Search PubMed⌕ Search

Biomedical subjects

C Halpin

Publications and source records attributed to C Halpin.

At least 19 recordsLinked to original sources
PubMed2001

Selective inner hair cell loss in premature infants and cochlea pathological patterns from neonatal intensive care unit autopsies.

BACKGROUND: Deafness and handicapping sensorineural hearing impairment occur frequently in neonatal intensive care unit survivors for unknown reasons. PATIENTS AND METHODS: Hearing was tested early and repeatedly in neonatal intensive care unit patients with an auditory brainstem response (ABR) screener. The temporal bones of 15 nonsurvivors (30 ears) were fixed promptly (average, 5 hours) after death for histological evaluation. RESULTS: Among these patients, 12 failed the ABR screen bilaterally, 1 passed unilaterally, and 2 passed bilaterally. Cochlear histopathologic conditions that could contribute to hearing loss included bilateral selective outer hair cell loss in 2 patients, bilateral selective inner hair cell loss in 3 (all premature), and a combination of both outer and inner hair cell loss in 2. Other hair cell abnormalities were noted; the 2 infants who had passed the ABR screen demonstrated normal histological features. Neuronal counts were normal. CONCLUSIONS: Auditory brainstem response failure among these neonatal intensive care unit infants who died was extremely common in part owing to an unexpected histological alteration, selective inner hair cell loss among premature newborns, that should be detectable uniquely by the ABR testing method. Additional histological patterns suggest more than one cause for neonatal intensive care unit hearing loss. Hair cell loss patterns seem frequently compatible with in utero damage.

Cochlea↗
PubMed2001

Strong decrease in lignin content without significant alteration of plant development is induced by simultaneous down-regulation of cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) in tobacco plants.

Different transgenic tobacco lines down-regulated for either one or two enzymes of the monolignol pathway were compared for their lignin content and composition, and developmental patterns. The comparison concerned CCR and CAD down-regulated lines (homozygous or heterozygous for the transgene) and the hybrids resulting from the crossing of transgenic lines individually altered for CCR or CAD activities. Surprisingly, the crosses containing only one allele of each antisense transgene, exhibit a dramatic reduction of lignin content similar to the CCR down-regulated parent but, in contrast to this transgenic line, display a normal phenotype and only slight alterations of the shape of the vessels. Qualitatively the lignin of the double transformant displays characteristics more like the wild type control than either of the other transgenics. In the transgenics with a low lignin content, the transformations induced other biochemical changes involving polysaccharides, phenolic components of the cell wall and also soluble phenolics. These results show that the ectopic expression of a specific transgene may have a different impact depending on the genetic background and suggest that the two transgenes present in the crosses may operate synergistically to reduce the lignin content. In addition, these data confirm that plants with a severe reduction in lignin content may undergo normal development at least in controlled conditions.

Alcohol Oxidoreductases↗
PubMed2001

Enabling technologies for manipulating multiple genes on complex pathways.

Many complex biochemical pathways in plants have now been manipulated genetically, usually by suppression or over-expression of single genes. Further exploitation of the potential for plant genetic manipulation, both as a research tool and as a vehicle for plant biotechnology, will require the co-ordinate manipulation of multiple genes on a pathway. This goal is currently very difficult to achieve. A number of approaches have been taken to combine or 'pyramid' transgenes in one plant and have met with varying degrees of success. These approaches include sexual crossing, re-transformation, co-transformation and the use of linked transgenes. Novel, alternative 'enabling' technologies are also being developed that aim to use single transgenes to manipulate the expression of multiple genes. A chimeric transgene with linked partial gene sequences placed under the control of a single promoter can be used to co-ordinately suppress numerous plant endogenous genes. Constructs modelled on viral polyproteins can be used to simultaneously introduce multiple protein-coding genes into plant cells. In the course of our work on the lignin biosynthetic pathway, we have tested both conventional and novel methods for achieving co-ordinate suppression or over-expression of up to three plant lignin genes. In this article we review the literature concerning the manipulation of multiple genes in plants. We also report on our own experiences and results using different methods to perform directed manipulation of lignin biosynthesis in tobacco.

Amino Acid Sequence↗
PubMed2000

Dilated cardiomyopathy and sensorineural hearing loss: a heritable syndrome that maps to 6q23-24.

