Expanding the phenotype of NUP85 mutations beyond nephrotic syndrome to primary autosomal recessive microcephaly and Seckel syndrome spectrum disorders.

Primary autosomal recessive microcephaly and Seckel syndrome spectrum disorders (MCPH-SCKS) include a heterogeneous group of autosomal recessive inherited diseases characterized by primary (congenital) microcephaly, the absence of visceral abnormalities, and a variable degree of cognitive impairment, short stature and facial dysmorphism. Recently, biallelic variants in the nuclear pore complex (NPC) component nucleoporin 85 gene (NUP85) were reported to cause steroid-resistant nephrotic syndrome (SRNS). Here, we report biallelic variants in NUP85 in two pedigrees with an MCPH-SCKS phenotype spectrum without SRNS, thereby expanding the phenotypic spectrum of NUP85-linked diseases. Structural analysis predicts the identified NUP85 variants cause conformational changes that could have an effect on NPC architecture or on its interaction with other NUPs. We show that mutant NUP85 is, however, associated with a reduced number of NPCs but unaltered nucleocytoplasmic compartmentalization, abnormal mitotic spindle morphology, and decreased cell viability and proliferation in one patient's cells. Our results also indicate the link of common cellular mechanisms involved in MCPH-SCKS spectrum disorders and NUP85-associated diseases. In addition to the previous studies, our results broaden the phenotypic spectrum of NUP85-linked human disease and propose a role for NUP85 in nervous system development.

Proteome changes in autosomal recessive primary microcephaly.

BACKGROUND/AIM: Autosomal recessive primary microcephaly (MCPH) is a rare and genetically heterogeneous group of disorders characterized by intellectual disability and microcephaly at birth, classically without further organ involvement. MCPH3 is caused by biallelic variants in the cyclin-dependent kinase 5 regulatory subunit-associated protein 2 gene CDK5RAP2. In the corresponding Cdk5rap2 mutant or Hertwig's anemia mouse model, congenital microcephaly as well as defects in the hematopoietic system, germ cells and eyes have been reported. The reduction in brain volume, particularly affecting gray matter, has been attributed mainly to disturbances in the proliferation and survival of early neuronal progenitors. In addition, defects in dendritic development and synaptogenesis exist that affect the excitation-inhibition balance. Here, we studied proteomic changes in cerebral cortices of Cdk5rap2 mutant mice. MATERIAL AND METHODS: We used large-gel two-dimensional gel (2-DE) electrophoresis to separate cortical proteins. 2-DE gels were visualized by a trained observer on a light box. Spot changes were considered with respect to presence/absence, quantitative variation and altered mobility. RESULT: We identified a reduction in more than 30 proteins that play a role in processes such as cell cytoskeleton dynamics, cell cycle progression, ciliary functions and apoptosis. These proteome changes in the MCPH3 model can be associated with various functional and morphological alterations of the developing brain. CONCLUSION: Our results shed light on potential protein candidates for the disease-associated phenotype reported in MCPH3.

PTRH2 is Necessary for Purkinje Cell Differentiation and Survival and its Loss Recapitulates Progressive Cerebellar Atrophy and Ataxia Seen in IMNEPD Patients.

Hom ozygous variants in the peptidyl-tRNA hydrolase 2 gene (PTRH2) cause infantile-onset multisystem neurologic, endocrine, and pancreatic disease. The objective is to delineate the mechanisms underlying the core cerebellar phenotype in this disease. For this, we generated constitutive (Ptrh2LoxPxhCMVCre, Ptrh2-/- mice) and Purkinje cell (PC) specific (Ptrh2LoxPxPcp2Cre, Ptrh2ΔPCmice) Ptrh2 mutant mouse models and investigated the effect of the loss of Ptrh2 on cerebellar development. We show that Ptrh2-/- knockout mice had severe postnatal runting and lethality by postnatal day 14. Ptrh2ΔPC PC specific knockout mice survived until adult age; however, they showed progressive cerebellar atrophy and functional cerebellar deficits with abnormal gait and ataxia. PCs of Ptrh2ΔPC mice had reduced cell size and density, stunted dendrites, and lower levels of ribosomal protein S6, a readout of the mammalian target of rapamycin pathway. By adulthood, there was a marked loss of PCs. Thus, we identify a cell autonomous requirement for PTRH2 in PC maturation and survival. Loss of PTRH2 in PCs leads to downregulation of the mTOR pathway and PC atrophy. This suggests a molecular mechanism underlying the ataxia and cerebellar atrophy seen in patients with PTRH2 mutations leading to infantile-onset multisystem neurologic, endocrine, and pancreatic disease.

