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Biomedical subjects

E Bakker

Publications and source records attributed to E Bakker.

At least 55 records · Page 3Linked to original sources
PubMed2000

Selectivity of potentiometric ion sensors.

Selectivities of solvent polymeric membrane ion-selective electrodes (ISEs) are quantitatively related to equilibria at the interface between the sample and the electrode membrane. However, only correctly determined selectivity coefficients allow accurate predictions of ISE responses to real-world samples. Moreover, they are also required for the optimization of ionophore structures and membrane compositions. Best suited for such purposes are potentiometric selectivity coefficients as defined already in the 1960s. This paper briefly reviews the basic relationships and focuses on possible biases in the determination of selectivity coefficients. The traditional methods to determine selectivity coefficients (separate solution method, fixed interference method) are still the same as those originally proposed by IUPAC in 1976. However, several precautions are needed to obtain meaningful data. For example, errors arise when the response to a weakly interfering ion is also influenced by the primary ion leaching from the membrane. Wrong selectivity coefficients may be also obtained when the interfering agent is highly preferred and the electrode shows counterion interference. Recent advances show how such pitfalls can be avoided. A detailed recipe to determine correct potentiometric selectivity coefficients unaffected by such biases is presented.

Artifacts↗
PubMed2000

Sarcoglycanopathies in Dutch patients with autosomal recessive limb girdle muscular dystrophy.

Within a group of 76 sporadic/autosomal recessive limb girdle muscular dystrophy (LGMD) patients we tried to identify those with LGMD type 2C-E. Muscle biopsy specimens of 40 index patients, who had 22 affected sibs, were analyzed immuno-histochemically for the presence of three subunits: alpha-, beta-, and gamma-sarcoglycans. Abnormal sarcoglycan expression was established in eight patients, with six affected sibs. In one patient gamma-sarcoglycan was absent, and both alpha- and beta-sarcoglycans were reduced. In the remaining seven patients gamma-sarcoglycan was (slightly) reduced, and alpha- and beta-sarcoglycans were absent or reduced. By DNA sequencing mutations were detected in one of the three sarcoglycan genes in all eight cases. Three patients had mutations in the alpha-, three in the beta-, and two in the gamma-sarcoglycan gene. The patients with sarcoglycanopathy comprised the more severely affected cases (P=0.04). In conclusion, sarcoglycanopathy was identified in 23 % (14/62) of the autosomal recessive LGMD patients.

Adolescent↗
PubMed2000

Dystrophin nonsense mutation induces different levels of exon 29 skipping and leads to variable phenotypes within one BMD family.

Within one X-linked muscular dystrophy family, different phenotypes for three males occurred: (1) a severely affected Becker patient with cardiomyopathy, (2) a mildly affected Becker patient, and (3) an apparently healthy male with elevated serum CK levels. In the muscle biopsy specimen of patient2 one out of four antibodies (NCL-DYS1) showed absence of dystrophin. The protein truncation test detected a truncated dystrophin for both muscle tissue and lymphocytes of this patient next to an additional near normal size fragment in muscle. Genomic sequence analysis revealed a nonsense mutation in exon 29 (4148C > T) of the dystrophin gene. Sequence analysis of the mRNA fragment of the larger peptide showed skipping of exon 29, restoring an open reading frame. Consequently, the epitope of the antibody NCL-DYS1 is mapped to exon 29. The variable clinical features of the three relatives from healthy to severely affected therefore seems to be related to the level of skipping of exon 29. This finding underscores the future potential of gene therapeutic strategies aimed at inducing exon skipping in Duchenne muscular dystrophy, to generate a much milder disease.

Adult↗
PubMed2000

Changes in the toilet training of children during the last 60 years: the cause of an increase in lower urinary tract dysfunction?

