Kathryn McFadden

DAWN: a framework to identify autism genes and subnetworks using gene expression and genetics

BackgroundDe novo loss-of-function (dnLoF) mutations are found twofold more often in autism spectrum disorder (ASD) probands than their unaffected siblings. Multiple independent dnLoF mutations in the same gene implicate the gene in risk and hence provide a systematic, albeit arduous, path forward for ASD genetics. It is likely that using additional non-genetic data will enhance the ability to identify ASD genes.MethodsTo accelerate the search for ASD genes, we developed a novel algorithm, DAWN, to model two kinds of data: rare variations from exome sequencing and gene co-expression in the mid-fetal prefrontal and motor-somatosensory neocortex, a critical nexus for risk. The algorithm casts the ensemble data as a hidden Markov random field in which the graph structure is determined by gene co-expression and it combines these interrelationships with node-specific observations, namely gene identity, expression, genetic data and the estimated effect on risk.ResultsUsing currently available genetic data and a specific developmental time period for gene co-expression, DAWN identified 127 genes that plausibly affect risk, and a set of likely ASD subnetworks. Validation experiments making use of published targeted resequencing results demonstrate its efficacy in reliably predicting ASD genes. DAWN also successfully predicts known ASD genes, not included in the genetic data used to create the model.ConclusionsValidation studies demonstrate that DAWN is effective in predicting ASD genes and subnetworks by leveraging genetic and gene expression data. The findings reported here implicate neurite extension and neuronal arborization as risks for ASD. Using DAWN on emerging ASD sequence data and gene expression data from other brain regions and tissues would likely identify novel ASD genes. DAWN can also be used for other complex disorders to identify genes and subnetworks in those disorders.

Subepineurial injection in ultrasound-guided interscalene needle tip placement.

Introduction: The neural elements of the brachial plexus between the anterior and middle scalene muscles are readily visible by ultrasound. However, the epineurium of these nerve structures is difficult to discern on ultrasound imaging because of the proximity of the scalene muscles to the nerve elements, and this may lead to unintentional subepineurial injection (SEI). To evaluate whether typical needle tip placement under ultrasound guidance results in SEI, as opposed to extraneural injection, we undertook this cadaver study. Materials and Methods: Six nonpreserved cadavers served as subjects for 10 injections. After imaging revealed the hypoechoic fascicles of the brachial plexus at the interscalene level, the tip of a 22-gauge, 5-cm short-bevel needle was inserted into a position adjacent to one of the fascicles by ultrasound guidance. At this point, 0.1 to 0.2 mL of india ink solution was injected. The brachial plexus at this level was then dissected and removed. The nerve elements discolored by the ink were removed, fixed, and stained for histologic analysis and were then examined for evidence of subepineurial ink deposition. Four nerve segments, which were unaffected by the injected ink, served as controls. These were subjected to topical india ink application for a 60-min period and were then washed, fixed, and stained for histologic analysis. Results: In all 10 interscalene sites, ultrasonography revealed multiple hypoechoic nodules that could be traced proximally to the spine, as in live subjects. On gross analysis after dissection, the superficial nerve elements of the brachial plexus appeared to be stained by the ink. On histologic examination, 5 of 10 nerve specimens revealed ink within the epineurium (subepineurial), whereas in the other 5, it had not penetrated this barrier. The india ink did not penetrate the perineurium in any of the specimens. Among control specimens, none had evidence of subepineurial ink. Conclusions: In a cadaver model of needle tip placement for ultrasound-guided interscalene block, we found that SEI occurred more frequently than expected.

Evidence for dysregulation of axonal growth and guidance in the etiology of ASD

Current theories concerning the cause of autism spectrum disorders (ASDs) have converged on the concept of abnormal development of brain connectivity. This concept is supported by accumulating evidence from functional imaging, diffusion tensor imaging, and high definition fiber tracking studies which suggest altered microstructure in the axonal tracts connecting cortical areas may underly many of the cognitive manifestations of ASD. Additionally, large-scale genomic studies implicate numerous gene candidates known or suspected to mediate neuritic outgrowth and axonal guidance in fetal and perinatal life. Neuropathological observations in postmortem ASD brain samples further support this model and include subtle disturbances of cortical lamination and subcortical axonal morphology. Of note is the relatively common finding of poor differentiation of the gray–white junction associated with an excess superficial white matter or “interstitial” neurons (INs). INs are thought to be remnants of the fetal subplate, a transient structure which plays a key role in the guidance and morphogenesis of thalamocortical and cortico-cortical connections and the organization of cortical columnar architecture. While not discounting the importance of synaptic dysfunction in the etiology of ASD, this paper will briefly review the cortical abnormalities and genetic evidence supporting a model of dysregulated axonal growth and guidance as key developmental processes underlying the clinical manifestations of ASD.