Primidone improves symptoms in TRPM3-linked developmental and epileptic encephalopathy with spike-and-wave activation in sleep.

Developmental and epileptic encephalopathy with continuous spike-and-wave activation in sleep (CSWS) or DEE-SWAS is an age-dependent disease, often accompanied by a decline in cognitive abilities. Early successful treatment of CSWS is associated with a better cognitive outcome. We retrospectively analyzed the clinical, electrophysiological, radiological, and genetic data of children with DEE-SWAS associated with melastatin-related transient receptor type 3 gene (TRPM3) missense variants. We report two unrelated children with pharmacoresistant DEE-SWAS and developmental delay/regression and different heterozygous de novo missense variants in the TRPM3 gene (NM_001366145.2; c.3397 T > C/p.Ser1133Pro, c.2004G > A/p.Val1002Met). The variant p.Val1002Met (previously known as p.Val990Met or p.Val837Met) and p.Ser1133Pro were recently shown to result in a gain-of-function effect. Based on this finding, previous drug resistance, and the experimentally demonstrated inhibitory effect of primidone on TRPM3, we initiated an individualized therapy with this drug. In both children, developmental regression was stopped, psychomotor development improved, and CSWS was no longer detectable. To our knowledge, this is the first report of a treatment with primidone in TRPM3-associated CSWS. Our results highlight the importance of early genetic diagnosis in patients with epilepsy and the possibility of precision medicine, which should be considered in the future in individuals with a TRPM3-linked DEE-SWAS.

WWOX developmental and epileptic encephalopathy: Understanding the epileptology and the mortality risk.

OBJECTIVE: WWOX is an autosomal recessive cause of early infantile developmental and epileptic encephalopathy (WWOX-DEE), also known as WOREE (WWOX-related epileptic encephalopathy). We analyzed the epileptology and imaging features of WWOX-DEE, and investigated genotype-phenotype correlations, particularly with regard to survival. METHODS: We studied 13 patients from 12 families with WWOX-DEE. Information regarding seizure semiology, comorbidities, facial dysmorphisms, and disease outcome were collected. Electroencephalographic (EEG) and brain magnetic resonance imaging (MRI) data were analyzed. Pathogenic WWOX variants from our cohort and the literature were coded as either null or missense, allowing individuals to be classified into one of three genotype classes: (1) null/null, (2) null/missense, (3) missense/missense. Differences in survival outcome were estimated using the Kaplan-Meier method. RESULTS: All patients experienced multiple seizure types (median onset = 5 weeks, range = 1 day-10 months), the most frequent being focal (85%), epileptic spasms (77%), and tonic seizures (69%). Ictal EEG recordings in six of 13 patients showed tonic (n = 5), myoclonic (n = 2), epileptic spasms (n = 2), focal (n = 1), and migrating focal (n = 1) seizures. Interictal EEGs demonstrated slow background activity with multifocal discharges, predominantly over frontal or temporo-occipital regions. Eleven of 13 patients had a movement disorder, most frequently dystonia. Brain MRIs revealed severe frontotemporal, hippocampal, and optic atrophy, thin corpus callosum, and white matter signal abnormalities. Pathogenic variants were located throughout WWOX and comprised both missense and null changes including five copy number variants (four deletions, one duplication). Survival analyses showed that patients with two null variants are at higher mortality risk (p-value = .0085, log-rank test). SIGNIFICANCE: Biallelic WWOX pathogenic variants cause an early infantile developmental and epileptic encephalopathy syndrome. The most common seizure types are focal seizures and epileptic spasms. Mortality risk is associated with mutation type; patients with biallelic null WWOX pathogenic variants have significantly lower survival probability compared to those carrying at least one presumed hypomorphic missense pathogenic variant.

