Mutations disrupting neuritogenesis genes confer risk for cerebral palsy

Impaired microtubule dynamics contribute to microthrombocytopenia in RhoB-deficient mice

Megakaryocytes are large cells in the bone marrow that give rise to blood platelets. Platelet biogenesis involves megakaryocyte maturation, the localization of the mature cells in close proximity to bone marrow sinusoids, and the formation of protrusions, which are elongated and shed within the circulation. Rho GTPases play important roles in platelet biogenesis and function. RhoA-deficient mice display macrothrombocytopenia and a striking mislocalization of megakaryocytes into bone marrow sinusoids and a specific defect in G-protein signaling in platelets. However, the role of the closely related protein RhoB in megakaryocytes or platelets remains unknown. In this study, we show that, in contrast to RhoA deficiency, genetic ablation of RhoB in mice results in microthrombocytopenia (decreased platelet count and size). RhoB-deficient platelets displayed mild functional defects predominantly upon induction of the collagen/glycoprotein VI pathway. Megakaryocyte maturation and localization within the bone marrow, as well as actin dynamics, were not affected in the absence of RhoB. However, in vitro-generated proplatelets revealed pronouncedly impaired microtubule organization. Furthermore, RhoB-deficient platelets and megakaryocytes displayed selective defects in microtubule dynamics/stability, correlating with reduced levels of acetylated α-tubulin. Our findings imply that the reduction of this tubulin posttranslational modification results in impaired microtubule dynamics, which might contribute to microthrombocytopenia in RhoB-deficient mice. Importantly, we demonstrate that RhoA and RhoB are localized differently and have selective, nonredundant functions in the megakaryocyte lineage.

Management of arthrofibrosis in neuromuscular disorders: a review

Arthrofibrosis, or rigid contracture of major articular joints, is a significant morbidity of many neurodegenerative disorders. The pathogenesis depends on the mechanism and severity of the precipitating neuromuscular disorder. Most neuromuscular disorders, whether spastic or hypotonic, culminate in decreased joint range of motion. Limited range of motion precipitates a cascade of pathophysiological changes in the muscle-tendon unit, the joint capsule, and the articular cartilage. Resulting joint contractures limit functional mobility, posing both physical and psychosocial burdens to patients, economic burdens on the healthcare system, and lost productivity to society. This article reviews the pathophysiology of arthrofibrosis in the setting of neuromuscular disorders. We describe current non-surgical and surgical interventions for treating arthrofibrosis of commonly affected joints. In addition, we preview several promising modalities under development to ameliorate arthrofibrosis non-surgically and discuss limitations in the field of arthrofibrosis secondary to neuromuscular disorders.

Human Cerebellar Development and Transcriptomics: Implications for Neurodevelopmental Disorders

Developmental abnormalities of the cerebellum are among the most recognized structural brain malformations in human prenatal imaging. Yet reliable information regarding their cause in humans is sparse, and few outcome studies are available to inform prognosis. We know very little about human cerebellar development, in stark contrast to the wealth of knowledge from decades of research on cerebellar developmental biology of model organisms, especially mice. Recent studies show that multiple aspects of human cerebellar development significantly differ from mice and even rhesus macaques, a nonhuman primate. These discoveries challenge many current mouse-centric models of normal human cerebellar development and models regarding the pathogenesis of several neurodevelopmental phenotypes affecting the cerebellum, including Dandy-Walker malformation and medulloblastoma. Since we cannot model what we do not know, additional normative and pathological human developmental data are essential, and new models are needed.

Gene-Environment Interactions During the First Thousand Days Influence Childhood Neurological Diagnosis

Gene-environment (G x E) interactions significantly influence neurologic outcomes. The maternal-placental-fetal (MPF) triad, neonate, or child less than 2 years may first exhibit significant brain disorders. Neuroplasticity during the first 1000 days will more likely result in life-long effects given critical periods of development. Developmental origins and life-course principles help recognize changing neurologic phenotypes across ages. Dual diagnostic approaches are discussed using representative case scenarios to highlight time-dependent G x E interactions that contribute to neurologic sequelae. Horizontal analyses identify clinically relevant phenotypic form and function at different ages. Vertical analyses integrate the approach using systems-biology from genetic through multi-organ system interactions during each developmental age to understand etiopathogenesis. The process of ontogenetic adaptation results in immediate or delayed positive and negative outcomes specific to the developmental niche, expressed either as a healthy child or one with neurologic sequelae. Maternal immune activation, ischemic placental disease, and fetal inflammatory response represent prenatal disease pathways that contribute to fetal brain injuries. These processes involve G x E interactions within the MPF triad, phenotypically expressed as fetal brain malformations or destructive injuries within the MPF triad. A neonatal minority express encephalopathy, seizures, stroke, and encephalopathy of prematurity as a continuum of trimester-specific G x E interactions. This group may later present with childhood sequelae. A healthy neonatal majority present at older ages with sequelae such as developmental disorders, epilepsy, mental health diseases, tumors, and neurodegenerative disease, often during the first 1000 days. Effective preventive, rescue, and reparative neuroprotective strategies require consideration of G x E interactions interplay over time. Addressing maternal and pediatric health disparities will maximize medical equity with positive global outcomes that reduce the burden of neurologic diseases across the lifespan.

Cerebral palsy diagnosis and the impact on hip surveillance enrollment

AIM

To investigate the diagnosis at enrollment in the Child Health British Columbia Hip Surveillance Program for Children with Cerebral Palsy (CP) and review the etiologies of children enrolled without a CP diagnosis.

METHOD

Data from 959 children (543 males, 416 females; mean [SD] age at enrollment 6 years 8 months [4 years 2 months]) enrolled in the program between September 2015 and December 2019 were retrospectively reviewed. Enrollment diagnosis, Gross Motor Function Classification System level, migration percentage, and age at enrollment were included. Chart reviews were completed to confirm diagnoses for all children. Etiologies were compared to a list of conditions that are included and excluded from CP registries.