BACKGROUND: Dilated cardiomyopathy (DCM) and sensorineural hearing loss (SNHL) are prevalent disorders that occur alone or as components of complex multisystem syndromes. Multiple genetic loci have been identified that, when mutated, cause DCM or SNHL. However, the isolated coinheritance of these phenotypes has not been previously recognized. METHODS AND RESULTS: Clinical evaluations of 2 kindreds demonstrated autosomal-dominant transmission and age-related penetrance of both SNHL and DCM in the absence of other disorders. Moderate-to-severe hearing loss was evident by late adolescence, whereas ventricular dysfunction produced progressive congestive heart failure after the fourth decade. DNA samples from the larger kindred (29 individuals) were used to perform a genome-wide linkage study. Polymorphic loci on chromosome 6q23 to 24 were coinherited with the disease (maximum logarithm of odds score, 4.88 at locus D6S2411). The disease locus must lie within a 2.8 cM interval between loci D6S975 and D6S292, a location that overlaps an SNHL disease locus (DFNA10). However, DFNA10 does not cause cardiomyopathy. The epicardin gene, which encodes a transcription factor expressed in the myocardium and cochlea, was assessed as a candidate gene by nucleotide sequence analysis; no mutations were identified. CONCLUSIONS: A syndrome of juvenile-onset SNHL and adult-onset DCM is caused by a mutation at 6q23 to 24 (locus designated CMD1J). Recognition of this cardioauditory disorder allows for the identification of young adults at risk for serious heart disease, thereby enabling early intervention. Definition of the molecular cause of this syndrome may provide new information about important cell physiology common to both the ear and heart.

Adult↗
PubMed1999

Self-processing 2A-polyproteins--a system for co-ordinate expression of multiple proteins in transgenic plants.

Achieving co-ordinate, high-level and stable expression of multiple transgenes in plants is currently difficult. Expression levels are notoriously variable and influenced by factors that act independently on transgenes at different genetic loci. Instability of expression due to loss, re-arrangement or silencing of transgenes may occur, and is exacerbated by increasing numbers of transgenic loci and repeated use of homologous sequences. Even linking two or more genes within a T-DNA does not necessarily result in co-ordinate expression. Linking proteins in a single open reading frame--a polyprotein--is a strategy for co-ordinate expression used by many viruses. After translation, polyproteins are processed into constituent polypeptides, usually by proteinases encoded within the polyprotein itself. However, in foot-and-mouth disease virus (FMDV), a sequence (2A) of just 16-20 amino acids appears to have the unique capability to mediate cleavage at its own C-terminus by an apparently enzyme-independent, novel type of reaction. This sequence can also mediate cleavage in a heterologous protein context in a range of eukaryotic expression systems. We have constructed a plasmid in which the 2A sequence is inserted between the reporter genes chloramphenicol acetyltransferase (CAT) and beta-glucuronidase (GUS), maintaining a single open reading frame. Here we report that expression of this construct in wheatgerm lysate and transgenic plants results in efficient cleavage of the polyprotein and co-ordinate expression of active CAT and GUS. Self-processing polyproteins using the FMDV 2A sequence could therefore provide a system for ensuring co-ordinated, stable expression of multiple introduced proteins in plant cells.

Amino Acid Sequence↗
PubMed1999

Hereditary postlingual sensorineural hearing loss mapping to chromosome Xq21.

BACKGROUND: Mutations on the X-chromosome clinically manifesting different phenotypes of hearing loss have been mapped to the long arm at different loci, DFN1-DFN3. Another defect in a family with sex-linked, postlingual, progressive sensorineural hearing loss was mapped to Xq. METHODS: Clinically, the family was evaluated by physical and audiometric examination of 17 members including computerized tomographic (CT) evaluation of the proband. Molecular evaluation consisted of polymerase chain reaction amplification of patient genomic DNA and resolution 32P-labeled fragments by polyacrylamide gels. Inheritance of DNA alleles and deafness were analyzed using the MLINK computer program. RESULTS: Five affected males demonstrated symmetrical sensorineural hearing loss as significant as 100 decibels (dB). Two carrier females had a milder loss with frequency findings of 10 dB to 60 dB. Computerized tomography (CT) evaluation of the temporal bones of the proband was normal. The odds were 200:1 that the responsible gene was linked to locus DXS986 (maximum lod score = 2.3 at 0 = 0). Analysis of recombination events defined by family members demonstrates that the responsible gene lies in a 21 cM (30 MB) interval, between loci DXS12175 and 1106. The disease locus in this family does not appear to map to DFN1 or DFN3. CONCLUSION: The family described here, with affected males who have progressive, postlingual sensorineural hearing loss and mildly affected females maps most compatibly to the DFN2 locus. Analysis of hereditary deafness in this family refines the DFN2 locus to a 9.2 Mb region in chromosome X band q21 between DXS990 and DXS106.

