A new satellite of manganese revealed by extended-range high-energy-resolution fluorescence detection

The discovery of a new physical process in manganese metal is reported. This process will also be present for all manganese-containing materials in condensed matter. The process was discovered by applying our new technique of XR-HERFD (extended-range high-energy-resolution fluorescence detection), which was developed from the popular high-resolution RIXS (resonant inelastic X-ray scattering) and HERFD approaches. The acquired data are accurate to many hundreds of standard deviations beyond what is regarded as the criterion for `discovery'. Identification and characterization of many-body processes can shed light on the X-ray absorption fine-structure spectra and inform the scientist on how to interpret them, hence leading to the ability to measure the dynamical nanostructures which are observable using the XR-HERFD method. Although the many-body reduction factor has been used universally in X-ray absorption spectroscopy in analysis over the past 30 years (thousands of papers per year), this experimental result proves that many-body effects are not representable by any constant reduction factor parameter. This paradigm change will provide the foundation for many future studies and X-ray spectroscopy.

High-accuracy transmission and fluorescence XAFS of zinc at 10 K, 50 K, 100 K and 150 K using the hybrid technique

The most accurate measurements of the mass attenuation coefficient for metals at low temperature for the zinc K-edge from 9.5 keV to 11.5 keV at temperatures of 10 K, 50 K, 100 K and 150 K using the hybrid technique are reported. This is the first time transition metal X-ray absorption fine structure (XAFS) has been studied using the hybrid technique and at low temperatures. This is also the first hybrid-like experiment at the Australian Synchrotron. The measured transmission and fluorescence XAFS spectra are compared and benchmarked against each other with detailed systematic analyses. A recent method for modelling self-absorption in fluorescence has been adapted and applied to a solid sample. The XAFS spectra are analysed using eFEFFIT to provide a robust measurement of the evolution of nanostructure, including such properties as net thermal expansion and mean-square relative displacement. This work investigates crystal dynamics, nanostructural evolution and the results of using the Debye and Einstein models to determine atomic positions. Accuracies achieved, when compared with the literature, exceed those achieved by both relative and differential XAFS, and represent a state-of-the-art for future structural investigations. Bond length uncertainties are of the order of 20-40 fm.

High-accuracy measurement of mass attenuation coefficients and the imaginary component of the atomic form factor of zinc from 8.51 keV to 11.59 keV, and X-ray absorption fine structure with investigation of zinc theory and nanostructure

High-accuracy X-ray mass attenuation coefficients were measured from the first X-ray Extended Range Technique (XERT)-like experiment at the Australian Synchrotron. Experimentally measured mass attenuation coefficients deviate by ∼50% from the theoretical values near the zinc absorption edge, suggesting that improvements in theoretical tabulations of mass attenuation coefficients are required to bring them into better agreement with experiment. Using these values the imaginary component of the atomic form factor of zinc was determined for all the measured photon energies. The zinc K-edge jump ratio and jump factor are determined and results raise significant questions regarding the definitions of quantities used and best practice for background subtraction prior to X-ray absorption fine-structure (XAFS) analysis. The XAFS analysis shows excellent agreement between the measured and tabulated values and yields bond lengths and nanostructure of zinc with uncertainties of from 0.1% to 0.3% or 0.003 Å to 0.008 Å. Significant variation from the reported crystal structure was observed, suggesting local dynamic motion of the standard crystal lattice. XAFS is sensitive to dynamic correlated motion and in principle is capable of observing local dynamic motion beyond the reach of conventional crystallography. These results for the zinc absorption coefficient, XAFS and structure are the most accurate structural refinements of zinc at room temperature.

