Diagnostic Yield of Exome Sequencing in Cerebral Palsy and Implications for Genetic Testing Guidelines: A Systematic Review and Meta-analysis

Genetic pathways in cerebral palsy: a review of the implications for precision diagnosis and understanding disease mechanisms

ABSTRACT

Cerebral palsy is a diagnostic term utilized to describe a group of permanent disorders affecting movement and posture. Patients with cerebral palsy are often only capable of limited activity, resulting from non-progressive disturbances in the fetal or neonatal brain. These disturbances severely impact the child's daily life and impose a substantial economic burden on the family. Although cerebral palsy encompasses various brain injuries leading to similar clinical outcomes, the understanding of its etiological pathways remains incomplete owing to its complexity and heterogeneity. This review aims to summarize the current knowledge on the genetic factors influencing cerebral palsy development. It is now widely acknowledged that genetic mutations and alterations play a pivotal role in cerebral palsy development, which can be further influenced by environmental factors. Despite continuous research endeavors, the underlying factors contributing to cerebral palsy remain are still elusive. However, significant progress has been made in genetic research that has markedly enhanced our comprehension of the genetic factors underlying cerebral palsy development. Moreover, these genetic factors have been categorized based on the identified gene mutations in patients through clinical genotyping, including thrombosis, angiogenesis, mitochondrial and oxidative phosphorylation function, neuronal migration, and cellular autophagy. Furthermore, exploring targeted genotypes holds potential for precision treatment. In conclusion, advancements in genetic research have substantially improved our understanding of the genetic causes underlying cerebral palsy. These breakthroughs have the potential to pave the way for new treatments and therapies, consequently shaping the future of cerebral palsy research and its clinical management. The investigation of cerebral palsy genetics holds the potential to significantly advance treatments and management strategies. By elucidating the underlying cellular mechanisms, we can develop targeted interventions to optimize outcomes. A continued collaboration between researchers and clinicians is imperative to comprehensively unravel the intricate genetic etiology of cerebral palsy.

Cerebral Palsy: A Current Perspective

Cerebral palsy (CP) is the most common cause of motor disability in children. Insults to the brain at different times lead to diverse injuries. As a result, CP is an extremely heterogeneous clinical diagnosis, presenting differently in each individual and at various ages. With improving survival rates of preterm newborns, increasing active resuscitation of extremely preterm newborns, and widespread availability of extensive genetic testing soon after birth, it is imperative to focus on earlier diagnosis and long-term outcomes of CP. CP is primarily classified into 4 categories based on type of motor impairment, functional ability, distribution, and etiology. As the understanding of CP has evolved significantly in the last 2 decades, the methods of early detection of CP have consequently advanced. Appropriate diagnosis is essential for proper education and counseling of affected families, and introduction of therapeutic interventions as early as possible. In this review, we focus on early brain development and provide an overview of the etiology, classification, diagnosis, early therapeutic options, and prognosis of CP.

Etiology and Ontogeny of Cerebral Palsy: Implications for Practice and Research

Cerebral palsy (CP) has been recognized as a group of neurologic disorders with varying etiologies and ontogenies. While a percentage of CP cases arises during labor, the expanded use of electronic fetal monitoring (EFM) to include prevention of CP has resulted in decades of vastly increased interventions that have not significantly reduced the incidence of CP for infants born at term in the USA. Litigation alleging that poor obstetrical practice caused CP in most of these affected children has led to contentious arguments regarding the actual etiologies of this condition and often resulted in substantial monetary awards for plaintiffs. Recent advances in genetic testing using whole exome sequencing have revealed that at least one-third of CP cases in term infants are genetic in origin and therefore not labor-related. Here, we will present and discuss previous attempts to sort out contributing etiologies and ontogenies of CP, and how these newer diagnostic techniques are rapidly improving our ability to better detect and understand such cases. In light of these developments, we present our vision for an overarching spectrum for proper categorization of CP cases into that the following groups: (1) those begun at conception from genetic causes (nonpreventable); (2) those stemming from adverse antenatal/pre-labor events (possibly preventable with heightened antepartum assessment); (3) Those arising from intrapartum events (potentially preventable by earlier interventions); (4) Those occurring shortly after birth (possibly preventable with closer neonatal monitoring); (5) Those that appear later in the postnatal period from non-labor-related causes such as untreated infections or postnatal intracranial hemorrhages.

