Pediatric neurodegenerative white matter processes: leukodystrophies and beyond

Gender-Specific Fine Motor Skill Learning Is Impaired by Myelin-Targeted Neurofibromatosis Type 1 Gene Mutation

Neurofibromatosis type 1 (NF1) is caused by mutations in the NF1 gene. The clinical presentation of NF1 includes diverse neurological issues in pediatric and adult patients, ranging from learning disabilities, motor skill issues, and attention deficit disorder, to increased risk of depression and dementia. Preclinical research suggests that abnormal neuronal signaling mediates spatial learning and attention issues in NF1; however, drugs that improve phenotypes in models show inconclusive results in clinical trials, highlighting the need for a better understanding of NF1 pathophysiology and broader therapeutic options. Most NF1 patients show abnormalities in their brain white matter (WM) and myelin, and links with NF1 neuropathophysiology have been suggested; however, no current data can clearly support or refute this idea. We reported that myelin-targeted Nf1 mutation impacts oligodendrocyte signaling, myelin ultrastructure, WM connectivity, and sensory-motor behaviors in mice; however, any impact on learning and memory remains unknown. Here, we adapted a voluntary running test-the complex wheel (CW; a wheel with unevenly spaced rungs)-to delineate fine motor skill learning curves following induction of an Nf1 mutation in pre-existing myelinating cells (pNf1 mice). We found that pNf1 mutant females experience delayed or impaired learning in the CW, while proper learning in pNf1 males is predominantly disrupted; these phenotypes add complexity to the gender-dependent learning differences in the mouse strain used. No broad differences in memory of acquired CW skills were detected in any gender, but gene-dose effects were observed at the studied time points. Finally, nitric oxide signaling regulation differentially impacted learning in wild type (WT)/pNf1, male/female mice. Our results provide evidence for fine motor skill learning issues upon induction of an Nf1 mutation in mature myelinating cells. Together with previous connectivity, cellular, and molecular analyses, these results diversify the potential treatments for neurological issues in NF1.

Volume and Infusion Rate Dynamics of Intraparenchymal Central Nervous System Infusion in a Large Animal Model

Thalamic infusion of adeno-associated viral (AAV) vectors has been shown to have therapeutic effects in neuronopathic lysosomal storage diseases. Preclinical studies in sheep model of Tay-Sachs disease demonstrated that bilateral thalamic injections of AAV gene therapy are required for maximal benefit. Translation of thalamic injection to patients carries risks in that (1) it has never been done in humans, and (2) dosing scale-up based on brain weight from animals to humans requires injection of larger volumes. To increase the safety margin of this infusion, a flexible cannula was selected to enable simultaneous bilateral thalamic infusion in infants while monitoring by imaging and/or to enable awake infusions for injection of large volumes at low infusion rates. In this study, we tested various infusion volumes (200-800 μL) and rates (0.5-5 μL/min) to determine the maximum tolerated combination of injection parameters. Animals were followed for ∼1 month postinjection with magnetic resonance imaging (MRI) performed at 14 and 28 days. T1-weighted MRI was used to quantify thalamic damage followed by histopathological assessment of the brain. Trends in data show that infusion volumes of 800 μL (2 × the volume required in sheep based on thalamic size) resulted in larger lesions than lower volumes, where the long infusion times (between 13 and 26 h) could have contributed to the generation of larger lesions. The target volume (400 μL, projected to be sufficient to cover most of the sheep thalamus) created the smallest lesion size. Cannula placement alone did result in damage, but this is likely associated with an inherent limitation of its use in a small brain due to the length of the distal rigid portion and lack of stable fixation. An injection rate of 5 μL/min at a volume ∼1/3 of the thalamus (400-600 μL) appears to be well tolerated in sheep both clinically and histopathologically.

The spectrum of leukodystrophies in children: Experience at a tertiary care centre from North India

Objective:

The objective of this study is to retrospectively collect and then describe the clinico-radiographical profile of confirmed cases of leukodystrophy who presented over a 5-year period to a tertiary care teaching hospital in North India.

Materials and Methods:

The case records of 80 confirmed cases of leukodystrophy were reviewed and the cases have been described in terms of their clinical presentation and neuroimaging findings.