In-depth analysis reveals complex molecular aetiology in a cohort of idiopathic cerebral palsy.

Cerebral palsy is the most prevalent physical disability in children; however, its inherent molecular mechanisms remain unclear. In the present study, we performed in-depth clinical and molecular analysis on 120 idiopathic cerebral palsy families, and identified underlying detrimental genetic variants in 45% of these patients. In addition to germline variants, we found disease-related postzygotic mutations in ∼6.7% of cerebral palsy patients. We found that patients with more severe motor impairments or a comorbidity of intellectual disability had a significantly higher chance of harbouring disease-related variants. By a compilation of 114 known cerebral-palsy-related genes, we identified characteristic features in terms of inheritance and function, from which we proposed a dichotomous classification system according to the expression patterns of these genes and associated cognitive impairments. In two patients with both cerebral palsy and intellectual disability, we revealed that the defective TYW1, a tRNA hypermodification enzyme, caused primary microcephaly and problems in motion and cognition by hindering neuronal proliferation and migration. Furthermore, we developed an algorithm and demonstrated in mouse brains that this malfunctioning hypermodification specifically perturbed the translation of a subset of proteins involved in cell cycling. This finding provided a novel and interesting mechanism for congenital microcephaly. In another cerebral palsy patient with normal intelligence, we identified a mitochondrial enzyme GPAM, the hypomorphic form of which led to hypomyelination of the corticospinal tract in both human and mouse models. In addition, we confirmed that the aberrant Gpam in mice perturbed the lipid metabolism in astrocytes, resulting in suppressed astrocytic proliferation and a shortage of lipid contents supplied for oligodendrocytic myelination. Taken together, our findings elucidate novel aspects of the aetiology of cerebral palsy and provide insights for future therapeutic strategies.

Family Burden and Epilepsy Surgery in Children with Drug-Resistant Epilepsy.

INTRODUCTION: Family burden (FB) in pediatric patients with drug-resistant epilepsy (DRE) is significantly higher than that in children with non-DRE. Epilepsy surgery is an established approach to treat DRE, and this study examines the impact of pediatric epilepsy surgery on FB. METHODS: We retrospectively analyzed data of families and pediatric patients with focal structural DRE treated with epilepsy surgery at our epilepsy center from April 2018 to November 2021. We examined the relationship between cognitive, behavioral, and epilepsy-specific data and the FB measured with the German version of the Impact on Family Scale before and after epilepsy surgery. RESULTS: The study cohort included 31 children with DRE at a mean age of 9 years at surgery (range = 0-16) and a mean epilepsy duration of 3 years (range = 0-14). Cognitive impairment correlated with FB in children with DRE prior to surgery. At the last assessment, 14.5 months (mean, range = 6-24) after epilepsy surgery, 87.2% of patients were seizure-free, FB values had decreased by 75.0%, and behavioral problems had decreased by 85,7%. Cognitive functions remained stable following epilepsy surgery. CONCLUSION: In children with DRE, epilepsy surgery reduces FB. Given the considerable impact of families on the development and wellbeing of their children, the impact of epilepsy surgery should be communicated to affected families.

Homozygous mutation in MCM7 causes autosomal recessive primary microcephaly and intellectual disability.