High-accuracy mass attenuation coefficients and X-ray absorption spectroscopy of zinc - the first X-ray Extended Range Technique-like experiment in Australia

The first X-ray Extended Range Technique (XERT)-like experiment at the Australian Synchrotron, Australia, is presented. In this experiment X-ray mass attenuation coefficients are measured across an energy range including the zinc K-absorption edge and X-ray absorption fine structure (XAFS). These high-accuracy measurements are recorded at 496 energies from 8.51 keV to 11.59 keV. The XERT protocol dictates that systematic errors due to dark current nonlinearities, correction for blank measurements, full-foil mapping to characterize the absolute value of attenuation, scattering, harmonics and roughness are measured over an extended range of experimental parameter space. This results in data for better analysis, culminating in measurement of mass attenuation coefficients across the zinc K-edge to 0.023-0.036% accuracy. Dark current corrections are energy- and structure-dependent and the magnitude of correction reached 57% for thicker samples but was still large and significant for thin samples. Blank measurements scaled thin foil attenuation coefficients by 60-500%; and up to 90% even for thicker foils. Full-foil mapping and characterization corrected discrepancies between foils of up to 20%, rendering the possibility of absolute measurements of attenuation. Fluorescence scattering was also a major correction. Harmonics, roughness and bandwidth were explored. The energy was calibrated using standard reference foils. These results represent the most extensive and accurate measurements of zinc which enable investigations of discrepancies between current theory and experiments. This work was almost fully automated from this first experiment at the Australian Synchrotron, greatly increasing the possibility for large-scale studies using XERT.

Preliminary exploration of the use of the Children's Eating Behaviour Questionnaire (CEBQ) and Feeding Practices and Structure Questionnaire (FPSQ) in Vietnamese mothers

OBJECTIVE

This preliminary pilot study aims to explore the use of the Feeding Practices and Structure Questionnaire (FPSQ) and Children's Eating Behaviour Question (CEBQ) in a sample of Vietnamese mothers.

SUBJECTS/METHODS

Cross-sectional data from the FPSQ and CEBQ were collected from a convenience sample of mothers (n = 102) who attended the Ho Chi Minh City Nutrition Centre in Viet Nam. Mothers had at least one child aged 2-5 years. The reliability of the questionnaire subscales was tested using Cronbach's alpha coefficients. Face validity was assessed using dialogue from a translation-back-translation procedure undertaken by an expert committee, and cognitive interviews conducted in a subsample of mothers (n = 6). Based on these findings, exploratory factor analyses (EFAs) were performed to assess the underlying structures of both questionnaires in this sample.

RESULTS

Cronbach's alpha coefficients for the original questionnaires ranged from 0.23 to 0.92. Limitations in translation and comprehension of items surfaced, warranting modifications of the questionnaires, which were subsequently examined using EFA. EFA of the FPSQ and CEBQ revealed a six-factor structure with 23 items, and a six-factor structure with 27 items, respectively, which were interpretable solutions for this sample. Cronbach's alpha coefficients were >0.70 for all subscales in the revised questionnaires.

CONCLUSIONS

Modified versions of the FPSQ and CEBQ are proposed for use in Viet Nam. However, prior to their use, further reliability and validity testing must be undertaken in larger samples, including assessment of test-retest reliability and construct validity, as well as confirmatory factor analysis to verify the proposed factor structures.

High accuracy determination of photoelectric cross sections, X-ray absorption fine structure and nanostructure analysis of zinc selenide using the X-ray extended range technique

Measurements of mass attenuation coefficients and X-ray absorption fine structure (XAFS) of zinc selenide (ZnSe) are reported to accuracies typically better than 0.13%. The high accuracy of the results presented here is due to our successful implementation of the X-ray extended range technique, a relatively new methodology, which can be set up on most synchrotron X-ray beamlines. 561 attenuation coefficients were recorded in the energy range 6.8-15 keV with measurements concentrated at the zinc and selenium pre-edge, near-edge and fine-structure absorption edge regions. This accuracy yielded detailed nanostructural analysis of room-temperature ZnSe with full uncertainty propagation. Bond lengths, accurate to 0.003 Å to 0.009 Å, or 0.1% to 0.3%, are plausible and physical. Small variation from a crystalline structure suggests local dynamic motion beyond that of a standard crystal lattice, noting that XAFS is sensitive to dynamic correlated motion. The results obtained in this work are the most accurate to date with comparisons with theoretically determined values of the attenuation showing discrepancies from literature theory of up to 4%, motivating further investigation into the origin of such discrepancies.

