Biomedical subjects

H Stöhr

Publications and source records attributed to H Stöhr.

At least 19 recordsLinked to original sources

PubMed2005

[VMD2 and its role in Best's disease and other retinopathies].

Best's vitelliform macular dystrophy (Best's disease) is an autosomal dominant disease of the central retina and is caused by mutations in the VMD2 gene located on the long arm of chromosome 11. VMD2 encodes bestrophin, a transmembrane protein with putative Ca(2+)-dependent chloride channel activity at the basolateral portion of the retinal pigment epithelium. The N-terminal half of bestrophin reveals high sequence homology to three bestrophin-like proteins in humans but also to protein sequences from evolutionarily distant organisms. Most of the known VMD2 mutations are located within this presumably important functional part of the protein and cause amino acid substitutions and small in-frame deletions of single amino acid residues. The pathogenicity of VMD2 mutations is likely based on a dominant negative effect possibly by oligomerization of normal and mutated bestrophin molecules to form a defective ion channel. Missense mutations in VMD2 were also shown to be associated with vitreoretinochoroidopathy and ocular developmental abnormalities. In this case, the pathogenic sequence changes influence the peptide sequences but simultaneously alter the regulation of mRNA splicing and maturation. Different disease mechanisms may therefore be responsible for the distinct phenotypes associated with VMD2 mutations.

Bestrophins↗

PubMed2004

Cloning and characterization of the murine Vmd2 RFP-TM gene family.

Mutations in the human vitelliform macular dystrophy type 2 (VMD2) gene are known to cause autosomal dominant Best macular dystrophy (BMD), a degenerative disorder of the central retina. VMD2, together with VMD2L1, VMD2L2 and VMD2L3, belong to a closely related gene family characterized by several transmembrane (TM) spanning helical domains and an invariant arginine, phenylalanine and proline (RFP) tripeptide motif, thus termed VMD2 RFP-TM. The four genes are thought to encode a novel family of anion channels. We now report the cloning and characterization of the murine orthologs by combining biocomputational analyses and molecular genetic approaches. While the murine Vmd2, Vmd2l1 and Vmd2l3 genes are functional, murine Vmd2l2p was found to be a non-transcribed pseudogene. Expression profiling of the murine Vmd2 RFP-TM family members revealed tissue-restricted expression with predominant transcription of Vmd2 in testis, of Vmd2l1 in colon and of Vmd2l3 in heart. Differential splicing was observed for Vmd2l3 in a number of tissues (e.g. in brain, retina/RPE, kidney) although the functional importance of the splice variants remains to be determined.

Alternative Splicing↗

PubMed2001

Cloning and characterization of the human retina-specific gene MPP4, a novel member of the p55 subfamily of MAGUK proteins.

To identify novel retina-specific genes systematically, we are performing expression profiling of retina ESTs that have been assembled in the human UniGene clusters. In this study, we report the 2619-bp full-length cDNA cloning and genomic organization of a gene corresponding to an EST cluster that was demonstrated to be exclusively present in retinal tissue. Alignment of the deduced amino acid sequence to sequence from protein databases revealed this gene, termed MPP4, to be a member of the membrane-associated guanylate kinase (MAGUK) protein family. It consists of 637 amino acids and contains the characteristic MAGUK motifs: an N-terminal PDZ domain, a central src homology 3 region (SH3), and a C-terminal guanylate kinase-like (GUK) domain. Due to the presence of only one PDZ motif, MPP4 is part of the p55 subfamily, named after the major palmitoylated erythrocyte membrane protein p55/MPP1. MAGUK proteins serve as molecular scaffolds to coordinate the membrane-associated cytoskeleton, ion channel and receptor clustering, signaling pathways, and the formation of cellular junctions. The abundant expression of MPP4 in the human retina suggests an important but so far unknown function in this tissue. Colocalization of MPP4 and autosomal recessive retinitis pigmentosa 26 (RP26) on chromosome 2q31-q33 makes this transcript an attractive candidate for the disease gene.

Alternative Splicing↗

PubMed2001

Functional and biological test of a 20 channel implantable stimulator in sheep in view of functional electrical stimulation walking for spinal cord injured persons.

