Sébastien Perreault

Recurrence patterns across medulloblastoma subgroups: an integrated clinical and molecular analysis

BACKGROUND Recurrent medulloblastoma is a therapeutic challenge because it is almost always fatal. Studies have confirmed that medulloblastoma consists of at least four distinct subgroups. We sought to delineate subgroup-specific differences in medulloblastoma recurrence patterns. METHODS We retrospectively identified a discovery cohort of all recurrent medulloblastomas at the Hospital for Sick Children (Toronto, ON, Canada) from 1994 to 2012 (cohort 1), and established molecular subgroups using a nanoString-based assay on formalin-fixed paraffin-embedded tissues or frozen tissue. The anatomical site of recurrence (local tumour bed or leptomeningeal metastasis), time to recurrence, and survival after recurrence were assessed in a subgroup-specific manner. Two independent, non-overlapping cohorts (cohort 2: samples from patients with recurrent medulloblastomas from 13 centres worldwide, obtained between 1991 and 2012; cohort 3: samples from patients with recurrent medulloblastoma obtained at the NN Burdenko Neurosurgical Institute [Moscow, Russia] between 1994 and 2011) were analysed to confirm and validate observations. When possible, molecular subgrouping was done on tissue obtained from both the initial surgery and at recurrence. RESULTS Cohort 1 consisted of 30 patients with recurrent medulloblastomas; nine with local recurrences, and 21 with metastatic recurrences. Cohort 2 consisted of 77 patients and cohort 3 of 96 patients with recurrent medulloblastoma. Subgroup affiliation remained stable at recurrence in all 34 cases with available matched primary and recurrent pairs (five pairs from cohort 1 and 29 pairs from cohort 2 [15 SHH, five group 3, 14 group 4]). This finding was validated in 17 pairs from cohort 3. When analysed in a subgroup-specific manner, local recurrences in cohort 1 were more frequent in SHH tumours (eight of nine [89%]) and metastatic recurrences were more common in group 3 and group 4 tumours (17 of 20 [85%] with one WNT, p=0·0014, local vs metastatic recurrence, SHH vs group 3 vs group 4). The subgroup-specific location of recurrence was confirmed in cohort 2 (p=0·0013 for local vs metastatic recurrence, SHH vs group 3 vs group 4,), and cohort 3 (p<0·0001). Treatment with craniospinal irradiation at diagnosis was not significantly associated with the anatomical pattern of recurrence. Survival after recurrence was significantly longer in patients with group 4 tumours in cohort 1 (p=0·013) than with other subgroups, which was confirmed in cohort 2 (p=0·0075), but not cohort 3 (p=0·70). INTERPRETATION Medulloblastoma does not change subgroup at the time of recurrence, reinforcing the stability of the four main medulloblastoma subgroups. Significant differences in the location and timing of recurrence across medulloblastoma subgroups have potential treatment ramifications. Specifically, intensified local (posterior fossa) therapy should be tested in the initial treatment of patients with SHH tumours. Refinement of therapy for patients with group 3 or group 4 tumours should focus on metastases.

Medulloblastoma Genotype Dictates Blood Brain Barrier Phenotype.

The childhood brain tumor, medulloblastoma, includes four subtypes with very different prognoses. Here, we show that paracrine signals driven by mutant β-catenin in WNT-medulloblastoma, an essentially curable form of the disease, induce an aberrant fenestrated vasculature that permits the accumulation of high levels of intra-tumoral chemotherapy and a robust therapeutic response. In contrast, SHH-medulloblastoma, a less curable disease subtype, contains an intact blood brain barrier, rendering this tumor impermeable and resistant to chemotherapy. The medulloblastoma-endothelial cell paracrine axis can be manipulated in vivo, altering chemotherapy permeability and clinical response. Thus, medulloblastoma genotype dictates tumor vessel phenotype, explaining in part the disparate prognoses among medulloblastoma subtypes and suggesting an approach to enhance the chemoresponsiveness of other brain tumors.