Conformation Analysis of Ferrocene and Decamethylferrocene via Full-Potential Modeling of XANES and XAFS Spectra

Recent high-accuracy X-ray absorption measurements of the sandwich organometallics ferrocene (Fc) and decamethylferrocene (DmFc) at temperatures close to liquid helium are compared with new full-potential modeling of X-ray absorption fine structure (XAFS) covering the near-edge region (XANES) and above up to k = 7 Å(-1). The implementation of optimized calculations of the oscillatory part of the spectrum from the package FDMX allows detailed study of the spectra in regions of the photoelectron momentum most sensitive to differences in the molecular stereochemistry. For Fc and DmFc, this corresponds to the relative rotation of the cyclopentadienyl rings. When applied to high-accuracy XAFS of Fc and DmFc, the FDMX theory gives clear evidence for the eclipsed conformation for Fc and the staggered conformation for DmFc for frozen solutions at ca. 15 K. This represents the first clear experimental assignment of the solution structures of Fc and DmFc and reveals the potential of high-accuracy XAFS for structural analysis.

Structural investigation of mM Ni(II) complex isomers using transmission XAFS: the significance of model development

High-accuracy transmission XAFS determined using the hybrid technique has been used to refine the geometries of bis(N-n-propyl-salicylaldiminato) nickel(II) (n-pr Ni) and bis(N-i-propyl-salicylaldiminato) nickel(II) (i-pr Ni) complexes which have approximately square planar and tetrahedral metal coordination. Multiple-scattering formalisms embedded in FEFF were used for XAFS modelling of the complexes. Here it is shown that an IFEFFIT-like package using weighting from experimental uncertainty converges to a well defined XAFS model. Structural refinement of (i-pr Ni) was found to yield a distorted tetrahedral geometry providing an excellent fit, χr(2) = 2.94. The structure of (n-pr Ni) is best modelled with a distorted square planar geometry, χr(2) = 3.27. This study demonstrates the insight that can be obtained from the propagation of uncertainty in XAFS analysis and the consequent confidence which can be obtained in hypothesis testing and in analysis of alternate structures ab initio. It also demonstrates the limitations of this (or any other) data set by defining the point at which signal becomes embedded in noise or amplified uncertainty, and hence can justify the use of a particular k-range for one data set or a different range for another. It is demonstrated that, with careful attention to data collection, including the correction of systematic errors with statistical analysis of uncertainty (the hybrid method), it is possible to obtain reliable structural information from dilute solutions using transmission XAFS data.

Structure determination from XAFS using high-accuracy measurements of x-ray mass attenuation coefficients of silver, 11 keV-28 keV, and development of an all-energies approach to local dynamical analysis of bond length, revealing variation of effective thermal contributions across the XAFS spectrum

We use the x-ray extended range technique (XERT) to experimentally determine the mass attenuation coefficient of silver in the x-ray energy range 11 kev-28 kev including the silver K absorption edge. The results are accurate to better than 0.1%, permitting critical tests of atomic and solid state theory. This is one of the most accurate demonstrations of cross-platform accuracy in synchrotron studies thus far. We derive the mass absorption coefficients and the imaginary component of the form factor over this range. We apply conventional XAFS analytic techniques, extended to include error propagation and uncertainty, yielding bond lengths accurate to approximately 0.24% and thermal Debye-Waller parameters accurate to 30%. We then introduce the FDMX technique for accurate analysis of such data across the full XAFS spectrum, built on full-potential theory, yielding a bond length accuracy of order 0.1% and the demonstration that a single Debye parameter is inadequate and inconsistent across the XAFS range. Two effective Debye-Waller parameters are determined: a high-energy value based on the highly-correlated motion of bonded atoms (σ(DW) = 0.1413(21) Å), and an uncorrelated bulk value (σ(DW) = 0.1766(9) Å) in good agreement with that derived from (room-temperature) crystallography.