A newly developed implantable stimulator with 20 output channels, mainly intended for the stimulation of lower extremities in paraplegics, was implanted in 6 sheep over a time period of 26 weeks. Five epineural electrodes each were used to contact various nerves at different locations to elicit hip and knee extension and flexion and to make carrousel and selective stimulation possible. Different electrode application strategies in view of paraplegic standing and walking were investigated. Additional implanted electrodes allowed M-wave monitoring for selectivity investigations in 3 sheep. Stimulator, electrode leads, and electrodes proved to be reliable. Selective stimulation with electrodes placed on the trunk of the sciatic nerve could be demonstrated but with bad reproducibility. Histological investigation of the tissues surrounding electrodes and leads showed the expected stable foreign body response. Strong hip and knee extension could be gained in all cases while only weak flexion forces could be elicited in most cases. Muscle biopsies showed that daily stimulation for 8 h at threshold level caused an increase in muscle Type I fibers and a decrease in Type IIc fibers. Implants and electrodes fulfill the most important functional and biological criteria for their clinical application for paraplegic walking. The intention to provide selective flexion functions via epineural stimulation could not be demonstrated sufficiently in this animal model.

Animals↗

PubMed2001

[Aphasia and dementia].

Primary progressive aphasia (PPA) is an uncommon neurodegenerative syndrome characterized by a relatively isolated dissolution of language function at the beginning, followed by deterioration of general cognitive function and of activities of daily living after 2 or more years. On account of neuropathological and clinical findings, PPA is supposed to form part of the spectrum of frontotemporal lobar degeneration. We present a case study of a 66-year-old woman with a probable fluent progressive aphasia. She initially experienced word amnesia and developed after 2 - 3 years gradual regression of word comprehension, over-fluent speech with semantic paraphasias, and at last generalized dementia. In addition to minor bilateral cortical volume reduction on CCT, MRI showed left temporal lobe atrophy involving hippocampus, SPECT revealed reduced uptake left frontal and temporal.

Aged↗

PubMed2001

Evaluation of the G protein coupled receptor-75 (GPR75) in age related macular degeneration.

BACKGROUND: A long term project was initiated to identify and to characterise genes that are expressed exclusively or preferentially in the retina as candidates for a genetic susceptibility to age related macular degeneration (AMD). A transcript represented by a cluster of five human expressed sequence tags (ESTs) derived exclusively from retinal cDNA libraries was identified. METHODS: Northern blot and RT-PCR analyses confirmed preferential retinal expression of the gene, which encodes a G protein coupled receptor, GPR75. Following isolation of the full length cDNA and determination of the genomic organisation, the coding sequence of GPR75 was screened for mutations in 535 AMD patients and 252 controls from Germany, the United States, and Italy. Employed methods included single stranded conformational polymorphism (SSCP) analysis, denaturing high performance liquid chromatography (DHPLC), and direct sequencing. RESULTS: Nine different sequence variations were identified in patients and control individuals. Three of these (-30A>C, 150G>A, and 346G>A) likely represent polymorphic variants. Each of six alterations (-4G>A, N78K, P99L, S108T, T135P, and Q234X) were found once in single AMD patients and were considered variants that could affect the protein function and potentially cause retinal pathology. CONCLUSION: The presence of six potential pathogenic variants in a cohort of 535 AMD patients alone does not provide statistically significant evidence for the association of sequence variation in GPR75 with genetic predisposition to AMD. However, a possible connection between the variants and age related retinal pathology cannot be discarded. Functional studies are needed to clarify the role of GPR75 in retinal physiology.

Adult↗

PubMed2000

A comprehensive survey of sequence variation in the ABCA4 (ABCR) gene in Stargardt disease and age-related macular degeneration.