RESULTS

Diagnosis at enrollment was CP for 612 (64%), possible CP for 120 (13%), and 'other' for 220 (23%). No diagnosis was provided for seven (<1%). CP was confirmed for 700 (73%), including 106 (11.1%) enrolled as 'possible CP' or 'other'; 56 (5.8%) did not have CP due to progressive conditions. Migration percentage was similar across all groups at enrollment.

INTERPRETATION

One in four children were enrolled in hip surveillance without a diagnosis of CP or possible CP. Encouraging participation in hip surveillance when children meet the clinical criteria for CP but do not have a confirmed CP diagnosis can improve access to care.

Quantifying concordant genetic effects of de novo mutations on multiple disorders

Exome sequencing on tens of thousands of parent-proband trios has identified numerous deleterious de novo mutations (DNMs) and implicated risk genes for many disorders. Recent studies have suggested shared genes and pathways are enriched for DNMs across multiple disorders. However, existing analytic strategies only focus on genes that reach statistical significance for multiple disorders and require large trio samples in each study. As a result, these methods are not able to characterize the full landscape of genetic sharing due to polygenicity and incomplete penetrance. In this work, we introduce EncoreDNM, a novel statistical framework to quantify shared genetic effects between two disorders characterized by concordant enrichment of DNMs in the exome. EncoreDNM makes use of exome-wide, summary-level DNM data, including genes that do not reach statistical significance in single-disorder analysis, to evaluate the overall and annotation-partitioned genetic sharing between two disorders. Applying EncoreDNM to DNM data of nine disorders, we identified abundant pairwise enrichment correlations, especially in genes intolerant to pathogenic mutations and genes highly expressed in fetal tissues. These results suggest that EncoreDNM improves current analytic approaches and may have broad applications in DNM studies.

Neurodevelopmental disorders, immunity, and cancer are connected

Immunity could be viewed as the common factor in neurodevelopmental disorders and cancer. The immune and nervous systems coevolve as the embryo develops. Immunity can release cytokines that activate MAPK signaling in neural cells. In specific embryonic brain cell types, dysregulated signaling that results from germline or embryonic mutations can promote changes in chromatin organization and gene accessibility, and thus expression levels of essential genes in neurodevelopment. In cancer, dysregulated signaling can emerge from sporadic somatic mutations during human life. Neurodevelopmental disorders and cancer share similarities. In neurodevelopmental disorders, immunity, and cancer, there appears an almost invariable involvement of small GTPases (e.g., Ras, RhoA, and Rac) and their pathways. TLRs, IL-1, GIT1, and FGFR signaling pathways, all can be dysregulated in neurodevelopmental disorders and cancer. Although there are signaling similarities, decisive differentiating factors are timing windows, and cell type specific perturbation levels, pointing to chromatin reorganization. Finally, we discuss drug discovery.

Impaired neurogenesis alters brain biomechanics in a neuroprogenitor-based genetic subtype of congenital hydrocephalus

Hydrocephalus, characterized by cerebral ventricular dilatation, is routinely attributed to primary defects in cerebrospinal fluid (CSF) homeostasis. This fosters CSF shunting as the leading reason for brain surgery in children despite considerable disease heterogeneity. In this study, by integrating human brain transcriptomics with whole-exome sequencing of 483 patients with congenital hydrocephalus (CH), we found convergence of CH risk genes in embryonic neuroepithelial stem cells. Of all CH risk genes, TRIM71/lin-41 harbors the most de novo mutations and is most specifically expressed in neuroepithelial cells. Mice harboring neuroepithelial cell-specific Trim71 deletion or CH-specific Trim71 mutation exhibit prenatal hydrocephalus. CH mutations disrupt TRIM71 binding to its RNA targets, causing premature neuroepithelial cell differentiation and reduced neurogenesis. Cortical hypoplasia leads to a hypercompliant cortex and secondary ventricular enlargement without primary defects in CSF circulation. These data highlight the importance of precisely regulated neuroepithelial cell fate for normal brain-CSF biomechanics and support a clinically relevant neuroprogenitor-based paradigm of CH.

NeuroSCORE is a genome-wide omics-based model that identifies candidate disease genes of the central nervous system

To identify candidate disease genes of central nervous system (CNS) phenotypes, we created the Neurogenetic Systematic Correlation of Omics-Related Evidence (NeuroSCORE). We identified five genome-wide metrics highly associated with CNS phenotypes to score 19,601 protein-coding genes. Genes scored one point per metric (range: 0-5), identifying 8298 scored genes (scores ≥ 1) and 1601 "high scoring" genes (scores ≥ 3). Using logistic regression, we determined the odds ratio that genes with a NeuroSCORE from 1 to 5 would be associated with known CNS-related phenotypes compared to genes that scored zero. We tested NeuroSCORE using microarray copy number variants (CNVs) in case-control cohorts and aggregate mouse model data. High scoring genes are associated with CNS phenotypes (OR = 5.5, p < 2E-16), enriched in case CNVs, and mouse ortholog genes that cause behavioral and nervous system abnormalities. We identified 1058 high scoring genes with no disease association in OMIM. Transforming the logistic regression results indicates high scoring genes have an 84-92% chance of being associated with a CNS phenotype. Top scoring genes include GRIA1, MAP4K4, SF1, TNPO2, and ZSWIM8. Finally, we interrogated CNVs in the Clinical Genome Resource, finding the majority of clinically significant CNVs contain high scoring genes. These findings can direct future research and improve molecular diagnostics.

Microdeletion of 16q24.1-q24.2-A unique etiology of Lymphedema-Distichiasis syndrome and neurodevelopmental disorder

Interstitial deletions of 16q24.1–q24.2 are associated with alveolar capillary dysplasia, congenital renal malformations, neurodevelopmental disorders, and congenital abnormalities. Lymphedema–Distichiasis syndrome (LDS; OMIM # 153400) is a dominant condition caused by heterozygous pathogenic variants in FOXC2. Usually, lymphedema and distichiasis occur in puberty or later on, and affected individuals typically achieve normal developmental milestones. Here, we describe a boy with congenital lymphedema, distichiasis, bilateral hydronephrosis, and global developmental delay, with a de novo microdeletion of 894 kb at 16q24.1–q24.2. This report extends the phenotype of both 16q24.1–q24.2 microdeletion syndrome and of LDS. Interestingly, the deletion involves only the 3′‐UTR part of FOXC2.