High-accuracy X-ray absorption spectra from mM solutions of nickel (II) complexes with multiple solutions using transmission XAS

A new approach is introduced for determining X-ray absorption spectroscopy (XAS) spectra on absolute and relative scales using multiple solutions with different concentrations by the characterization and correction of experimental systematics. This hybrid technique is a development of standard X-ray absorption fine structure (XAFS) along the lines of the high-accuracy X-ray extended range technique (XERT) but with applicability to solutions, dilute systems and cold cell environments. This methodology has been applied to determining absolute XAS of bis(N-n-propyl-salicylaldiminato) nickel(II) and bis(N-i-propyl-salicylaldiminato) nickel(II) complexes with square planar and tetrahedral structures in 15 mM and 1.5 mM dilute solutions. It is demonstrated that transmission XAS from dilute systems can provide excellent X-ray absorption near-edge structure (XANES) and XAFS spectra, and that transmission measurements can provide accurate measurement of subtle differences including coordination geometries. For the first time, (transmission) XAS of the isomers have been determined from low-concentration solutions on an absolute scale with a 1-5% accuracy, and with relative precision of 0.1% to 0.2% in the active XANES and XAFS regions after inclusion of systematic corrections.

Measurement of the X-ray mass attenuation coefficients of silver in the 5-20 keV range

The X-ray mass attenuation coefficients of silver were measured in the energy range 5-20 keV with an accuracy of 0.01-0.2% on a relative scale down to 5.3 keV, and of 0.09-1.22% on an absolute scale to 5.0 keV. This analysis confirms that with careful choice of foil thickness and careful correction for systematics, especially including harmonic contents at lower energies, the X-ray attenuation of high-Z elements can be measured with high accuracy even at low X-ray energies (<6 keV). This is the first high-accuracy measurement of X-ray mass attenuation coefficients of silver in the low energy range, indicating the possibility of obtaining high-accuracy X-ray absorption fine structure down to the L1 edge (3.8 keV) of silver. Comparison of results reported here with an earlier data set optimized for higher energies confirms accuracy to within one standard error of each data set collected and analysed using the principles of the X-ray extended-range technique (XERT). Comparison with theory shows a slow divergence towards lower energies in this region away from absorption edges. The methodology developed can be used for the XAFS analysis of compounds and solutions to investigate structural features, bonding and coordination chemistry.

A step toward standardization: development of accurate measurements of X-ray absorption and fluorescence

This paper explains how to take the counting precision available for XAFS (X-ray absorption fine structure) and attenuation measurements, of perhaps one part in 10(6) in special cases, to produce a local variance below 0.01% and an accuracy of attenuation of the order 0.01%, with an XAFS accuracy at a similar level leading to the determination of dynamical bond lengths to an accuracy similar to that obtained by standard and experienced crystallographic measurements. This includes the necessary corrections for the detector response to be linear, including a correction for dark current and air-path energy dependencies; a proper interpretation of the range of sample thicknesses for absorption experiments; developments of methods to measure and correct for harmonic contamination, especially at lower energies without mirrors; the significance of correcting for the actual bandwidth of the beam on target after monochromation, especially for the portability of results and edge structure from one beamline to another; definitions of precision, accuracy and XAFS accuracy suitable for theoretical model analysis; the role of additional and alternative high-accuracy procedures; and discusses some principles regarding data formats for XAFS and for the deposition of data sets with manuscripts or to a database. Increasingly, the insight of X-ray absorption and the standard of accuracy needed requires data with high intrinsic precision and therefore with allowance for a range of small but significant systematic effects. This is always crucial for absolute measurements of absorption, and is of equal importance but traditionally difficult for (usually relative) measurements of fluorescence XAFS or even absorption XAFS. Robust error analysis is crucial so that the significance of conclusions can be tested within the uncertainties of the measurements. Errors should not just include precision uncertainty but should attempt to include estimation of the most significant systematic error contributions to the results. This is essential if the results are to be subject to deposition in a central accessible reference database; it is also crucial for specifying a standard data format for portability and ease of use by depositors and users. In particular this will allow development of theoretical formulations to better serve the world-wide XAFS community, and a higher and more easily comparable standard of manuscripts.