OBJECTIVE: To analyse the changes in toilet training of children in Belgium in the last three generations and to seek a possible cause for the apparent increase in lower urinary tract dysfunction over that period. PATIENTS AND METHODS: A questionnaire (25 questions) was developed and completed by 321 people who had toilet-trained 812 children. The population was divided into three groups according to the age of those who trained the children. RESULTS: There has been a major change in toilet training in the last 60 years; the age at which toilet training began has been significantly postponed. One reason for starting training, i.e. bladder control during the afternoon nap (which can probably be considered as an indication of sufficient bladder capacity) has become less important. Season (summer) has become a more important factor, as has starting school. Training by bladder drill, formerly widely used, was progressively abandoned and a more liberal attitude adopted by the youngest parents. CONCLUSION: There seems to be good concordance between the programmes currently proposed for treating bladder dysfunction in children and the traditional bladder-training methods used by parents 60 years ago. To start bladder training when the child stays dry during the afternoon nap and using bladder drill might help to avoid permanent bladder dysfunction. The lack of formal bladder training may be responsible for an increase in lower urinary tract dysfunction.

Adult↗
PubMed2000

Extension of the clinical range of facioscapulohumeral dystrophy: report of six cases.

Consensual diagnostic criteria for facioscapulohumeral dystrophy (FSHD) include onset of the disease in facial or shoulder girdle muscles, facial weakness in more than 50% of affected family members, autosomal dominant inheritance in familial cases, and evidence of myopathic disease in at least one affected member without biopsy features specific to alternative diagnoses. Six patients did not meet most of these criteria but were diagnosed as FSHD by DNA testing, which showed small EcoRI fragments on chromosome 4q. Their clinical signs and symptoms and results of auxiliary investigations are reported. The patients presented with foot extensor, thigh, or calf muscle weakness. None of them had apparent facial weakness, only one complained of weakness in the shoulders, none had a positive family history. Expert physical examination, however, showed a typical facial expression, an abnormal shoulder configuration on lifting the arms, or scapular winging. This raised the suspicion of FSHD, whereupon DNA analysis was done. In conclusion, the clinical expression of FSHD is much broader than indicated by the nomenclature. The possibility to perform DNA tests is likely to greatly expand the clinical range of FSHD.

Adult↗
PubMed1999

Determination of complex formation constants of lipophilic neutral ionophores in solvent polymeric membranes with segmented sandwich membranes.

A potentiometric method to determine ionophore complex formation constants in solvent polymeric membrane phases, proposed originally by Russian researchers, is critically evaluated and compared to other established methods. It requires membrane potential measurements on two-layer sandwich membranes, where only one side contains the ionophore. The resulting initial membrane potential reflects the ion activity ratio at both aqueous phase--membrane interfaces and can be conveniently used to calculate complex formation constants in situ. This method is potentially useful, since it does not require the use of a reference ion or second ionophore in the measurement. In this paper, the five ionophores valinomycin, BME-44, ETH 2120, tert-butylcalix[4]arene tetraethyl ester, and S,S'-methylenebis(diisobutyldithiocarbamate) are characterized in poly(vinyl chloride) (PVC) plasticized with dioctyl sebacate (DOS) and compared with other established methods. The resulting formation constants correspond well to literature values. The influence of varying membrane concentrations and different anionic site additives is studied and found to be relatively small. Experiments are also performed with and without lipophilic inert electrolytes and with ionophore-free sandwich membranes to illustrate the effect of ion pairing and the membrane internal diffusion potential on the response of such sandwich membranes. These experiments suggest that ions are completely associated in PVC-DOS membranes, but that such ion pairs are rather nonspecific. Diffusion potentials seem to play a minor role with these systems. The results are explained with theory. This work indicates that the characterization of electrically charged ionophores, anion-selective ionophores, and ionophores in membrane matrixes other than PVC plasticized with DOS may now be experimentally accessible.

Ionophores↗
PubMed1999

Renewable pH cross-sensitive potentiometric heparin sensors with incorporated electrically charged H+ ionophores.

