of phosphocholine to NTP nor the intracellular pH was significantly different in DEX-treated cells.

Competition between Li+ and Mg2+ for the phosphate groups in the human erythrocyte membrane and ATP: an NMR and fluorescence study

We investigated the mechanism of competition between Li+ and Mg2+ in Li(+)-loaded human red blood cells (RBCs) by making 7Li and 31P NMR and fluorescence measurements. We used 7Li NMR relaxation times to probe Li+ binding to the human RBC membrane and ATP; an increase in Mg2+ concentration caused an increase in both 7Li T1 and T2 values in packed Li(+)-loaded RBCs, in suspensions of Li(+)-loaded RBC ghosts, in suspensions of Li(+)-containing RBC membrane, and in aqueous solutions of ATP, indicating competition between Li+ and Mg2+ for binding sites in the membrane and ATP. We found that increasing concentrations of either Li+ or Mg2+ in the presence of human RBC membrane caused an increase in the 31P NMR chemical shift anisotropy parameter, which describes the observed axially symmetric powder pattern, indicating metal ion binding to the phosphate groups in the membrane. Competition between Li+ and Mg2+ for phosphate groups in ATP and in the RBC membrane was also observed by both fluorescence measurements and 31P NMR spectroscopy at low temperature. The ratio of the stoichiometric binding constants of Mg2+ to Li+ to the RBC membrane was approximately 20; the ratio of the conditional binding constants in the presence of a free intracellular ATP concentration of 0.2 mM was approximately 4, indicating that Li+ competes for approximately 20% of the Mg(2+)-binding sites in the RBC membrane. Our results indicate that, regardless of the spectroscopic method used, Li+ competes with Mg2+ for phosphate groups in both ATP and the RBC membrane; the extent of metal ion competition for the phosphate head groups of the phospholipids in the RBC membrane is enhanced by the presence of ATP. Competition between Li+ and Mg2+ for anionic phospholipids or Mg(2+)-activated proteins present in cell membranes may constitute the basis of a general molecular mechanism for Li+ action in human tissues.

Competition between Li+ and Mg2+ for ATP and ADP in aqueous solution: a multinuclear NMR study

We used 7Li NMR spin-lattice relaxation times and 31P NMR chemical shifts to study the binding of Li+ and Mg2+ to the phosphate moieties of ATP and ADP. To examine the binding of Li+ and Mg2+ to the base and ribose moieties, we used 1H and 13C NMR chemical shifts. The 7Li NMR relaxation times of Li+/Mg2+ mixtures of ATP or ADP increased with increasing concentrations of Mg2+, suggesting competition between the two ions for adenine nucleotides. No significant binding of Li+ and Mg2+ to the base and ribose moieties occurred. At the pH and ionic strength used, 2:1 and 1:1 species of the Li(+)-ATP and Li+-ADP complexes were present, with the 2:1 species predominating. In contrast, 1:1 species predominated for the Mg(2+)-ADP and Mg(2+)-ATP complexes. We calculated the Li(+)-nucleotide binding constants in the presence and absence of Mg2+ and found them to be somewhat greater in the presence of Mg2+. Although competition between Li+ and Mg2+ for ATP and ADP phosphate binding sites in solution is consistent with the 31P chemical shift data, the possibility that the Li+ and Mg2+ form mixed complexes with the phosphate groups of ATP or ADP cannot be ruled out.

Measurement of lithium transport in RBC from psychiatric patients receiving lithium carbonate and normal individuals by 7Li NMR spectroscopy

A reproducible 7Li nuclear magnetic resonance (NMR) method, based on a modified inversion recovery (MIR) pulse sequence, was used to discriminate between intra- and extracellular lithium concentrations in red blood cell (RBC) suspensions. The rates of Na(+)-Li+ countertransport determined by the 7Li NMR method were significantly correlated with the measurements made by atomic absorption (AA) for 14 psychiatric patients receiving lithium carbonate (r = 0.937) and 14 normal individuals (r = 0.931). As expected, the rates of Na(+)-Li+ countertransport measured by MIR were significantly lower for the psychiatric patients receiving lithium carbonate than for normal individuals. The 7Li NMR method provides RBC Li+ countertransport information comparable to AA for psychiatric patients and normal individuals. A description of the advantages of the 7Li NMR method in contrast to the AA method, including the study of Li+ interactions with RBC components such as membrane proteins and anionic phospholipids, is included.