New consistency tests for high-accuracy measurements of X-ray mass attenuation coefficients by the X-ray extended-range technique

An extension of the X-ray extended-range technique is described for measuring X-ray mass attenuation coefficients by introducing absolute measurement of a number of foils - the multiple independent foil technique. Illustrating the technique with the results of measurements for gold in the 38-50 keV energy range, it is shown that its use enables selection of the most uniform and well defined of available foils, leading to more accurate measurements; it allows one to test the consistency of independently measured absolute values of the mass attenuation coefficient with those obtained by the thickness transfer method; and it tests the linearity of the response of the counter and counting chain throughout the range of X-ray intensities encountered in a given experiment. In light of the results for gold, the strategy to be ideally employed in measuring absolute X-ray mass attenuation coefficients, X-ray absorption fine structure and related quantities is discussed.

Multi-wavelength elemental contrast absorption imaging

We report experimental demonstrations of a quantitative technique for elemental mapping. The technique operates in full-field imaging mode and uses three intensity measurements at energies across an absorption edge of an element of interest to obtain its elemental distribution. The experimental results show that the technique can overcome some limitations in the conventional Absorption Edge Contrast Imaging. The technique allows for an accurate determination of the elemental distribution in a compound sample even at a low level of percentage composition. It is also robust to the choice of energy intervals.

Quantitative phase imaging with polychromatic x-ray sources

We introduce theoretically and demonstrate experimentally a contrast transfer function based phase retrieval algorithm that reconstructs the projected thickness of an homogeneous sample using a polychromatic x-ray source. We show excellent quantitative recovery of test samples in 2D using a synchrotron source with significant harmonic contamination, and in 3D using a laboratory source.

Measuring the linearity of X-ray detectors: consequences for absolute attenuation, scattering and absolute Bragg intensities

The linearity of response of X-ray detectors is tested. Examples of linearity tests demonstrate the remarkable range of linear response of flowing-gas ion chambers in the synchrotron environment. The diagnostic is also highly sensitive to the presence in the X-ray beam of harmonic X-rays diffracted by a higher-order reflection of the monochromator. The remarkable range of linearity of ion chambers has enabled the accurate measurement of the absolute X-ray attenuation of a number of elements. It should now be possible to measure the absolute intensity of Bragg reflections, provided such measurements are carried out with extended-face single crystals. The advantages of the extended-face crystal technique for Bragg intensity measurements are summarized and a number of approaches to absolute Bragg intensity measurement are discussed.

X-ray absorption fine structure for single crystals

X-ray absorption fine structure measurements are a prime tool at synchrotrons around the world, accounting for over 30% of all synchrotron research. They are incisive tools for elucidating local structure, ionization state and coordination geometry. However, in general, it has not been possible to apply them to perfect or near-perfect crystals, and their dominant application is to micro-samples, powders, metals and solutions. The reasons for this are given, and an experimental technique to yield high-precision data for good crystals is developed. This widens the applicability of the technique dramatically, and permits standards and calibration samples to be used and transferred for new types of measurement. It is shown that this is particularly appropriate for discrete measurements of absorption, X-ray absorption fine structure and X-ray absorption near-edge spectroscopy, and in cases of strong oscillations.

Extracting coherent modes from partially coherent wavefields

A method for numerically recovering the coherent modes and their occupancies from a known mutual optical intensity function is described. As an example, the technique is applied to previously published experimental data from an x-ray undulator source. The data are found to be described by three coherent modes, and the functional forms and relative occupancies of these modes are recovered.