Stargardt disease (STGD) is a common autosomal recessive maculopathy of early and young-adult onset and is caused by alterations in the gene encoding the photoreceptor-specific ATP-binding cassette (ABC) transporter (ABCA4). We have studied 144 patients with STGD and 220 unaffected individuals ascertained from the German population, to complete a comprehensive, population-specific survey of the sequence variation in the ABCA4 gene. In addition, we have assessed the proposed role for ABCA4 in age-related macular degeneration (AMD), a common cause of late-onset blindness, by studying 200 affected individuals with late-stage disease. Using a screening strategy based primarily on denaturing gradient gel electrophoresis, we have identified in the three study groups a total of 127 unique alterations, of which 90 have not been previously reported, and have classified 72 as probable pathogenic mutations. Of the 288 STGD chromosomes studied, mutations were identified in 166, resulting in a detection rate of approximately 58%. Eight different alleles account for 61% of the identified disease alleles, and at least one of these, the L541P-A1038V complex allele, appears to be a founder mutation in the German population. When the group with AMD and the control group were analyzed with the same methodology, 18 patients with AMD and 12 controls were found to harbor possible disease-associated alterations. This represents no significant difference between the two groups; however, for detection of modest effects of rare alleles in complex diseases, the analysis of larger cohorts of patients may be required.

ATP-Binding Cassette Transporters↗

PubMed2000

cDNA cloning, genomic structure, and chromosomal localization of three members of the human fatty acid desaturase family.

The insertion of double bonds into specific positions of fatty acids is achieved by the action of distinct desaturase enzymes. Here we report the cloning and characterization of three members of the fatty acid desaturase (FADS) gene family in humans. Initially identified as cDNA fragments by direct cDNA selection within a defined 1.4-Mb region in 11q12-q13.1, full-length fatty acid desaturase-1 (FADS1) and fatty acid desaturase-2 (FADS2) transcripts were obtained by EST sequence assembly. A third member, fatty acid desaturase-3 (FADS3), was identified in silico revealing 62 and 70% nucleotide sequence identity with FADS1 and FADS2, respectively. The three genes are clustered within 92 kb of genomic DNA located 2 kb telomeric to FEN1 and 50 kb centromeric to VMD2 and are likely to have arisen evolutionarily from gene duplication as they share a remarkably similar exon/intron organization. Protein database searches identified FADS1, FADS2, and FADS3 as fusion products composed of an N-terminal cytochrome b5-like domain and a C-terminal multiple membrane-spanning desaturase portion.

Amino Acid Sequence↗

PubMed2000

[Central nervous system activation in opioid dependent patients, evaluation with Fourier analysis of pupillary oscillations].

The aim of the present investigation was to determine whether Fourier analysis of pupillary oscillations permits detection of differences in the activation of the central nervous system of opioid-addicted patients. We analysed pupillary oscillations during the recording period of static pupillometry, which lasted 25.6 s. Using Fourier analysis, the spectrum was divided into five frequency bands (0.0-0.20, 0.21-0.40, 0.41-0.60, 0.61-0.80, 0.81-1.0 Hz); the total spectrum (0-1 Hz) was also assessed. Three groups of patients were selected: the group addicted to heroin (consuming exclusively heroin) consisted of 26 patients with a mean age of 25.0 +/- 6.3 years, the methadone substitution group of 20 patients with a mean age of 30.9 +/- 8.2 years, and the morphine substitution group of 20 patients with a mean age of 33.2 +/- 4.6 years. The 3 patient groups were compared with normal controls of similar age (25.1 +/- 4.6 years). In the frequency band of 0.0-0.20 Hz the morphine group showed significantly lower amplitudes than the heroin group. Also in the frequency band of 0.41-0.60 Hz the morphine group differed significantly from the other groups concerning lower amplitudes, reflecting deactivation. In the total spectrum of 0 to 1 Hz the differences between these two groups were significant. Comparison with normal controls also showed significant differences. The groups were further divided according to dose (high/low): Patients of the heroin group as well as those of the methadone and morphine groups who had consumed higher doses showed greater activation of the central nervous system. In conclusion the morphine group was more deactivated than the methadone and heroin group and patients who received higher doses of the substances showed greater central nervous activation. Thus, the measurement of central nervous activation by means of Fourier analysis of pupillary oscillations might be useful in monitoring substitution therapy.

Adult↗

PubMed2000

cDNA cloning and genomic structure of a novel gene (C11orf9) localized to chromosome 11q12-->q13.1 which encodes a highly conserved, potential membrane-associated protein.

