A rare inherited homozygous missense variant in PLA2G6 influences susceptibility to infantile neuroaxonal dystrophy: a case report.

Background: Infantile neuroaxonal dystrophy (INAD) is an ultra-rare early-onset autosomal recessive neurodegenerative disorder due to PLA2G6 variants. The clinical symptoms of INAD patients display considerable diversity, and many PLA2G6 variants are still not thoroughly investigated in relation to their associated clinical presentations. Case Description: A 16-month-old boy was admitted to our hospital due to regression of acquired motor and speech abilities that had persisted for 4 months. The patient was born to a healthy consanguineous couple after 41 weeks of pregnancy and natural delivery. Before 12 months old, he had normal motor development milestones. On admission, he also showed astasia-abasia, weakness of distal muscles, and diminished patellar tendon reflex. Brain magnetic resonance imaging (MRI) revealed cerebellar atrophy. Auditory brainstem response (ABR) indicated moderately severe hearing loss. With chromosome microarray analysis (CMA), we identified several copy number-neutral regions of runs of homozygosity (ROH) in the patient. Whole-exome sequencing (WES) further revealed that the patient harbored a homozygous missense variant NM_003560.2: c.1778C>T, p.Pro593Leu (rs1451486649) in the PLA2G6 gene. In the patient's asymptomatic parents and brother, the PLA2G6 c.1778C>T variant stayed in heterozygous status as confirmed by Sanger sequencing. The patient was finally diagnosed with INAD. Conclusions: We report an INAD child with a rare PLA2G6 c.1778C>T homozygous missense variant and associated clinical symptoms. The family-based cosegregation analysis reveals that the PLA2G6 c.1778C>T homozygous variant contributes to the pathogenesis of INAD.

[Clinical phenotype and genetic analysis of a child featuring short stature and multiple skeletal dysplasia].

OBJECTIVE: To analyze the clinical phenotype and genetic basis for a child featuring familial short stature. METHODS: A child who was admitted to Huzhou Maternal and Child Health Care Hospital on October 7, 2021 for growth retardation and pectus carinatum was selected as the study subject. Physical exam and medical imaging was performed. The child was subjected to whole exome sequencing, and candidate variants were verified by Sanger sequencing and bioinformatic analysis. RESULTS: The child, a 1-year-old male, had manifested with slightly short stature (Z = -2.03), midfacial dysplasia, and multiple skeletal dysplasia such as pectus carinatum, irregular vertebral morphology, and defect of lumbar anterior bones. His mother, maternal grandmother and great-maternal grandfather also had short stature. WES revealed that the child has harbored a heterozygous c.2858dupA (p.Asp953GlufsTer476) frameshifting variant of the ACAN gene, which was inherited from his mother. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the c.2858dup (p.Sp953Glufster476) variant was classified as likely pathogenic (PVS1+PM2_Supporting). The patient has shown marked improved height after receiving 11 months of treatment with human recombinant growth hormone (supplemental dose) starting from 20 months of age. CONCLUSION: The ACAN: c.2858dup (p.Asp953GlufsTer476) variant probably underlay the pathogenesis of short stature in this child.

Transient dynamics of the phase transition in VO2 revealed by mega-electron-volt ultrafast electron diffraction.

Vanadium dioxide (VO2) exhibits an insulator-to-metal transition accompanied by a structural transition near room temperature. This transition can be triggered by an ultrafast laser pulse. Exotic transient states, such as a metallic state without structural transition, were also proposed. These unique characteristics let VO2 have great potential in thermal switchable devices and photonic applications. Although great efforts have been made, the atomic pathway during the photoinduced phase transition is still not clear. Here, we synthesize freestanding quasi-single-crystal VO2 films and examine their photoinduced structural phase transition with mega-electron-volt ultrafast electron diffraction. Leveraging the high signal-to-noise ratio and high temporal resolution, we observe that the disappearance of vanadium dimers and zigzag chains does not coincide with the transformation of crystal symmetry. After photoexcitation, the initial structure is strongly modified within 200 femtoseconds, resulting in a transient monoclinic structure without vanadium dimers and zigzag chains. Then, it continues to evolve to the final tetragonal structure in approximately 5 picoseconds. In addition, only one laser fluence threshold instead of two thresholds suggested in polycrystalline samples is observed in our quasi-single-crystal samples. Our findings provide essential information for a comprehensive understanding of the photoinduced ultrafast phase transition in VO2.