Experimental measurement of the four-dimensional coherence function for an undulator x-ray source

A full measurement of the four-dimensional coherence function from an undulator beam line is reported. The analysis is based on the observation that the data are consistent with a coherence function that is mathematically separable. The effective source size can be altered by changing the width of the exit slit, and the complete coherence function is presented for two settings. We find, to within experimental error, that the four-dimensional complex degree of coherence can be described as a real Gaussian function that depends only on the difference of the spatial coordinates.

Recovering the complete coherence function of a generalized Schell model field

We prove that in the absence of phase singularities, a generalized Schell model partially coherent field is fully defined by its intensity in three planes. We discuss the implications of this result for the problem of characterizing wave fields.

Fresnel coherent diffractive imaging

We present an x-ray coherent diffractive imaging experiment utilizing a nonplanar incident wave and demonstrate success by reconstructing a nonperiodic gold sample at 24 nm resolution. Favorable effects of the curved beam illumination are identified.

Phase-space reconstruction of focused x-ray fields

We apply the method of phase-space tomography to reconstruct x-ray beams focused using a compound refractive lens. We show that it is possible to decouple the effect of aberrations in the optical system from the field and hence measure both them and the original field. We recover the complex coherence function and find that it is consistent with expectations.

X-ray imaging: a generalized approach using phase-space tomography

We discuss the role of coherence in x-ray imaging and consider how phase-space tomography can be used to extract information about partial coherence. We describe the application of phase-space tomography to x-ray imaging and recover the spatial coherence properties of a one-dimensional soft (1.5 keV) x-ray beam from a synchrotron undulator source. We present phase-space information from a Young's experiment and observe negative regions in the quasi-probability distribution. We show that, given knowledge of the coherence of the beam, we can use partially coherent diffraction data to recover fully coherent information, and we present some simple experimental demonstrations of this capability.

Synchrotron beam coherence: a spatially resolved measurement

We report a precise and spatially resolved measurement of the complex degree of coherence of a one-dimensional 1.5-keV beam produced by a third-generation synchrotron source. The method of phase-space tomography is used, which requires only measurements of the x-ray intensity. We find that the field is statistically stationary to within experimental error, the correlations are very well approximated by a Gaussian distribution, and the measured coherence length is in excellent agreement with expectations.

X-ray mass attenuation coefficient of silicon: theory versus experiment

We compare new experimental x-ray total mass attenuation coefficients of silicon obtained with the x-ray extended-range technique (XERT) from 5 to 20 keV with theoretical calculations and earlier experimental measurements over a 5 to 50 keV energy range. The accuracy of between 0.27% and 0.5% of the XERT data allows us to probe alternate atomic and solid state wave function calculations and to test dominant scattering mechanisms. Discrepancies between experimental results and theoretical computations of the order of 5% are discussed in detail. No single theoretical computation is currently able to reproduce the experimental results over the entire 5 to 50 keV energy range investigated.

Observation of an x-ray vortex

Phase singularities are a ubiquitous feature of waves of all forms and represent a fundamental aspect of wave topology. An optical vortex phase singularity occurs when there is a spiral phase ramp about a point phase singularity. We report an experimental observation of an optical vortex in a field consisting of 9-keV x-ray photons. The vortex is created with an x-ray optical structure that imparts a spiral phase distribution to the incident wave field and is observed by use of diffraction about a wire to create a division-of-wave-front interferometer.

The human homologue (PEG3) of the mouse paternally expressed gene 3 (Peg3) is maternally imprinted but not mutated in women with familial recurrent hydatidiform molar pregnancies

OBJECTIVES

We mapped a locus for autosomal recessive molar pregnancies with biparental genomic contribution to chromosome 19q13.4 between D19S924 and D19S890. This 5-Mb region is homologous to proximal mouse chromosome 7 and contains a cluster of Krüppel-type zinc finger genes, including the human homologue of the mouse imprinted genes: the paternally expressed gene 3 (PEG3) and the maternally expressed Zim1 genes. We analyzed the PEG3 gene for mutations in women with familial recurrent hydatidiform moles and to determine its imprinting status in humans.

