Neurodevelopmental Trajectories and Psychiatric Morbidity: Lessons Learned From the 22q11.2 Deletion Syndrome

Mainstreaming Diagnostic Genetic Testing and Precision Medicine for Autism Spectrum Disorder: The Role of Child and Adolescent Psychiatrists

Autism Spectrum Disorder (ASD) is a neurodevelopmental psychiatric condition that shares significant clinical and genetic overlap with intellectualdisability (ID) and other neurodevelopmental disorders. Genetic testingin ASD lags far behind that for ID, even though Professional Societiesrecommend genetic testing for all ASD individuals and insurance reimbursement is relatively good. The core competencies for child and adolescent psychiatrists include determining the etiology and diagnosisfor all childhood psychopathology, including ID and ASD. Child psychiatrists should recommend and order genetic testing by exomeor genome sequencing on all children with ASD.

A comprehensive overview of neuropsychiatric symptoms in adolescents with 22q11.2 deletion syndrome

BACKGROUND

The 22q11.2 deletion syndrome (22q11DS) is associated with a variety of neuropsychiatric outcomes that vary across deletion carriers. We adopted a dimensional approach to provide a comprehensive overview of neuropsychiatric symptom expression in adolescents with 22q11DS and further our understanding of the observed phenotypical heterogeneity.

METHODS

Participants were 208 adolescents with 22q11DS between 10 and 19 years old. Semi-structured clinical interviews and IQ tests were used to quantify symptom expression on multiple symptom dimensions, some reflecting DSM-IV diagnostic domains. We investigated symptom expression in those with and without a formal DSM-IV classification and examined between and within symptom dimensions. We used correlation analyses to explore associations between different symptom dimensions.

RESULTS

We demonstrated inter-individual differences in symptom expression, both between and within neuropsychiatric symptom dimensions. On most symptom dimensions, more than 50% of adolescents expressed at least one clinically relevant symptom. In addition, a significant proportion of youth without a formal DSM-IV diagnosis reported clinically relevant symptoms (e.g. >85% of those without an ADHD diagnosis reported ADHD symptoms). The exploratory correlation analysis indicated mostly positive correlations between symptom dimensions.

CONCLUSIONS

The finding that most adolescents with 22q11DS express neuropsychiatric symptoms, even in the absence of a DSM-IV classification, has substantial ramifications for guiding adequate support. Findings may spur further research into the dimensional structure of neuropsychiatric symptoms in 22q11DS and aid in uncovering mechanisms that contribute to symptom expression. Ultimately, this provides leads to improve clinical care for 22q11DS and to understand phenotypical variation in other high-risk genetic variants.

Integrative genetic analysis: cornerstone of precision psychiatry

The role of genetic testing in the domain of neurodevelopmental and psychiatric disorders (NPDs) is gradually changing from providing etiological explanation for the presence of NPD phenotypes to also identifying young individuals at high risk of developing NPDs before their clinical manifestation. In clinical practice, the latter implies a shift towards the availability of individual genetic information predicting a certain liability to develop an NPD (e.g., autism, intellectual disability, psychosis etc.). The shift from mostly a posteriori explanation to increasingly a priori risk prediction is the by-product of the systematic implementation of whole exome or genome sequencing as part of routine diagnostic work-ups during the neonatal and prenatal periods. This rapid uptake of genetic testing early in development has far-reaching consequences for psychiatry: Whereas until recently individuals would come to medical attention because of signs of abnormal developmental and/or behavioral symptoms, increasingly, individuals are presented based on genetic liability for NPD outcomes before NPD symptoms emerge. This novel clinical scenario, while challenging, also creates opportunities for research on prevention interventions and precision medicine approaches. Here, we review why optimization of individual risk prediction is a key prerequisite for precision medicine in the sphere of NPDs, as well as the technological and statistical methods required to achieve this ambition.

