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Biomedical subjects

J Kaplan

Publications and source records attributed to J Kaplan.

At least 19 recordsLinked to original sources
PubMed2005

[Leber congenital amaurosis: comprehensive survey of genetic heterogeneity. A clinical definition update].

Leber congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies, responsible for congenital blindness. Disease-associated mutations have been hitherto reported in seven genes. These genes are all expressed preferentially in the photoreceptor cells or the retinal pigment epithelium, but they are involved in strikingly different physiologic pathways, resulting in an unforeseeable pathophysiologic variety. This broad genetic and physiologic heterogeneity, which could greatly increase in the coming years, hinders molecular diagnosis in LCA patients. Genotyping is, however, required to establish genetically defined subgroups of patients ready for therapy. Here we report a comprehensive mutational analysis of all the known genes in 179 unrelated LCA patients, including 52 familial and 127 sporadic (27/127 consanguineous) cases. Mutations were identified in 47.5% of patients. GUCY2D accounted for by far the largest part of the LCA cases in our series (21.2%), followed by CRB1 (10%), RPE65 (6.1%), RPGRIP1 (4.5%), AIPL1 (3.4%), TULP1 (1.7%) and CRX (0.6%). The clinical history of all patients with mutations was carefully revisited in the search for phenotype variations. Genotype-phenotype correlations were found that made it possible to divide patients into two main groups. The first one includes patients whose symptoms fit the traditional definition of LCA, i.e., congenital or very early cone-rod dystrophy, while the second group gathers patients affected with severe yet progressive rod-cone dystrophy. In addition, objective ophthalmologic data subdivided each group into two subtypes. Based on these findings, we have drawn decisional flowcharts directing the molecular analysis of LCA genes in a given case. These flowcharts will hopefully lighten the onerous task of genotyping new patients, but only if the most precise clinical history since birth is available.

Animals↗
PubMed2005

[Hereditary macular dystrophies].

Hereditary macular dystrophies are degenerative diseases of the central area of the retina associating primary anomalies of the retinal pigment epithelium and sensory retina. These conditions, whose hallmark is a loss of visual acuity, are a major cause of blindness and affect patients at all ages. Macular dystrophies group diseases that are heterogenous at the genetic level, as well as at the clinical, histological and physiopathological levels. Monogenic macular dystrophies are rare autosomal dominant conditions, with the exception of Stargardt disease in its typical form, which is not only relatively frequent but is also inherited as an autosomal recessive trait. During the last few years, the molecular bases of these conditions have begun to be elucidated with the identification of several responsible genes. For some macular dystrophies, this new information has confirmed pre-existing hypotheses on their pathophysiology, but for others, the discovery of the disease gene has added further complexity to the disease process. Two contradictory concepts were particularly highlighted by these genetic studies. Several phenotypes previously described as different clinical entities were brought together by the identification of mutations in the same gene, and converselyome conditions that were clinically assigned the same name, often heterogeneous at the clinical level, appeared genetically and physiopathologically heterogeneous. In addition, it is worth noting that the monogenic macular dystrophy genes were often regarded as potential factors for susceptibility to age-related macular degenerations. However, to date, only ABCA4 mutations have been associated with a minority of this frequent multifactorial condition. The aim of this article is to give a progress report on the monogenic macular dystrophy genes and to review current knowledge concerning the pathophysiology of these conditions.

Humans↗
PubMed2004

De novo design of catalytic proteins.

The de novo design of catalytic proteins provides a stringent test of our understanding of enzyme function, while simultaneously laying the groundwork for the design of novel catalysts. Here we describe the design of an O(2)-dependent phenol oxidase whose structure, sequence, and activity are designed from first principles. The protein catalyzes the two-electron oxidation of 4-aminophenol (k(cat)/K(M) = 1,500 M(-1).min(-1)) to the corresponding quinone monoimine by using a diiron cofactor. The catalytic efficiency is sensitive to changes of the size of a methyl group in the protein, illustrating the specificity of the design.

Aminophenols↗
PubMed2004

Use of recombinant factor VIIa to treat life-threatening non-surgical bleeding in a post-partum patient.

Ongoing bleeding from patients who have an acquired coagulopathy post-surgery is a common problem. Strategies that are available to combat this problem revolve around the replacement of coagulation factors, platelets, and red blood cells as necessary. These strategies are not always successful and a more direct approach to activating the coagulation system can be more effective and in some instances life saving. We describe the use of recombinant factor VIIa in a patient with ongoing post partum bleeding.

Adult↗
PubMed2004

Preliminary treatment planning and dosimetry for a clinical trial of neutron capture therapy using a fission converter epithermal neutron beam.