Brachial plexus root injection in a human cadaver model: Injectate distribution and effects on the neuraxis

Background The potential for injection into the brachial plexus root at cervical levels must be considered during interscalene block or chronic pain interventions in the neck, but this phenomenon has not been well studied. In this investigation, we performed injections into the brachial plexus roots of unembalmed cadavers, with real-time ultrasound guidance, to evaluate the proximal and distal spread of the injected fluids, the potential of the injectate to reach the neuraxis, and whether the injectate could migrate into the actual substance of the spinal cord itself. Methods A solution of particulate dye mixed with local anesthetic was injected into 8 brachial plexus roots at a lower cervical level, in unembalmed cadaver specimens, utilizing an automated pump and pressure monitor. Two injections were made adjacent to nerve roots as controls. The specimens were then dissected, and gross and microscopic analysis utilized to determine the distribution of the dye and the structures affected. Results The mean peak pressure achieved during plexus root injections was 48.9 psi. After injections into the plexus root, dye was evident within the neural tissue at the level of injection and spread primarily distally in the plexus. In 1 of 8 injections into the brachial plexus root, the dye in the injectate spread proximally into the spinal canal, but in none of the injections was the spinal cord affected by the dye. Conclusions Injection directly into the neural tissue of a brachial plexus root in a cadaver model produced high pressures suggestive of intrafascicular injection and widespread flow of the injectate through the distal brachial plexus. However, proximal movement of the dye-containing injectate was more restricted, with only 1 of the injections leading to epidural spread and no apparent effects on the spinal cord.

Copy Number Variants for Schizophrenia and Related Psychotic Disorders in Oceanic Palau: Risk and Transmission in Extended Pedigrees

BACKGROUND We report on copy number variants (CNVs) found in Palauan subjects ascertained for schizophrenia and related psychotic disorders in extended pedigrees in Palau. We compare CNVs found in this Oceanic population with those seen in other samples, typically of European ancestry. Assessing CNVs in Palauan extended pedigrees yields insight into the evolution of risk CNVs, such as how they arise, are transmitted, and are lost from populations by stochastic or selective processes, none of which are easily measured from case-control samples. METHODS DNA samples from 197 subjects affected with schizophrenia and related psychotic disorders, 185 of their relatives, and 159 control subjects were successfully characterized for CNVs using Affymetrix Genomewide Human SNP Array 5.0. RESULTS Copy number variants thought to be associated with risk for schizophrenia and related disorders also occur in affected individuals in Palau, specifically 15q11.2 and 1q21.1 deletions, partial duplication of IL1RAPL1 (Xp21.3), and chromosome X duplications (Klinefelters syndrome). Partial duplication within A2BP1 appears to convey an eightfold increased risk in male subjects (95% confidence interval, .8-84.4) but not female subjects (odds ratio = .4, 95% confidence interval, .03-4.9). Affected-only linkage analysis using this variant yields a logarithm of the odds score of 3.5. CONCLUSIONS This study reveals CNVs that confer risk to schizophrenia and related psychotic disorders in Palau, most of which have been previously observed in samples of European ancestry. Only a few of these CNVs show evidence that they have existed for many generations, consistent with risk variants diminishing reproductive success.

Information Processing, Neural Connectivity, and Neuronal Organization

Twenty years ago we proposed a neurobiological model of autism as a widespread disorder of association cortex and the development of connectivity of neocortical systems. We have subsequently provided substantial behavioral and neurofunctional evidence in support of this model. Neuropsychological studies with high functioning children and adults reveal the selective involvement of higher order cognitive processing across a broad range of domains and functions. Studies of face and object processing relate these processing deficits to the difficulty with automatic integration of multiple features, in contrast to the integrity of performance relying on individual features. The results of systematic functional magnetic resonance imaging studies of many social, cognitive, and language systems have added to our original model with evidence of functional underconnectivity of neural systems and disturbances in cortical specialization. Our model is also supported by the neuroimaging and neuropathology findings from other research groups that provide evidence of disturbances in cortico-cortical white matter (WM) connections but not interhemispheric or long tract WM connections with an increase in local connectivity that supports basic cognitive processes. Recent studies of neocortical growth and neuronal organization are consistent with our model and provide further details about potential mechanisms that complete the sequence from genes to behavior. Data continue to accumulate that support the basic tenets of this information processing, neural connectivity, and neuronal organization model and the specific neurodevelopmental mechanisms from which neurobiologically based, behaviorally defined disorder of autism arises.