Developmental perspectives on the origins of psychotic disorders: The need for a transdiagnostic approach

Research on serious mental disorders, particularly psychosis, has revealed highly variable symptom profiles and developmental trajectories prior to illness-onset. As Dante Cicchetti pointed out decades before the term "transdiagnostic" was widely used, the pathways to psychopathology emerge in a system involving equifinality and multifinality. Like most other psychological disorders, psychosis is associated with multiple domains of risk factors, both genetic and environmental, and there are many transdiagnostic developmental pathways that can lead to psychotic syndromes. In this article, we discuss our current understanding of heterogeneity in the etiology of psychosis and its implications for approaches to conceptualizing etiology and research. We highlight the need for examining risk factors at multiple levels and to increase the emphasis on transdiagnostic developmental trajectories as a key variable associated with etiologic subtypes. This will be increasingly feasible now that large, longitudinal datasets are becoming available and researchers have access to more sophisticated analytic tools, such as machine learning, which can identify more homogenous subtypes with the ultimate goal of enhancing options for treatment and preventive intervention.

Cognitive, adaptive and daily life functioning in adults with 22q11.2 deletion syndrome

BACKGROUND

22q11.2 deletion syndrome (22q11.2DS) is associated with cognitive impairments and an increased risk of psychopathology. Most of the research has been conducted in children and adolescents, although the majority of affected individuals live well into adulthood. Hence, limited data are available on functional outcomes in adults.

AIMS

To provide more insight in cognitive and adaptive abilities, and daily life functioning (marital status, living situation and work situation) in adults with 22q11.2DS.

METHOD

This retrospective study included 250 Dutch-speaking adults (16-69 years) with 22q11.2DS from three sites in The Netherlands and Belgium. Data on full-scale IQ (FSIQ) scores (assessed with the Wechsler Adult Intelligence Scale), adaptive functioning (assessed with the Vineland Adaptive Behavior Scale II), and functional outcomes including marital status, living and work situation were systematically collected from clinical files. In addition, we examined predictors of adaptive functioning.

RESULTS

The majority of individuals in our adult sample demonstrated a low level of adaptive functioning (65%). In contrast to previous findings in children and adolescents, the majority functioned at an intellectual disability level (56%). Male sex, lower FSIQ and autism spectrum disorder were predictors of lower adaptive functioning (P = 0.016, P < 0.001 and P = 0.16, respectively).

CONCLUSIONS

These results suggest that low levels of cognitive and adaptive functioning are common in adults with 22q11.2DS. Future longitudinal and multicentre studies including older patients (>40 years) are needed to further investigate cognitive and adaptive trajectories and their interactions with physical and psychiatric comorbidities.

Safety and feasibility of home-based transcranial alternating current stimulation in youths with 22q11.2 deletion syndrome

Neurodevelopmental disorders such as attention deficit and/or hyperactivity disorder (ADHD) and schizophrenia are characterized by core impairment in executive functions (EF). Despite the development of various behavioral interventions to enhance EF, the evidence is still scarce. Alternatively, non-invasive brain stimulation tools such as transcranial alternating current stimulation (tACS) has emerged as a potential strategy to alleviate cognitive deficits. Previous studies have demonstrated the safety, feasibility, and efficacy of one single tACS session in different clinical populations. However, the effects of tACS appear limited and need to be sustained to be considered an effective cognitive neurorehabilitation tool. Recent studies have used home-based, repeated tACS sessions in individuals with neurodegenerative diseases. To our knowledge, the safety and feasibility of such an intensive protocol remains to be tested in a younger population with neurodevelopmental disorders. Using a randomized double-blind sham-controlled design, we administered home-based, repeated tACS sessions to seven individuals aged 14-25 with 22q11.2 deletion syndrome (22q11.2DS), which confers an increased risk for neurodevelopmental disorders. We aimed to assess the safety, tolerability, and feasibility of tACS. Findings from this ongoing clinical trial revealed a favorable safety profile, with frequent yet transient and mainly mild adverse effects. The intervention proved to be feasible, shown by very high adherence rates and positive user experiences. Future studies should therefore investigate whether prolonged exposure to tACS can lead to long-lasting cognitive outcomes.

Clinical trial registration

ClinicalTrials.gov, identifier NCT05664412.