Polymer membrane-based potentiometric sensors have been developed earlier to provide a rapid and direct method of analysis for polyions such as heparin, a natural anticoagulant administered to prevent thrombus formation during cardiovascular surgery. These heparin sensors are irreversible, requiring a membrane renewal procedure between measurements which currently prevents the sensors from being used for continuous monitoring of blood heparin. A newly developed heparin sensor is shown here to allow an alternate and more practical method of membrane renewal. The electrically charged H+ ionophore 5-(octadecanoyloxy)-2-(4-nitrophenylazo)-phenol (ETH 2412) is incorporated as an additional ionophore into a heparin-sensing membrane. This membrane will respond to pH only at low H+ concentrations, while sample anions are coextracted with H+ ions into the membrane at physiological pH. In buffered samples at physiological pH, the sensors will therefore respond to heparin via an ion-exchange mechanism with chloride anions. The pH cross-sensitive heparin-sensing membranes are shown to give an excellent potentiometric response toward heparin in aqueous samples at physiological pH and Cl-levels as well as in undiluted whole blood with no loss of heparin response. The membrane renewal is accomplished by moderately increasing the pH of the sample, causing heparin to diffuse out of the membrane with H+ ions. Reproducibilities are, with less than 1 mV standard deviation, improved over the classical system. Unlike the high NaCl concentration used to strip heparin from the previously established heparin sensor, the pH change used here could ultimately be performed locally at the sample-membrane interface, allowing the sensor to be used for automated long-term monitoring of heparin in blood. A theoretical model is presented to explain the experimental results.

Algorithms↗
PubMed1999

Voltammetric and amperometric transduction for solvent polymeric membrane ion sensors.

This paper describes basic response features of solvent polymeric membrane ion sensors with voltammetric and amperometric transduction. The model systems used here contain no ionophore for simplicity reasons. Reasonable simplifications of the theory are introduced that allow one to understand the response mechanism in view of a practical application of these sensors. It is shown that ion-sensing membranes preferentially contain no ion-exchanger properties in order to function optimally in a voltammetric mode. As with the systems studied by Kihara, both liquid-polymer interfaces of the membrane are preferably polarizable. Specifically, they contain the highly lipophilic electrolyte tetradodecylammonium tetrakis(4-chlorophenyl)borate (ETH 500) in the membrane to improve lifetime, increase the magnitude of the potential window, and prohibit exchange reactions with sample ions. An ohmic behavior that is associated with an assisted electrolyte-transfer process is observed only above a threshold potential which can be quantitatively predicted by theory. The threshold potential depends on the nature and activity of sample anions and cations in the sample and inner filling solution of the membrane electrode. Within the experimental conditions discussed in this paper, these sensors seem to measure sample ion activities, not concentrations, since the rate-limiting step is the diffusion of extracted ions away from the interface into the membrane bulk. Similarly, no effect of sample stirring on the measured current is observed. This contrasts to work done on liquid-liquid electrolyte-transfer reactions, where large diffusion coefficients in the organic phase often lead to substantial sample depletion effects. The detection of anions and cations with the same membrane is demonstrated in a cyclic voltammetric mode. Direct continuous detection of one type of anion is accomplished by pulsed amperometry to ensure a rapid, repetitive renewal of the membrane composition between measurements.

Electrochemistry↗
PubMed1999

Signs and symptoms of Duchenne muscular dystrophy and Becker muscular dystrophy among carriers in The Netherlands: a cohort study.