Ultrafast isolated molecule imaging without crystallization.

Crystallography is the standard for determining the atomic structure of molecules. Unfortunately, many interesting molecules, including an extensive array of biological macromolecules, do not form crystals. While ultrashort and intense X-ray pulses from free-electron lasers are promising for imaging single isolated molecules with the so-called "diffraction before destruction" technique, nanocrystals are still needed for producing sufficient scattering signal for structure retrieval as implemented in serial femtosecond crystallography. Here, we show that a femtosecond laser pulse train may be used to align an ensemble of isolated molecules to a high level transiently, such that the diffraction pattern from the highly aligned molecules resembles that of a single molecule, allowing one to retrieve its atomic structure with a coherent diffraction imaging technique. In our experiment with CO2 molecules, a high degree of alignment is maintained for about 100 fs, and a precisely timed ultrashort relativistic electron beam from a table-top instrument is used to record the diffraction pattern within that duration. The diffraction pattern is further used to reconstruct the distribution of CO2 molecules with atomic resolution. Our results mark a significant step toward imaging noncrystallized molecules with atomic resolution and open opportunities in the study and control of dynamics in the molecular frame that provide information inaccessible with randomly oriented molecules.

Light-induced dimension crossover dictated by excitonic correlations.

In low-dimensional systems with strong electronic correlations, the application of an ultrashort laser pulse often yields novel phases that are otherwise inaccessible. The central challenge in understanding such phenomena is to determine how dimensionality and many-body correlations together govern the pathway of a non-adiabatic transition. To this end, we examine a layered compound, 1T-TiSe2, whose three-dimensional charge-density-wave (3D CDW) state also features exciton condensation due to strong electron-hole interactions. We find that photoexcitation suppresses the equilibrium 3D CDW while creating a nonequilibrium 2D CDW. Remarkably, the dimension reduction does not occur unless bound electron-hole pairs are broken. This relation suggests that excitonic correlations maintain the out-of-plane CDW coherence, settling a long-standing debate over their role in the CDW transition. Our findings demonstrate how optical manipulation of electronic interaction enables one to control the dimensionality of a broken-symmetry order, paving the way for realizing other emergent states in strongly correlated systems.

Optical manipulation of electronic dimensionality in a quantum material.

Exotic phenomena can be achieved in quantum materials by confining electronic states into two dimensions. For example, relativistic fermions are realized in a single layer of carbon atoms1, the quantized Hall effect can result from two-dimensional (2D) systems2,3, and the superconducting transition temperature can be considerably increased in a one-atomic-layer material4,5. Ordinarily, a 2D electronic system can be obtained by exfoliating the layered materials, growing monolayer materials on substrates, or establishing interfaces between different materials. Here we use femtosecond infrared laser pulses to invert the periodic lattice distortion sectionally in a three-dimensional (3D) charge density wave material (1T-TiSe2), creating macroscopic domain walls of transient 2D ordered electronic states with unusual properties. The corresponding ultrafast electronic and lattice dynamics are captured by time-resolved and angle-resolved photoemission spectroscopy6 and ultrafast electron diffraction at energies of the order of megaelectronvolts7. Moreover, in the photoinduced 2D domain wall near the surface we identify a phase with enhanced density of states and signatures of potential opening of an energy gap near the Fermi energy. Such optical modulation of atomic motion is an alternative path towards realizing 2D electronic states and will be a useful platform upon which novel phases in quantum materials may be discovered.