Exome sequencing reveals genetic heterogeneity and clinically actionable findings in children with cerebral palsy

Cerebral palsy (CP) is the most common motor disability in children. To ascertain the role of major genetic variants in the etiology of CP, we conducted exome sequencing on a large-scale cohort with clinical manifestations of CP. The study cohort comprised 505 girls and 1,073 boys. Utilizing the current gold standard in genetic diagnostics, 387 of these 1,578 children (24.5%) received genetic diagnoses. We identified 412 pathogenic and likely pathogenic (P/LP) variants across 219 genes associated with neurodevelopmental disorders, and 59 P/LP copy number variants. The genetic diagnostic rate of children with CP labeled at birth with perinatal asphyxia was higher than the rate in children without asphyxia (P = 0.0033). Also, 33 children with CP manifestations (8.5%, 33 of 387) had findings that were clinically actionable. These results highlight the need for early genetic testing in children with CP, especially those with risk factors like perinatal asphyxia, to enable evidence-based medical decision-making.

Clinical characteristics and rehabilitation potential in children with cerebral palsy based on MRI classification system

Background

The correlation of clinical characteristics of cerebral palsy (CP) and the magnetic resonance imaging classification system (MRICS) for (CP) is inconsistent. Specifically, the variance in rehabilitation potential across MRICS remains underexplored.

Aims

To investigate the clinical characteristics and potential for rehabilitation in children with CP based on MRICS.

Materials and methods

Children with CP admitted to the Department of Rehabilitation, Children's Hospital of Chongqing Medical University between 2017 and 2021 were included in the study. Qualified cases underwent a follow-up period of at least one year. The clinical characteristics of CP among different MRICS were analyzed, then the rehabilitation potential was explored by a retrospective cohort study.

Results

Among the 384 initially enrolled children, the male-to-female ratio was 2.3:1, and the median age of diagnosis was 6.5 months (interquartile range: 4-12). The most prevalent MRICS categorization was predominant white matter injury (40.6%), followed by miscellaneous (29.2%) and predominant gray matter injury (15.6%). For the predominant white matter injury and miscellaneous categories, spastic diplegia emerged as the leading subtype of CP, with incidences of 59.6% and 36.6%, respectively, while mixed CP (36.7%) was the most common type in children with predominant gray matter. Notably, 76.4% of children with predominant white matter injury were classified as levels I-III on the gross motor function classification system (GMFCS), indicating significantly less severity than other groups (χ2 = 12.438, p = 0.013). No significant difference across MRICS categories was observed for the manual ability classification system (MACS) (H = 8.176, p = 0.085). Rehabilitation potential regarding fine motor function and adaptability based on Gesell assessment was dependent on MRICS over the follow-up period. Children with normal MRI scans exhibited superior rehabilitation outcomes. Commencing rehabilitation at an earlier stage produced consistent and beneficial results in terms of fine motor function and adaptability across all MRICS categories. Moreover, participants below 2 years of age demonstrated enhanced rehabilitation potential regarding fine motor outcomes and adaptability within the MRICS framework.

Conclusion

MRICS displayed a significant association with clinical characteristics and rehabilitation efficacy in children with CP.

A bibliometric analysis of cerebral palsy from 2003 to 2022

Purpose

This bibliometric study explores cerebral palsy (CP) research from 2003 to 2022 to reveal the topic hotspots and collaborations.

Methods

We retrieved studies on CP from the Web of Science Core Collection from 2003 to 2022 and then used CiteSpace and Bibliometrix to perform a bibliometric analysis and attain knowledge mapping, including publication outputs, funding, journals, authors, institutions, countries/territories, keywords, collaborative relationships, and topic hotspots.

Results

In total, 8,223 articles were published from 2003 to 2022. During this period, the number of publications increased continuously. Developmental Medicine and Child Neurology was the most productive and frequently co-cited journal. Boyd was the most productive and influential author, with 143 publications and 4,011 citations. The United States and Vrije Universiteit Amsterdam were the most productive countries and institutions, respectively. Researchers and institutions from the USA, Australia, and Canada constituted the core research forces, with extensive collaborations worldwide. The most common keywords were gait (553), rehabilitation (440), spasticity (325), botulinum toxin (174), therapy (148), upper extremity (141), quality of life (140), disability (115), pain (98), electromyography (97), kinematics (90), balance (88), participation (85), and walking (79).