Pathology of the Gallbladder in a Child with Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by deficient activity of arylsulfatase A, leading to an accumulation of sulfatide in myelinating cells and progressive central and peripheral demyelination. Sulfatide also accumulates in various organs, most notably the gallbladder. Gallbladder mucosal hyperplasia with papillomatosis, in the setting of abdominal pain and hemobilia, is often demonstrated by sonography. We present a histologic and ultrastructural description of these alterations in a 5-year-old girl with MLD who presented with abdominal pain and feeding intolerance. Gross and light microscopic analysis demonstrated diffuse villous hyperplasia of the gallbladder mucosa with intraepithelial and intravillous macrophage accumulations of metachromatic material. Electron microscopic analysis demonstrated this material to comprise numerous membrane-bound inclusions composed of concentrically lamellated, dense material. The rarity of descriptions of this finding prompted this case report.

Management of symptomatic intrathecal catheter-associated inflammatory masses

OBJECTIVE Intrathecal catheter-associated inflammatory masses (CIMs) are a serious complication of implanted drug pumps. The goal of this study was to review our experience with CIMs, including the pathology of all resected CIMs, and identify objective data which may guide management. METHODS We performed a retrospective review of 13 patients who developed symptomatic CIMs during continuous intrathecal opioid therapy for chronic pain. Eight patients presented with pain plus neurologic deficit and 5 patients presented with pain alone. RESULTS CIM resection via laminectomy and intradural exploration was ultimately performed in 8 patients, 3 of whom were initially treated with a non-resective surgical approach (catheter repositioning or pump removal) that failed. All 3 patients who experienced a failure with non-resective surgery had CIMs located in the thoracic spine with a maximum diameter≥13 mm and 2 of these patients had neurologic deficits on presentation. CONCLUSIONS Our experience, with the largest reported single-surgeon series of patients harboring CIMs, favors early resection, especially in patients with neurologic deficit. Resection may also be a prudent first-line strategy for patients with larger thoracic masses (≥13 mm) regardless of neurologic status. Neurologic deficits engendered by CIM usually improve after resection and the majority of patients in our series would have still elected to have an intrathecal pump for pain control knowing a CIM would have developed.

Correlation of ultrasound appearance, gross anatomy, and histology of the femoral nerve at the femoral triangle

PurposeCorrelation between ultrasound appearance, gross anatomic characteristics, and histologic structure of the femoral nerve (FN) is lacking. Utilizing cadavers, we sought to characterize the anatomy of the FN, and provide a quantitative measure of its branching. We hypothesize that at the femoral crease, the FN exists as a group of nerve branches, rather than a single nerve structure, and secondarily, that this transition into many branches is apparent on ultrasonography.Materials and methodsNineteen preserved cadavers were investigated. Ultrasonography was sufficient to evaluate the femoral nerve in nine specimens; gross dissection was utilized in all 19. Anatomic characteristics were recorded, including distances from the inguinal ligament to femoral crease, first nerve branch, and complete arborization of the nerve. The nerves from nine specimens were excised for histologic analysis.ResultsOn ultrasound, the nerve became more flattened, widened, and less discrete as it coursed distally. Branching of the nerve was apparent in 12 of 18 images, with mean distance from inguinal ligament of 3.9 (1.0) cm. However, upon dissection, major branching of the femoral nerve occurred at 3.1 (1.0) cm distal to the inguinal ligament, well proximal to the femoral crease. Histologic analysis was consistent with findings at dissection.ConclusionThe femoral nerve arborizes into multiple branches between the inguinal ligament and the femoral crease. Initial branching is often high in the femoral triangle. As hypothesized, the FN exists as a closely associated group of nerve branches at the level of the femoral crease; however, the termination of the nerve into multiple branches is not consistently apparent on ultrasonography.

Neuropathology of 22q11 Deletion Syndrome in an Infant

The 22q11 deletion syndrome (22q11DS) is the most common microdeletion syndrome in humans and one of the chromosomal conditions most associated with psychosis and autism spectrum disorder. To date, only 2 neuropathologic studies of 22q11DS have been reported. Findings included polymicrogyria, neuronal heterotopias, excess subcortical white-matter (interstitial) neurons, significant white-matter gliosis/hypomyelination, and microvasculopathy. Here, we report on a 3-month-old infant with documented 22q11DS, tetralogy of Fallot, and pulmonary atresia. The brain exhibited tortuous cerebral vessels and proportionately smaller occipital lobes. Histologic examination revealed cerebral white-matter pathology and subtle differences in cortical lamination, including an excess of interstitial white-matter neurons compared with a sample of age-matched controls. There was a 15% increase in DARPP-32+ medium spiny neurons in the anterior-superior caudate. In this first neuropathologic report of an infant with 22q11DS, the findings were similar to previously reported manifestations and are likely secondary to perfusion issues, developmental microvasculopathy, and abnormal frontal cortical development.