Dysregulation of multiple signaling pathways: A possible cause of cerebral palsy

Cerebral palsy (CP) is a lifelong disability characterized by the impairment of brain functions that result in improper posture and abnormal motor patterns. Understanding this brain abnormality and the role of genetic, epigenetic, and non-genetic factors such as signaling pathway dysregulation and cytokine dysregulation in the pathogenesis of CP is a complex process. Hypoxic-ischemic injury and prematurity are two well-known contributors of CP. Like in the case of other neurodevelopmental disorders such as intellectual disability and autism, the genomic constituents in CP are highly complex. The neuroinflammation that is triggered by maternal cytokine response plays a critical role in the pathogenesis of fetal inflammation response, which is one of the contributing factors of CP, and it continues even after the birth of children suffering from CP. Canonical Wnt signaling pathway is important for the development of mammalian fetal brain and it regulates distinct processes including neurogenesis. The glycogen synthase kinase-3 (GSK-3) antagonistic activity in the Wnt signaling pathway plays a crucial role in neurogenesis and neural development. In this review, we investigated several genetic and non-genetic pathways that are involved in the pathogenesis of CP and their regulation, impairment, and implications for causing CP during embryonic growth and developmental period. Investigating the role of these pathways help to develop novel therapeutic interventions and biomarkers for early diagnosis and treatment. This review also helps us to comprehend the mechanical approach of various signaling pathways, as well as their consequences and relevance in the understanding of CP.

A Newly Identified Int22h1/Int22h2‐Mediated Xq28 Duplication Syndrome Case Misdiagnosed as Cerebral Palsy

Cerebral palsy (CP) is a nonprogressive, early-onset neurodevelopmental disorder affecting ∼2 to 3/1,000 children worldwide. It is characterized by movement/postural disabilities accompanied by sensitive, perceptual, cognitive, communicational, behavioral, and musculoskeletal perturbations. Many CP patients are thought to have genetic etiologies overlapping those of other neurodevelopmental conditions. Herein, we reported a newly discovered case (the 36th case to date) of a female patient (misdiagnosed with CP until age 19) with the rare X-linked intellectual disability syndrome resulting from an int22h1/int22h2-mediated Xq28 duplication. A microarray analysis revealed a ∼0.4 Mb duplication within the 154.1 to 154.6 Mb subregion of Xq28 (hg19, CRCh37), confirming a diagnosis of the rare int22h1/int22h2-mediated Xq28 duplication intellectual disability syndrome. Atypical T2 hyperintensities were also observed. This case report builds upon the limited cohort of X-linked intellectual disability syndrome patients and reiterates the growing observations pertaining to the phenotypic overlap between genetic CP cases and other neurodevelopmental disorders.

Cerebral Palsy in Child Neurology and Neurodevelopmental Disabilities Training: An Unmet Need

BACKGROUND

Cerebral palsy (CP) is the most common cause of childhood motor disability. However, there is limited guidance on training of child neurologists and neurodevelopmental disability specialists in the care of individuals with cerebral palsy. We sought to determine training program directors' impressions of the importance and adequacy of training in the diagnosis and management of cerebral palsy.

METHODS

In this cross-sectional study, all 82 child neurology and neurodevelopmental disability program directors were asked to complete a survey querying program characteristics, aspects of training in cerebral palsy, importance of cerebral palsy training, and perceived competence at graduation in cerebral palsy care.

RESULTS

There were 35 responses (43% response rate). Nearly all program directors (91%) reported "learning to diagnose cerebral palsy" as very important, and most (71%) felt that "learning to manage cerebral palsy" was very important. Although most program directors reported trainees to be very or extremely competent in cerebral palsy diagnosis (77%), only 43% of program directors felt that trainees were very or extremely competent in cerebral palsy management. Time spent with cerebral palsy faculty was associated with higher reported competence in cerebral palsy diagnosis (P = .03) and management (P < .01). The presence of a cerebral palsy clinic was associated with higher reported competence in cerebral palsy management (P = .03).

CONCLUSIONS

Child neurology and neurodevelopmental disability program directors reported that training in cerebral palsy is important for residents; however, a significant proportion felt that residents were not very well prepared to manage cerebral palsy. The development of cerebral palsy curricula and exposure to cerebral palsy clinics may improve training, translating to better care of individuals with cerebral palsy.

Variants in Mitochondrial ATP Synthase Cause Variable Neurologic Phenotypes

OBJECTIVE

ATP synthase (ATPase) is responsible for the majority of ATP production. Nevertheless, disease phenotypes associated with mutations in ATPase subunits are extremely rare. We aimed at expanding the spectrum of ATPase-related diseases.

METHODS

Whole-exome sequencing in cohorts with 2,962 patients diagnosed with mitochondrial disease and/or dystonia and international collaboration were used to identify deleterious variants in ATPase-encoding genes. Findings were complemented by transcriptional and proteomic profiling of patient fibroblasts. ATPase integrity and activity were assayed using cells and tissues from 5 patients.

RESULTS

We present 10 total individuals with biallelic or de novo monoallelic variants in nuclear ATPase subunit genes. Three unrelated patients showed the same homozygous missense ATP5F1E mutation (including one published case). An intronic splice-disrupting alteration in compound heterozygosity with a nonsense variant in ATP5PO was found in one patient. Three patients had de novo heterozygous missense variants in ATP5F1A, whereas another 3 were heterozygous for ATP5MC3 de novo missense changes. Bioinformatics methods and populational data supported the variants' pathogenicity. Immunohistochemistry, proteomics, and/or immunoblotting revealed significantly reduced ATPase amounts in association to ATP5F1E and ATP5PO mutations. Diminished activity and/or defective assembly of ATPase was demonstrated by enzymatic assays and/or immunoblotting in patient samples bearing ATP5F1A-p.Arg207His, ATP5MC3-p.Gly79Val, and ATP5MC3-p.Asn106Lys. The associated clinical profiles were heterogeneous, ranging from hypotonia with spontaneous resolution (1/10) to epilepsy with early death (1/10) or variable persistent abnormalities, including movement disorders, developmental delay, intellectual disability, hyperlactatemia, and other neurologic and systemic features. Although potentially reflecting an ascertainment bias, dystonia was common (7/10).

