Characterizing cognitive control abilities in children with 16p11.2 deletion using adaptive 'video game' technology: a pilot study

Assessing cognitive abilities in children is challenging for two primary reasons: lack of testing engagement can lead to low testing sensitivity and inherent performance variability. Here we sought to explore whether an engaging, adaptive digital cognitive platform built to look and feel like a video game would reliably measure attention-based abilities in children with and without neurodevelopmental disabilities related to a known genetic condition, 16p11.2 deletion. We assessed 20 children with 16p11.2 deletion, a genetic variation implicated in attention deficit/hyperactivity disorder and autism, as well as 16 siblings without the deletion and 75 neurotypical age-matched children. Deletion carriers showed significantly slower response times and greater response variability when compared with all non-carriers; by comparison, traditional non-adaptive selective attention assessments were unable to discriminate group differences. This phenotypic characterization highlights the potential power of administering tools that integrate adaptive psychophysical mechanics into video-game-style mechanics to achieve robust, reliable measurements.

Relationship between M100 Auditory Evoked Response and Auditory Radiation Microstructure in 16p11.2 Deletion and Duplication Carriers

BACKGROUND AND PURPOSE

Deletion and duplication of chromosome 16p11.2 (BP4-BP5) have been associated with developmental disorders such as autism spectrum disorders, and deletion subjects exhibit a large (20-ms) delay of the auditory evoked cortical response as measured by magnetoencephalography (M100 latency). The purpose of this study was to use a multimodal approach to test whether changes in white matter microstructure are associated with delayed M100 latency.

MATERIALS AND METHODS

Thirty pediatric deletion carriers, 9 duplication carriers, and 39 control children were studied with both magnetoencephalography and diffusion MR imaging. The M100 latency and auditory system DTI measures were compared between groups and tested for correlation.

RESULTS

In controls, white matter diffusivity significantly correlated with the speed of the M100 response. However, the relationship between structure and function appeared uncoupled in 16p11.2 copy number variation carriers. The alterations to auditory system white matter microstructure in the 16p11.2 deletion only partially accounted for the 20-ms M100 delay. Although both duplication and deletion groups exhibit abnormal white matter microstructure, only the deletion group has delayed M100 latency.

CONCLUSIONS

These results indicate that gene dosage impacts factors other than white matter microstructure, which modulate conduction velocity.

Distinguishing 3 classes of corpus callosal abnormalities in consanguineous families

OBJECTIVE

We sought to create a classification system for pediatric corpus callosal abnormalities (CCA) based upon midline sagittal brain MRI. We used the term CCA for patients with structural variants of the corpus callosum, excluding patients with interhemispheric cyst variant or pure dysplasia without hypoplasia. Currently, no system exists for nonsyndromic forms of CCA, and attempts to create such a system have been hampered by highly variable morphology in patients with sporadic CCA. We reasoned that any useful strategy should classify affected family members within the same type, and that phenotypic variability should be minimized in patients with recessive disease.

METHODS

We focused recruitment toward multiplex consanguineous families, ascertained 30 patients from 19 consanguineous families, and analyzed clinical features together with brain imaging.

RESULTS

We identified 3 major CCA classes, including hypoplasia, hypoplasia with dysplasia, and complete agenesis. Affected individuals within a given multiplex family usually displayed the same variant of the class of abnormality and they always displayed the same class of abnormality within each family, or they displayed complete agenesis. The system was validated among a second cohort of 10 sporadic patients with CCA.

CONCLUSIONS

The data suggest that complete agenesis may be a common end-phenotype, and implicate multiple overlapping pathways in the etiology of CCA.