The mental health and traumatic experiences of mothers of children with 22q11DS

Background: 22q11 Deletion Syndrome (22q11DS) is the most common microdeletion syndrome with broad phenotypic variability, leading to significant morbidity and some mortality. The varied health problems associated with 22q11DS and the evolving phenotype (both medical and developmental/behavioural) across the lifespan can strongly impact the mental health of patients as well as their caregivers. Like caregivers of children with other chronic diseases, caregivers of children with 22q11DS may experience an increased risk of traumatisation and mental health symptoms.Objective: The study's primary objective was to assess the frequency of traumatic experiences and mental health symptoms among mothers of children with 22q11DS. The secondary objective was to compare their traumatic experiences to those of mothers of children with other neurodevelopmental disorders (NDDs).Method: A total of 71 mothers of children diagnosed with 22q11DS completed an online survey about their mental health symptoms and traumatic experiences. Descriptive statistics were used to summarise the prevalence of their mental health symptoms and traumatic experiences. Logistic regression models were run to compare the traumatic experiences of mothers of children with 22q11DS to those of 335 mothers of children with other neurodevelopmental disorders (NDDs).Results: Many mothers of children with 22q11DS experienced clinically significant mental health symptoms, including depression (39%), anxiety (25%), and post-traumatic stress disorder (PTSD) symptoms (30%). The types of traumatic events experienced by mothers of children with 22q11DS differed from those of mothers of children with other NDDs as they were more likely to observe their child undergoing a medical procedure, a life-threatening surgery, or have been with their child in the intensive care unit.Conclusion: 22q11DS caregivers are likely to require mental health support and trauma-informed care, tailored to the specific needs of this population as they experience different kinds of traumatic events compared to caregivers of children with other NDDS.

The effectiveness and tolerability of pharmacotherapy for psychosis in 22q11.2 Deletion Syndrome: A systematic review

OBJECTIVE

The 22q11.2 Deletion Syndrome (22q11.2DS) is the most common microdeletion in humans with over 180 phenotypic expressions. Approximately 30-40% of affected individuals will develop psychosis and 25% meet the criteria for schizophrenia. Despite this, pharmacotherapy for managing psychosis in 22q11.2DS is poorly understood and 22q11.2DS psychosis is frequently labelled as treatment resistant. The objectives of this paper are to evaluate the effectiveness and tolerability of pharmacotherapy for 22q11.2DS psychosis and evaluate the evidence for treatment resistance.

METHOD

A systematic search was performed using CINAHL, The Cochrane Library (Cochrane Database of Systematic Reviews; Cochrane Central Register of Controlled Trials and Cochrane Clinical Answers), EMBASE, PsycINFO, PubMed, Scopus and Web of Science Core Collection from inception to December 2022. It yielded 39 case reports, 6 case series and 1 retrospective study which met the inclusion criteria.

RESULTS

Based on the current literature, individuals with 22q11.2DS psychosis experience a greater rate of medical co-morbidities such as cardiac arrhythmias, seizures and movement disorders, which complicate pharmacotherapy. Poor tolerability rather than poor clinical response motivates the switching of antipsychotics, which may explain the labelling of treatment resistance in the literature.

CONCLUSION

There are insufficient data to recommend a single antipsychotic for 22q11.2DS psychosis. Nonetheless, with proactive management of co-morbidities, antipsychotic medication in 22q11.2DS psychosis is an effective treatment commonly resulting in improvement in quality of life.

Chromosome 22q11.2 Deletion Syndrome: A Comprehensive Review of Molecular Genetics in the Context of Multidisciplinary Clinical Approach

The 22q11.2 deletion syndrome is a multisystemic disorder characterized by a marked variability of phenotypic features, making the diagnosis challenging for clinicians. The wide spectrum of clinical manifestations includes congenital heart defects-most frequently conotruncal cardiac anomalies-thymic hypoplasia and predominating cellular immune deficiency, laryngeal developmental defects, midline anomalies with cleft palate and velar insufficiency, structural airway defects, facial dysmorphism, parathyroid and thyroid gland hormonal dysfunctions, speech delay, developmental delay, and neurocognitive and psychiatric disorders. Significant progress has been made in understanding the complex molecular genetic etiology of 22q11.2 deletion syndrome underpinning the heterogeneity of clinical manifestations. The deletion is caused by chromosomal rearrangements in meiosis and is mediated by non-allelic homologous recombination events between low copy repeats or segmental duplications in the 22q11.2 region. A range of genetic modifiers and environmental factors, as well as the impact of hemizygosity on the remaining allele, contribute to the intricate genotype-phenotype relationships. This comprehensive review has been aimed at highlighting the molecular genetic background of 22q11.2 deletion syndrome in correlation with a clinical multidisciplinary approach.