INTERPRETATION

Our results establish evidence for a previously unrecognized role of ATPase nuclear-gene defects in phenotypes characterized by neurodevelopmental and neurodegenerative features. ANN NEUROL 2022;91:225-237.

Mendelian etiologies identified with whole exome sequencing in cerebral palsy

Objectives

Cerebral palsy (CP) is the most common childhood motor disability, yet its link to single‐gene disorders is under‐characterized. To explore the genetic landscape of CP, we conducted whole exome sequencing (WES) in a cohort of patients with CP.

Methods

We performed comprehensive phenotyping and WES on a prospective cohort of individuals with cryptogenic CP (who meet criteria for CP; have no risk factors), non‐cryptogenic CP (who meet criteria for CP; have at least one risk factor), and CP masqueraders (who could be diagnosed with CP, but have regression/progressive symptoms). We characterized motor phenotypes, ascertained medical comorbidities, and classified brain MRIs. We analyzed WES data using an institutional pipeline.

Results

We included 50 probands in this analysis (20 females, 30 males). Twenty‐four had cryptogenic CP, 20 had non‐cryptogenic CP, five had CP masquerader classification, and one had unknown classification. Hypotonic‐ataxic subtype showed a difference in prevalence across the classification groups (p = 0.01). Twenty‐six percent of participants (13/50) had a pathogenic/likely pathogenic variant in 13 unique genes (ECHS1, SATB2, ZMYM2, ADAT3, COL4A1, THOC2, SLC16A2, SPAST, POLR2A, GNAO1, PDHX, ACADM, ATL1), including one patient with two genetic disorders (ACADM, PDHX) and two patients with a SPAST‐related disorder. The CP masquerader category had the highest diagnostic yield (n = 3/5, 60%), followed by the cryptogenic CP category (n = 7/24, 29%). Fifteen percent of patients with non‐cryptogenic CP (n = 3/20) had a Mendelian disorder on WES.

Interpretation

WES demonstrated a significant prevalence of Mendelian disorders in individuals clinically diagnosed with CP, including in individuals with known CP risk factors.

How can same-gene mutations promote both cancer and developmental disorders?

The question of how same-gene mutations can drive both cancer and neurodevelopmental disorders has been puzzling. It has also been puzzling why those with neurodevelopmental disorders have a high risk of cancer. Ras, MEK, PI3K, PTEN, and SHP2 are among the oncogenic proteins that can harbor mutations that encode diseases other than cancer. Understanding why some of their mutations can promote cancer, whereas others promote neurodevelopmental diseases, and why even the same mutations may promote both phenotypes, has important clinical ramifications. Here, we review the literature and address these tantalizing questions. We propose that cell type–specific expression of the mutant protein, and of other proteins in the respective pathway, timing of activation (during embryonic development or sporadic emergence), and the absolute number of molecules that the mutations activate, alone or in combination, are pivotal in determining the pathological phenotypes—cancer and (or) developmental disorders.

The phenotypic spectrum of PCDH12 associated disorders - Five new cases and review of the literature

PCDH12 is a member of the non-clustered protocadherin family of calcium-dependent cell adhesion proteins, which are involved in the regulation of brain development and endothelial adhesion. To date, only 15 families have been reported with PCDH12 associated disease. The main features previously associated with PCDH12 deficiency are developmental delay, movement disorder, epilepsy, microcephaly, visual impairment, midbrain malformations, and intracranial calcifications. Here, we report novel clinical features such as onset of epilepsy after infancy, episodes of transient developmental regression, and dysplasia of the medulla oblongata associated with three different novel truncating PCDH12 mutations in five cases (three children, two adults) from three unrelated families. Interestingly, our data suggests a clinical overlap with interferonopathies, and we show an elevated interferon score in two pediatric patients. This case series expands the genetic and phenotypic spectrum of PCDH12 associated diseases and highlights the broad clinical variability.

Genetic testing in individuals with cerebral palsy

AIM To determine which patients with cerebral palsy (CP) should undergo genetic testing, we compared the rate of likely causative genetic variants from whole-exome sequencing in individuals with and without environmental risk factors. METHOD Patients were part of a convenience and physician-referred cohort recruited from a single medical center, and research whole-exome sequencing was completed. Participants were evaluated for the following risk factors: extreme preterm birth, brain bleed or stroke, birth asphyxia, brain malformations, and intrauterine infection. RESULTS A total of 151 unrelated individuals with CP (81 females, 70 males; mean age 25y 7mo [SD 17y 5mo], range 3wks-72y) participated. Causative genetic variants were identified in 14 participants (9.3%). There was no significant difference in diagnostic rate between individuals with risk factors (10 out of 123; 8.1%) and those without (4 out of 28; 14.3%) (Fisher's exact p=0.3). INTERPRETATION While the rate of genetic diagnoses among individuals without risk factors was higher than those with risk factors, the difference was not statistically significant at this sample size. The identification of genetic diagnoses in over 8% of cases with risk factors suggests that these might confer susceptibility to environmental factors, and that further research should include individuals with risk factors. What this paper adds There is no significant difference in diagnostic rate between individuals with and without risk factors. Genetic variants may confer susceptibility to environmental risk factors. Six causative variants were identified in genes not previously associated with cerebral palsy. Global developmental delay/intellectual disability is positively associated with a genetic etiology. Extreme preterm birth, stroke/brain hemorrhage, and older age are negatively associated with a genetic etiology.

Hereditary spastic paraplegia initially diagnosed as cerebral palsy

Introduction

Spastic diplegia presenting in infancy is common to both cerebral palsy (CP) and hereditary spastic paraplegia (HSP). We report the clinical and genetic features of a cohort of Alberta patients with a diagnosis of HSP, who were initially diagnosed with CP.

Methods

Fourteen patients with an initial diagnosis of CP were identified from an Alberta registry of HSP patients via chart review. Whole exome sequencing (WES) was performed to identify genetic causes.