ARHGEF9 disruption in a female patient is associated with X linked mental retardation and sensory hyperarousal

We identified a female patient with mental retardation and sensory hyperarousal. She has a de novo paracentric inversion of one X chromosome with completely skewed inactivation of the normal X chromosome. We aimed to identify whether a single gene or gene region caused her cognitive and behavioural impairment and that of others. Fluorescent in situ hybridisation (FISH) showed that the centromeric breakpoint disrupts a single gene: ARHGEF9 (CDC42 guanine nucleotide exchange factor (GEF) 9). We also found that the levels of the ARHGEF9 transcript from the patient are 10-fold less than those found in control samples. ARHGEF9 encodes a RhoGEF family protein: collybistin (hPEM), which is highly expressed in the brain. Collybistin can regulate actin cytoskeletal dynamics and may also modulate GABAergic and glycinergic neurotransmission through binding of a scaffolding protein, gephyrin, at the synapse. This potential dual role may explain both the mental retardation and hyperarousal observed in our patient.

Diffusion abnormalities and reduced volume of the ventral cingulum bundle in agenesis of the corpus callosum: a 3T imaging study

BACKGROUND AND PURPOSE

Patients with agenesis of the corpus callosum (AgCC) exhibit cognitive and behavioral impairments that are not replicated by surgical transection of the callosum, suggesting that other anatomic changes may contribute to the observed clinical findings. The purpose of this study was to determine whether the ventral cingulum bundle (VCB) is affected in patients with AgCC by using diffusion tensor imaging (DTI) and volumetry.

MATERIALS AND METHODS

Twelve participants with AgCC (8 males and 4 females; mean age, 30 +/- 20) and 12 control subjects matched for age and sex (mean age, 37 +/- 19) underwent MR imaging and DTI at 3T. 3D fiber tracking of the VCB was generated from DTI and the average fractional anisotropy (FA) was computed for the tracked fibers. Additionally, the volume, cross-sectional area, and length of the VCB were measured by manually drawn regions of interest on thin-section coronal T1-weighted images. The Student t test was used to compare these results.

RESULTS

Compared with controls, subjects with AgCC demonstrated significantly reduced FA in the right VCB (P = .0098) and reduced volume and cross-sectional areas of both the left and right VCB (P < .001 for all metrics). The length of the VCB was also significantly reduced in the complete AgCC subgroup compared with controls (P = .030 in the right and P = .046 in the left, respectively).

CONCLUSIONS

Patients with AgCC have abnormal microstructure and reduced volume of the VCB, suggesting that abnormalities in intrahemispheric white matter tracts may be an important contributor to the clinical syndrome in patients with AgCC.

Variability of homotopic and heterotopic callosal connectivity in partial agenesis of the corpus callosum: a 3T diffusion tensor imaging and Q-ball tractography study

BACKGROUND AND PURPOSE

Little is known about the anatomic connectivity of callosal axons in individuals with partial agenesis of the corpus callosum (pAgCC). We used tractography based on both diffusion tensor imaging (DTI) and high angular resolution diffusion imaging (HARDI) to investigate interhemispheric white matter connectivity in pAgCC.

MATERIALS AND METHODS

DTI and HARDI were performed at 3T on 6 individuals with pAgCC and 8 control subjects. For HARDI analysis, a Q-ball reconstruction method capable of visualizing multiple intravoxel fiber orientations was used. In both DTI and HARDI, whole-brain 3D fiber tractography was performed by using deterministic streamline algorithms. Callosal fibers were then segmented to identify separately connections between homologous cortical regions (homotopic fibers) and nonhomologous regions (heterotopic fibers) by using manually drawn regions of interest.

RESULTS

In control individuals, we observed densely connected homotopic fibers. However, in individuals with pAgCC, we identified not only homotopic connections but also heterotopic connections in 4 of 6 subjects. Furthermore, the observed homotopic connections in pAgCC did not necessarily correlate with the position or size of the residual callosum. The nature of homotopic and heterotopic connectivity varied considerably among subjects with pAgCC, and HARDI recovered more callosal fibers than DTI.