BACKGROUND: Carriers of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) may show muscle weakness or dilated cardiomyopathy. Studies focusing on skeletal-muscle involvement were done before DNA analysis was possible. We undertook a cross-sectional study in a population of definite carriers to estimate the proportion and to assess the clinical profile of carriers with symptoms. We also assessed a possible correlation between genotype and phenotype. METHODS: Carriers of DMD and BMD, aged 18-60 years, were traced through the files of the central register kept at the Department of Human Genetics in Leiden, Netherlands. For each carrier who agreed to participate a medical history was taken, and muscle-strength assessment by hand-held dynamometry and manual muscle testing and cardiological assessment were done. FINDINGS: 129 carriers of muscular dystrophy (85 DMD, 44 BMD) participated in the study. In 90 women from 52 (70%) families, 37 different mutations were found. 28 (22%) women had symptoms. 22 (17%) had muscle weakness, varying from mild to moderately severe. Muscle weakness was found in carriers of DMD and BMD, but dilated cardiomyopathy was found only in seven (8%) carriers of DMD, of whom one had concomitant muscle weakness. There was an unexpectedly high proportion of left-ventricle dilation (18%). No genotype-phenotype correlation was found. INTERPRETATION: Clinical manifestation of muscle weakness, dilated cardiomyopathy, or both can be found in about a fifth of carriers of DMD and BMD. If left-ventricle dilation is taken into account, the proportion of carriers with symptoms is even higher, amounting to 40%.

Adolescent↗
PubMed1999

Diagnostic Notch3 sequence analysis in CADASIL: three new mutations in Dutch patients. Dutch CADASIL Research Group.

To confirm the clinical diagnosis in individual Dutch patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), we performed direct sequence analysis of the abnormal gene, Notch3, in patients from 11 families without prior linkage analysis to chromosome 19. Eleven missense mutations involving the loss or gain of a cysteine residue were found, of which 3 are new. Exon 4 is a mutation hotspot (9 of 11 families). Notch3 sequence analysis of CADASIL patients in a diagnostic laboratory is a feasible procedure to confirm the clinical diagnosis in individual patients.

Cerebral Arterial Diseases↗
PubMed1999

Improving measurement stability and reproducibility of potentiometric sensors for polyions such as heparin.

The growing importance of polymer membrane-based potentiometric polyion sensors in biomedical research and clinical measurements has brought up the question of how accurate and reproducible these sensors are. Indeed, recent research has revealed that these sensors behave quite differently than classical ion-selective electrodes. This paper explores ways to improve measurement reproducibility and long term potential stability by considering the unique pseudo steady-state response mechanism of the polyion sensors developed so far. Heparin may be stripped out of the phase boundary membrane surface with a high sample NaCl concentration and this characteristic is used to modify the calibration procedure in order to avoid memory effects. It is also attempted to reduce long term potential drifts by continuously stripping heparin out of the membrane at the membrane-inner filling solution side.

Biosensing Techniques↗
PubMed1999

A protein truncation test for Emery-Dreifuss muscular dystrophy (EMD): detection of N-terminal truncating mutations.

X-linked Emery-Dreifuss muscular dystrophy (EMD) is caused by mutations in the emerin gene. Since the emerin gene is ubiquitously expressed and since all EMD mutations published so far should be detectable by an RNA-based mutation assay, we have designed a protein truncation test for emerin. To facilitate the detection of mutations in the translation initiation site, reported for several EMD-cases, the standard tailed forward PTT-primer had to be modified. The effectiveness of the assay was established by a mutation scan in four EMD-patients. Two patients could be shown to carry emerin mutations, one affecting the ATG translation initiation codon. The PTT-assay did not detect a mutation in the two other patients. Since an immunohistochemical analysis of patient-derived cells revealed normal emerin levels, these patients are thus affected by another muscular dystrophy, most likely autosomal dominant EMD.

Codon↗
PubMed1999

Cardiac involvement in carriers of Duchenne and Becker muscular dystrophy.

