Biomedical subjects

A Kahn

Publications and source records attributed to A Kahn.

At least 109 records · Page 6Linked to original sources

PubMed1998

A novel CNS gene required for neuronal migration and involved in X-linked subcortical laminar heterotopia and lissencephaly syndrome.

X-SCLH/LIS syndrome is a neuronal migration disorder with disruption of the six-layered neocortex. It consists of subcortical laminar heterotopia (SCLH, band heterotopia, or double cortex) in females and lissencephaly (LIS) in males, leading to epilepsy and cognitive impairment. We report the characterization of a novel CNS gene encoding a 40 kDa predicted protein that we named Doublecortin and the identification of mutations in four unrelated X-SCLH/LIS cases. The predicted protein shares significant homology with the N-terminal segment of a protein containing a protein kinase domain at its C-terminal part. This novel gene is highly expressed during brain development, mainly in fetal neurons including precursors. The complete disorganization observed in lissencephaly and heterotopia thus seems to reflect a failure of early events associated with neuron dispersion.

Adolescent↗

PubMed1998

A binding site for nuclear receptors is required for the differential expression of the aldolase A fast-twitch muscle promoter in body and head muscles.

In hind limb muscles, the aldolase A muscle-specific promoter is specifically expressed in glycolytic fast-twitch fibers. Here, we show that in addition, it is expressed at higher levels in trunk and limb muscles than in neck and head muscles independent of their fiber-type content. We have identified by analysis of transgenic mice a DNA element that is required for this differential expression and, to a lesser extent, for fiber-type specificity. We show that members of the nuclear receptor superfamily bind this element in skeletal muscle nuclear extracts. Interestingly, in gel mobility shift assays, different complexes were formed with this sequence in tongue nuclear extracts compared with limb or trunk muscle nuclear extracts. Therefore, binding of distinct nuclear receptors to a single regulatory sequence appears to be associated with the location-dependent expression of the aldolase A muscle-specific promoter.

Animals↗

PubMed1998

Gene transfer to Schwann cells after peripheral nerve injury: a delivery system for therapeutic agents.

We transferred a reporter gene to Schwann cells to test whether they might serve as an endoneurial delivery system for therapeutic proteins. A replication-defective adenoviral vector carrying the gene for beta-galactosidase (lacZ) was injected into the distal segment of intact or crushed sciatic nerves of adult rats, and the expression of lacZ was histochemically assessed. Less than 1% of the Schwann cells became reactive in intact nerves, but up to 18% of the proliferating Schwann cells of injured nerves expressed lacZ. Gene expression decayed with time but might persist for up to 2 months. It was enhanced by immunosuppression: daily cyclosporin A injections reduced both proliferation of Schwann cells and lymphocytic infiltration of the nerve, whereas tolerance induced by a single intrathymic injection of the vector 4 days after birth abolished the inflammatory response but not the proliferation of Schwann cells. The vector itself did not impede axonal regeneration. The results indicate that adenoviral gene transfer to Schwann cells in injured nerves is possible and suggest that induced production of neurotrophic factor may represent a therapeutic supplement to surgical nerve repair.

Animals↗

PubMed1998

Polysomnographic study of the autonomic nervous system in potential victims of sudden infant death syndrome.

To determine the influence of sleep stages and night-time distribution on cardiac autonomic activity, the polysomnographic recordings of 18 victims of sudden infant death syndrome (SIDS) and of 36 control infants were studied. Autoregressive spectral analyses of heart rate (HR), using both short-term and whole-night methods, were evaluated as a function of sleep stages. The two main peaks of normalized LF and HF were computed during the night and the sympathovagal balance (LF/HF) was determined. In both NREM and REM sleep, SIDS infants were characterized by significantly lower normalized HF powers and higher LF/HF ratios. This finding was observed in both short-term and whole-night HR spectral analyses. In addition, SIDS victims were characterized by the presence of a high desynchronized peak of sympathetic tonus in the late hours of the night, a finding not seen in the control subjects. This report adds further indirect evidence for a possible sleep-related impairment of autonomic controls in some infants who died of SIDS.

Autonomic Nervous System↗

PubMed1998

Gamma-ray irradiation induces B7.1 costimulatory molecule neoexpression in various murine tumor cells.