Conclusion

This study provides a systematic and comprehensive analysis of the CP-related literature. It reveals that Developmental Medicine and Child Neurology is the most active journal in this field. The USA, Vrije Universiteit Amsterdam, and Boyd are the top countries, institutions, and authors, respectively. Emerging treatment methods, complication management, and functional recovery comprise the future research directions and potential topic hotspots for CP.

Clinical Characteristics Suggestive of a Genetic Cause in Cerebral Palsy: A Systematic Review

BACKGROUND

Cerebral palsy (CP) is a clinical diagnosis and was long categorized as an acquired disorder, but more and more genetic etiologies are being identified. This review aims to identify the clinical characteristics that are associated with genetic CP to aid clinicians in selecting candidates for genetic testing.

METHODS

The PubMed database was systematically searched to identify genes associated with CP. The clinical characteristics accompanying these genetic forms of CP were compared with published data of large CP populations resulting in the identification of potential indicators of genetic CP.

RESULLTS

Of 1930 articles retrieved, 134 were included. In these, 55 CP genes (described in two or more cases, n = 272) and 79 candidate genes (described in only one case) were reported. The most frequently CP-associated genes were PLP1 (21 cases), ARG1 (17 cases), and CTNNB1 (13 cases). Dyskinesia and the absence of spasticity were identified as strong potential indicators of genetic CP. Presence of intellectual disability, no preterm birth, and no unilateral distribution of symptoms were classified as moderate genetic indicators.

CONCLUSIONS

Genetic causes of CP are increasingly identified. The clinical characteristics associated with genetic CP can aid clinicians regarding to which individual with CP to offer genetic testing. The identified potential genetic indicators need to be validated in large CP cohorts but can provide the first step toward a diagnostic algorithm for genetic CP.

Comprehensive whole-genome sequence analyses provide insights into the genomic architecture of cerebral palsy

We performed whole-genome sequencing (WGS) in 327 children with cerebral palsy (CP) and their biological parents. We classified 37 of 327 (11.3%) children as having pathogenic/likely pathogenic (P/LP) variants and 58 of 327 (17.7%) as having variants of uncertain significance. Multiple classes of P/LP variants included single-nucleotide variants (SNVs)/indels (6.7%), copy number variations (3.4%) and mitochondrial mutations (1.5%). The COL4A1 gene had the most P/LP SNVs. We also analyzed two pediatric control cohorts (n = 203 trios and n = 89 sib-pair families) to provide a baseline for de novo mutation rates and genetic burden analyses, the latter of which demonstrated associations between de novo deleterious variants and genes related to the nervous system. An enrichment analysis revealed previously undescribed plausible candidate CP genes (SMOC1, KDM5B, BCL11A and CYP51A1). A multifactorial CP risk profile and substantial presence of P/LP variants combine to support WGS in the diagnostic work-up across all CP and related phenotypes.

A Call for Early Detection of Cerebral Palsy

Cerebral palsy (CP) is the most common physical disability across the lifespan, but historically, CP has not been diagnosed before the age of 2 years. Barriers to early diagnosis ranged from lack of available biomarkers, absence of curative treatments, perceived stigma associated with a lifelong diagnosis, and a desire to rule out other diagnoses first. Most importantly, the fundamental question that remained was whether children would benefit from earlier detection and intervention given the paucity of research. However, evidence-based guidelines published in 2017 demonstrated that the General Movements Assessment, the Hammersmith Infant Neurological Examination, and neuroimaging can be combined with other elements such as a clinical history and standardized motor assessments to provide the highest predictive value for diagnosing CP as early as age 3 months in high-risk newborns. Implementation of these guidelines has been successful in decreasing the age at CP diagnosis, particularly in high-risk infant follow-up clinics with expertise in performing these assessments. Early detection of CP allows for clinical and research opportunities investigating earlier interventions during a critical period of neuroplasticity, with the goal of improving developmental trajectories for children and their families. New guidelines and research are now being developed with a focus on early, targeted interventions that continue to be studied, along with global detection initiatives.

