Getting DNA twist rigidity from single molecule experiments

We use an elastic rod model with contact to study the extension versus rotation diagrams of single supercoiled DNA molecules. We reproduce quantitatively the supercoiling response of overtwisted DNA and, using experimental data, we get an estimation of the effective supercoiling radius and of the twist rigidity of B-DNA. We find that unlike the bending rigidity, the twist rigidity of DNA seems to vary widely with the nature and concentration of the salt buffer in which it is immerged

Torsional Directed Walks, Entropic Elasticity, and DNA Twist Stiffness

DNA and other biopolymers differ from classical polymers due to their torsional stiffness. This property changes the statistical character of their conformations under tension from a classical random walk to a problem we call the `torsional directed walk'. Motivated by a recent experiment on single lambda-DNA molecules [Strick et al., Science 271 (1996) 1835], we formulate the torsional directed walk problem and solve it analytically in the appropriate force regime. Our technique affords a direct physical determination of the microscopic twist stiffness C and twist-stretch coupling D relevant for DNA functionality. The theory quantitatively fits existing experimental data for relative extension as a function of overtwist over a wide range of applied force; fitting to the experimental data yields the numerical values C=120nm and D=50nm. Future experiments will refine these values. We also predict that the phenomenon of reduction of effective twist stiffness by bend fluctuations should be testable in future single-molecule experiments, and we give its analytic form.Comment: Plain TeX, harvmac, epsf; postscript available at http://dept.physics.upenn.edu/~nelson/index.shtm

Clinical and Molecular Assessment in a Female with Fragile X Syndrome and Tuberous Sclerosis.

Fragile X syndrome (FXS) and tuberous sclerosis (TSC) are genetic disorders that result in intellectual disability and an increased prevalence of autism spectrum disorders (ASD). While the clinical presentation of each disorder is distinct, the molecular causes are linked to a disruption in the mTORC1 (mammalian Target of Rapamycin Complex 1) and ERK1/2 (Extracellular signal-Regulated Kinase) signaling pathways. We assessed the clinical and molecular characteristics of an individual seen at the UC Davis MIND Institute with a diagnosis of FXS and TSC. Clinical evaluation of physical, behavioral, and cognitive impairments were performed. Additionally, total and phosphorylated proteins along the mTORC1 and ERK1/2 pathways were measured in primary fibroblast cell lines from the proband. In this case the phenotypic effects that result in a human with both FXS and TSC are shown to be severe. Changes in mTORC1 and ERK1/2 signaling proteins and global protein synthesis were not found to be noticeably different between four cohorts (typically developing, FMR1 full mutation, FMR1 full mutation and TSC1 loss of function mutation, and TSC1 loss of function mutation); however cohort sizes prevented stringent comparisons. It has previously been suggested that disruption of the mTORC1 pathway was reciprocal in TSC and FXS double knock-out mouse models so that the regulation of these pathways were more similar to wild-type mice compared to mice harboring a Fmr1(-/y) or Tsc2(-/+) mutation alone. However, in this first reported case of a human with a diagnosis of both FXS and TSC, substantial clinical impairments, as a result of these two disorders were observed. Differences in the mTORC and ERK1/2 pathways were not clearly established when compared between individuals with either disorder, or both

A Randomized Controlled Trial of Sertraline in Young Children With Autism Spectrum Disorder.

Objective: Selective serotonin reuptake inhibitors like sertraline have been shown in observational studies and anecdotal reports to improve language development in young children with fragile X syndrome (FXS). A previous controlled trial of sertraline in young children with FXS found significant improvement in expressive language development as measured by the Mullen Scales of Early Learning (MSEL) among those with comorbid autism spectrum disorder (ASD) in post hoc analysis, prompting the authors to probe whether sertraline is also indicated in nonsyndromic ASD. Methods: The authors evaluated the efficacy of 6 months of treatment with low-dose sertraline in a randomized, double-blind, placebo-controlled trial in 58 children with ASD aged 24 to 72 months. Results: 179 subjects were screened for eligibility, and 58 were randomized to sertraline (32) or placebo (26). Eight subjects from the sertraline arm and five from the placebo arm discontinued. Intent-to-treat analysis showed no significant difference from placebo on the primary outcomes (MSEL expressive language raw score and age equivalent combined score) or secondary outcomes. Sertraline was well tolerated, with no difference in side effects between sertraline and placebo groups. No serious adverse events possibly related to study treatment occurred. Conclusion: This randomized controlled trial of sertraline treatment showed no benefit with respect to primary or secondary outcome measures. For the 6-month period, treatment in young children with ASD appears safe, although the long-term side effects of low-dose sertraline in early childhood are unknown. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT02385799

