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Biomedical subjects

R Ramsden

Publications and source records attributed to R Ramsden.

At least 19 recordsLinked to original sources
PubMed1999

Phenobarbital responsiveness conferred by the 5'-flanking region of the rat CYP2B2 gene in transgenic mice.

Phenobarbital (PB) is a prototype for a class of agents that produce marked transcriptional activation of a number of genes, including certain cytochrome P-450s. We used transgenic mouse approaches and multiple gene reporters to assess the functional consequences of specific deletions and site-specific mutations within the 2.5kb 5'-flanking region of the rat CYP2B2 gene. Protein-DNA interactions at the PBRU domain also were characterized. Using the transgenic models, we demonstrate that sequences between -2500 and -1700bp of the CYP2B2 gene are critical for PB induction; mice with 1700 or 800bp of 5'-flanking CYP2B2 sequence are not PB responsive. DNA affinity enrichment techniques and immunoblotting and electromobility shift assays were used to determine that nuclear factor 1 (NF-1) interacts strongly with a site centered at -2200bp in the PB responsive unit (PBRU) of CYP2B2. To test the functional contribution of NF-1 in PB activation, we introduced specific mutations within the PBRU NF-1 element and demonstrated that these mutations completely ablate the binding interaction. However, transgenic mice incorporating the mutant NF-1 sequence within an otherwise wild-type -2500/CYP2B2 transgene maintained full PB responsiveness. These results indicate that, despite the avidity of the respective DNA-protein interaction within the PBRU in vitro, NF-1 interaction is not an essential factor directing PB transcriptional activation in vivo.

Animals↗
PubMed1999

Feingold syndrome--a cause of profound deafness.

A case of Feingold syndrome is presented with a previously undescribed association of bilateral profound hearing impairment. Computed tomography (CT) scanning revealed severe narrowing of the internal auditory meatuses at the peripheral end with non-existent auditory nerves. This pathology is significant in the future habilitation of the child, as cochlear implantation is not possible. Children with multiple congenital anomalies should have radiological investigations before hopes are raised with respect to cochlear implantation.

Abnormalities, Multiple↗
PubMed1997

Cochlear implantation in otosclerosis: a unique positioning and programming problem.

A case is reported in which a Nucleus 22 channel cochlear implant was inserted into the basal turn of the cochlea of a patient with advanced otosclerosis. It then passed out of the anterior end of the basal turn into an otospongiotic cavity related to the cochlea. Seven electrodes were located in the basal turn and it was possible to map them sufficiently well for the patient to derive considerable benefit from the implant. The problem of implant induced facial nerve stimulation in otospongiosis is also discussed.

Cochlear Implants↗
PubMed1997

Cochlear implantation after bacterial meningitis: the dangers of delay.

A case is described of a child of 2.6 years who developed total deafness after acute bacterial meningitis. Rapid obliteration of the cochleas due to osteoneogenesis led to limited cochlear implantation. The case is made for fast tracking these children to cochlear implant teams before neoossification becomes established.

Acute Disease↗
PubMed1995

Nucleus 20-channel and 21-channel auditory brain stem implants: first European experiences.

Central electrical stimulation of the auditory pathway can allow hearing in patients suffering from deafness localized in the auditory nerve. Developments in a multichannel auditory brain stem implant based on the Nucleus Mini 22 cochlear implant with transcutaneous signal transmission is discussed. The device has been implanted in seven European patients who suffered from neurofibromatosis type 2. Preliminary speech perception results and patient satisfaction are encouraging, and the data presented include some limited open-set speech recognition.

Auditory Threshold↗
PubMed1994

Hearing loss.

Explore the source record for details and available documents.

Deafness↗
PubMed1993

Phenobarbital induction and tissue-specific expression of the rat CYP2B2 gene in transgenic mice.

To investigate molecular events regulating the transcription of genes inducible by phenobarbital, transgenic mouse strains were developed incorporating rat cytochrome P450 2B2 (CYP2B2) genes. Expression in mouse tissues was analyzed for two series of rat CYP2B2 gene constructs, of 19 and 39 kilobase pairs total length, each containing the entire coding region, introns, and 3'-flanking sequences of CYP2B2, but differing in the respective lengths of 5'-flanking sequence. One group of mice, whose transgene included the complete 2B2 gene but only 800 base pairs of 5'-proximal sequence, were not phenobarbital-inducible in mouse liver or in any extrahepatic tissue; rather, these genes were expressed at very high levels constitutively and selectively in only kidney and liver. A second group of mice with an identical transgene, except for the presence of an additional 19 kilobase pairs of 5'-flanking sequence, expressed 2B2 only in the liver and at high levels only after phenobarbital treatment, analogous to the expression pattern observed for the endogenous CYP2B2 gene in the rat. These results demonstrate that, in vivo, phenobarbital induction and tissue-specific control requires interaction of regulatory elements far upstream of the core CYP2B2 promoter region and upstream of motifs indicated previously as determinants of phenobarbital responsiveness.