A cross-sectional study in a cohort of DNA proven carriers of Duchenne (DMD) and Becker (BMD) muscular dystrophy was undertaken with the following objectives: (1) to estimate the frequency of electrocardiographic (ECG) and echocardiographic abnormalities; (2) to establish the proportion of carriers with dilated cardiomyopathy and (3) to assess possible associations between dilated cardiomyopathy and genotype. One hundred and twenty nine DMD and BMD carriers, aged 18-60 years, were traced through the files of the central register kept at the department of Human Genetics in Leiden. Investigations included full medical history, physical examination, ECG and two-dimensional and M-mode echocardiographic examination. Forty-seven percent had ECG changes. Thirty-six percent (DMD 41%, BMD 27%) had at least one abnormality as is usually found in the male patients. Echocardiographic examination was abnormal in 36% (DMD 38%, BMD 34%). Dilated cardiomyopathy was found in seven DMD carriers (8%), and in none of BMD carriers. In addition, 18% had left ventricle dilatation (DMD 19%, BMD 16%). Only 38% had a completely normal investigation of the heart. We found no association between genotype and cardiac manifestations. Our study underlines that cardiac involvement is part of the dystrophinopathies. Carriers should be told about the increased risk of this complication when asking genetic advice. It also implicates that a complete cardiological evaluation should be performed at least once in all carriers. If left ventricle dilatation or dilated cardiomyopathy is present a yearly follow up is needed, in order to start timely therapy.

Adolescent↗
PubMed1999

Calpainopathy-a survey of mutations and polymorphisms.

Limb-girdle muscular dystrophy type 2A (LGMD2A) is an autosomal recessive disorder characterized mainly by symmetrical and selective atrophy of the proximal limb muscles. It derives from defects in the human CAPN3 gene, which encodes the skeletal muscle-specific member of the calpain family. This report represents a compilation of the mutations and variants identified so far in this gene. To date, 97 distinct pathogenic calpain 3 mutations have been identified (4 nonsense mutations, 32 deletions/insertions, 8 splice-site mutations, and 53 missense mutations), 56 of which have not been described previously, together with 12 polymorphisms and 5 nonclassified variants. The mutations are distributed along the entire length of the CAPN3 gene. Thus far, most mutations identified represent private variants, although particular mutations have been found more frequently. Knowledge of the mutation spectrum occurring in the CAPN3 gene may contribute significantly to structure/function and pathogenesis studies. It may also help in the design of efficient mutation-screening strategies for calpainopathies.

Amino Acid Sequence↗
PubMed1999

EXT-mutation analysis and loss of heterozygosity in sporadic and hereditary osteochondromas and secondary chondrosarcomas.

Osteochondromas occur as sporadic solitary lesions or as multiple lesions, characterizing the hereditary multiple exostoses syndrome (EXT). Approximately 15% of all chondrosarcomas arise within the cartilaginous cap of an osteochondroma. EXT is genetically heterogeneous, and two genes, EXT1 and EXT2, located on 8q24 and 11p11-p12, respectively, have been cloned. It is still unclear whether osteochondroma is a developmental disorder or a true neoplasm. Furthermore, it is unclear whether inactivation of both alleles of an EXT gene, according to the tumor-suppressor model, is required for osteochondroma development, or whether a single EXT germline mutation acts in a dominant negative way. We therefore studied loss of heterozygosity and DNA ploidy in eight sporadic and six hereditary osteochondromas. EXT1- and EXT2-mutation analysis was performed in a total of 34 sporadic and hereditary osteochondromas and secondary peripheral chondrosarcomas. We demonstrated osteochondroma to be a true neoplasm, since aneuploidy was found in 4 of 10 osteochondromas. Furthermore, LOH was almost exclusively found at the EXT1 locus in 5 of 14 osteochondromas. Four novel constitutional cDNA alterations were detected in exon 1 of EXT1. Two patients with multiple osteochondromas demonstrated a germline mutation combined with loss of the remaining wild-type allele in three osteochondromas, indicating that, in cartilaginous cells of the growth plate, inactivation of both copies of the EXT1 gene is required for osteochondroma formation in hereditary cases. In contrast, no somatic EXT1 cDNA alterations were found in sporadic osteochondromas. No mutations were found in the EXT2 gene.

Adolescent↗