Adolescent↗
PubMed1998

Brown-midrib maize (bm1)--a mutation affecting the cinnamyl alcohol dehydrogenase gene.

Brown-midrib (bm) mutants of maize have modified lignin of reddish-brown colour. Although four independent bm loci are known, only one of the mutant genes has been previously identified. We report here that maize bm1, one of the less characterised mutants, shows severely reduced CAD activity in lignified tissues, resulting in the production of a modified lignin. Both the total lignin content and the structure of the polymer are altered by the mutation. We further describe the isolation and characterisation of the maize CAD cDNA and mapping of the CAD gene. CAD maps very closely to the known location of bm1 and co-segregates with the bm1 locus in two independent recombinant inbred populations. These data strongly support the premise that maize bm1 directly affects expression of the CAD gene.

Alcohol Oxidoreductases↗
PubMed1996

Cloning and sequence analysis of laccase-encoding cDNA clones from tobacco.

Three laccase-encoding cDNAs were cloned from a tobacco stem cDNA library. One of them contains a full length sequence coding for a cationic laccase. The predicted polypeptide sequence shows 48% identity with sycamore laccase. Amino acid comparisons with other laccases and ascorbate oxidases have shown that this new plant laccase sequence also contains four potential copper binding regions which are highly conserved among the blue copper oxidases.

Amino Acid Sequence↗
PubMed1996

A gene for non-syndromic autosomal dominant progressive postlingual sensorineural hearing loss maps to chromosome 14q12-13.

We report a novel locus responsible for postlingual progressive sensorineural hearing loss (designated DFNA9) that maps to chromosome 14q12-13. A large kindred with autosomal dominant transmission of non-syndromic hearing loss was clinically studied. Hearing in affected individuals deteriorated at approximately 20 years of age and progressed to anacusis in the fifth decade. A random genome-wide search using polymorphic short tandem repeats demonstrated linkage with D14S121 (maximum two point LOD score = 6.19, theta = 0). Haplotype analysis of recombination events defined a 9 cM disease interval, between D14S252 and D14S49.

Adult↗
PubMed1996

Vestibular neurectomy: retrosigmoid-intracanalicular versus retrolabyrinthine approach.

Selective vestibular neurectomy is an effective treatment for intractable vertigo of peripheral vestibular origin when preservation of hearing is a goal. The retrolabyrinthine and retrosigmoid-intracanalicular approaches have been used predominantly at our institutions over the last 10 years. The results and complications of these two techniques were compared. No significant differences were found between hearing results in these two patient groups. The retrosigmoid-internal auditory can approach yielded better control of recurrent episodic vertigo, as well as superior ablation of postoperative ice-water caloric responses (p < 0.05). Surgical complications, including the incidence of cerebrospinal fluid leakage (greater in retrolabyrinthine approach) and postoperative headache (more prevalent in retrosigmoid approach), were also analyzed. To further evaluate the results of this study, data were reanalyzed and compared with previously published reports of selective vestibular nerve section.

Adult↗
PubMed1995

The impact of dexamethasone on hearing loss in experimental pneumococcal meningitis.

Bacterial meningitis, particularly that resulting from Streptococcus pneumoniae, is a common cause of acquired profound sensorineural deafness in children. The pathogenesis of meningogenic hearing loss has been investigated in an experimental rabbit model. In this study significant deafness was documented within the first 15 hours of infection. Initiation of antibiotic therapy at this time diminished the severity of hearing loss in most animals. The addition of dexamethasone to antibiotic therapy prevented the development of profound deafness. These results suggest this model will be useful in developing antiinflammatory strategies to improve the outcome of bacterial meningitis.

Animals↗
PubMed1994

Low-frequency sensorineural loss: clinical evaluation and implications for hearing aid fitting.