Results

From 90 families in the database, individuals in 29 families had a pediatric presentation of spasticity, with 20 presenting under 3 years of age. Individuals from 14 families had received an initial diagnosis of CP and correct diagnosis was made after neurogenetic assessment due to symptom progression. All had early onset (<3 years) of symptoms. WES identified pathogenic or likely pathogenic mutations in nine cases involving six genes: ATL1, PLP1, PNPLA6, SACS, SPAST, and SYNE1. In five families, WES did not reveal a genetic etiology but progression of symptoms and positive family history suggests HSP is the most likely diagnosis.

Conclusion

In our cohort, 70% of HSP children presenting with spasticity under 3 years had been misdiagnosed with CP. In a young child presenting with spastic diplegia without clear history of prematurity, intrauterine growth restriction, infection or vascular insult, it is important to consider HSP. Accurate diagnosis has implications for prognosis, management, and recurrence risk.

An Emerging Role for Epigenetics in Cerebral Palsy

Cerebral palsy is a set of common, severe, motor disabilities categorized by a static, nondegenerative encephalopathy arising in the developing brain and associated with deficits in movement, posture, and activity. Spastic CP, which is the most common type, involves high muscle tone and is associated with altered muscle function including poor muscle growth and contracture, increased extracellular matrix deposition, microanatomic disruption, musculoskeletal deformities, weakness, and difficult movement control. These muscle-related manifestations of CP are major causes of progressive debilitation and frequently require intensive surgical and therapeutic intervention to control. Current clinical approaches involve sophisticated consideration of biomechanics, radiologic assessments, and movement analyses, but outcomes remain difficult to predict. There is a need for more precise and personalized approaches involving omics technologies, data science, and advanced analytics. An improved understanding of muscle involvement in spastic CP is needed. Unfortunately, the fundamental mechanisms and molecular pathways contributing to altered muscle function in spastic CP are only partially understood. In this review, we outline evidence supporting the emerging hypothesis that epigenetic phenomena play significant roles in musculoskeletal manifestations of CP.

Systematic Analysis of Brain MRI Findings in Adaptor Protein Complex 4-Associated Hereditary Spastic Paraplegia

BACKGROUND AND OBJECTIVES

AP-4-associated hereditary spastic paraplegia (AP-4-HSP: SPG47, SPG50, SPG51, SPG52) is an emerging cause of childhood-onset hereditary spastic paraplegia and mimic of cerebral palsy. This study aims to define the spectrum of brain MRI findings in AP-4-HSP and to investigate radioclinical correlations.

METHODS

We performed a systematic qualitative and quantitative analysis of 107 brain MRI studies from 76 individuals with genetically confirmed AP-4-HSP and correlation with clinical findings including surrogates of disease severity.

RESULTS

We define AP-4-HSP as a disorder of gray and white matter and demonstrate that abnormal myelination is common and that metrics of reduced white matter volume correlate with severity of motor symptoms. We identify a common diagnostic imaging signature consisting of (1) a thin splenium of the corpus callosum, (2) an absent or thin anterior commissure, (3) characteristic signal abnormalities of the forceps minor ("ears of the grizzly sign"), and (4) periventricular white matter abnormalities. The presence of 2 or more of these findings has a sensitivity of ∼99% for detecting AP-4-HSP; the combination of all 4 is found in ∼45% of cases. Compared to other HSPs with a thin corpus callosum, the absent anterior commissure appears to be specific to AP-4-HSP. Our analysis identified a subset of patients with polymicrogyria, underscoring the role of AP-4 in early brain development. These patients displayed a higher prevalence of seizures and status epilepticus, many at a young age.

DISCUSSION

Our findings define the MRI spectrum of AP-4-HSP, providing opportunities for early diagnosis, identification of individuals at risk for complications, and a window into the role of the AP-4 complex in brain development and neurodegeneration.

Placental pathology: Pathways leading to or associated with perinatal brain injury in experimental neurology, special issue: Placental mediated mechanisms of perinatal brain injury

Perinatal brain injury is a multifactorial process. In utero placental physiology plays a major role in neuroprotection and the normal development of the fetal central nervous system. Advances in placental pathology have clarified several specific mechanisms of injury and the histologic lesions most strongly associated with them. This review provides an updated summary of the relevant placental anatomy and physiology, the specific placental pathways leading to brain injury, the revised Amsterdam classification system for placental pathology, and the known associations of specific placental lesions with subtypes of adverse neurologic outcomes.

Yield of clinically reportable genetic variants in unselected cerebral palsy by whole genome sequencing

Cerebral palsy (CP) is the most common cause of childhood physical disability, with incidence between 1/500 and 1/700 births in the developed world. Despite increasing evidence for a major contribution of genetics to CP aetiology, genetic testing is currently not performed systematically. We assessed the diagnostic rate of genome sequencing (GS) in a clinically unselected cohort of 150 singleton CP patients, with CP confirmed at >4 years of age. Clinical grade GS was performed on the proband and variants were filtered, and classified according to American College of Medical Genetics and Genomics–Association for Molecular Pathology (ACMG-AMP) guidelines. Variants classified as pathogenic or likely pathogenic (P/LP) were further assessed for their contribution to CP. In total, 24.7% of individuals carried a P/LP variant(s) causing or increasing risk of CP, with 4.7% resolved by copy number variant analysis and 20% carrying single nucleotide or indel variants. A further 34.7% carried one or more rare, high impact variants of uncertain significance (VUS) in variation intolerant genes. Variants were identified in a heterogeneous group of genes, including genes associated with hereditary spastic paraplegia, clotting and thrombophilic disorders, small vessel disease, and other neurodevelopmental disorders. Approximately 1/2 of individuals were classified as likely to benefit from changed clinical management as a result of genetic findings. In addition, no significant association between genetic findings and clinical factors was detectable in this cohort, suggesting that systematic sequencing of CP will be required to avoid missed diagnoses.