CONCLUSION

Individuals with pAgCC demonstrate a remarkable diversity of callosal connectivity, including a number of heterotopic tracts that are absent in healthy subjects. The patterns of their callosal connections cannot be predicted from the appearance of their callosal fragments on conventional MR imaging. More tracts and more extensive fibers within tracts are recovered with HARDI than with DTI.

Agenesis of the corpus callosum: an MR imaging analysis of associated abnormalities in the fetus

BACKGROUND AND PURPOSE

Anomalies associated with callosal agenesis (ACC) found postnatally have been well documented. However, to our knowledge, no detailed MR imaging analysis of associated anomalies has been reported in a large cohort of fetuses with ACC. This study will assess those anomalies and compare them with postnatal cohorts of ACC, to identify associated fetal brain abnormalities that may give insight into etiology and outcome.

MATERIALS AND METHODS

All cases of ACC diagnosed on fetal MR imaging during an 11-year period were retrospectively reviewed, including fetal MR imaging, postnatal MR imaging, and autopsy findings. Neurodevelopmental outcome was classified as poor in children with seizures and/or severe neurodevelopmental impairment or in cases of neonatal death.

RESULTS

Twenty-nine cases of ACC were identified. Median gestational age was 26.14 weeks (range, 19.71-36.43 weeks). Twenty-three fetuses had delayed sulcation and/or too-numerous cortical infoldings (abnormal morphology). Fifteen fetuses had cerebellar and/or brain stem abnormalities. Fetal MR imaging findings suggested a genetic syndrome in 5 fetuses and an acquired etiology or genetic/metabolic disorder in 2 fetuses. Findings were confirmed in 8 cases with postnatal MR imaging, except for delayed sulcation and small vermis, and in 4 cases with autopsy, except for periventricular nodular heterotopia and abnormalities in areas not examined by autopsy. Neurodevelopmental outcome was good in 7 and poor in 9 children. Abnormal sulcal morphology and/or infratentorial abnormalities were present in those with poor outcome and absent in those with good outcome.

CONCLUSIONS

ACC is infrequently isolated in fetuses. Abnormal sulcation is common and suggests more diffuse white matter dysgenesis in these fetuses.

ARHGEF9 disruption in a female patient is associated with X linked mental retardation and sensory hyperarousal

INTRODUCTION

We identified a female patient with mental retardation and sensory hyperarousal. She has a de novo paracentric inversion of one X chromosome with completely skewed inactivation of the normal X chromosome.

OBJECTIVE

We aimed to identify whether a single gene or gene region caused her cognitive and behavioural impairment and that of others.

RESULTS

Fluorescent in situ hybridisation (FISH) showed that the centromeric breakpoint disrupts a single gene: ARHGEF9 (CDC42 guanine nucleotide exchange factor (GEF) 9). The telomeric break lies in a gene poor region. We also found that the levels of the ARHGEF9 transcript from the patient are 10-fold less than those found in control samples. Consequently, we sequenced the coding exons and intron/exon borders of the ARHGEF9 gene in 99 probands from families with X linked mental retardation (XLMR) and 477 mentally retarded males in whom a diagnosis of Fragile X syndrome had been excluded. We did not identify any pathogenic changes; however, we did identify intronic nucleotide changes that might alter splicing.

CONCLUSION

ARHGEF9 encodes a RhoGEF family protein: collybistin (hPEM), which is highly expressed in the developing and adult brain. Collybistin can regulate actin cytoskeletal dynamics and may also modulate GABAergic and glycinergic neurotransmission through binding of a scaffolding protein, gephyrin, at the synapse. This potential dual role may explain both the mental retardation and hyperarousal observed in our patient. While ARHGEF9 appears to be an uncommon cause of mental retardation in males, it should be considered in patients with mental retardation and sensory hyperarousal.