A Phase I/II clinical trial of neutron capture therapy (NCT) was conducted at Harvard-MIT using a fission converter epithermal neutron beam. This epithermal neutron beam has nearly ideal performance characteristics (high intensity and purity) and is well-suited for clinical use. Six glioblastoma multiforme (GBM) patients were treated with NCT by infusion of the tumor-selective amino acid boronophenylalanine-fructose (BPA-F) at a dose of 14.0 g/m(2) body surface area over 90 min followed by irradiation with epithermal neutrons. Treatments were planned using NCTPlan and an accelerated version of the Monte Carlo radiation transport code MCNP 4B. Treatments were delivered in two fractions with two or three fields. Field order was reversed between fractions to equalize the average blood boron concentration between fields. The initial dose in the dose escalation study was 7.0 RBEGy, prescribed as the mean dose to the whole brain volume. This prescription dose was increased by 10% to 7.7 RBEGy in the second cohort of patients. A pharmacokinetic model was used to predict the blood boron concentration for determination of the required beam monitor units with good accuracy; differences between prescribed and delivered doses were 1.5% or less. Estimates of average tumor doses ranged from 33.7 to 83.4 RBEGy (median 57.8 RBEGy), a substantial improvement over our previous trial where the median value of the average tumor dose was 25.8 RBEGy.

Aged↗
PubMed2003

[Macular dystrophies].

Macular dystrophies are a group of hereditary disorders of the macula occurring in children or young adults. The most frequent in France will be presented in detail: Best disease, Stargardt macular dystrophy, cone dystrophy, X-linked retinoschisis, pattern dystrophy, and malattia leventinese. Molecular biology studies have now mapped and identified the genes involved in these macular dystrophies. Analysis of the features of fundus examination will lead to further examinations such as fluorescein angiography, indocyanine green angiography, optical coherent tomography, electroretinography, or electrooculography, in order to confirm the diagnosis. We will also present the differential diagnosis of each of these macular dystrophies.

Adult↗
PubMed2002

Prospective study of etiologic agents of community-acquired pneumonia in patients with HIV infection.

OBJECTIVES: To study prospectively HIV-positive patients admitted to the hospital because of pneumonia by extensive laboratory tests to determine specific microbiologic diagnoses and to establish the best clinical diagnosis after review of all available data by expert clinicians. METHODS: Patients admitted to one of two hospitals had extensive questionnaires completed and defined diagnostic tests performed on blood, sputum, urine and bronchoalveolar lavage specimens, when available. RESULTS: A total of 230 patients had a diagnosis of pneumonia verified. A definite or probable etiologic diagnosis was made in 155 (67%) of these patients. Pneumocystis carinii caused 35% of all cases of pneumonia. Twenty-seven percent of cases of pneumonia with a single etiology had a definite or probable bacterial etiology. 'Atypical agents' were distinctly uncommon. Few clinical or laboratory parameters could differentiate specific etiologies. CONCLUSIONS: P. carinii continues to be a common cause of pneumonia in these patients. The rarity of 'atypical agents' could simplify the empiric approach to therapy. Despite the use of extensive testing we did not find a definite etiology in a large number of cases.

AIDS-Related Opportunistic Infections↗
PubMed2002

Genomics and medicine: hopes and challenges.

The major impact of the completion of the human genome sequence is the understanding of disease etiology with deduced therapy. The catalog of monogenic diseases should be easily completed through in silico cloning. The major challenge today is to decipher the polygenic and multifactorial etiology of common diseases, such as cancer, cardiovascular, nutritional, allergic, auto-immune, degenerative disorders. In fact every gene, when mutated, is a potential disease gene, and we end up with the new concept of 'reverse medicine', by which we will derive new morbid entities and pathogenic pathways from the knowledge of the structure and function of every gene. A new molecular and supramolecular integrated physiology will help build a molecular pathophysiology of the different syndromes, from which etiologic therapy will derive. The revolution in nosology, the problem of predictive medicine when therapeutic curative or preventive measure are lagging behind, are some of the novel challenges that molecular medicine has to face.

Costs and Cost Analysis↗
PubMed2001

YFH1-mediated iron homeostasis is independent of mitochondrial respiration.

The human gene frataxin and its yeast homolog YFH1 affect mitochondrial function. Deficits in frataxin result in Friedreich ataxia, while deletion of YFH1 results in respiratory incompetence. We determined that as long as respiratory incompetent yeast express Yfh1p they do not accumulate excessive mitochondrial iron. Deletion of YFH1 in respiratory incompetent yeast results in mitochondrial iron accumulation, while the reintroduction of Yfh1p results in mitochondrial iron export. Further, overexpression of Yfh1p has no effect on oxygen consumption in wild-type yeast grown in either fermentative or respiratory carbon sources. We conclude that the effect of Yfh1p on mitochondrial iron metabolism is independent of respiratory activity.

DNA, Mitochondrial↗
PubMed2001

Mutation spectrum and splicing variants in the OPA1 gene.

Optic atrophy type 1 (OPA1, MIM 165500) is a dominantly inherited optic neuropathy that features low visual acuity leading in many cases to legal blindness. We have recently shown, with others, that mutations in the OPA1 gene encoding a dynamin-related mitochondrial protein, underlie the dominant form of optic atrophy. Here we report that OPA1 has eight mRNA isoforms as a result of the alternative splicing of exon 4 and two novel exons named 4b and 5b. In addition, we screened a cohort of 19 unrelated patients with dominant optic atrophy by direct sequencing of the 30 OPA1 exons (including exons 4b and 5b) and found mutations in 17 (89%) of them of which 8 were novel. A majority of these mutations were truncative (65%) and located in exons 8 to 28, but a number of them were amino acid changes predominantly found in the GTPase domain (exons 8 to 15). We hypothesize that at least two modifications of OPA1 may lead to dominant optic atrophy, that is alteration in GTPase activity and loss of the last seven C-terminal amino acids that putatively interact with other proteins.