The challenges of clinical trials in fragile X syndrome

RATIONALE: Advances in understanding the underlying mechanisms of conditions such as fragile X syndrome (FXS) and autism spectrum disorders have revealed heterogeneous populations. Recent trials of novel FXS therapies have highlighted several challenges including subpopulations with possibly differential therapeutic responses, the lack of specific outcome measures capturing the full range of improvements of patients with FXS, and a lack of biomarkers that can track whether a specific mechanism is responsive to a new drug and whether the response correlates with clinical improvement. OBJECTIVES: We review the phenotypic heterogeneity of FXS and the implications for clinical research in FXS and other neurodevelopmental disorders. RESULTS: Residual levels of fragile X mental retardation protein (FMRP) expression explain in part the heterogeneity in the FXS phenotype; studies indicate a correlation with both cognitive and behavioral deficits. However, this does not fully explain the extent of phenotypic variance observed or the variability of drug response. Post hoc analyses of studies involving the selective mGluR5 antagonist mavoglurant and the GABAB agonist arbaclofen have uncovered significant therapeutic responses following patient stratification according to FMR1 promoter methylation patterns or baseline severity of social withdrawal, respectively. Future studies designed to quantify disease modification will need to develop new strategies to track changes effectively over time and in multiple symptom domains. CONCLUSION: Appropriate selection of patients and outcome measures is central to optimizing future clinical investigations of these complex disorders

A pilot open label, single dose trial of fenobam in adults with fragile X syndrome

ObjectiveA pilot open label, single dose trial of fenobam, an mGluR5 antagonist, was conducted to provide an initial evaluation of safety and pharmacokinetics in adult males and females with fragile X syndrome (FXS).MethodsTwelve subjects, recruited from two fragile X clinics, received a single oral dose of 50-150 mg of fenobam. Blood for pharmacokinetic testing, vital signs and side effect screening was obtained at baseline and numerous time points for 6 h after dosing. Outcome measures included prepulse inhibition (PPI) and a continuous performance test (CPT) obtained before and after dosing to explore the effects of fenobam on core phenotypic measures of sensory gating, attention and inhibition.ResultsThere were no significant adverse reactions to fenobam administration. Pharmacokinetic analysis showed that fenobam concentrations were dose dependent but variable, with mean (SEM) peak values of 39.7 (18.4) ng/ml at 180 min after the 150 mg dose. PPI met a response criterion of an improvement of at least 20% over baseline in 6 of 12 individuals (4/6 males and 2/6 females). The CPT did not display improvement with treatment due to ceiling effects.ConclusionsClinically significant adverse effects were not identified in this study of single dose fenobam across the range of dosages utilised. The positive effects seen in animal models of FXS treated with fenobam or other mGluR5 antagonists, the apparent lack of clinically significant adverse effects, and the potential beneficial clinical effects seen in this pilot trial support further study of the compound in adults with FXS

A Quantitative Assessment of Tremor and Ataxia in Female FMR1

The fragile X-associated tremor/ataxia syndrome (FXTAS) is a relatively common cause of balance problems leading to gait disturbances in older males (40%) with the premutation. FXTAS is less common in females. We utilized the CATSYS system, a quantitative measure of movement, in 23 women with FXTAS (mean age 62.7; SD 12.3), 90 women with the premutation without FXTAS (mean age 52.9; SD 9.4), and 37 controls (mean age 56.53; SD 7.8). CATSYS distinguished differences between carriers with and without FXTAS in postural tremor, postural sway, hand coordination, and reaction time tasks. Differences were also seen between carriers without FXTAS and controls in finger tapping, reaction time, and one postural sway task. However, these differences did not persist after statistical correction for multiple comparisons. Notably, there were no differences across groups in intention tremor. This is likely due to the milder symptoms in females compared to males with FXTAS

Autism phenotype in fragile X premutation males is not associated with FMR1 expression: a preliminary evaluation

To explore the association between autism phenotype and FMR1 protein (FMRP), FMR1 mRNA and CGG repeat length in 31 male FMR1 premutation carriers aged 3.0 to 27.9 years old (mean 13.0 ± SD 6.5) using the ADOS communication, social interactive and total scores. FMRP levels were determined using the sandwich Enzyme-linked Immunosorbent Assay (ELISA) method, FMR1 mRNA expression levels were measured by qRT-PCR, and CGG repeat size was determined using Southern blot and PCR analyses. There was no significant difference in FMRP, CGG repeat length, and FMR1 mRNA between fifteen subjects without (ASD / PDDNOS / autism and sixteen subjects with ASD / PDDNOS / autism. ADOS scores were not significantly associated with either FMRP or FMR1 mRNA, This preliminary evaluation found that autism phenotype is not associated with the level of expression of either FMR1 mRNA or FMRP. However, CGG was significantly negative associated with both ADOS communication score (p= 0.0173) and ADOS total score (p= 0.0358).This work was supported by National Institute of Health grants HD036071, HD02274, DE019583, DA024854, AG032119, AG032115, MH77554; National Center for Advancing Translational Sciences grant UL1RR024146 and UL1TR000153; and Health and Human Services Administration of Developmental Disabilities grant 90DD05969

Visual attention and autistic behavior in infants with fragile X syndrome

Fragile X syndrome (FXS) is the leading known inherited cause of intellectual disability and the most common known biological cause of autism. Approximately 25% to 50% of males with FXS meet full diagnostic criteria for autism. Despite the high comorbidity between FXS and autism and the ability to diagnose FXS prenatally or at birth, no studies have examined indicators of autism in infants with FXS. The current study focused on indices of visual attention, one of the earliest and most robust behavioral indicators of autism in idiopathic (non-FXS) autism. Analyses revealed lower HR variability, shallower HR decelerations, and prolonged look durations in 12-month old infants with FXS that were correlated with severity of autistic behavior but not mental age