The use of gene-modified tumor cells as a strategy for active immunotherapy is currently undergoing intensive fundamental and clinical research. Most clinical trials use gamma-ray-irradiated tumor cells as vaccine, although little is known about the effects of irradiation on the immunogenicity of tumor cells. In particular, no data have been reported so far concerning the effects of gamma-ray irradiation on the expression of B7 molecules in tumor cells. In this paper, we show a neoexpression of the B7.1 molecule after gamma-ray irradiation in tumor cell lines from different tissues, while the B7.2 molecule remains unexpressed in all the cell lines tested. Furthermore, the induction of B7.1 molecule membrane expression after irradiation is shown to result from the neoexpression of B7.1 mRNA, and to be reproduced with H2O2 oxidative stress. These data could explain the enhanced immunogenicity of many tumor cells after irradiation, and could lead to new immunotherapy protocols.

Animals↗

PubMed1998

Decreased growth hormone response to glucagon in infants after an apnea of infancy.

We studied glucagon-induced growth hormone secretion in 9 patients with apnea of infancy and in 55 siblings of children who had died of sudden infant death syndrome, who were included as a comparison group. We observed a 33% decrease in growth hormone secretion in patients with apnea of infancy. However, linear growth remained normal. This finding could be related to either repeated episodes of hypoxia or to abnormal maturation of the autonomous nervous system.

Apnea↗

PubMed1998

Auditory arousal thresholds are higher when infants sleep in the prone position.

OBJECTIVE: To evaluate the possibility that infants sleeping in the prone position have higher arousal thresholds to auditory challenges than when sleeping in the supine position. STUDY DESIGN: Polygraphic recordings were performed for 1 night in 25 healthy infants with a median age of 9 weeks. The infants were exposed to white noises of increasing intensities while sleeping successively in the prone and supine positions, or vice versa. Arousal thresholds were defined by the auditory stimuli needed to induce polygraphic arousals. RESULTS: Three infants were excluded from the study because they awoke while their position was being changed. For the 22 infants included in the analysis, more intense auditory stimuli were needed to arouse the infants in the prone position than those in the supine body position (p = 0.011). Arousal thresholds were higher in the prone than in the supine position in 15 infants; unchanged in 4 infants; and lower in the prone position in 3 infants (p = 0.007). CONCLUSIONS: Infants show higher arousal thresholds to auditory challenges when sleeping in the prone position than when sleeping in the supine position. The finding could be relevant to mechanisms concerned with the reported association between sudden deaths and the prone sleeping position in infants.

Auditory Threshold↗

PubMed1998

Adenovirus-mediated transfer of the neurotrophin-3 gene into skeletal muscle of pmn mice: therapeutic effects and mechanisms of action.

Several neurotrophic factors (CNTF, BDNF, IGF-1) have been suggested for the treatment of motor neuron diseases. In ALS patients, however, the repeated subcutaneous injection of these factors as recombinant proteins is complicated by their toxicity or poor bioavailability. We have constructed an adenovirus vector coding for neurotrophin-3 (AdNT-3) allowing for stable and/or targeted delivery of NT-3 to motoneurons. The intramuscular administration of this vector was tested in the mouse mutant pmn (progressive motor neuronopathy). AdNT-3-treated pmn mice showed prolonged lifespan, improved neuromuscular function, reduced motor axonal degeneration and efficient reinnervation of muscle fibres. NT-3 protein and also adenovirus vectors, when injected into muscle, can be transported by motoneurons via retrograde axonal transport to their cell bodies in the spinal cord. Using ELISA and RT-PCR analyses in muscle, spinal cord and serum of AdNT-3-treated pmn mice, we have investigated the contribution of these processes to the observed therapeutic effects. Our results suggest that most if not all therapeutic benefit was due to the continuous systemic liberation of adenoviral NT-3. Therefore, viral gene therapy vectors auch as adenoviruses, AAVs, lentiviruses and new types of gene transfer not based on viral vectors that allow for efficient in vivo liberation of neurotrophic factors have potential for the future treatment of human motor neuron diseases.

Adenoviridae↗

PubMed1998

Diagnostic approach to obstructive sleep apnea in children.