Inhibition of the formation of the complement membrane-attack complex by a monoclonal antibody to the complement component C8 alpha subunit

The effect of nine monoclonal antibodies to complement component C8 on the interaction of C9 with preformed cell-surface C5b-8 complexes and on the functional insertion of C8 into the membrane-attack complex (MAC) was investigated. None of the antibodies prevented C9 insertion into a preformed C5b-8 complex. One antibody (F1) directed to the C8 alpha subunit clearly inhibited formation of a functional MAC. It is proposed that this antibody prevents the C8 alpha subunit unfolding and distorting the bilayer to allow C9 insertion.

The preparation and characterization of monoclonal antibodies to human complement component C8 and their use in purification of C8 and C8 subunits

1. Ten mouse monoclonal antibodies to human complement component C8 were prepared. It was found that six of these antibodies reacted with the alpha-subunit, two with the beta-subunit and two with the gamma-subunit, when assessed by immunoblotting after separation of C8 subunits by SDS/polyacrylamide-gel electrophoresis. 2. Epitope analysis of the ten monoclonal antibodies in a competitive binding assay showed that the six antibodies to the alpha-subunit could be classified in four overlapping epitope groups. The antibodies to the beta- and gamma-subunits bound to a single antigenic site on each, but also cross-reacted with the antigenic sites on the alpha-subunit. 3. Monoclonal anti-C8 immunoaffinity columns were used to purify C8 from fresh human plasma and to prepare C8-depleted serum. Immunoaffinity purified C8 was biologically active when assessed by using haemolysis assays of sheep and rabbit erythrocytes. 4. Salt elution was used to purify either alpha gamma- or beta-subunits when C8 was respectively bound to an anti-beta or anti-alpha immunoaffinity column. The purified subunits reconstituted C8-depleted serum when added together in a haemolysis assay.

Immunocytochemical localisation of complement components C8 and C9 in human diseased muscle. The role of complement in muscle fibre damage

The localisation of the complement components C8 and C9 was studied immunocytochemically in human diseased muscle to determine the role of complement in muscle fibre damage. Monoclonal antibodies to 2 epitopes of C9 and a monoclonal antibody to the alpha subunit of C8 were applied to frozen sections of muscle biopsies from 9 cases of dermatomyositis, 5 cases of polymyositis, 7 cases of Duchenne muscular dystrophy and 4 cases of Becker muscular dystrophy. These were compared with 6 control biopsies which were morphologically normal. In all cases of inflammatory myopathies several non-necrotic fibres showed discrete peripheral patches of C9 and to a lesser extent C8. In the muscular dystrophies peripheral C9 was observed on a few non-necrotic fibres and basophilic fibres showed C9 between the fibres as well as at the periphery. In all cases necrotic fibres labelled intensely with C9 and C8 but intensities varied with the different monoclonal antibodies. This was thought to result from differences in the polymerisation of the C9 molecule in the membrane attack complex. Complement C8 and C9 were also localised to blood vessels in 3 cases of muscular dystrophy, 2 cases of polymyositis and all cases of juvenile dermatomyositis. No complement was observed in the control samples. Our results provide evidence for the sublytic formation of the membrane attack complex (MAC) on non-necrotic fibres in inflammatory myopathies and muscular dystrophy. This sublytic formation of the MAC may induce sublethal metabolic damage, mediated by calcium, and suggests a primary role of complement in muscle damage not only in inflammatory disorders but also muscular dystrophy.