Spread of excitation in the cochlea places fundamental limits on the interpretation of audiometric pure-tone hearing loss as a simple map of dysfunction along the cochlear partition, and histologic evidence from human temporal bones will be presented to demonstrate the insensitivity of the audiogram to variations in pathology in the case of low-frequency hearing loss. This article will describe a clinical procedure using simultaneous pure-tone masking to improve upon the localization of cochlear disease, particularly for low-frequency hearing losses, and a model for using the Articulation Index (AI) to develop prognoses for hearing aid performance in these cases, which can then be tested. Fourteen patients with low-frequency hearing loss were divided into two groups based upon threshold shifts caused by a pure-tone masker: those that showed normal low-frequency threshold shifts and those that showed marked shifts at frequencies below the masker, indicating greater loss of function than shown by the unmasked audiogram. Hypothetical audiograms were then generated to model a complete loss of apical function for all patients. Measured speech recognition scores were then compared to AI predictions for the actual and hypothetical audiograms. Best agreement for the patients showing normal masking shifts was between the measured scores and the AI for the actual audiogram, whereas the best agreement for the patients showing marked shifts was with the AI for the hypothetical audiogram. The implications for hearing aid recommendation and fitting in these cases are discussed.

Acoustic Stimulation↗
PubMed1993

Progression of hearing loss in experimental pneumococcal meningitis: correlation with cerebrospinal fluid cytochemistry.

The development of hearing loss and concomitant cerebrospinal fluid (CSF) cytochemical changes in a model of pneumococcal meningitis were examined. Rabbits were injected intracisternally with 10(5) pneumococci. Auditory evoked potentials to clicks and to 10- and 1-kHz tone bursts were recorded hourly; CSF was analyzed every 4 h. Sensorineural hearing loss developed in all animals beginning 12 h after infection and progressed to severe deafness. The onset of hearing loss was preceded by a CSF leukocytosis of > 2000 cells/microL and elevation of CSF protein and lactate concentrations to > or = 1 mg/mL. Temporal bone histopathology showed pneumococci and leukocytes extending from the CSF to the perilymph via the cochlear aqueduct. Hearing loss can develop early in the course of meningitis and is preceded by the abrupt onset of inflammatory changes in CSF. Progression of hearing loss is rapid and proceeds from cochlear base to apex in parallel with the degree of inflammation.

Animals↗
PubMed1992

Identification and characterisation of cDNA clones encoding cinnamyl alcohol dehydrogenase from tobacco.

Cinnamyl alcohol dehydrogenase (CAD, EC 1.1.1.195) is an enzyme involved in lignin biosynthesis. We have previously isolated pure CAD enzyme as two closely related polypeptides of 44 and 42.5 kDa from tobacco stems. In this paper, we report partial amino acid sequences of these two polypeptides. Based on the peptide sequences mixed oligonucleotides were used to screen a tobacco stem cDNA library and CAD cDNA clones encoding the two polypeptides were identified. DNA sequence comparisons indicate very high sequence identity between these clones both in the coding and in the 5' and 3' untranslated sequences. The close similarity between the two CAD genes leads us to suggest that they do not represent different isoforms but are the same gene from each of the two parental lines of Nicotiana tabacum cv. Samsun. Sequence comparisons with alcohol dehydrogenase 1 (ADH1) from yeast shows sequence similarities of ca. 30%, while comparisons with maize, barley and potato ADH1 sequences show similarities of not more than 23%.

Alcohol Dehydrogenase↗
PubMed1992

The effect of cochlear hearing loss on auditory brain stem response latency.

The effect of audiometric configuration on the auditory brain stem response was studied in a large patient sample, and wave I latencies, wave V latencies, and the I-V interwave intervals were compared to those from a previous report. Patients with notched hearing losses showed longer wave V latencies and I-V interwave intervals than those with other audiometric configurations, but the magnitude of the effect was relatively small, and the confidence limit for cochlear diagnosis was essentially the same as that based upon a cochlear hearing loss population without regard to audiometric configuration.

Acoustic Stimulation↗
PubMed1992

Long-term hearing results in patients after surgical removal of acoustic tumors with hearing preservation.

Long-term hearing results are described in 18 patients after suboccipital removal of unilateral acoustic neurinomas. Follow-up ranged from 3.4 to 10.4 years with a mean of 5.4 years. Fourteen patients (78%) experienced no significant decline in long-term hearing. Four patients (22%) experienced a significant decline in long-term hearing as defined by a drop in pure-tone average (0.5, 1, and 2 kHz), or a significant decline in Speech Discrimination Scores (SDS). Changes in hearing did not correlate with tumor size, preoperative hearing, intraoperative change in hearing, the interval between initial symptoms and surgery, sex, or age.

Audiometry, Evoked Response↗