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César Payán-Gómez,1 Julian Ramirez-Cheyne,2,3 Wilmar Saldarriaga2,3 1Deparment of Biology, Faculty of Natural Sciences, Universidad del Rosario, Bogotá, Colombia; 2Health Faculty, Universidad del Valle, Cali, Colombia; 3Hospital Universitario del Valle, Cali, ColombiaCorrespondence: Wilmar SaldarriagaHealth Faculty, Universidad del Valle, Calle 4b #36 00, Building 116 Office 29, Cali, ColombiaTel/Fax +57 3182800698Email wilmar.saldarriaga@correounivalle.edu.coAbstract: Fragile X syndrome (FXS), is an X-linked inherited genetic disease. FXS is the leading cause of inherited intellectual disability and autism in the world. Those affected are characterized by intellectual disability, language deficit, typical facies, and macroorchidism. Alterations in the FMR1 gene have been associated with FXS. The majority of people with this condition have an allele with an expansion of more than 200 repeats in a tract of CGGs within the 5ʹ untranslated region, and this expansion is associated with a hypermethylated state of the gene promoter. FXS has incomplete penetrance and variable expressivity. Intellectual disability is present in 100% of males and 60% of females. Autism spectrum disorder symptoms appear in 50% to 60% of males and 20% of females. Other characteristics such as behavioral and physical alterations have significant variations in presentation frequency. The molecular causes of the variable phenotype in FXS patients are becoming clear: these causes are related to the FMR1 gene itself and to secondary, modifying gene effects. In FXS patients, size and methylation mosaicisms are common. Secondary to mosaicism, there is a variation in the quantity of FMR1 mRNA and the protein coded by the gene Fragile Mental Retardation Protein (FMRP). Potential modifier genes have also been proposed, with conflicting results. Characterizing patients according to CGG expansion, methylation status, concentration of mRNA and FMRP, and genotypification for possible modifier genes in a clinical setting offers an opportunity to identify predictors for treatment response evaluation. When intervention strategies become available to modulate the course of the disease they could be crucial for selecting patients and identifying the best therapeutic intervention. The purpose of this review is to present the information available about the molecular causes of the variability of the expression incomplete penetrance and variable expressivity in FXS and their potential clinical applications.Keywords: FMR1, FMRP, methylation, mosaicisms, modifier, genes

The control of metallic and superconducting behavior of YBCO layers using YBCO(S)/LCMO(AF)/LCMO(F) trilayers via in-plane current injection from La(sub 1/3)Ca(sub 2/3)MnO3 ferromagnetic (F) layers through an La(sub 2/3)Ca(sub 1/3)MnO3 antiferromagnetic (AF) layer with a Neel temperature of 140 K acting as an insulator barrier is presented. The interactions in the F-AF and AF-superconducting (S) interfaces in the trilayer are very important for the quasiparticle-injection effects into the S layers.

We measured current-voltage characteristics of circular deoxyribonucleic acid (DNA) bundle samples embedded in a water mantle lying on a nylon porous membrane between vacuum-evaporated gold electrodes. The nonlinear behavior observed at room temperature on samples of different molecular sizes and variable concentration was interpreted as a long-range conduction mechanism that takes place by means of charge hopping through the network of molecules. A tunneling process acting as an additional transport channel inside single molecules between energetically appropriate bases was inferred. Our data also suggest at low bias a thermionic emission mechanism by means of which the charges move from one electrode, overcoming a potential barrier. Characteristic energies involved in the transport were reproducibly measured. [ABSTRACT FROM AUTHOR]

We fabricated ∼200 nm thin (001)-oriented films of the ferromagnetic metallic perovskite La2/3Ca1/3MnO3 on single crystal (001)-SrTiO3 substrates by dc-sputtering at high oxygen pressure. The samples feature a Curie temperature TC∼260 K and a magnetic moment μ(T→0 K)∼3 μB per Mn atom. The magnetization loops are nearly square-shaped with a coercive field Hc(5 K)=0.03 T that decreases linearly in temperature down to TC. At low temperature, the magnetization shows a decrease ΔM∼T2 and the resistivity an increase Δρ∼T2 as is expected for itinerant electron ferromagnets where single particle excitations dominate. As a further indication of the high quality of the samples, the resistivity without external magnetic field peaks right at TC with a maximum value ρ(H=0,T=TC) of only ∼2 mΩ cm. The magnetoresistance ratio Δρ/ρ0=[ρ(H,T)-ρ(H=0,T)]/ρ(H=0,T) also reaches its maximum value at TC, with Δρ/ρ0(H=6 T,T=TC)∼-50%. The complete absence of this colossal magnetoresistance effect in the low-temperature limit is a further indication of the high sample quality which may be due to a high degree of oxygenation as a result of our preparation condictions. The relation ρ(H,T)=ρmexp[-M(H,T)/M0] observed below TC as well as the temperature characteristic of the resistivity above TC can both be explained by a simple magnetic polaron hopping tunneling model where the tunneling barrier height depends in a simple way on the relative orientation of the local magnetization at both ends of the hopping path. However, here it must be considered that the polarons completely change their character at TC from large and delocalized to small and highly localized entities. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study the crystalline and interface structure of RBa[sub 2]Cu[sub 3]O[sub 7]/La[sub 1-x]A[sub x]MnO[sub 3] superlattices (R=Y, Gd; A=Ca, Sr) grown on mismatched MgO substrates by means of nondestructive x-ray diffraction. The diffraction patterns are adjusted to a model of the structure which includes interface roughness and interdiffusion. Our results show that these disorder mechanisms cannot be neglected and should be taken into account to understand the physical properties of these superlattices. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The temperature dependence of the magnetization along with magnetization hysteresis loops are measured on dc sputtered [La.sub.2/3][Ca.sub.1/3]Mn[O.sub.3]/Y[Ba.sub.2][Cu.sub.3][O.sub.7-[delta]]/[La.sub.2/3][Ca.sub.1/3]Mn[O.sub.3] and [La.sub.2/3][Ca.sub.1/3]Mn[O.sub.3]/[La.sub.1/3][Ca.sub.2/3]Mn[O.sub.3]/Y[Ba.sub.2][Cu.sub.3][O.sub.7-[delta]] trilayered structures are analyzed. A paramagnetic Meissner effect is detected in field-cooling (FC) magnetization measurements when the magnetic field is applied perpendicular to the structure film.