Results:

The cases have been grouped into five categories: Hypomyelinating, demyelinating, disorders with vacuolization, cystic, and miscellaneous. The commonest leukodystrophies are megalencephalic leukoencephalopathy with subcortical cysts (MLC), Pelizaeus-Merzbacher disease (PMD), and metachromatic leukodystrophy (MLD). A notable proportion of hypomyelinating disorders were uncharacterized.

Conclusions:

Leukodystrophies at this point of time have no definite cure. They have a progressively downhill clinical course. Early diagnosis is imperative for appropriate genetic counseling. A simplified approach to diagnose common leukodystrophies has also been provided. It is important to develop a registry, which can provide valuable epidemiological data to prioritize research in this field, which has many unanswered questions.

Segmentation of the canine corpus callosum using diffusion-tensor imaging tractography

OBJECTIVE

We set out to determine functional white matter (WM) connections passing through the canine corpus callosum; these WM connections would be useful for subsequent studies of canine brains that serve as models for human WM pathway disease. Based on prior studies, we anticipated that the anterior corpus callosum would send projections to the anterior cerebral cortex whereas progressively posterior segments would send projections to more posterior cortex.

MATERIALS AND METHODS

A postmortem canine brain was imaged using a 7-T MRI system producing 100-μm-isotropic-resolution diffusion-tensor imaging analyzed by tractography. Using regions of interest (ROIs) within cortical locations, which were confirmed by a Nissl stain that identified distinct cortical architecture, we successfully identified six important WM pathways. We also compared fractional anisotropy (FA), apparent diffusion coefficient (ADC), radial diffusivity, and axial diffusivity in tracts passing through the genu and splenium.

RESULTS

Callosal fibers were organized on the basis of cortical destination (e.g., fibers from the genu project to the frontal cortex). Histologic results identified the motor cortex on the basis of cytoarchitectonic criteria that allowed placement of ROIs to discriminate between frontal and parietal lobes. We also identified cytoarchitecture typical of the orbital frontal, anterior frontal, and occipital regions and placed ROIs accordingly. FA, ADC, radial diffusivity, and axial diffusivity values were all higher in posterior corpus callosum fiber tracts.

CONCLUSION

Using six cortical ROIs, we identified six major WM tracts that reflect major functional divisions of the cerebral hemispheres, and we derived quantitative values that can be used for study of canine models of human WM pathologic states.

Recurrent subacute post-viral onset of ataxia associated with a PRF1 mutation

Inflammation is an important contributor to pediatric and adult neurodegeneration. Understanding the genetic determinants of neuroinflammation provides valuable insight into disease mechanism. We characterize a disorder of recurrent immune-mediated neurodegeneration. We report two sisters who presented with neurodegeneration triggered by infections. The proband, a previously healthy girl, presented at 22.5 months with ataxia and dysarthria following mild gastroenteritis. MRI at onset showed a symmetric signal abnormality of the cerebellar and peritrigonal white matter. Following a progressive course of partial remissions and relapses, she died at 5 years of age. Her older sister had a similar course following varicella infection, she died within 13 months. Both sisters had unremarkable routine laboratory testing, with exception of a transient mild cytopenia in the proband 19 months after presentation. Exome sequencing identified a biallelic perforin1 mutation (PRF1; p.R225W) previously associated with familial hemophagocytic lymphohistiocytosis (FHL). In contrast to FHL, these girls did not have hematopathology or cytokine overproduction. However, 3 years after disease onset, the proband had markedly deficient interleukin-1 beta (IL-1β) production. These observations extend the spectrum of disease associated with perforin mutations to immune-mediated neurodegeneration triggered by infection and possibly due to primary immunodeficiency.

Voice disorders in children with classic galactosemia

Children with classic galactosemia are at risk for motor speech disorders resulting from disruptions in motor planning and programming (childhood apraxia of speech or CAS) or motor execution (dysarthria). In the present study of 33 children with classic galactosemia, 21% were diagnosed with CAS, 3% with ataxic dysarthria, and 3% with mixed CAS-dysarthria. Voice disorders due to laryngeal insufficiency were common in children with dysarthria and co-occurred with CAS. Most (58%) of the children with classic galactosemia had decreased respiratory-phonatory support for speech, and 33% had disturbed vocal quality that was indicative of cerebellar dysfunction. Three children, two diagnosed with CAS and one not diagnosed with a motor speech disorder, had vocal tremors. Treatment of voice dysfunction in neurogenic speech disorders is discussed.