Genome-Wide Association Study Identifies Genetic Risk Factors for Spastic Cerebral Palsy

BACKGROUND

Although many clinical risk factors of spastic cerebral palsy (CP) have been identified, the genetic basis of spastic CP is largely unknown. Here, using whole-genome genetic information linked to a deidentified electronic health record (BioVU) with replication in the UK Biobank and FinnGen, we perform the first genome-wide association study (GWAS) for spastic CP.

OBJECTIVE

To define the genetic basis of spastic CP.

METHODS

Whole-genome data were obtained using the multi-ethnic genotyping array (MEGA) genotyping array capturing single-nucleotide polymorphisms (SNPs), minor allele frequency (MAF) > 0.01, and imputation quality score (r2) > 0.3, imputed based on the 1000 genomes phase 3 reference panel. Threshold for genome-wide significance was defined after Bonferroni correction for the total number of SNPs tested (P < 5.0 × 10-8). Replication analysis (defined as P < .05) was performed in the UK Biobank and FinnGen.

RESULTS

We identify 1 SNP (rs78686911) reaching genome-wide significance with spastic CP. Expression quantitative trait loci (eQTL) analysis suggests that rs78686911 decreases expression of GRIK4, a gene that encodes a high-affinity kainate glutamatergic receptor of largely unknown function. Replication analysis in the UK Biobank and FinnGen reveals additional SNPs in the GRIK4 loci associated with CP.

CONCLUSION

To our knowledge, we perform the first GWAS of spastic CP. Our study indicates that genetic variation contributes to CP risk.

Biallelic loss-of-function variants in the splicing regulator NSRP1 cause a severe neurodevelopmental disorder with spastic cerebral palsy and epilepsy

PURPOSE

Alternative splicing plays a critical role in mouse neurodevelopment, regulating neurogenesis, cortical lamination, and synaptogenesis, yet few human neurodevelopmental disorders are known to result from pathogenic variation in splicing regulator genes. Nuclear Speckle Splicing Regulator Protein 1 (NSRP1) is a ubiquitously expressed splicing regulator not known to underlie a Mendelian disorder.

METHODS

Exome sequencing and rare variant family-based genomics was performed as a part of the Baylor-Hopkins Center for Mendelian Genomics Initiative. Additional families were identified via GeneMatcher.

RESULTS

We identified six patients from three unrelated families with homozygous loss-of-function variants in NSRP1. Clinical features include developmental delay, epilepsy, variable microcephaly (Z-scores -0.95 to -5.60), hypotonia, and spastic cerebral palsy. Brain abnormalities included simplified gyral pattern, underopercularization, and/or vermian hypoplasia. Molecular analysis identified three pathogenic NSRP1 predicted loss-of-function variant alleles: c.1359_1362delAAAG (p.Glu455AlafsTer20), c.1272dupG (p.Lys425GlufsTer5), and c.52C>T (p.Gln18Ter). The two frameshift variants result in a premature termination codon in the last exon, and the mutant transcripts are predicted to escape nonsense mediated decay and cause loss of a C-terminal nuclear localization signal required for NSRP1 function.

CONCLUSION

We establish NSRP1 as a gene for a severe autosomal recessive neurodevelopmental disease trait characterized by developmental delay, epilepsy, microcephaly, and spastic cerebral palsy.

Resistance to Neuromuscular Blockade by Rocuronium in Surgical Patients with Spastic Cerebral Palsy

Individuals with spastic cerebral palsy (CP) often exhibit altered sensitivities to neuromuscular blocking agents (NMBAs) used for surgical intubation. We assessed usage of the NMBA rocuronium in patients with spastic CP and evaluated potential modifiers of dosing including gross motor function classification system (GMFCS) level, birthweight, gestational age, and the use of anticonvulsant therapy. In a case-control study, surgical patients with spastic CP (n = 64) or with idiopathic or non-neuromuscular conditions (n = 73) were enrolled after informed consent/assent. Patient data, GMFCS level, anticonvulsant use, and rocuronium dosing for intubation and post-intubation neuromuscular blockade were obtained from medical records. Findings reveal participants with CP required more rocuronium per body weight for intubation than controls (1.00 ± 0.08 versus 0.64 ± 0.03 mg/kg; p < 0.0001). Dosing increased with GMFCS level (Spearman's rho = 0.323; p = 0.005), and participants with moderate to severe disability (GMFCS III-V) had elevated rocuronium with (1.21 ± 0.13 mg/kg) or without (0.86 ± 0.09 mg/kg) concurrent anticonvulsant therapy. Children born full-term or with birthweight >2.5 kg in the CP cohort required more rocuronium than preterm and low birthweight counterparts. Individuals with CP exhibited highly varied and significant resistance to neuromuscular blockade with rocuronium that was related to GMFCS and gestational age and weight at birth.

DIAPH1 Variants in Non-East Asian Patients With Sporadic Moyamoya Disease

Importance

Moyamoya disease (MMD), a progressive vasculopathy leading to narrowing and ultimate occlusion of the intracranial internal carotid arteries, is a cause of childhood stroke. The cause of MMD is poorly understood, but genetic factors play a role. Several familial forms of MMD have been identified, but the cause of most cases remains elusive, especially among non-East Asian individuals.

Objective

To assess whether ultrarare de novo and rare, damaging transmitted variants with large effect sizes are associated with MMD risk.

Design, Setting, and Participants

A genetic association study was conducted using whole-exome sequencing case-parent MMD trios in a small discovery cohort collected over 3.5 years (2016-2019); data were analyzed in 2020. Medical records from US hospitals spanning a range of 1 month to 1.5 years were reviewed for phenotyping. Exomes from a larger validation cohort were analyzed to identify additional rare, large-effect variants in the top candidate gene. Participants included patients with MMD and, when available, their parents. All participants who met criteria and were presented with the option to join the study agreed to do so; none were excluded. Twenty-four probands (22 trios and 2 singletons) composed the discovery cohort, and 84 probands (29 trios and 55 singletons) composed the validation cohort.

Main Outcomes and Measures

Gene variants were identified and filtered using stringent criteria. Enrichment and case-control tests assessed gene-level variant burden. In silico modeling estimated the probability of variant association with protein structure. Integrative genomics assessed expression patterns of MMD risk genes derived from single-cell RNA sequencing data of human and mouse brain tissue.