BACKGROUND: Minichromosomal maintenance (MCM) complex components 2, 4, 5 and 6 have been linked to human disease with phenotypes including microcephaly and intellectual disability. The MCM complex has DNA helicase activity and is thereby important for the initiation and elongation of the replication fork and highly expressed in proliferating neural stem cells. METHODS: Whole-exome sequencing was applied to identify the genetic cause underlying the neurodevelopmental disease of the index family. The expression pattern of Mcm7 was characterised by performing quantitative real-time PCR, in situ hybridisation and immunostaining. To prove the disease-causative nature of identified MCM7, a proof-of-principle experiment was performed. RESULTS: We reported that the homozygous missense variant c.793G>A/p.A265T (g.7:99695841C>T, NM_005916.4) in MCM7 was associated with autosomal recessive primary microcephaly (MCPH), severe intellectual disability and behavioural abnormalities in a consanguineous pedigree with three affected individuals. We found concordance between the spatiotemporal expression pattern of Mcm7 in mice and a proliferative state: Mcm7 expression was higher in early mouse developmental stages and in proliferative zones of the brain. Accordingly, Mcm7/MCM7 levels were detectable particularly in undifferentiated mouse embryonal stem cells and human induced pluripotent stem cells compared with differentiated neurons. We further demonstrate that the downregulation of Mcm7 in mouse neuroblastoma cells reduces cell viability and proliferation, and, as a proof-of-concept, that this is counterbalanced by the overexpression of wild-type but not mutant MCM7. CONCLUSION: We report mutations of MCM7 as a novel cause of autosomal recessive MCPH and intellectual disability and highlight the crucial function of MCM7 in nervous system development.

ß-Ureidopropionase deficiency due to novel and rare UPB1 mutations affecting pre-mRNA splicing and protein structural integrity and catalytic activity.

ß-Ureidopropionase is the third enzyme of the pyrimidine degradation pathway and catalyses the conversion of N-carbamyl-ß-alanine and N-carbamyl-ß-aminoisobutyric acid to ß-alanine and ß-aminoisobutyric acid, ammonia and CO2. To date, only a limited number of genetically confirmed patients with a complete ß-ureidopropionase deficiency have been reported. Here, we report on the clinical, biochemical and molecular findings of 10 newly identified ß-ureidopropionase deficient individuals. Patients presented mainly with neurological abnormalities and markedly elevated levels of N-carbamyl-ß-alanine and N-carbamyl-ß-aminoisobutyric acid in urine. Analysis of UPB1, encoding ß-ureidopropionase, showed 5 novel missense variants and two novel splice-site variants. Functional expression of the UPB1 variants in mammalian cells showed that recombinant ß-ureidopropionase carrying the p.Ala120Ser, p.Thr129Met, p.Ser300Leu and p.Asn345Ile variant yielded no or significantly decreased ß-ureidopropionase activity. Analysis of the crystal structure of human ß-ureidopropionase indicated that the point mutations affect substrate binding or prevent the proper subunit association to larger oligomers and thus a fully functional ß-ureidopropionase. A minigene approach showed that the intronic variants c.[364 + 6 T > G] and c.[916 + 1_916 + 2dup] led to skipping of exon 3 and 8, respectively, in the process of UPB1 pre-mRNA splicing. The c.[899C > T] (p.Ser300Leu) variant was identified in two unrelated Swedish ß-ureidopropionase patients, indicating that ß-ureidopropionase deficiency may be more common than anticipated.

Successful treatment of adult Dravet syndrome patients with cenobamate.

Dravet syndrome (DS) is a rare, drug-resistant, severe developmental and epileptic encephalopathy caused by pathogenic variants in the α subunit of the voltage-gated sodium channel gene SCN1A. Hyperexcitability in DS results from loss of function in inhibitory interneurons. Thus sodium channel blockers are usually contraindicated in patients with DS as they may lead to disease aggravation. Cenobamate (CNB) is a novel antiseizure medication (ASM) with promising rates of seizure freedom in patients with focal-onset, drug-resistant epilepsy. CNB blocks persistent sodium currents by promoting the inactive states of sodium channels. In a multi-center study, we analyzed retrospectively the effect of an add-on therapy of CNB in adult patients with DS. We report four adult patients with DS in whom the use of CNB resulted in a significant seizure reduction of more than 80%, with a follow-up of up to 542 days. CNB was the first drug in these patients that resulted in a long-lasting and significant seizure reduction. No severe adverse events occurred. We highlight CNB as an ASM that may lead to a clinically meaningful reduction of seizure frequency in adult patients with DS. It is unclear, however, if all patients with DS benefit, requiring further investigation and functional experiments.