Fragmentation of the Golgi Apparatus Induced by the Overexpression of Wild-Type and Mutant Human Tau Forms in Neurons

Tau is a microtubule-associated protein enriched in the axonal compartment. In several neurodegenerative diseases including Alzheimers disease, hyperphosphorylated tau accumulates in the somatodendritic compartment, self-aggregates, and forms neurofibrillary tangles. A fragmentation of the neuronal Golgi apparatus (GA) was also observed in Alzheimers disease. In the present study, we examined the effect of overexpressing human tau on the organization of the neuronal GA in rat hippocampal cultures and in JNPL3 mice expressing tau mutant P301L. GA fragmentation was noted in a significantly higher percentage of hippocampal neurons overexpressing wild-type human tau than in control neurons over-expressing green fluorescent protein (GFP) alone. Most importantly, in neurons overexpressing mutant forms of human tau (P301L, V337M, or R406W), the percentage of neurons with a fragmented GA was 10% higher than that of neurons overexpressing wild-type human tau. In JNPL3 mice, a significantly higher percentage of motor neurons presented a fragmented GA compared to control mice. Interestingly, fragmentation of the GA was more frequent in neurons containing an accumulation and aggregation of hyperphosphorylated tau in the cell body than in neurons without these features. In both primary hippocampal neurons and JNPL3 mice, the tau-induced GA fragmentation was not caused by apoptosis. The pre-sent results implicate tau in GA fragmentation and show that this event occurs before the formation of neurofibrillary tangles.

Increased Association Between Rough Endoplasmic Reticulum Membranes and Mitochondria in Transgenic Mice That Express P301L Tau

In several neurodegenerative diseases, including Alzheimer disease, the neuronal microtubule-associated protein tau becomes hyperphosphorylated, accumulates in the somatodendritic compartment, and aggregates into insoluble filaments. The consequences of the accumulation of hyperphosphorylated tau in the somatodendritic compartment remain poorly characterized at the early stage of disease before the formation of tau insoluble filaments. We investigated the ultrastructural changes induced by this accumulation in the neuronal soma of motor neurons in asymptomatic JNPL3 mice that overexpress mutant tau, P301L. More numerous contacts between rough endoplasmic reticulum (RER) membranes and mitochondria were observed in JNLP3 mice compared with wild-type mice. This correlated with a preferential increase of the amount of tau at the surface of RER membranes but not at the surface of mitochondria, as revealed by tau immunogold labeling. Using a subcellular fractionation procedure, an increased amount of phosphorylated tau was identified in the rough microsome subfraction, wherein the RER marker, ribophorin, was enriched. A similar increase was noted in the rough microsome subfraction isolated from Alzheimer disease brains. The association of hyperphosphorylated tau with ER membranes was confirmed by double immunogold labeling of the subfraction enriched in ER membranes isolated from Alzheimer disease brains. These results suggest that more contacts between RER membranes and mitochondria resulting from the accumulation of tau at the surface of RER membranes might contribute to tau-induced neurodegeneration.

Transient Creatine Phosphokinase Elevations in Children: A Single-Center Experience

OBJECTIVES To determine the etiologies and evolution of rhabdomyolysis in children. STUDY DESIGN We performed a retrospective study of patients with rhabdomyolysis who were seen in our tertiary care university-affiliated pediatric hospital. Patients in outpatient clinics, seen in the emergency department, or admitted from 2001 to 2002 were selected. With a standardized case report form, we collected predetermined data from each patients chart. RESULTS A total of 130 patients with rhabdomyolysis were included in the study (male, 56%; mean age, 7.5 ± 5.9 years). The median elevation of creatine phosphokinase was 2207 IU/L (range, 1003 to 811 428 IU/L). The most frequent diagnoses were viral myositis (29, 22.3%), trauma (24, 18.4%), surgery (24, 18.4%), hypoxia (12 , 9.2%), and drug reaction (8, 6.2%). Metabolic myopathy was found only in one patient (0.8%). In 17 patients (13.1%), no definite diagnosis could be made. CONCLUSIONS Etiologies of rhabdomyolysis in children are varied and differ from those reported in adults. In most patients, rhabdomyolysis is benign and without recurrence. In our series, rhabdomyolysis was the initial symptom of a metabolic myopathy in only one patient.

Time-Dependent Structural Changes of the Dentatothalamic Pathway in Children Treated for Posterior Fossa Tumor

BACKGROUND AND PURPOSE: Injury to the dentatothalamic pathway that originates in the cerebellum has been suggested as a mechanism for neurologic complications in children treated for posterior fossa tumors. We hypothesized that time-dependent changes occur in the dentatothalamic pathway. MATERIALS AND METHODS: Diffusion tensor evaluation was performed in 14 children (median age, 4.1 years; age range, 1–20 years) who underwent serial MR imaging at 3T as part of routine follow-up after posterior fossa tumor resection with or without adjuvant therapy. Tensor metrics were obtained in the acute (≤1 week), subacute (1 to <6 months), and chronic (≥6 months) periods after surgery. We evaluated the following dentatothalamic constituents: bilateral dentate nuclei, cerebellar white matter, and superior cerebellar peduncles. Serial dentate nuclei volumes were also obtained and compared with the patients baseline. RESULTS: The most significant tensor changes to the superior cerebellar peduncles and cerebellar white matter occurred in the subacute period, regardless of the tumor pathology or therapy regimen, with signs of recovery in the chronic period. However, chronic volume loss and reduced mean diffusivity were observed in the dentate nuclei and did not reverse. This atrophy was associated with radiation therapy and symptoms of ataxia. CONCLUSIONS: Longitudinal diffusion MR imaging in children treated for posterior fossa tumors showed time-dependent tensor changes in components of the dentatothalamic pathway that suggest evolution of structural damage with inflammation and recovery of tissue directionality. However, the dentate nuclei did not show tensor or volumetric recovery, suggesting that the injury may be chronic.