Results

Of the 24 patients in the discovery cohort, 14 (58.3%) were men and 18 (75.0%) were of European ancestry. Three of 24 discovery cohort probands contained 2 do novo (1-tailed Poisson P = 1.1 × 10-6) and 1 rare, transmitted damaging variant (12.5% of cases) in DIAPH1 (mammalian diaphanous-1), a key regulator of actin remodeling in vascular cells and platelets. Four additional ultrarare damaging heterozygous DIAPH1 variants (3 unphased) were identified in 3 other patients in an 84-proband validation cohort (73.8% female, 77.4% European). All 6 patients were non-East Asian. Compound heterozygous variants were identified in ena/vasodilator-stimulated phosphoproteinlike protein EVL, a mammalian diaphanous-1 interactor that regulates actin polymerization. DIAPH1 and EVL mutant probands had severe, bilateral MMD associated with transfusion-dependent thrombocytopenia. DIAPH1 and other MMD risk genes are enriched in mural cells of midgestational human brain. The DIAPH1 coexpression network converges in vascular cell actin cytoskeleton regulatory pathways.

Conclusions and Relevance

These findings provide the largest collection to date of non-East Asian individuals with sporadic MMD harboring pathogenic variants in the same gene. The results suggest that DIAPH1 is a novel MMD risk gene and impaired vascular cell actin remodeling in MMD pathogenesis, with diagnostic and therapeutic ramifications.

Mutation in ZDHHC15 Leads to Hypotonic Cerebral Palsy, Autism, Epilepsy, and Intellectual Disability

Objective

To determine whether mutations reported for ZDHHC15 can cause mixed neurodevelopmental disorders, we performed both functional studies on variant pathogenicity and ZDHHC15 function in animal models.

Methods

We examined protein function of 4 identified variants in ZDHHC15 in a yeast complementation assay and locomotor defects of loss-of-function genotypes in a Drosophila model.

Results

Although we assessed multiple patient variants, only 1 (p.H158R) affected protein function. We report a patient with a diagnosis of hypotonic cerebral palsy, autism, epilepsy, and intellectual disability associated with this bona fide damaging X-linked variant. Features include tall forehead with mild brachycephaly, down-slanting palpebral fissures, large ears, long face, facial muscle hypotonia, high-arched palate with dental crowding, and arachnodactyly. The patient had mild diminished cerebral volume, with left-sided T2/FLAIR hyperintense periatrial ovoid lesion. We found that loss-of-function mutations in orthologs of this gene cause flight and coordinated movement defects in Drosophila.

Conclusions

Our findings support a functional expansion of this gene to a role in motor dysfunction. Although ZDHHC15 mutations represent a rare cause of neurodevelopmental disability, candidate variants need to be carefully assessed before pathogenicity can be determined.

Diagnostic yield of chromosomal microarray and trio whole exome sequencing in cryptogenic cerebral palsy

OBJECTIVE

To determine the yield of genetic diagnoses using chromosomal microarray (CMA) and trio whole exome sequencing (WES), separately and combined, among patients with cryptogenic cerebral palsy (CP).

METHODS

Trio WES of patients with prior CMA analysis for cryptogenic CP, defined as disabling, non-progressive motor symptoms beginning before the age of 3 years without known cause.

RESULTS

Given both CMA analysis and trio WES, clinically significant genetic findings were identified for 58% of patients (26 of 45). Diagnoses were eight large CNVs detected by CMA and 18 point mutations detected by trio WES. None had more than one severe mutation. Approximately half of events (14 of 26) were de novo. Yield was significantly higher in patients with CP with comorbidities (69%, 22 of 32) than in those with pure motor CP (31%, 4 of 13; p=0.02). Among patients with genetic diagnoses, CNVs were more frequent than point mutations among patients with congenital anomalies (OR 7.8, 95% CI 1.2 to 52.4) or major dysmorphic features (OR 10.5, 95% CI 1.4 to 73.7). Clinically significant mutations were identified in 18 different genes: 14 with known involvement in CP-related disorders and 4 responsible for other neurodevelopmental conditions. Three possible new candidate genes for CP were ARGEF10, RTF1 and TAOK3.

CONCLUSIONS

Cryptogenic CP is genetically highly heterogeneous. Genomic analysis has a high yield and is warranted in all these patients. Trio WES has higher yield than CMA, except in patients with congenital anomalies or major dysmorphic features, but these methods are complementary. Patients with negative results with one approach should also be tested by the other.

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.

Variant recurrence confirms the existence of a FBXO31-related spastic-dystonic cerebral palsy syndrome

The role of genetics in the causation of cerebral palsy has become the focus of many studies aiming to unravel the heterogeneous etiology behind this frequent neurodevelopmental disorder. A recent paper reported two unrelated children with a clinical diagnosis of cerebral palsy, who carried the same de novo c.1000G > A (p.Asp334Asn) variant in FBXO31, encoding a widely studied tumor suppressor not previously implicated in monogenic disease. We now identified a third individual with the recurrent FBXO31 de novo missense variant, featuring a spastic-dystonic phenotype. Our data confirm a link between variant FBXO31 and an autosomal dominant neurodevelopmental disorder characterized by prominent motor dysfunction.

Adults with Cerebral Palsy Require Ongoing Neurologic Care: A Systematic Review

Cerebral palsy (CP) neurologic care and research efforts typically focus on children. However, most people with CP are adults. Adults with CP are at increased risk of new neurologic conditions, such as stroke and myelopathy, that require ongoing neurologic surveillance to distinguish them from baseline motor impairments. Neurologic factors could also contribute to the motor function decline, chronic pain, and chronic fatigue that are commonly experienced by adults with CP. Based on a systematic literature review, we suggest (1) guidelines for neurologic surveillance and neurologist referral and (2) clinical research questions regarding the evolving neurologic risks for adults with CP. ANN NEUROL 2021;89:860-871.