Cerebral Abnormalities in Spina Bifida: A Neuropathological Study.

INTRODUCTION: Spina bifida (SB) is the most common neural tube defect in humans. Here, we analyzed systematically the neuropathological findings of the brain in SB cases. METHODS: 79 cases with SB aperta (SBA) and 6 cases with SB occulta (SBO) autopsied at the Charité Neuropathology from 1974 to 2000 were re-evaluated retrospectively. For this, case files and spinal cord as well as brain sections were studied. RESULTS: While no brain malformations were detected in SBO cases, 95% of SBA cases had brain malformations. Main brain anomalies identified were hydrocephalus (71%), Chiari II malformation (36%), heterotopia (34%), other cerebellar anomalies (36%), gyrification defects (33%), and ependymal denudation (29%). Hydrocephalus was observed as early as gestational week 17 and was highly associated to Chiari II and ependymal denudation. In 55% SBA was accompanied by further anomalies not primarily affecting the CNS. CONCLUSION: We confirm using neuropathologic methods brain malformations in most SBA but none in SBO cases. In addition to our previous radiologic study, we now demonstrate the high prevalence of cerebellar malformations and cerebral heterotopias in SBA. The early detection of hydrocephalus and Chiari II malformation in fetuses raises the question whether these arise parallel rather than in strict temporal sequence.

A missense mutation in SNRPE linked to non-syndromal microcephaly interferes with U snRNP assembly and pre-mRNA splicing.

Malfunction of pre-mRNA processing factors are linked to several human diseases including cancer and neurodegeneration. Here we report the identification of a de novo heterozygous missense mutation in the SNRPE gene (c.65T>C (p.Phe22Ser)) in a patient with non-syndromal primary (congenital) microcephaly and intellectual disability. SNRPE encodes SmE, a basal component of pre-mRNA processing U snRNPs. We show that the microcephaly-linked SmE variant is unable to interact with the SMN complex and as a consequence fails to assemble into U snRNPs. This results in widespread mRNA splicing alterations in fibroblast cells derived from this patient. Similar alterations were observed in HEK293 cells upon SmE depletion that could be rescued by the expression of wild type but not mutant SmE. Importantly, the depletion of SmE in zebrafish causes aberrant mRNA splicing alterations and reduced brain size, reminiscent of the patient microcephaly phenotype. We identify the EMX2 mRNA, which encodes a protein required for proper brain development, as a major mis-spliced down stream target. Together, our study links defects in the SNRPE gene to microcephaly and suggests that alterations of cellular splicing of specific mRNAs such as EMX2 results in the neurological phenotype of the disease.

Improvement of bladder function after bladder augmentation surgery: a report of 26 years of clinical experience.

INTRODUCTION: To assess the long-term effect of bladder augmentation surgery in patients with spina bifida and to identify risk factors for severe bladder dysfunction requiring bladder augmentation. METHODS: A retrospective analysis was performed on 178 patients with spina bifida, 23 of them underwent bladder augmentation. Surgery outcome was evaluated according to urodynamic assessments at three follow-up time points per patient up to 120 months postoperatively. The results were compared to the preoperative situation and to the non-operated control group. Bladder function was evaluated using the modified Hostility score. To identify risk factors for bladder dysfunction requiring bladder augmentation, characteristics such as type of spina bifida, lesion level and therapy of bladder dysfunction were analyzed. RESULTS: A high spinal lesion level is a risk factor for requiring bladder augmentation. In the BA group, significantly more thoracic lesions were found than NBA group, BA: 26.1%, NBA: 8.4% (p = 0.021). With bladder augmentation surgery, the modified Hostility score decreased from a preoperative median value of 4.3 ± 1.4 to 1.6 ± 1.0 at the third postoperative follow-up (FU3 = 61-120 months after surgery). In the reference group, the score of the last urological assessment was 2.0 ± 1.5. The age at which clean intermittent catheterization or anticholinergic medication started had no significant influence on the decision to perform bladder augmentation. DISCUSSION/CONCLUSION: Spina bifida patients with bladder augmentation had a significant improvement of the bladder function even at long-term follow-up. A high level of spinal lesion was a predisposing factor for requiring a bladder augmentation.