Obstructive sleep apnea syndrome (OSAS) in childhood is a disorder of breathing during sleep characterized by prolonged partial upper airway obstruction and/or intermittent complete obstruction that disrupts normal ventilation during sleep and normal sleep patterns. A spectrum of severity related to the degree of upper airway resistance, to the duration of the disease, to the presence or absence of hypoxemia episodes, and to certain clinical features can be described. Symptomatic children may not fit the criteria for diagnosis established for OSAS in adults; age-specific standards are needed. Both anatomical factors that increase upper airway resistance, e.g. adenotonsillar hypertrophy, and functional processes that decrease upper airway tone, e.g. REM sleep, contribute to the pathogenesis of pediatric OSAS. Sequelae of OSAS in children include neurobehavioural abnormalities, stunting of growth, and cor pulmonale. Both the history and physical examination should target the sleeping child; parents often report loud snoring, difficulty breathing, and obstructive apneas. The gold standard investigation to establish the diagnosis and to quantitate disease severity is overnight polysomnography. Home cardiopulmonary sleep studies have been shown to be an accurate and practical alternative to overnight laboratory polysomnography for routine evaluation of non-complex children with adenotonsillar hypertrophy. Children with documented severe OSAS are at increased post-operative risk for airway compromise and should be observed and monitored carefully. Adenotonsiliectomy is the most common therapy for OSAS in children; as a second-line treatment, the use of nasal CPAP in children with OSAS has been very successful in experienced hands.

Journal Article↗

PubMed1998

The human pH aldolase A promoter directs widespread but muscle-predominant expression in transgenic mice.

In order to identify regulatory elements that direct widespread in vivo expression of a linked gene, we have examined one of the human aldolase A alternative promoters, the ubiquitous pH promoter, which is active in most foetal and adult tissues. We have used the pH promoter region to drive expression of an heterologous CAT reporter gene in transgenic mice. We show that a short 820 bp pH promoter fragment is able to confer a ubiquitous and reproducible activity pattern on the CAT reporter gene in most of the transgenic lines analysed, with a particularly high level of expression in adult skeletal muscle. Activity of this transgene was detected from early embryonic stages. Therefore, this pH promoter region appears to be a powerful tool to direct ubiquitous and early expression of a transgene in vivo. Deletion analysis revealed that: (i) the region between -651 and -369 bp relative to the pH promoter transcription start site includes DNA elements capable of overriding effects of the surrounding chromatin at the integration site, (ii) the region between -285 and -211 bp is involved in pH promoter tissue-specific expression pattern in skeletal muscle and/or nervous tissues, (iii) the region located between -211 and -108 bp is necessary for its ubiquitous and muscle-predominant activity and (iv) the most proximal region downstream from -108 bp is still sufficient to confer an activity in brain and lung.

Animals↗

PubMed1998

Selective repopulation of normal mouse liver by Fas/CD95-resistant hepatocytes.

Hepatocyte transplantation might represent a potential therapeutic alternative to liver transplantation in the future; however, transplanted cells have a limited capacity to repopulate the liver, as they do not proliferate under normal conditions. Recently, studies in urokinase (uPA) transgenic mice and in fumarylacetoacetate hydrolase (FAH)-deficient mice have shown that the liver can be repopulated by genetically engineered hepatocytes harboring a selective advantage over resident hepatocytes. We have reported that transgenic mice expressing human Bcl-2 in their hepatocytes are protected from Fas/CD95-mediated liver apoptosis. We now show that Bcl-2 transplanted hepatocytes selectively repopulate the liver of mice treated with nonlethal doses of the anti-Fas antibody Jo2. FK 506 immunosuppressed mice were transplanted by splenic injection with Bcl-2 hepatocytes. The livers of female recipients were repopulated by male Bcl-2 transgenic hepatocytes, as much as 16%, after 8 to 12 administrations of Jo2. This only occurred after anti-Fas treatment, confirming that resistance to Fas-induced apoptosis constituted the selective advantage of these transplanted hepatocytes. Thus, we have demonstrated a method for increasing genetic reconstitution of the liver through selective repopulation with modified transgenic hepatocytes, which will allow optimization of cell and gene therapy in the liver.

Animals↗

PubMed1998

Exhaustive screening of the acid beta-glucosidase gene, by fluorescence-assisted mismatch analysis using universal primers: mutation profile and genotype/phenotype correlations in Gaucher disease.