Breaking 50 Femtosecond Resolution Barrier in MeV Ultrafast Electron Diffraction with a Double Bend Achromat Compressor.

We propose and demonstrate a novel scheme to produce ultrashort and ultrastable MeV electron beam. In this scheme, the electron beam produced in a photocathode radio frequency (rf) gun first expands under its own Coulomb force with which a positive energy chirp is imprinted in the beam longitudinal phase space. The beam is then sent through a double bend achromat with positive longitudinal dispersion where electrons at the bunch tail with lower energies follow shorter paths and thus catch up with the bunch head, leading to longitudinal bunch compression. We show that with optimized parameter sets, the whole beam path from the electron source to the compression point can be made isochronous such that the time of flight for the electron beam is immune to the fluctuations of rf amplitude. With a laser-driven THz deflector, the bunch length and arrival time jitter for a 20 fC beam after bunch compression are measured to be about 29 fs (FWHM) and 22 fs (FWHM), respectively. Such an ultrashort and ultrastable electron beam allows us to achieve 50 femtosecond (FWHM) resolution in MeV ultrafast electron diffraction where lattice oscillation at 2.6 THz corresponding to Bismuth A_{1g} mode is clearly observed without correcting both the short-term timing jitter and long-term timing drift. Furthermore, oscillating weak diffuse scattering signal related to phonon coupling and decay is also clearly resolved thanks to the improved temporal resolution and increased electron flux. We expect that this technique will have a strong impact in emerging ultrashort electron beam based facilities and applications.

[Genetic analysis of a rare case of Pitt-Hopkins syndrome due to partial deletion of TCF4 gene].

OBJECTIVE: To explore the genetic basis for a child featuring delayed intellectual development. METHODS: The child and his parents were subjected to conventional G-banding karyotyping and single nucleotide polymorphism array (SNP-array) analysis. Suspected copy number variations (CNVs) were verified in both parents. RESULTS: No karyotypic abnormality was found with the child and his parents. SNP-array results for both parents were normal. The child was found to harbor a de novo 172 kb deletion at 18q21.2 with a physical position of 52 957 042-53 129 237. The deletion only involved one OMIM gene, namely TCF4, resulting in removal of its exons 6 to 8. CONCLUSION: The SNP-array assay has facilitated with the diagnosis of this child. Deletion of 18q21.2 region probably accounts for the Pitt-Hopkins syndrome (PTHS) in this patient.

[Identification of a c.1A>G initial codon variation of ARX gene in a child with severe mental retardation].

OBJECTIVE: To explore the genetic basis for a child featuring severe mental retardation. METHODS: The child was subjected to target region capture and next generation sequencing. Suspected variants were verified by Sanger sequencing. RESULTS: The child was found to harbor a hemizygous c.1A>G (pMet1?) variation of the ARX gene, for which his mother was a heterozygous carrier. The mutation was unreported previously and was predicted to be "probably pathogenic" by bioinformatic analysis. CONCLUSION: The c.1A>G (pMet1?) variant of the ARX gene may underlie the occurrence of severe mental retardation in this child.

[Analysis of SYNE1 gene variant in an infant featuring epilepsy and developmental disorders].

OBJECTIVE: To explore the clinical features and molecular basis for a child featuring infantile epilepsy and developmental disorders. METHODS: Clinical data and peripheral blood samples of the child and his parents were collected. The coding regions of genes associated with nervous system development were subjected to target region capture sequencing. RESULTS: The child developed generalized spasm at 3 months and was diagnosed with epilepsy at 6 months of age. He was treated with Depakin but was diagnosed with mental retardation and developmental retardation at 3 years of age. A novel heterozygous c.3842T to G variant of the SYNE1 gene was detected. His father was found to carry the same variant and had a history of convulsions in infancy but with no mental or developmental anomalies. CONCLUSION: A novel variant of SYNE1 gene was identified in this child, and the prognosis may be poor.