Importance of urodynamic evaluation of bladder function after secondary untethering in spina bifida patients: single center experience of 30 years.

INTRODUCTION: A TCS after primary closure of meningomyeloceles is a known complication of the spina bifida disease. Data on the outcome after SSCU surgery is heterogeneous and lacking standardization. Thus we aimed to find a reliable system for assessment of the bladder function before and after SSCU surgery and document postoperative outcome. METHODS: A retrospective study was performed on a cohort of patients with spina bifida diagnosis. In total, 130 patients underwent 182 SSCU surgeries, 56 of those met our inclusion criteria. A classification system, including two different methods, was used. The AC system used baseline pressure and detrusor over activity to define three levels of bladder dysfunction, the second method ranked the severity of bladder dysfunction by awarding points from 0 to 2 for bladder capacity, maximal detrusor pressure during autonomous contractions, leak point pressure and vesicoureteral reflux A high score is correlated with a severe bladder dysfunction. RESULTS: Gender distribution was equally (male: n = 29; 51.8%; female: n = 27; 48.2%). The median age at SSCU was 902 years (range 0.5-22.8 years). After SSCU, the stage improved in 11 patients (19.6%), worsened in 11 (19.6%) patients and remained the same in 34 patients (60.7%) after intervention (AC score). Non-worsening was observed in a total of 45 cases (80.4%) (p < 0.001). MHS score (n = 27, 48.2%) improved, remained unchanged (n = 12, 21.4%), 17 patients worsened (30.4%). Non-worsening in postoperative bladder functional outcome was demonstrated in 39 cases (69.6%) over all (p < 0.005). Regardless of whether bladder function is categorized by AC or MHS, postoperative outcome worsened significantly when SSCU was performed due to increasing deterioration in motor function alone (p < 0.05). Of the 24 cases with NOD as indication, 22 (91.7%) had an unchanged (n = 10; 41.7%) or improved (n = 12; 50.0%), meaning positive neuro-orthopedic outcome, only 2 (8.3%) deteriorated (p < 0.001). CONCLUSION: Our study presents reliable evaluation systems for bladder function in spina bifida patients. Since indications for SSCU surgery differ, it is important to know the possible effects on bladder function after this surgical procedure. Even a mild impairment of bladder function has a risk to deteriorate after SSCU surgery. Particularly interesting becomes this with regard to the fact that the prevalence of TCS might become more frequent with the rising numbers of prenatal closures of meningomyeloceles.

Zebrafish modeling mimics developmental phenotype of patients with RAPGEF1 mutation.

RAPGEF1 is a guanine nucleotide exchange factor responsible for transmitting extracellular signals to the Ras family of GTPase located at the inside of membrane. Here, we report for the first time a homozygous mutation of RAPGEF1 in a consanguineous family with two siblings affected by neuropsychiatric disorder. To confirm the correlation of the mutation and the phenotype, we utilized in silico analysis and established a zebrafish model. Survival rate was reduced in the rapgef1a-knockdown model, and the zebrafish showed global morphological abnormalities, particularly of brain and blood vessels. Co-application of human RAPGEF1 wildtype mRNA effectively rescued the abnormal phenotype, while that of RAPGEF1 mRNA carrying the human mutation did not. This work is the first report of a human Mendelian disease associated with RAPGEF1 and the first report of a zebrafish model built for this gene. The phenotype of zebrafish model provides further evidence that defective RAPGEF1 may lead to global developmental delay in human patients.

Abnormal brain structure and behavior in MyD88-deficient mice.