Efficacy and safety of lacosamide as an adjunctive therapy for refractory focal epilepsy in paediatric patients: a retrospective single-centre study.

AIM Lacosamide is an antiepileptic drug approved for the treatment of focal epilepsy in adult patients. The aim of this observational study was to review our centres experience with lacosamide and to characterize its effectiveness and tolerability as an adjunctive antiepileptic drug in a retrospective cohort of children with refractory focal epilepsy. METHODS We retrospectively reviewed the medical records of 22 patients who received lacosamide from November 2009 to April 2014 at the CHU Ste-Justine, University of Montreal. Treatment responders were defined as children with a ≥50% reduction in seizure frequency compared to baseline, and this was determined three months after the initiation of treatment and at the last follow-up visit. RESULTS We included 14 boys and eight girls with a mean age of 12.9 years (SD: 5.2; range: 5.2-20.7 years) at the initiation of treatment. The average length of follow-up was 11.9 months. Patients had previously received an average of 7.5 antiepileptic drugs. The mean number of concomitant antiepileptic drugs was 2.3. The mean initial and maintenance doses were 2.9 and 8.4 mg/kg/d, respectively. Thirteen (59%) and ten (45%) patients were responders after three months of treatment and at the last follow-up visit, respectively. One became seizure-free. Adverse effects were reported in 11 patients and none were severe. Responders and non-responders were identical with respect to all studied parameters except gender, with the proportion of responders being greater in girls than in boys (75% vs 29%; p=0.035). CONCLUSION Our study adds evidence that lacosamide appears to be a safe and effective adjunctive therapy for children with refractory focal epilepsy.

Café-au-lait Macules and Neurofibromatosis Type 1: A Review of the Literature

BACKGROUND The first sign of neurofibromatosis type 1 (NF1) in a child is often the presence of multiple café-au-lait macules. Although previous studies reported that almost individuals with multiple café-au-lait macules will eventually develop NF1 based on clinical criteria, recent studies and clinical observations suggest that a significant percentage of them do not have NF1. METHODS We conducted the first systematic review of the literature on the prevalence of definitive NF1 among patients referred for isolated café-au-lait macules, searching more precisely for the proportion of those patients who do not have NF1. Because we now know that the presence of café-au-lait macules and freckling might not distinguish between NF1 and other conditions such as Legius syndrome, definitive NF1 was defined as the presence of café-au-lait macules with or without freckling plus one of the following: Lisch nodules, neurofibroma, plexiform neurofibroma, bone dysplasia, optic pathway glioma, or familial history of NF1. RESULTS Six articles reported sufficient data to meet our inclusion criteria. Grouping all studies together, we found that 19.5% to 57.1% of all patients with isolated café-au-lait macules did not have a diagnosis of NF1 after follow-up or genetic testing. CONCLUSION A significant portion of the patients presenting with isolated café-au-lait macules at initial consultation might not have NF1. Genetic testing could help guide the follow-up of those patients, but further evidence is required to make recommendations.

Potential brain language reorganization in a boy with refractory epilepsy; an fNIRS-EEG and fMRI comparison.

As part of a presurgical investigation for a resection of a tumor located in the left temporal brain region, we evaluated pre- and postsurgical language lateralization in a right-handed boy with refractory epilepsy. In this study, we compared functional near infrared spectroscopy (fNIRS) results obtained while the participant performed expressive and receptive language tasks with those obtained using functional magnetic resonance imaging (fMRI). This case study illustrates the potential for NIRS to contribute favorably to the localization of language functions in children with epilepsy and cognitive or behavioral problems and its potential advantages over fMRI in presurgical assessment. Moreover, it suggests that fNIRS is sensitive in localizing an atypical language network or potential brain reorganization related to epilepsy in young patients.

Long-Term Sequelae

Over the last decades, the outcome of children with central nervous system tumors has significantly improved. The latest data from the Surveillance Epidemiology and End Results estimated that 74 % of children with brain tumors survive beyond 5 years. However as those survivors become young adults, the incidence of late effects is being more apparent.