Social Determinants of Genetics Referral and Completion Rates Among Child Neurology Patients

Objective

To investigate clinical, social, and systems-level determinants predictive of genetics clinic referral and completion of genetics clinic visits among child neurology patients.

Methods

Electronic health record data were extracted from patients 0-18 years old who were evaluated in child neurology clinics at a single tertiary care institution between July 2018 to January 2020. Variables aligned with the Health Equity Implementation Framework. Referral and referral completion rates to genetics and cardiology clinics were compared among Black vs White patients using bivariate analysis. Demographic variables associated with genetics clinic referral and visit completion were identified using logistic regressions.

Results

In a cohort of 11,371 child neurology patients, 304 genetics clinic referrals and 82 cardiology clinic referrals were placed. In multivariate analysis of patients with Black or White ethnoracial identity (n=10,601), genetics clinic referral rates did not differ by race, but were significantly associated with younger age, rural address, neurodevelopmental disorder diagnosis, number of neurology clinic visits, and provider type. The only predictors of genetics clinic visit completion number of neurology clinic visits and race/ethnicity, with White patients being twice as likely as Black patients to complete the visit. Cardiology clinic referrals and visit completion did not differ by race/ethnicity.

Interpretation

Although race/ethnicity was not associated with differences in genetics clinic referral rates, White patients were twice as likely as Black patients to complete a genetics clinic visit after referral. Further work is needed to determine whether this is due to systemic/structural racism, differences in attitudes toward genetic testing, or other factors.

Redefining cerebral palsies as a diverse group of neurodevelopmental disorders with genetic aetiology

Cerebral palsy is a clinical descriptor covering a diverse group of permanent, non-degenerative disorders of motor function. Around one-third of cases have now been shown to have an underlying genetic aetiology, with the genetic landscape overlapping with those of neurodevelopmental disorders including intellectual disability, epilepsy, speech and language disorders and autism. Here we review the current state of genomic testing in cerebral palsy, highlighting the benefits for personalized medicine and the imperative to consider aetiology during clinical diagnosis. With earlier clinical diagnosis now possible, we emphasize the opportunity for comprehensive and early genomic testing as a crucial component of the routine diagnostic work-up in people with cerebral palsy.

Uncertainties regarding cerebral palsy diagnosis: opportunities to operationalize the consensus definition

Background and Objectives

Cerebral palsy (CP), the most common motor disability of childhood, is variably diagnosed. We hypothesized that child neurologists and neurodevelopmentalists, often on the frontlines of CP diagnosis in North America, harbor uncertainties regarding the practical application of the most recent CP consensus definition from 2006.

Methods

We conducted a cross-sectional survey of child neurologists and neurodevelopmentalists at the 2022 Child Neurology Society Annual Meeting. Attendees were provided the 2006 CP consensus definition and asked whether they had any uncertainties about the practical application of the definition across four hypothetical clinical vignettes.

Results

Of 230 attendees, 164 responded to the closing survey questions (71%). 145/164 (88%) expressed at least one uncertainty regarding the clinical application of the 2006 definition. Overwhelmingly, these areas of uncertainty focused on: 1) Age, both with regards to the minimum age of diagnosis and the maximum age of brain disturbance or motor symptom onset, (67/164, 41%), and 2) Interpretation of the term "non-progressive" (48/164, 29%). The vast majority of respondents (157/164, 96%) answered 'Yes' to the question: Do you think we should revise the 2006 consensus definition of CP?

Discussion

We propose that the uncertainties we identified could be addressed by operationalizing the 2006 consensus definition to support a more uniform CP diagnosis. To address the most common CP diagnostic uncertainties we identified, we propose 3 points of clarification based on the available literature: 1) Motor symptoms/signs should be present by 2 years old; 2) CP can and should be diagnosed as early as possible, even if activity limitation is not yet present, if motor symptoms/signs can be reasonably predicted to yield activity limitation (e.g. by using standardized examination instruments, Brain MRI, and a suggestive clinical history); and 3) The clinical motor disability phenotype should be non-progressive through 5 years old. We anticipate that operationalizing the 2006 definition of CP in this manner could clarify the uncertainties we identified among child neurologists and neurodevelopmentalists and reduce the diagnostic variability that currently exists.