Updated clinical practice recommendations for managing children with 22q11.2 deletion syndrome

This review aimed to update the clinical practice guidelines for managing children and adolescents with 22q11.2 deletion syndrome (22q11.2DS). The 22q11.2 Society, the international scientific organization studying chromosome 22q11.2 differences and related conditions, recruited expert clinicians worldwide to revise the original 2011 pediatric clinical practice guidelines in a stepwise process: (1) a systematic literature search (1992-2021), (2) study selection and data extraction by clinical experts from 9 different countries, covering 24 subspecialties, and (3) creation of a draft consensus document based on the literature and expert opinion, which was further shaped by survey results from family support organizations regarding perceived needs. Of 2441 22q11.2DS-relevant publications initially identified, 2344 received full-text reviews, including 1545 meeting criteria for potential relevance to clinical care of children and adolescents. Informed by the available literature, recommendations were formulated. Given evidence base limitations, multidisciplinary recommendations represent consensus statements of good practice for this evolving field. These recommendations provide contemporary guidance for evaluation, surveillance, and management of the many 22q11.2DS-associated physical, cognitive, behavioral, and psychiatric morbidities while addressing important genetic counseling and psychosocial issues.

Relationship between high trait anxiety in 22q11.2 deletion syndrome and the difficulties in medical, welfare, and educational services

Aim

The 22q11.2 deletion syndrome (22q11DS) is associated with a high prevalence of mental health comorbidities. However, not enough attention has been paid to the elevated prevalence of high trait anxiety that begins early in life and may be enduring. We sought to identify specific medical, welfare, or educational difficulties associated with high trait anxiety in 22q11DS.

Methods

A questionnaire-based survey was conducted for the parents of 22q11DS individuals (N = 125). First, a multiple regression analysis was conducted to confirm the hypothesis that high trait anxiety in individuals with 22q11DS would be associated with parents' psychological distress. This was based on 19 questionnaire options regarding what difficulties the parents currently face about their child's disease, characteristics, and traits. Next, we explored what challenges faced in medical, welfare, and educational services would be associated with the trait anxiety in their child.

Results

The multiple regression analysis confirmed that the high trait anxiety was significantly associated with parental psychological distress (β = 0.265, p = 0.018) among the 19 clinical/personal characteristics of 22q11DS. Furthermore, this characteristic was associated with various difficulties faced in the medical care, welfare, and education services, and the parent-child relationship.

Conclusion

To our knowledge, this is the first study to clarify quantitatively how the characteristic of high anxiety level in 22q11DS individuals is related to the caregivers' perceived difficulties in medical, welfare, and educational services. These results suggest the necessity of designing service structures informed of the fact that high trait anxiety is an important clinical feature of the syndrome.

Educational challenges for 22q11.2 deletion syndrome in Japan: Findings from a mixed methods survey

BACKGROUND

The 22q11.2 deletion syndrome (22q11DS) is characterised by a changing pattern of overlapping intellectual, physical, and mental disabilities along the course of one's life. However, the impact of overlapping disorders (multimorbidity) on educational challenges remains unclear.

METHOD

A survey was conducted with 88 caregivers of individuals with 22q11DS. A quantitative analysis of educational challenges and support needs divided into age groups (7-12, 13-15, 16-18, and 19 years and over) and a qualitative analysis of the free-text items in the questionnaire was conducted.

RESULTS

Caregivers were more interested in comprehensive developmental support when their children were younger, and the emphasis shifted to concerns regarding environments that matched individual characteristics at older ages. Furthermore, when there are multiple disabilities or disorders, support is concentrated on the more obvious disabilities, and the lack of support for the less superficially obvious disabilities associated with multiple difficulties, including mental health problems, can be a challenge for people with 22q11DS and their families.