Mutation analysis of theFRAS1 gene demonstrates new mutations in a propositus with Fraser syndrome

Fraser syndrome (OMIM 219000) is a rare, autosomal recessive condition with classical features of cryptophthalmos, syndactyly, ambiguous genitalia, laryngeal, and genitourinary malformations, oral clefting and mental retardation. Mutations causing loss of function of the FRAS1 gene have been demonstrated in five patients with Fraser syndrome. However, no phenotype-genotype correlation was established and there was evidence for genetic heterogeneity. Fraser syndrome is rare and the FRAS1 gene has 75 exons, complicating mutation screening in affected patients. We have screened two patients who fulfilled the diagnostic criteria for Fraser syndrome and three patients with related phenotypes (two patients with Manitoba oculotrichoanal syndrome and one patient with unilateral cryptophthalmos and labial fusion) for mutations in FRAS1 to increase the molecular genetic data in patients with Fraser syndrome and related conditions. We report two new mutations in a patient with Fraser syndrome, a frameshift mutation and a deletion of two amino acids that we consider pathogenic as both alter the NG2-like domain of the protein. Although we are still unable to clarify a phenotype-genotype relationship in Fraser syndrome, our data add to the list of mutations associated with this syndrome.

Genomic microarray analysis identifies candidate loci in patients with corpus callosum anomalies

Absence of the corpus callosum is often associated with cognitive deficits, autism, and epilepsy. Using a genomic microarray, the authors analyzed DNA from 25 patients with radiographically confirmed callosal anomalies and identified three patients with de novo copy number changes in chromosome regions 2q37, 6qter, and 8p. Chromosomal deletions and duplications may be a relatively common cause of cerebral malformations.

Periventricular heterotopia associated with chromosome 5p anomalies

Periventricular heterotopia (PH) is characterized by neuronal nodules along the lateral ventricles. Whereas mutations in X-linked FLNA cause such cortical malformations, the authors report two cases of PH localizing to chromosome 5p. Both subjects have complex partial seizures. MRI demonstrated bilateral nodular PH, with subcortical heterotopia or focal gliosis. FISH identified a duplication of 5p15.1 [46,XX,dup(5)(p15.1p15.1)] and a trisomy of 5p15.33 [46,XY,der(14)t(5;14)(p15.33;p11.2) mat]. These findings suggest a new PH locus along the telomeric end of chromosome 5p.

Mapping of unconventional myosins in mouse and human

Myosins are molecular motors that move along filamentous actin. Seven classes of myosin are expressed in vertebrates: conventional myosin, or myosin-II, as well as the 6 unconventional myosin classes-I, -V, -VI, -VII, -IX, and -X. We have mapped in mouse 22 probes encompassing all known unconventional myosins and, as a result, have identified 16 potential unconventional myosin genes. These genes include 7 myosins-I, 2 myosins-V, 1 myosin-VI, 3 myosins-VII, 2 myosins-IX, and 1 myosin-X. The map location of 5 of these genes was identified in human chromosomes by fluorescence in situ hybridization.

Mammalian myosin I alpha, I beta, and I gamma: new widely expressed genes of the myosin I family

A polymerase chain reaction strategy was devised to identify new members of the mammalian myosin I family of actin-based motors. Using cellular RNA from mouse granular neurons and PC12 cells, we have cloned and sequenced three 1.2-kb polymerase chain reaction products that correspond to novel mammalian myosin I genes designated MMI alpha, MMI beta, MMI gamma. The pattern of expression for each of the myosin I's is unique: messages are detected in diverse tissues including the brain, lung, kidney, liver, intestine, and adrenal gland. Overlapping clones representing full-length cDNAs for MMI alpha were obtained from mouse brain. These encode a 1,079 amino acid protein containing a myosin head, a domain with five calmodulin binding sites, and a positively charged COOH-terminal tail. In situ hybridization reveals that MMI alpha is highly expressed in virtually all neurons (but not glia) in the postnatal and adult mouse brain and in neuroblasts of the cerebellar external granular layer. Expression varies in different brain regions and undergoes developmental regulation. Myosin I's are present in diverse organisms from protozoa to vertebrates. This and the expression of three novel members of this family in brain and other mammalian tissues suggests that they may participate in critical and fundamental cellular processes.