We have cloned and characterized a novel gene (C11orf9) mapping to chromosome 11q12-->q13.1. The transcript was initially identified as a partial cDNA sequence in the course of constructing a transcript map of the region between markers D11S1765 and uteroglobin known to encompass the gene causing Best disease. Using a combination of EST mapping, computational exon prediction, RT-PCR, and 5'-RACE its 5. 7-kb full-length cDNA sequence was subsequently obtained. The C11orf9 gene consists of 26 exons spanning 33.1 kb of genomic DNA and is located about 4.3 kb centromeric to FEN1. Biocomputational analysis predicts that its conceptual translation product of 1,111 amino acids contains two transmembrane helices as well as two proline-rich regions. Alignment reveals significant homology to hypothetical peptides from several other species including C. elegans and D. melanogaster, indicating a high degree of conservation throughout evolution. Northern Blot and RT-PCR analyses demonstrate widespread expression of a single transcript but varying degrees of abundance among the individual tissues tested. Mutation analysis of the entire coding sequence excluded C11orf9 as the Best disease gene.

Amino Acid Sequence↗

PubMed2000

EST mining of the UniGene dataset to identify retina-specific genes.

Age-related macular degeneration (AMD) is a multifactorial disorder affecting the visual system with a high prevalence among the elderly population but with no effective therapy available at present. To better understand the pathogenesis of this disorder, the identification of the genetic factors and the determination of their contribution to AMD is needed. Towards this goal, we are pursuing a strategy that makes use of the EST data processed in the UniGene database and aims at the generation of a comprehensive catalogue of genes preferentially active in the human retina. Subsequently, these genes will be systematically assessed in AMD. We performed a retina EST sampling and obtained a total of 673 clusters containing only retina ESTs as well as 568 clusters with at least 30% of the ESTs in each cluster originating from retina cDNA libraries. Of these, 180 representative EST clusters with varying retina and non-retina EST contents were analyzed for their in vitro expression. This approach identified 39 transcripts with retina-specific expression. One of these genes (C18orf2) mapping to chromosome 18 was further characterized. Multiple C18orf2 transcripts display a complex pattern of differential splicing in the human retina. The various isoforms encode hypothetical polypeptides with no homologies to known proteins or protein motifs.

Alternative Splicing↗

PubMed1999

Mapping and genomic characterization of the gene encoding diacylglycerol kinase gamma (DAGK3): assessment of its role in dominant optic atrophy (OPA1).

The family of diacylglycerol kinases (DAGKs) is known to play an important role in signal transduction linked to phospholipid turnover. In the fruitfly Drosophila melanogaster, a human DAGK ortholog, DGK2, was shown to underlie the phenotype of the visual mutant retinal degeneration A (rdgA). Previously, the gene encoding a novel member of the human DAGK family, termed DAGK3, was cloned and demonstrated to be abundantly expressed in the human retina. Based on these findings we reasoned that DAGK3 might be an excellent candidate gene for a human eye disease. In the present study, we report the genomic organization of the human DAGK3 gene, which spans over 30 kb of genomic DNA interrupted by 23 introns. In addition, we have mapped the gene locus by fluorescence in situ hybridization to 3q27-28, overlapping the chromosomal region known to contain the gene underlying dominant optic atrophy (OPA1), the most common form of hereditary atrophy of the optic nerve. Mutational analysis of the entire coding region of DAGK3 in 19 unrelated German OPA1 patients has not revealed any disease-causing mutations, therefore excluding DAGK3 as a major cause underlying OPA1.

Adolescent↗

PubMed1999

Standing up with denervated muscles in humans using functional electrical stimulation.