CONCLUSIONS

This study suggests a need for increased focus on multimorbidity and associated disabilities in school education that are difficult to observe because of their mildness or borderline levels if present alone.

A genetics-first approach to understanding autism and schizophrenia spectrum disorders: the 22q11.2 deletion syndrome

Recently, increasing numbers of rare pathogenic genetic variants have been identified that are associated with variably elevated risks of a range of neurodevelopmental outcomes, notably including Autism Spectrum Disorders (ASD), Schizophrenia Spectrum Disorders (SSD), and Intellectual Disability (ID). This review is organized along three main questions: First, how can we unify the exclusively descriptive basis of our current psychiatric diagnostic classification system with the recognition of an identifiable, highly penetrant genetic risk factor in an increasing proportion of patients with ASD or SSD? Second, what can be learned from studies of individuals with ASD or SSD who share a common genetic basis? And third, what accounts for the observed variable penetrance and pleiotropy of neuropsychiatric phenotypes in individuals with the same pathogenic variant? In this review, we focus on findings of clinical and preclinical studies of the 22q11.2 deletion syndrome (22q11DS). This particular variant is not only one of the most common among the increasing list of known rare pathogenic variants, but also one that benefits from a relatively long research history. Consequently, 22q11DS is an appealing model as it allows us to: (1) elucidate specific genotype-phenotype associations, (2) prospectively study behaviorally defined classifications, such as ASD or SSD, in the context of a known, well-characterized genetic basis, and (3) elucidate mechanisms underpinning variable penetrance and pleiotropy, phenomena with far-reaching ramifications for research and clinical practice. We discuss how findings from animal and in vitro studies relate to observations in human studies and can help elucidate factors, including genetic, environmental, and stochastic, that impact the expression of neuropsychiatric phenotypes in 22q11DS, and how this may inform mechanisms underlying neurodevelopmental expression in the general population. We conclude with research priorities for the field, which may pave the way for novel therapeutics.

Environmental Influences on the Relation between the 22q11.2 Deletion Syndrome and Mental Health: A Literature Review

22q11.2 deletion syndrome (22q11DS) is a clinically heterogeneous genetic syndrome, associated with a wide array of neuropsychiatric symptoms. The clinical presentation is likely to be influenced by environmental factors, yet little is known about this. Here, we review the available research literature on the role of the environment in 22q11DS. We find that within-patient design studies have mainly investigated the role of parental factors, stress, and substance use, reporting significant effects of these factors on the clinical profile. Case-control studies have been less successful, with almost no reports of significant moderating effects of the environment. We go on to hypothesize which specific environmental measures are most likely to interact with the 22q11 deletion, based on the genes in this region and their involvement in molecular pathways. We end by discussing potential reasons for the limited findings so far, including modest sample sizes and limited availability of environmental measures, and make recommendations how to move forward.

Association between retinal vascular measures and brain white matter lesions in schizophrenia

OBJECTIVE

Recent studies have examined retinal vascular abnormalities in schizophrenia as retinal vascular imaging is a non-invasive proxy to cerebral microvasculature. However, relation between retinal vascular abnormalities and brain structure is not well examined in schizophrenia. Hence in this study, for the first time, we examined the relationship between retinal vascular measures and brain white matter lesions in schizophrenia. We examined brain white matter lesions as they are considered a predictive marker for future adverse cerebrovascular event.

METHODS

We acquired retinal vascular images of both eyes using a non-mydriatic camera and calculated retinal vascular diameter, tortuosity, trajectory and fractal dimension using validated methods. All patients underwent Magnetic Resonance Imaging of bran and we computed white matter hypo-intensities using Freesurfer software. We performed a linear regression analysis to examine the relationship between white matter hypo-intensities and retinal vascular measures controlling for age, sex, fasting blood sugar, creatinine, whole-brain volume, and antipsychotic dose.

RESULTS

The regression model was significant in Schizophrenia patients (R=0.983;R2 =0.966;-F=10.849;p = 0.008) but not in healthy volunteers (R=0.828;R2 =0.686;F=0.182; p = 0.963). Among the retinal vascular measures, arterial tortuosity (β = 0.963;p-0.002), tortuosity (β = -1.002;p = 0.001) and fractal dimension (β = -0.688;p = 0.014) were significant predictors of white matter lesions.