While the original protein Toll in Drosophila melanogaster regulates both host defense and morphogenesis, the role of its ortholog Toll-like receptors (TLRs), the interleukin 1 receptor (IL-1R) family, and the associated signaling pathways in mammalian brain development and structure is poorly understood. Because the adaptor protein myeloid differentiation primary response protein 88 (MyD88) is essential for downstream signaling of most TLRs and IL-1R, we systematically investigated the effect of MyD88 deficiency on murine brain structure during development and on behavior. In neonatal Myd88-/- mice, neocortical thickness was reduced, while density of cortical neurons was increased. In contrast, microglia, astrocyte, oligodendrocyte, and proliferating cell numbers were unchanged in these mice compared to wild-type mice. In adult Myd88-/- mice, neocortical thickness was unaltered, but neuronal density in neocortex and hippocampus was increased. Neuron arborization was less pronounced in adult Myd88-/- mice compared to wild-type animals. In addition, numbers of microglia and proliferating cells were increased in the neocortex and subventricular zone, respectively, with unaltered astrocyte and oligodendrocyte numbers, and myelinization was enhanced in the adult Myd88-/- neocortex. These morphologic changes in the brain of adult Myd88-/- mice were accompanied by specific behavioral traits, such as decreased locomotor activity, increased anxiety-like behavior, but normal day/light activity, satisfactory learning, short- and long-term spatial memory, potential cognitive inflexibility, and increased hanging and locomotor behavior within their home cage. Taken together, MyD88 deficiency results in morphologic and cellular changes in the mouse brain, as well as in altered natural and specific behaviors. Our data indicate a pathophysiological significance of MyD88 for mammalian CNS development, structure, and function.

MN1 C-terminal truncation syndrome is a novel neurodevelopmental and craniofacial disorder with partial rhombencephalosynapsis.

MN1 encodes a transcriptional co-regulator without homology to other proteins, previously implicated in acute myeloid leukaemia and development of the palate. Large deletions encompassing MN1 have been reported in individuals with variable neurodevelopmental anomalies and non-specific facial features. We identified a cluster of de novo truncating mutations in MN1 in a cohort of 23 individuals with strikingly similar dysmorphic facial features, especially midface hypoplasia, and intellectual disability with severe expressive language delay. Imaging revealed an atypical form of rhombencephalosynapsis, a distinctive brain malformation characterized by partial or complete loss of the cerebellar vermis with fusion of the cerebellar hemispheres, in 8/10 individuals. Rhombencephalosynapsis has no previously known definitive genetic or environmental causes. Other frequent features included perisylvian polymicrogyria, abnormal posterior clinoid processes and persistent trigeminal artery. MN1 is encoded by only two exons. All mutations, including the recurrent variant p.Arg1295* observed in 8/21 probands, fall in the terminal exon or the extreme 3' region of exon 1, and are therefore predicted to result in escape from nonsense-mediated mRNA decay. This was confirmed in fibroblasts from three individuals. We propose that the condition described here, MN1 C-terminal truncation (MCTT) syndrome, is not due to MN1 haploinsufficiency but rather is the result of dominantly acting C-terminally truncated MN1 protein. Our data show that MN1 plays a critical role in human craniofacial and brain development, and opens the door to understanding the biological mechanisms underlying rhombencephalosynapsis.

Lumbar Puncture Opening Pressure in Patients with Spinal Muscular Atrophy.

The announcement of a hydrocephalus as a possible side effect in patients with spinal muscular atrophy (SMA) receiving the drug nusinersen, promoted major concern and warrants further evaluation. In this retrospective monocentric study, we analyzed clinical data, lumbar puncture opening pressure (LOP) measurement, and ophthalmologic and neuroimaging results in 34 patients with SMA types 1 to 3 undergoing treatment with nusinersen. None of the patients reported symptoms indicative of increased intracranial pressure. In our cohort, the LOP was >20 cm H2O in 25 patients (70.5%), and within this group ≥28 cm H2O in 12 patients (35.3%), in two patients, it was increased prior to treatment initiation. Signs of increased intracranial pressure in ophthalmological assessments or brain imaging were only seen in one patient. We did not identify a correlation between increased LOP and SMA type, scoliosis, or age of the patients; however, it was slightly higher in patients receiving sedation. Our results raise the question whether the LOP is generally increased in SMA as part of the underlying disease, if so, what the etiology is, and whether the increased LOP needs to be treated.