Alternative Splicing↗
PubMed2001

Identification of a Candida albicans ferrichrome transporter and its characterization by expression in Saccharomyces cerevisiae.

Saccharomyces cerevisiae can accumulate iron through the uptake of siderophore-iron. Siderophore-iron uptake can occur through the reduction of the complex and the subsequent uptake of iron by the high affinity iron transporter Fet3p/Ftr1p. Alternatively, specific siderophore transporters can take up the siderophore-iron complex. The pathogenic fungus Candida albicans can also take up siderophore-iron. Here we identify a C. albicans siderophore transporter, CaArn1p, and characterize its activity. CaARN1 is transcriptionally regulated in response to iron. Through expression studies in S. cerevisiae strains lacking endogenous siderophore transporters, we demonstrate that CaArn1p specifically mediates the uptake of ferrichrome-iron. Iron-ferrichrome and gallium-ferrichrome, but not desferri-ferrichrome, could competitively inhibit the uptake of iron from ferrichrome. Uptake of siderophore-iron resulting from expression of CaARN1 under the control of the MET25-promoter in S. cerevisiae was independent of the iron status of the cells and of Aft1p, the iron-sensing transcription factor. These studies demonstrate that the expression of CaArn1p is both necessary and sufficient for the nonreductive uptake of ferrichrome-iron and suggests that the transporter may be the only required component of the siderophore uptake system that is regulated by iron and Aft1p.

Amino Acid Sequence↗
PubMed2001

hVPS41 is expressed in multiple isoforms and can associate with vesicles through a RING-H2 finger motif.

Vps41p, the protein encoded by the yeast gene VPS41, has been shown to mediate formation of AP-3 transport vesicles from the Golgi apparatus and to facilitate the docking and fusion of lysosomal vesicles. Although both of these activities involve transient association with membrane structures, the mechanisms that mediate those interactions have not been determined. Orthologues of VPS41 have been identified in humans, Drosophila, tomato, and Arabidopsis; the degree of sequence similarity among these genes suggests a highly conserved function. Here we provide evidence that hVps41, the human homologue of Vps41p, is expressed in two isoforms that differ in that one contains a C-terminal RING-H2 sequence motif. Transient expression analysis suggests that this RING-H2 domain is responsible for membrane association. This observation was further supported by the cytosolic localization of site-specific mutants. A truncated construct containing only the hVps41 RING-H2 domain was found to associate with a class of intracellular vesicles that originated from the Golgi and showed partial coincidence with the delta subunit of the adaptor protein complex-3. Together with information from the homologous yeast system, these results suggest that hVps41 may also be involved in the formation and fusion of transport vesicles from the Golgi.

Amino Acid Sequence↗
PubMed2001

CCC1 is a transporter that mediates vacuolar iron storage in yeast.

The budding yeast Saccharomyces cerevisiae can grow for generations in the absence of exogenous iron, indicating a capacity to store intracellular iron. As cells can accumulate iron by endocytosis we studied iron metabolism in yeast that were defective in endocytosis. We demonstrated that endocytosis-defective yeast (Delta end4) can store iron in the vacuole, indicating a transfer of iron from the cytosol to the vacuole. Using several different criteria we demonstrated that CCC1 encodes a transporter that effects the accumulation of iron and Mn(2+) in vacuoles. Overexpression of CCC1, which is localized to the vacuole, lowers cytosolic iron and increases vacuolar iron content. Conversely, deletion of CCC1 results in decreased vacuolar iron content and decreased iron stores, which affect cytosolic iron levels and cell growth. Furthermore Delta ccc1 cells show increased sensitivity to external iron. The sensitivity to iron is exacerbated by ectopic expression of the iron transporter FET4. These results indicate that yeast can store iron in the vacuole and that CCC1 is involved in the transfer of iron from the cytosol to the vacuole.

Cation Transport Proteins↗
PubMed2001

The role of sugar residues in molecular recognition by vancomycin.

The sugar residues of the glycopeptide antibiotic vancomycin contribute to the cooperativity of ligand binding, thereby increasing ligand affinity and enhancing antimicrobial activity. To assess the structural basis for these effects, we determined a 0.98 A X-ray crystal structure of the vancomycin aglycon and compared it to structures of several intact vancomycin:ligand complexes. The crystal structure reveals that the aglycon binds acetate anions and forms back-to-back dimeric complexes in a manner similar to that of intact vancomycin. However, the four independent copies of the aglycon in each asymmetric unit of the crystal exhibit a high degree of conformational heterogeneity. These results suggest that the sugar residues, in addition to enlarging and strengthening the dimer interface, provide steric constraints that limit the vancomycin molecule to a relatively small number of productive conformations.

Carbohydrates↗