DISCUSSION

The current study's findings support the conclusion that retinal vascular fractal dimension and tortuosity are associated with changes in cerebral white matter and may be considered proxy markers for cerebral microvasculature in schizophrenia. Considering the relationship between white matter lesions and stroke, these observations could have important clinical implications to screen schizophrenia patients for risk of adverse cerebrovascular event.

Anhedonia and Hyperhedonia in Autism and Related Neurodevelopmental Disorders

Although autism spectrum disorder (ASD) is defined by impaired social communication and restricted and repetitive behaviors and interests, ASD is also characterized by impaired motivational processes. The "social motivation theory of autism" describes how social motivation disruptions in ASD in early childhood may impede the drive to engage in reciprocal social behaviors and ultimately interfere with the development of neural networks critical for social communication (Chevallier et al., Trends Cogn Sci 16:231-239, 2012b). Importantly, clinical studies and preclinical research using model organisms for ASD indicate that motivational impairments in ASD are not constrained to social rewards but are evident in response to a range of nonsocial rewards as well. Additionally, translational studies on certain genetically defined neurodevelopmental disorders associated with ASD indicate that these syndromic forms of ASD are also characterized by motivational deficits and mesolimbic dopamine impairments. In this chapter we summarize clinical and preclinical research relevant to reward processing impairments in ASD and related neurodevelopmental disorders. We also propose a nosology to describe reward processing impairments in these disorders that uses a three-axes model. In this triaxial nosology, the first axis defines the direction of the reward response (i.e., anhedonic, hyperhedonic); the second axis defines the construct of the reward process (e.g., reward liking, reward wanting); and the third axis defines the context of the reward response (e.g., social, nonsocial). A more precise nosology for describing reward processing impairments in ASD and related neurodevelopmental disorders will aid in the translation of preclinical research to clinical investigations which will ultimately help to speed up the development of interventions that target motivational systems for ASD and related neurodevelopmental disorders.

Contribution of schizophrenia polygenic burden to longitudinal phenotypic variance in 22q11.2 deletion syndrome

While the recurrent 22q11.2 deletion is one of the strongest genetic risk factors for schizophrenia (SCZ), variability of its associated neuropsychiatric endophenotypes reflects its incomplete penetrance for psychosis development. To assess whether this phenotypic variability is linked to common variants associated with SCZ, we studied the association between SCZ polygenic risk score (PRS) and longitudinally acquired phenotypic information of the Swiss 22q11.2DS cohort (n = 97, 50% females, mean age 17.7 yr, mean visit interval 3.8 yr). The SCZ PRS with the best predictive performance was ascertained in the Estonian Biobank (n = 201,146) with LDpred. The infinitesimal SCZ PRS model showed the strongest capacity in discriminating SCZ cases from controls with one SD difference in SCZ PRS corresponding to an odds ratio (OR) of 1.73 (95% CI 1.57-1.90, P = 1.47 × 10^-29). In 22q11.2 patients, random-effects ordinal regression modelling using longitudinal data showed SCZ PRS to have the strongest effect on social anhedonia (OR = 2.09, P = 0.0002), and occupational functioning (OR = 1.82, P = 0.0003) within the negative symptoms course, and dysphoric mood (OR = 2.00, P = 0.002) and stress intolerance (OR = 1.76, P = 0.0002) within the general symptoms course. Genetic liability for SCZ was additionally associated with full scale cognitive decline (β = -0.25, P = 0.02) and with longitudinal volumetric reduction of the right and left hippocampi (β = -0.28, P = 0.005; β = -0.23, P = 0.02, respectively). Our results indicate that the polygenic contribution to SCZ acts upon the threshold-lowering first hit (i.e., the deletion). It modifies the endophenotypes of 22q11.2DS and augments the derailment of developmental trajectories of negative and general symptoms, cognition, and hippocampal volume.