Gaucher disease (GD) is one of the most prevalent lysosomal storage disorders and one of the rare genetic diseases now accessible to therapy. Outside the Ashkenazi Jewish community, a high molecular diversity is observed, leaving approximately 30% of alleles undetected. Nevertheless, very few exhaustive methods have been developed for extensive gene screening of a large series of patients. Our approach for a complete search of mutations was the association of fluorescent chemical cleavage of mismatches with a universal strand-specific labeling system. The glucocerebrosidase (GBA) gene was scanned by use of a set of six amplicons, comprising 11 exons, all exon/intron boundaries, and the promoter region. By use of this screening strategy, the difficulties due to the existence of a highly homologous pseudogene were easily overcome, and both GD mutant alleles were identified in all 25 patients studied, thus attesting to a sensitivity that approaches 100%. A total of 18 different mutations and a new glucocerebrosidase haplotype were detected. The mutational spectrum included eight novel acid beta-glucosidase mutations: IVS2 G(+1)-->T, I119T, R170P, N188K, S237P, K303I, L324P, and A446P. These data further indicate the genetic heterogeneity of the lesions causing GD. Established genotype/phenotype correlations generally were confirmed, but notable disparities were disclosed in several cases, thus underlining the limitation in the prognostic value of genotyping. The observed influence of multifactorial control on this monogenic disease is discussed.

Adolescent↗

PubMed1998

Adenovirus-mediated transfer of the acid alpha-glucosidase gene into fibroblasts, myoblasts and myotubes from patients with glycogen storage disease type II leads to high level expression of enzyme and corrects glycogen accumulation.

Glycogen storage disease type II (GSD II) is an autosomal recessive disorder caused by defects in the lysosomal acid alpha-glucosidase (GAA) gene. We investigated the feasibility of using a recombinant adenovirus containing the human GAA gene under the control of the cytomegalovirus promoter (AdCMV-GAA) to correct the enzyme deficiency in different cultured cells from patients with the infantile form of GSD II. In GAA-deficient fibroblasts infected with AdCMV-GAA, transduction and transcription of the human transgene resulted in de novo synthesis of GAA protein. The GAA enzyme activity was corrected from the deficient level to 12 times the activity of normal cells. The transduced cells overexpressed the 110 kDa precursor form of GAA, which was secreted into the culture medium and was taken up by recipient cells. The recombinant GAA protein was correctly processed and was active on both an artificial substrate 4-methylumbelliferyl-alpha-D-glucopyranoside (4MUG) and glycogen. In GAA-deficient muscle cells, a significant increase in cellular enzyme level, approximately 20-fold higher than in normal cells, was also observed after viral treatment. The transduced muscle cells were also able to efficiently secrete the recombinant GAA. Moreover, transfer of the human transgene resulted in normalization of cellular glycogen content with clearance of glycogen from lysosomes, as assessed by electron microscopy, in differentiated myotubes. These results demonstrate phenotypic correction of cultured skeletal muscle from a patient with infantile-onset GSD II using a recombinant adenovirus. We conclude that adenovirus-mediated gene transfer might be a suitable model system for further in vivo studies on delivering GAA to GSD II muscle, not only by direct cell targeting but also by a combination of secretion and uptake mechanisms.

Adenoviridae↗

PubMed1998

Retrovirus-mediated enzymatic correction of Tay-Sachs defect in transduced and non-transduced cells.

Tay-Sachs disease is a severe neurodegenerative disorder due to mutations in the HEXA gene coding for the alpha-chain of the alpha-beta heterodimeric lysosomal enzyme beta-hexosaminidase A (HexA). Because no treatment is available for this disease, we have investigated the possibility of enzymatic correction of HexA-deficient cells by HEXA gene transfer. Human HEXA cDNA was subcloned into a retroviral plasmid generating to G.HEXA vector. The best Psi-CRIP producer clone of G.HEXA retroviral particles was isolated, and murine HexA-deficient fibroblasts derived from hexa -/- mice were transduced with the G.HEXA vector. Transduced cells overexpressed the alpha-chain, resulting in the synthesis of interspecific HexA (human alpha-chain/murine beta-chain) and in a total correction of HexA deficiency. The alpha-chain was secreted in the culture medium and taken up by HexA-deficient cells via mannose-6-phosphate receptor binding, allowing for the restoration of intracellular HexA activity in non-transduced cells.