Failure of B cells in common variable immunodeficiency to transit from proliferation to differentiation is associated with altered B cell surface-molecule display

B cells from patients with common variable immunodeficiency (CVI) were investigated as to their surface-molecule display and their functional ability to transit through defined in vitro developmental stages. Patients' B cells were analyzed by dual color-flow cytometry and found to have an abnormal surface-molecule display characterized by depressed Leu 8 and CD21 expression. Membrane immunoglobulin (mu, delta, and light chain) were normally displayed. The lack of Leu 8 and CD21 expression did not represent the normal loss of these antigens from B cells with activation because the cells did not demonstrate enhanced display of activation markers, nor did they demonstrate enhanced display of early B cell molecules, such as common acute lymphocytic leukemia antigen or CD5. Small resting B cells from the patients were isolated and tested for their ability to respond functionally to a series of activation, proliferation, and differentiation signals. B cells from 14 of 17 patients failed to transit from proliferation to differentiation with increased immunoglobulin production when B cells were stimulated with T cell replacing factor +/- phorbol myristate acetate. Cells of one patient failed to proliferate, whereas B cells from the remaining two patients with CVI did not undergo activation (size change and RNA synthesis) when they were exposed to antimu antibody or low-dose phorbol myristate acetate. These studies demonstrate that most patients with CVI have B cells displaying an altered-surface phenotype that is associated with a specific functional defect in transiting from cell proliferation to differentiation and immunoglobulin production.

Human natural killer (NK) cells produce a late-acting B-cell differentiation activity

The supernatant of unstimulated purified NKH-1 bearing human natural killer (NK) cells was found to enhance ongoing immunoglobulin synthesis. This NK-Cell supernatant (NKSN) enhanced IgE, IgG, and IgA synthesis from corresponding B-cell lines without increasing thymidine incorporation or cell number. Separation of NKH-1+ cells into CD3- or CD3+ cells showed that this activity was produced by the CD3- population. Recombinant human interleukin (IL)-1, IL-2, IL-4, interferon (INF)-beta 1, INF-gamma, granulocyte-macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor (TNF)-alpha, or partially purified low molecular weight B-cell growth factor (BCGF) failed to provide the same enhancement of Ig synthesis. While the NKSN contained small amounts of IL-6 (0.1 U/ml) and IL-6 could increase Ig synthesis in vitro, the optimal IL-6 enhancement was far less than that observed with NKSN. NKSN also enhanced ongoing Ig synthesis from in vivo activated B cells obtained from peripheral blood or bone marrow but failed to induce Ig synthesis from resting or in vitro activated B cells. These results demonstrate that human NK (CD3-, NKH-1+) cells can produce B-cell differentiation activity capable of regulating Ig production in vivo, which appears to be distinct from the activity of previously described cytokines.

Functional and phenotypic characterization of human B lymphocyte subsets isolated by unit gravity sedimentation

We report the use of unit gravity sedimentation with a CelSep apparatus to generate two volumetrically similar but functionally and phenotypically distinct subsets of human peripheral blood B cells. One subset, comprised of small B lymphocytes, underwent a significant size change in response to anti-mu, proliferated synergistically to low concentrations of anti-mu plus B cell growth factor (BCGF) or phorbol myristate acetate plus BCGF, and could be induced to produce immunoglobulin in response to pokeweed-mitogen-derived T-lymphocyte-replacing factors. These cells were primarily sIg+, B1+, B2+, and were virtually free of monocytes (less than 0.01%). Unlike these resting B lymphocytes, the large cells proliferated directly to BCGF, without displaying synergy with anti-mu. These cells displayed very little B2 (less than 7%), did not increase in volume in the presence of anti-mu, and made more immunoglobulin in response to TRF than the small resting B lymphocytes. However, neither population synthesized immunoglobulin spontaneously. This technique, which is highly reproducible, not equipment intensive, and produces high cell recovery (greater than 90%), allows for a precise analysis of the steps involved in the maturation of a resting B lymphocyte to an immunoglobulin-secreting cell.