Animals↗
PubMed1993

Type 2 neurofibromatosis: the need for supraregional care?

The results of a U.K. study of 145 cases of type 2 neurofibromatosis has shown generally very poor operative results in terms of hearing and facial nerve preservation. Only 9 out of 118 vestibular schwannoma (acoustic neuroma) operations resulted in any clinically detectable hearing preservation and only 32 left the patient with good or normal (House grade I or II) ipsilateral facial nerve function. Although operation is still the definitive treatment of vestibular schwannoma (acoustic neuroma) and may be a lifesaving procedure, it appears that the evidence in favour of early operation is only valid when carried out in highly specialized centres. The special problems of NF2 cases who may go on to develop multiple spinal and cranial tumours making them wheelchair bound and blind as well as deaf warrants a careful experienced approach. Timing of operations may be critical for the enhancement of useful years of quality life. We therefore propose the setting up of a national NF2 register, with the management of cases at a few supraregional centres.

Adult↗
PubMed1992

A genetic study of type 2 neurofibromatosis in the United Kingdom. I. Prevalence, mutation rate, fitness, and confirmation of maternal transmission effect on severity.

A clinical and genetic study of type 2 neurofibromatosis (NF2) has been carried out in the United Kingdom. Virtually complete ascertainment of cases in the north-west of England was achieved and suggests a population incidence of 1 in 33,000 to 40,000. In the UK as a whole, 150 cases have been identified and been used to study the clinical and genetic features of NF2. The autosomal dominant inheritance of NF2 was confirmed, 49% of cases were assessed as representing new mutations, and the mutation rate was estimated to be 6.5 x 10(-6). Evidence to support a maternal gene effect was found in that age at onset was 18.17 years in 36 maternally inherited cases and 24.5 in 20 paternally inherited cases (p = 0.027). The preponderance of maternally inherited cases was also significant (p = 0.03). Data are presented which suggest that there are two types of NF2, one with later onset and bilateral vestibular schwannomas as the only usual feature, and the other with earlier onset and multiple other tumours. A considerable number of cases did not fall easily into one or other group and other factors such as maternal effect on severity and anticipation need to be considered.

Adolescent↗
PubMed1992

Null phenotype for cytochrome P450 2B2 in the rat results from a deletion of its structural gene.

The absence of phenobarbital (PB)-inducible cytochrome P450 2B2 (CYP2B2) in hepatic microsomes from Marshall 520 (M520) and Wistar Munich (WM) inbred strains of rat was previously reported [Biochem. Genet. 25:527-534 (1987)], and it was subsequently shown for M520 rats that corresponding CYP2B2 mRNA was not detected in hepatic extracts from either control or PB-treated animals [DNA 8:29-37 (1989)]. In the present study, solution hybridization was used to quantify PB-induced CYP2B2 and CYP2B1 mRNAs in livers from M520, WM, and outbred Sprague-Dawley rats, as well as additional inbred strains that express all known electrophoretic phenotypes for both of these closely related isozymes. Amounts of these mRNAs were also measured for F1 and F2 progenies of crosses involving M520 rats. The results indicated that the extent of PB induction of both isozymes appears to be independent of the electrophoretic phenotype. It was also shown that the null phenotype for CYP2B2 observed in M520 rats results from a mutation of a single autosomal gene and is inherited codominantly, regarding protein and mRNA phenotypes. Analyses of restriction digests and specific polymerase chain reaction products of hepatic DNAs revealed that the basis for the null phenotype of CYP2B2 in M520 and WM rats was a deletion of the CYP2B2 gene.

Alleles↗
PubMed1992

Netilmycin and vancomycin in the treatment of peritonitis in CAPD patients.

This study was undertaken to evaluate: 1. The efficacy of netilmycin and vancomycin as combined first line antimicrobial regime, compared to cefuroxime, in the treatment of peritonitis. 2. To measure the levels of netilmycin and vancomycin in the serum and dialysate. 3. To report on the use of this combination over a one year period and compare it with that of cefuroxime used during the previous one year.

Adult↗