Genetic Testing in Neurodevelopmental Disorders

Neurodevelopmental disorders are the most prevalent chronic medical conditions encountered in pediatric primary care. In addition to identifying appropriate descriptive diagnoses and guiding families to evidence-based treatments and supports, comprehensive care for individuals with neurodevelopmental disorders includes a search for an underlying etiologic diagnosis, primarily through a genetic evaluation. Identification of an underlying genetic etiology can inform prognosis, clarify recurrence risk, shape clinical management, and direct patients and families to condition-specific resources and supports. Here we review the utility of genetic testing in patients with neurodevelopmental disorders and describe the three major testing modalities and their yields - chromosomal microarray, exome sequencing (with/without copy number variant calling), and FMR1 CGG repeat analysis for fragile X syndrome. Given the diagnostic yield of genetic testing and the potential for clinical and personal utility, there is consensus that genetic testing should be offered to all patients with global developmental delay, intellectual disability, and/or autism spectrum disorder. Despite this recommendation, data suggest that a minority of children with autism spectrum disorder and intellectual disability have undergone genetic testing. To address this gap in care, we describe a structured but flexible approach to facilitate integration of genetic testing into clinical practice across pediatric specialties and discuss future considerations for genetic testing in neurodevelopmental disorders to prepare pediatric providers to care for patients with such diagnoses today and tomorrow.

Molecular Diagnostic Yield of Exome Sequencing in Patients With Cerebral Palsy

IMPORTANCE

Cerebral palsy is a common neurodevelopmental disorder affecting movement and posture that often co-occurs with other neurodevelopmental disorders. Individual cases of cerebral palsy are often attributed to birth asphyxia; however, recent studies indicate that asphyxia accounts for less than 10% of cerebral palsy cases.

OBJECTIVE

To determine the molecular diagnostic yield of exome sequencing (prevalence of pathogenic and likely pathogenic variants) in individuals with cerebral palsy.

DESIGN, SETTING, AND PARTICIPANTS

A retrospective cohort study of patients with cerebral palsy that included a clinical laboratory referral cohort with data accrued between 2012 and 2018 and a health care-based cohort with data accrued between 2007 and 2017.

EXPOSURES

Exome sequencing with copy number variant detection.

MAIN OUTCOMES AND MEASURES

The primary outcome was the molecular diagnostic yield of exome sequencing.

RESULTS

Among 1345 patients from the clinical laboratory referral cohort, the median age was 8.8 years (interquartile range, 4.4-14.7 years; range, 0.1-66 years) and 601 (45%) were female. Among 181 patients in the health care-based cohort, the median age was 41.9 years (interquartile range, 28.0-59.6 years; range, 4.8-89 years) and 96 (53%) were female. The molecular diagnostic yield of exome sequencing was 32.7% (95% CI, 30.2%-35.2%) in the clinical laboratory referral cohort and 10.5% (95% CI, 6.0%-15.0%) in the health care-based cohort. The molecular diagnostic yield ranged from 11.2% (95% CI, 6.4%-16.2%) for patients without intellectual disability, epilepsy, or autism spectrum disorder to 32.9% (95% CI, 25.7%-40.1%) for patients with all 3 comorbidities. Pathogenic and likely pathogenic variants were identified in 229 genes (29.5% of 1526 patients); 86 genes were mutated in 2 or more patients (20.1% of 1526 patients) and 10 genes with mutations were independently identified in both cohorts (2.9% of 1526 patients).

CONCLUSIONS AND RELEVANCE

Among 2 cohorts of patients with cerebral palsy who underwent exome sequencing, the prevalence of pathogenic and likely pathogenic variants was 32.7% in a cohort that predominantly consisted of pediatric patients and 10.5% in a cohort that predominantly consisted of adult patients. Further research is needed to understand the clinical implications of these findings.

Variability in Cerebral Palsy Diagnosis

BACKGROUND

Cerebral palsy (CP) is the most common childhood motor disability. The emergence of genetic CP etiologies, variable inclusion of hypotonic CP in international registries, and involvement of different medical disciplines in CP diagnosis can promote diagnostic variability. This variability could adversely affect patients' understanding of their symptoms and access to care. Therefore, we sought to determine the presence and extent of practice variability in CP diagnosis.

METHODS

We surveyed physicians in the United States and Canada interested in CP on the basis of membership in the American Academy of Cerebral Palsy and Developmental Medicine or the Child Neurology Society Neonatal Neurology, Movement Disorders, or Neurodevelopmental Disabilities Special Interest Groups. The survey included the 2007 consensus definition of CP and 4 hypothetical case scenarios.

RESULTS

Of 695 contacted physicians, 330 (47%) completed the survey. Two scenarios yielded consensus: (1) nonprogressive spastic diplegia after premature birth with periventricular leukomalacia on brain MRI (96% would diagnose CP) and (2) progressive spastic diplegia (92% would not diagnose CP). Scenarios featuring genetic etiologies or hypotonia as the cause of nonprogressive motor disability yielded variability: only 46% to 67% of practitioners would diagnose CP in these settings.

CONCLUSIONS

There is practice variability in whether a child with a nonprogressive motor disability due to a genetic etiology or generalized hypotonia will be diagnosed with CP. This variability occurred despite anchoring questions with the 2007 consensus definition of CP. On the basis of these results, we have suggested ways to reduce diagnostic variability, including clarification of the consensus definition.

Insights From Genetic Studies of Cerebral Palsy

Cohort-based whole exome and whole genome sequencing and copy number variant (CNV) studies have identified genetic etiologies for a sizable proportion of patients with cerebral palsy (CP). These findings indicate that genetic mutations collectively comprise an important cause of CP. We review findings in CP genomics and propose criteria for CP-associated genes at the level of gene discovery, research study, and clinical application. We review the published literature and report 18 genes and 5 CNVs from genomics studies with strong evidence of for the pathophysiology of CP. CP-associated genes often disrupt early brain developmental programming or predispose individuals to known environmental risk factors. We discuss the overlap of CP-associated genes with other neurodevelopmental disorders and related movement disorders. We revisit diagnostic criteria for CP and discuss how identification of genetic etiologies does not preclude CP as an appropriate diagnosis. The identification of genetic etiologies improves our understanding of the neurobiology of CP, providing opportunities to study CP pathogenesis and develop mechanism-based interventions.