IgE-enhancing activity directly and selectively affects activated B cells: evidence for a human IgE differentiation factor

T cells from highly atopic individuals spontaneously secrete in vitro a factor that specifically induces IgE synthesis from normal human B cells. We investigated the effects of such T cell supernatants derived from atopic individuals (TCSN-A) on functionally distinct B cell subsets to determine at what developmental stage B cells become responsive to this IgE-enhancing activity. B cells from normal and allergic donors were separated into subsets of small resting and large activated cells by density centrifugation or unit gravity sedimentation. When stimulated by TCSN-A, large activated B cells made more IgE than small resting B cells. The difference was as much as 3300% in comparing these subsets from allergic donors. Similarly, resting B cells stimulated by Staphylococcus aureus Cowan I (SAC) made 52 to 125% more IgE in response to TCSN-A than unstimulated small resting B cells. However, IgE production from large B cells, already activated in vivo, was not enhanced by the addition of SAC. Notably, the IgE level synthesized by in vivo large activated B cells from allergic persons was markedly greater than that seen with similar cells from normal donors, whereas resting B cells purified from allergic and normal donors produced comparable levels of IgE in response to TCSN-A. These results suggest that this enhancing activity functions as an IgE differentiation factor for activated B cells. This was further confirmed by the effects of TCSN-A on the IgM- and IgE-secreting EBV-transformed human B cell line K1D5. TCSN-A specifically enhanced IgE synthesis from these cells; TCSN from normal donors, IL 2, IFN-gamma, and BCGF did not. These results confirm that this activity functions as an IgE-specific differentiation factor, directly influencing activated B cells to synthesize IgE.

IgE-enhancing activity directly and selectively affects activated B cells: evidence for a human IgE differentiation factor

T cells from highly atopic individuals spontaneously secrete in vitro a factor that specifically induces IgE synthesis from normal human B cells. We investigated the effects of such T cell supernatants derived from atopic individuals (TCSN-A) on functionally distinct B cell subsets to determine at what developmental stage B cells become responsive to this IgE-enhancing activity. B cells from normal and allergic donors were separated into subsets of small resting and large activated cells by density centrifugation or unit gravity sedimentation. When stimulated by TCSN-A, large activated B cells made more IgE than small resting B cells. The difference was as much as 3300% in comparing these subsets from allergic donors. Similarly, resting B cells stimulated by Staphylococcus aureus Cowan I (SAC) made 52 to 125% more IgE in response to TCSN-A than unstimulated small resting B cells. However, IgE production from large B cells, already activated in vivo, was not enhanced by the addition of SAC. Notably, the IgE level synthesized by in vivo large activated B cells from allergic persons was markedly greater than that seen with similar cells from normal donors, whereas resting B cells purified from allergic and normal donors produced comparable levels of IgE in response to TCSN-A. These results suggest that this enhancing activity functions as an IgE differentiation factor for activated B cells. This was further confirmed by the effects of TCSN-A on the IgM- and IgE-secreting EBV-transformed human B cell line K1D5. TCSN-A specifically enhanced IgE synthesis from these cells; TCSN from normal donors, IL 2, IFN-gamma, and BCGF did not. These results confirm that this activity functions as an IgE-specific differentiation factor, directly influencing activated B cells to synthesize IgE.

A mechanism for the suppression of ongoing IgE synthesis

IgE synthesis from the human plasmacytoma U266/AF-10 was suppressed by addition of IgE immune complexes (IgE-IC). This suppression was isotype-specific as synthesis from other B cell lines was unaffected. Using IgE-IC constructed with a monoclonal antibody that recognizes PS protein-IgE and not ND IgE (the IgE protein made by U266/AF-10), we have shown that this suppression was mediated through the cross-linking of the Fc epsilon receptor.