METHODS

We used database searches and screened cDNA libraries to find the complete genomic structure of PEG3. Polymerase chain reaction (PCR) amplification and direct sequencing of coding exons and flanking introns were performed on genomic DNA from the affected women. Allele-specific methylation and expression were studied by methylation-sensitive Southern analysis of a 5' located CpG island and by reverse-transcription PCR of total lymphoblast-derived RNA of normal individuals who were informative for two expressed polymorphisms.

RESULTS

We did not detect any mutations in the coding region of PEG3 in the affected women. We observed allele-specific methylation of the CpG island and expression from the paternal allele in two independent informative pedigrees.

CONCLUSION

Consistent with the findings in the mouse, the human PEG3 gene is expressed from the paternal allele. Our data support that PEG3 is not mutated in women with familial recurrent hydatidiform moles, although mutations in the regulatory regions that might affect imprinting or transcriptional level of the gene could not be evaluated.

Influence of mutation type and X chromosome inactivation on Rett syndrome phenotypes

We screened 71 sporadic and 7 familial Rett syndrome (RTT) patients for MECP2 mutations by direct sequencing and determined the pattern of X chromosome inactivation (XCI) in 39 RTT patients. We identified 23 different disease-causing MECP2 mutations in 54 of 71 (76%) sporadic patients and in 2 of 7 (29%) familial cases. We compared electrophysiological findings, cerebrospinal fluid neurochemistry, and 13 clinical characteristics between patients carrying missense mutations and those carrying truncating mutations. Thirty-one of 34 patients (91%) with classic RTT had random XCI. Nonrandom XCI was associated with milder phenotypes, including a mitigated classic RTT caused by a rare early truncating mutation. Patients with truncating mutations have a higher incidence of awake respiratory dysfunction and lower levels of cerebrospinal fluid homovanillic acid. Scoliosis is more common in patients with missense mutations. These data indicate that different MECP2 mutations have similar phenotypic consequences, and random XCI plays an important role in producing the full phenotypic spectrum of classic RTT. The association of early truncating mutations with nonrandom XCI, along with the fact that chimeric mice lacking methyl-CpG-binding protein 2 (MeCP2) function die during embryogenesis, supports the notion that RTT is caused by partial loss of MeCP2 function.

Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein 2

Rett syndrome (RTT, MIM 312750) is a progressive neurodevelopmental disorder and one of the most common causes of mental retardation in females, with an incidence of 1 in 10,000-15,000 (ref. 2). Patients with classic RTT appear to develop normally until 6-18 months of age, then gradually lose speech and purposeful hand use, and develop microcephaly, seizures, autism, ataxia, intermittent hyperventilation and stereotypic hand movements. After initial regression, the condition stabilizes and patients usually survive into adulthood. As RTT occurs almost exclusively in females, it has been proposed that RTT is caused by an X-linked dominant mutation with lethality in hemizygous males. Previous exclusion mapping studies using RTT families mapped the locus to Xq28 (refs 6,9,10,11). Using a systematic gene screening approach, we have identified mutations in the gene (MECP2 ) encoding X-linked methyl-CpG-binding protein 2 (MeCP2) as the cause of some cases of RTT. MeCP2 selectively binds CpG dinucleotides in the mammalian genome and mediates transcriptional repression through interaction with histone deacetylase and the corepressor SIN3A (refs 12,13). In 5 of 21 sporadic patients, we found 3 de novo missense mutations in the region encoding the highly conserved methyl-binding domain (MBD) as well as a de novo frameshift and a de novo nonsense mutation, both of which disrupt the transcription repression domain (TRD). In two affected half-sisters of a RTT family, we found segregation of an additional missense mutation not detected in their obligate carrier mother. This suggests that the mother is a germline mosaic for this mutation. Our study reports the first disease-causing mutations in RTT and points to abnormal epigenetic regulation as the mechanism underlying the pathogenesis of RTT.