A report on the tunneling measurements on epitaxially grown heterostructures consisting of YBa2Cu3O(sub 7-delta)/La1/3Ca2/3MnO3/La2/3MnO3 layers is presented. Evidence of elastic tunneling in these planar junctions are obtained for an AF layer thickness of ~7 nm and at temperatures as high as 80 K.

The magnetic and electrical properties of ferromagnetic/superconducting/ferromagnetic trilayers, as a function of the thickness of the superconducting (SC) layer, are measured. The crystalline quality of the trilayers is analyzed by x-ray diffraction.

Epitaxial La(sub 2/3)Ca(sub 1/3)MnO3 (LCMO) thin films prepared by high-oxygen pressure puttering which show improved magnetic and magnetotransport properties are discussed. It is found that the magnetization loops are nearly square-shaped with a coercive field Hc (5K) =0.03 T that decreases linearly in temperature down to Curie temperature TCP.

The crystalline and interface structure of RBa2Cu3O7/ La (sub 1-x) AxMnO3 superlattices (R= Y, Gd: A= Ca, Sr) grown on mismatched MgO substrates by means of nondestructive -- ray diffraction. The results show that the individual layers present a roughness of 1 uc of the HTC material and an interdiffusion of 30 percent at the first 1.1 nm from the interface.

The temperature dependence of the magnetization along with magnetization hysteresis loops were measured on dc sputtered La2/3Ca1/3MnO3[ferromagnetic (F)]/YBa2Cu3O7-δ[superconductor(S)]/La2/3Ca1/3MnO3(F) and La2/3Ca1/3MnO3(F)/La1/3Ca2/3MnO3[antiferromagnetic (AF)]/YBa2Cu3O7δ(S) trilayered structures. The magnetic fields were applied both parallel (in-plane) and perpendicular (out-of-plane) to the film plane. Magnetization hysteresis loops, recorded at 5 K, shown a clear central peak around zero field when the magnetic field was applied perpendicular to the film plane and a typical ferromagnetic behavior when applied parallel. Additionally, the dependence of the magnetization on the temperature, performed under the zero-field-cooling (ZFC) and field-cooling (FC) regimens, evidenced the active presence of the diamagnetic and ferromagnetic phases both in the F/S/F and F/AF/S trilayers. Thus, the diamagnetic phase was clearly observed under the ZFC regimen, whereas a possible paramagnetic Meissner effect was observed under the FC regimen. [ABSTRACT FROM AUTHOR]

Evidence of elastic tunneling has been observed in YBa2Cu3O7-δ(S)/ La1/3Ca2/3MnO3(AF)/La2/3Ca1/3MnO3(F) junctions. S/AF/F trilayers with thicknesses of ∼100, ∼7, and ∼80 nm, respectively, were grown on SrTiO3 (001) substrates. Electrical measurements of the junctions at low temperatures under zero magnetic field display an asymmetry of the I-V and GsVd;dI /dV characteristics: for positive voltages, we observed a sharp peak at ∼20 meV at 15 K; for negative voltages we find at this temperature a peak around -15 meV in agreement with the value expected for YBa2Cu3O7-δ. The low values of the conductance G for voltages above the energy gap are discussed. [ABSTRACT FROM AUTHOR]

The magnetic and electrical properties of ferromagentic/superconducting/ferromagnetic trilayers as a function of the thickness of the superconducting sSCd layer sbetween 5 and 15 monolayersd were measured. La2/3Ca1/3MnO3/YBa2Cu3O7-δ /La2/3Ca1/3MnO3 trilayered films were fabricated in situ on (001) SrTiO3 single-crystal substrates using dc sputtering with high oxygen pressures (3.5 mbar). The crystalline quality of the trilayers was analyzed by x-ray diffraction. Transport and magnetic measurements revealed a weak dependence of the ferromagnet's (FMs) Curie temperature TFMC and the FM magnetization on the thickness of the SC layer, and a strong dependence of the superconducting transition temperature TC [ABSTRACT FROM AUTHOR]

We have grown Yba[SUB2]Cu[SUB3]O[SUB7-δ] (40 nm)/La[SUB1/3]Ca[SUB2/3]MnO[SUB3] (2 nm)/La[SUB2/3]Ca[SUB1/3]MnO[SUB3] (30 nm) junctions for quasiparticle-injection measurements. Ferromagnetic (F), antiferromagnetic (AF), and superconducting (S) thin films were sequentially grown "in situ" using a dc-sputtering technique at 850 °C in pure oxygen at pressures around 3.5 mbar. The temperature dependence of the resistivity of the junction, without any current injection, presented coexistence between magnetism and superconductivity with a metallic insulating transition at 186 K, and zero resistance at 52 K. When current was injected from the F layer into the S layer, superconductivity suppression was obtained at temperatures below 52 K; furthermore, small values of current injection were necessary to change the electrical behavior up to the critical temperature. A negative current gain (G) has been observed and described by the relation G ∝ ατ[SUBeff], where τ[SUBeff] is the relaxation time of the quasiparticle. The use of an AF layer as an insulating barrier is also discussed. [ABSTRACT FROM AUTHOR]