3T3 Cells↗

PubMed1998

Non-specific X-linked semidominant mental retardation by mutations in a Rab GDP-dissociation inhibitor.

Non-specific X-linked mental retardation (MRX) is a very common disorder which affects approximately 1 in 600 males. Despite this high frequency, little is known about the molecular defects underlying this disorder, mainly because of the clinical and genetic heterogeneity which is evident from linkage studies. Recently, a collaborative study using the candidate gene approach demonstrated the presence of mutations in GDIalpha, a Rab GDP-dissociation inhibitor encoded by a gene localized in Xq28, associated with non-specific mental retardation. GDIalpha is mainly a brain-specific protein that plays a critical role in the recycling of Rab GTPases involved in membrane vesicular transport. The study presented here was designed to assess the prevalence of mutations in the GDIalpha in mentally retarded patients and to discuss the clinical phenotypes observed in affected individuals. Mutation screening of the whole coding region of the GDIalpha gene, using a combination of denaturing gradient gel electrophoresis and direct sequencing, was carried out in 164 patients found negative for expansions across the FRAXA GCC repeat. In addition to the nonsense mutation recently reported in MRX48, we have identified a novel missense mutation in exon 11 of the GDIalpha gene in one familial form of non-specific mental retardation. In this family (family R), all affected males show moderate to severe mental retardation, and the X-linked semidominant inheritance is strongly suggested by the severe phenotypes in males with respect to mildly affected females or unaffected obligatory carriers. This study showed that the prevalence of GDIalpha mutations in non-specific mental retardation could be estimated to be 0.5-1%, and molecular diagnosis and genetic counselling in some cases of non-specific mental handicap can now be provided.

Female↗

PubMed1998

Inherited microdeletion in Xp21.3-22.1 involved in non-specific mental retardation.

X-linked mental retardation (XLMR) is a genetically and clinically heterogeneous common disorder. A cumulative frequency of about 1/600 male births was estimated by different authors, including the fragile X syndrome, which affects 1/4000 males. Given this very high cumulative frequency, identification of genes and molecular mechanisms involved in other XLMRs, represents a challenging task of considerable medical importance. In this report we describe clinical and molecular investigations in the family of a mentally retarded boy for whom a microdeletion in Xp21.3-22.1 was detected within the frame of a previously reported systematic search for deletion using STS-PCR screening. Thorough clinical investigation of the sibling showed that two affected brothers exhibit a moderate non-specific mental retardation without any additional neurological impairment, statural growth deficiency or characteristic dysmorphy. Molecular analysis revealed that the microdeletion observed in this family is an inherited defect which cosegregates with mental retardation as an X-linked recessive condition, since both non-deleted boys and transmitting mother are normal. These results and the inherited microdeletion detected within the same region associated with non-specific MR, reported by Raeymaekers et al., suggest that Xp21.3 MR locus is prone to deletions. Therefore, search for microdeletions in the eight families assigned by linkage analysis to this region might allow a better definition of the critical region and an identification of the gene involved in this X-linked mental retardation.

Child↗

PubMed1998

Cervical facet dislocation: management following delayed diagnosis.

This study examined the influence of early versus late initial presentation of patients with cervical spine facet dislocation on presentation, neurologic deficit, and the success of closed reduction. Thirty-four patients were studied, and approximately 35% presented at least 72 hours following their injury. Compared with patients who presented early, this late group demonstrated less neurologic deficit, and closed reduction was less likely to be successful. These findings suggest that a distinction should exist in the management algorithm between early versus late presentation of cervical facet dislocation.

Adolescent↗

PubMed1998

[Sudden infant death. Reduction of the incidence of death in Belgium].

Research works have led to a better knowledge of some of the major causes of sudden unexpected infant deaths. Sleep recording techniques and home monitoring programmes identify and protect some of infants at high risk. Sleep studies described some of the mechanisms responsible for lack of physiologic adaptation of infants to endogenous and environmental factors. Large scale education campaigns have been organized since 5 years to inform health professionals and families against the known risk factors for sudden death. A 60% reduction in infant mortality has since been observed. The efforts of prevention against these deaths have been coordinated by the National Infant Death Watch Tower in association with heath associations and the Ministry for health. A further reduction in infant mortality is expected in the years to come.

Belgium↗