MicroRNAs as Biomarkers for Birth Defects

It is estimated that 2-4% of live births will have a birth defect (BD). The availability of biomarkers for the prenatal detection of BDs will facilitate early risk assessment, prompt medical intervention and ameliorating disease severity. miRNA expression levels are often found to be altered in many diseases. There is, thus, a growing interest in determining whether miRNAs, particularly extracellular miRNAs, can predict, diagnose, or monitor BDs. These miRNAs, typically encapsulated in exosomes, are released by cells (including those of the fetus and placenta) into the extracellular milieu, such as blood, urine, saliva and cerebrospinal fluid, thereby enabling interaction with target cells. Exosomal miRNAs are stable, protected from degradation, and retain functionality. The observation that placental and fetal miRNAs can be detected in maternal serum, provides a strong rationale for adopting miRNAs as noninvasive prenatal biomarkers for BDs. In this mini-review, we examine the current state of research involving the use of miRNAs as prognostic and diagnostic biomarkers for BD.

Harnessing rare variants in neuropsychiatric and neurodevelopment disorders-a Keystone Symposia report

Neurodevelopmental neuropsychiatric disorders, such as autism spectrum disorder and schizophrenia, have strong genetic risk components, but the underlying mechanisms have proven difficult to decipher. Rare, high-risk variants may offer an opportunity to delineate the biological mechanisms responsible more clearly for more common idiopathic diseases. Indeed, different rare variants can cause the same behavioral phenotype, demonstrating genetic heterogeneity, while the same rare variant can cause different behavioral phenotypes, demonstrating variable expressivity. These observations suggest convergent underlying biological and neurological mechanisms; identification of these mechanisms may ultimately reveal new therapeutic targets. At the 2021 Keystone eSymposium "Neuropsychiatric and Neurodevelopmental Disorders: Harnessing Rare Variants" a panel of experts in the field described significant progress in genomic discovery and human phenotyping and raised several consistent issues, including the need for detailed natural history studies of rare disorders, the challenges in cohort recruitment, and the importance of viewing phenotypes as quantitative traits that are impacted by rare variants.

How does genetic variation modify ND-CNV phenotypes?

Rare copy-number variants (CNVs) associated with neurodevelopmental disorders (NDDs), i.e., ND-CNVs, provide an insight into the neurobiology of NDDs and, potentially, a link between biology and clinical outcomes. However, ND-CNVs are characterised by incomplete penetrance resulting in heterogeneous carrier phenotypes, ranging from non-affected to multimorbid psychiatric, neurological, and physical phenotypes. Recent evidence indicates that other variants in the genome, or 'other hits', may partially explain the variable expressivity of ND-CNVs. These may be other rare variants or the aggregated effects of common variants that modify NDD risk. Here we discuss the recent findings, current questions, and future challenges relating to other hits research in the context of ND-CNVs and their potential for improved clinical diagnostics and therapeutics for ND-CNV carriers.

Generation of a Mouse Model to Study the Noonan Syndrome Gene Lztr1 in the Telencephalon

The leucine zipper-like transcriptional regulator 1 (Lztr1) is a BTB-Kelch domain protein involved in RAS/MAPK pathway regulation. Mutations in LZTR1 are associated with cancers and Noonan syndrome, the most common RASopathy. The expression and function of Lztr1 in the developing brain remains poorly understood. Here we show that Lztr1 is expressed in distinct regions of the telencephalon, the most anterior region of the forebrain. Lztr1 expression was robust in the cortex, amygdala, hippocampus, and oligodendrocytes in the white matter. To gain insight into the impact of Lztr1 deficiency, we generated a conditional knockout (cKO) restricted to the telencephalon using Foxg1^IREScre/+. Lztr1 cKOs are viable to postnatal stages and show reduced Lztr1 expression in the telencephalon. Interestingly, Lztr1 cKOs exhibit an increase in MAPK pathway activation in white matter regions and subsequently show an altered expression of stage-specific markers in the oligodendrocyte lineage with increased oligodendrocyte progenitor cells (OPCs) and decreased markers of oligodendrocyte differentiation. Moreover, Lztr1 cKOs also exhibit an increased expression of the astrocyte marker GFAP. These results highlight the generation of a new mouse model to study Lztr1 deficiency in the brain and reveal a novel role for Lztr1 in normal oligodendrocyte and astrocyte development in the telencephalon.