The use of electrical stimulation for denervated muscles is still considered to be a controversial issue by many rehabilitation facilities and medical professionals because prior clinical experience has shown that treating denervated muscle tissue using exponential current over a long time period constitutes an impossible task. Despite this fact, we managed to evoke tetanic contractions in denervated muscle using a long duration stimulation with anatomically shaped electrodes and sufficiently high amplitudes. The pulse amplitudes, which were being used for this purpose, exceeded by far the MED-GV and EC regulations (300 mJ/impulse). For this reason, an application has recently been submitted to have the EC regulations changed accordingly. It takes a tetanic contraction to achieve the desired muscle fiber tension, constituting a hypertrophic stimulus. It is also an appropriate means of exercise, which is capable of creating the metabolic and structural conditions needed (e.g, increased mitochondrial volume and capillary density) to obtain satisfactory muscle performance. With patients suffering from a complete spinal cord injury at level D12/L1, having motor and sensory loss in both lower extremities, we were able to train denervated muscle using long-duration stimulation, evoking single muscle contractions at first, soon followed by tetanic contractions against gravity. To increase the efficacy of this functional electrical stimulation (FES) strengthening program, we used ankle weights. With daily FES training over a period of 1-2 years, denervated muscle was exercised until it produced torques between 16 and 38 Nm in the m. quadriceps. With that muscle force, it is possible to stand up from a sitting position in parallel bars. Our results show that denervated muscle in humans is indeed trainable and can perform functional activities with FES. Furthermore, this method of stimulation can assist in decubitus prevention and significantly improve the mobility of paraplegics.

Capillaries↗

PubMed1999

The FVII activating protease cleaves single-chain plasminogen activators.

A serine protease isolated from plasma sharing structural characteristics with a hepatocyte growth factor activator-like protease has been demonstrated recently to activate FVII. Accordingly, it was named 'FVII activator'. Until now an impact of this protease on the fibrinolytic system has not been reported. We islolated the protease from cryo-poor plasma by subsequent ion exchange chromatography and adsorption to immobilized heparin and/or aprotinin. Incubation of single-chain plasminogen activators (sc-PAs) with the FVII activator revealed significant activation of urokinase sc-PA (scu-PA) and tissue sc-PA (sct-PA) in vitro. It was enhanced in the presence of calcium and heparin. Compared to kallikrein, a more efficient activation of scu-PA was observed, whereas sct-PA appeared to be a poorer substrate for the FVI activator. At low protease concentrations and in the presence of heparin the scu-PA activation was comparable to plasmin. Employing recalcified whole blood thrombelastography, the lysis of initially formed fibrin was observed after addition of a combination of scu-PA and the FVII activator, whereas the scu-PA alone had a negligible effect at the concentration used. The study results as presented demonstrate that the FVII activator is a potent activator of sc-PAs in vitro. Whether it plays a physiological role in fibrinolysis deserves further investigation. Its comparatively high affinity to heparin assumes a function in cell surface or matrix events.

Blood Coagulation Factors↗

PubMed1999

Receptor test (pupillary dilatation after application of 0.01% tropicamide solution) and determination of central nervous activation (Fourier analysis of pupillary oscillations) in patients with Alzheimer's disease.

Memory loss and severe cognitive deficits in Alzheimer patients are supposed to be related to a reduction of acetylcholine as well as to central nervous deactivation. For the investigation of cholinergic deficits and deactivation, we used computer-assisted pupillometry. Cholinergic deficits caused by a particularly severe loss of cholinergic neurons may be responsible for cognitive and mnemonic performance deficits. The control of the pupillary diameter represents a balance between cholinergic and adrenergic innervation and is influenced directly or indirectly by central and autonomic nervous system inputs. Either of these systems could be affected in Alzheimer patients. A reduced innervation of the target muscle through neuronal cell death, axon retraction, reduced release, increased reuptake of altered amounts or function of neurotransmitter receptors seems to affect the pupillary response to cholinergic antagonists in Alzheimer patients. There is, however, no relationship between pupillary diameter and central deactivation, but between central nervous activation and pupillary oscillations which reflect the physiological corticodiencephalic activity, a relationship has to be assumed. Frequencies and amplitudes of pupillary oscillations measured by means of Fourier analysis are modulated corticodiencephalically. Therefore, Alzheimer patients were compared to healthy controls with respect to their pupillary diameters and responses to an acetylcholine antagonist. Twenty-nine patients, aged between 55 and 85 years, suffering from mild to moderate Alzheimer's disease (AD) and 29 normal controls of similar age (56-85 years) participated in the study. The cholinergic receptors of the pupil were blocked by the acetylcholine antagonist tropicamide. It could be assumed that the larger the pupillary dilatation, the larger the extent of cognitive deficits. Alzheimer patients show abnormal acetylcholine neurotransmission. Changes of pupillary diameter after instillation of 1 drop of 0.01% tropicamide solution were measured and Fourier analysis of pupillary oscillations was performed. Times of measurement were: 0 (baseline), 20, 40, 60, 80, and 100 min. After 4 min tropicamide was instilled. Forty min after the instillation of tropicamide into the left eye, the Alzheimer patients showed a pronounced dilatation of 41.57%. The dilatation in normal controls was 28.5%. Fourier analysis of pupillary oscillations (sum of frequency bands = power) demonstrated a marked deactivation (low amplitudes in low-frequency bands, but in contrast to our expectations no higher amplitudes in the higher frequency bands) in patients with AD which remained constant at all times of measurement. By means of discriminant analysis of pupillary diameter and pupillary oscillations (frequency band 0.00-1 Hz), 89. 7% were correctly predicted to be Alzheimer patients, 89% to be normal controls.