Brain malformations and cognitive performance in spina bifida.

AIM: To systematically characterize radiological features of patients with spina bifida, their relationship to cognitive function, and differences between spina bifida aperta (SBA) and spina bifida occulta (SBO). METHOD: In a retrospective study of 265 patients (117 females, 148 males; median age at imaging 11y, range 1-47y; SBA n=206, SBO n=59), the radiological phenotype was assessed through magnetic resonance imaging (MRI) (SBA n=171, SBO n=59). In 126 patients (SBA n=116, SBO n=10) Kaufman Assessment Battery for Children (KABC) or Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV) and Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV) were performed. RESULTS: Patients with spina bifida show numerous brain malformations, always present for SBA but rarely for SBO. The most frequent brain malformations in SBA included abnormal corpus callosum (69%), hypoplastic pons (50%), and hypoplastic mesencephalon (20%). Cognitive total IQ scores were below average in 44% (KABC) to 49% (WISC-IV) of children with SBA, while almost all children with SBO scored at least average. Stenogyria (p=0.006), pons (p=0.003), and mesencephalon hypoplasia (p=0.01) correlated with lower total IQ score and verbal comprehension. Various brain malformations correlate significantly with several cognitive domains, while lesion level only correlates with processing speed. INTERPRETATION: IQ scores were significantly lower in patients with SBA than in patients with SBO. Verbal competence, perceptual reasoning, and working memory were significantly impaired for SBA and correlated with stenogyria and abnormalities of the midbrain and corpus callosum. WHAT THIS PAPER ADDS: Brain malformations occur more frequently in spina bifida aperta (SBA) than in spina bifida occulta (SBO). Cognitive impairment is less frequent in SBO. Hydrocephalus, stenogyria, midbrain, and corpus callosum abnormalities are associated with lower cognitive function. Difference in prognosis in SBO versus SBA can alter prenatal counselling.

Assessment of myelination in infants and young children by T1 relaxation time measurements using the magnetization-prepared 2 rapid acquisition gradient echoes sequence.

BACKGROUND: Axonal myelination is an important maturation process in the developing brain. Increasing myelin content correlates with the longitudinal relaxation rate (R1=1/T1) in magnetic resonance imaging (MRI). OBJECTIVE: By using magnetization-prepared 2 rapid acquisition gradient echoes (MP2RAGE) on a 3-T MRI system, we provide R1 values and myelination rates for infants and young children. MATERIALS AND METHODS: Average R1 values in white and grey matter regions in 94 children without pathological MRI findings (age range: 3 months to 6 years) were measured and fitted by a saturating-exponential growth model. For comparison, R1 values of 36 children with different brain pathologies are presented. The findings were related to a qualitative evaluation using T2, magnetization-prepared rapid acquisition gradient echo (MP-RAGE) and MP2RAGE. RESULTS: R1 changes rapidly in the first 16 months of life, then much slower thereafter. R1 is highest in pre-myelinated structures in the youngest subjects, such as the posterior limb of the internal capsule (0.74-0.76±0.04 s-1) and lowest for the corpus callosum (0.37-0.44±0.03 s-1). The myelination rate is fastest in the corpus callosum and slowest in the deep grey matter. R1 is decreased in hypo- and dysmyelination disorders. Myelin maturation is clearly visible on MP2RAGE, especially in the first year of life. CONCLUSION: MP2RAGE permits a quantitative R1 mapping method with an examination time of approximately 6 min. The age-dependent R1 values for children without MRI-identified brain pathologies are well described by a saturating-exponential function with time constants depending on the investigated brain region. This model can serve as a reference for this age group and to search for indications of subtle pathologies. Moreover, the MP2RAGE sequence can also be used for the qualitative assessment of myelinated structures.