Aged↗

PubMed1999

[Fourier analysis of pupil oscillations for measuring central activation in psychosomatic patients].

The aim of the study was to answer the question if there are any differences in the central activation of different groups of psychosomatic patients and patients with eating disorders, which was measured by means of Fourier analysis of pupillary oscillations. A total of 132 patients (110 f, 22 m) with a mean age of 29.69 years (standard deviation: 9.9) participated in the study. In anorectic and bulimic patients high central activation was observed. Different groups of psychosomatic patients showed significant differences in their central nervous activation. In the group of subjects with the ICD-10 diagnosis F 41.3 (mixed anxiety disorders) the highest amplitudes was observed not only in the particular frequency bands but also in the total spectrum (power), which reflects high central activation. Reduced activation was found in subjects with somatoform autonomic function disorder of the upper and lower gastrointestinal tract (F 45.3). The measurement of central activation in psychosomatic disorders could have consequences for therapeutic interventions.

Adult↗

PubMed1998

[Psychometric diagnosis of dementia in clinical gerontopsychiatry practice].

An extensive battery of cognitive tests is conducted to detect dementia in geriatric patients. Based on the ICD-10 diagnostic criteria for dementia the diagnosis includes cognitive deficits such as memory impairment and other cognitive disturbances in various stages. To establish a profile of cognitive deficits and to detect early stages of dementia a combination of psychometric tests has proven to be effective and valid (MMSE, SKT, SIDAM, GDS/BCRS, clock drawing). To evaluate interrelations between these tests, correlations of total scores among 40 randomly chosen geriatric patients were calculated for all tests using the Spearman rank-order correlation. The cognitive test battery appears to be a reliable instrument for diagnosing people with dementia. Due to advantages and shortcomings of each test in evaluating various stages of dementia adequately, a combination of tests should be used.

Aged↗

PubMed1998

Mutations in a novel gene, VMD2, encoding a protein of unknown properties cause juvenile-onset vitelliform macular dystrophy (Best's disease).

Vitelliform macular dystrophy (Best's disease) is an autosomal dominant, early-onset form of macular degeneration in which the primary defect is thought to occur at the level of the retinal pigment epithelium. Genetic linkage has mapped the disease locus to chromosome 11q12-q13.1 within a 980 kb interval flanked by markers at loci D11S4076 and uteroglobin. To identify the disease gene, we systematically characterized genes from within the critical region and analysed the coding regions for mutations in 12 patients from large multigeneration Best's disease families. Following this approach, we identified a novel gene of unknown function carrying heterozygous mutations in all 12 probands. Of these, 10 result in distinct missense mutations of amino acids that are highly conserved throughout evolution, spanning a phylogenetic distance from Caenorhabditis elegans to human, and include V9M, A10T, W24C, R25Q, R218Q, Y227N, Y227C, V235M, P297A and F305S. One deletion mutation, DeltaI295, was found in two families and segregates with the disease in both cases. Northern blot analysis reveals tissue-specific expression for this gene, exclusively in the retinal pigment epithelium. In conclusion, our data provide strong evidence that mutations in the gene that we have identified cause Best's disease.

Amino Acid Sequence↗