Is it time to retire fragile X testing as a first-tier test for developmental delay, intellectual disability, and autism spectrum disorder?

Late-onset mitochondrial encephalopathy with lactic acidosis and stroke-like episodes and the role of serial imaging

Mitochondria are essential for human metabolic function. Over 350 genetic mutations are associated with mitochondrial diseases, which are inherited in a matrilineal fashion. In mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), defective mitochondrial function and resultant impaired cellular energy production compromise vascular perfusion in affected tissues. Early diagnostic criteria suggested the diagnosis should be considered in those under 40. However, a broader range of phenotypes are now recognised, including those that present for the first time later in life. The primary presenting feature in MELAS is a stroke-like episode invariably resulting in patients undergoing neuroradiological imaging. We present a case of a woman with a first presentation of a stroke-like episode and seizures in her 40s who was eventually diagnosed with MELAS. We detail her clinical presentation, treatment and diagnosis, emphasising the role of serial imaging in her diagnosis.

Genetic and metabolic investigations for neurodevelopmental disorders: position statement of the Canadian College of Medical Geneticists (CCMG)

PURPOSE AND SCOPE

The aim of this position statement is to provide recommendations for clinicians regarding the use of genetic and metabolic investigations for patients with neurodevelopmental disorders (NDDs), specifically, patients with global developmental delay (GDD), intellectual disability (ID) and/or autism spectrum disorder (ASD). This document also provides guidance for primary care and non-genetics specialists caring for these patients while awaiting consultation with a clinical geneticist or metabolic specialist.

METHODS OF STATEMENT DEVELOPMENT

A multidisciplinary group reviewed existing literature and guidelines on the use of genetic and metabolic investigations for the diagnosis of NDDs and synthesised the evidence to make recommendations relevant to the Canadian context. The statement was circulated for comment to the Canadian College of Medical Geneticists (CCMG) membership-at-large and to the Canadian Pediatric Society (Mental Health and Developmental Disabilities Committee); following incorporation of feedback, it was approved by the CCMG Board of Directors on 1 September 2022.

RESULTS AND CONCLUSIONS

Chromosomal microarray is recommended as a first-tier test for patients with GDD, ID or ASD. Fragile X testing should also be done as a first-tier test when there are suggestive clinical features or family history. Metabolic investigations should be done if there are clinical features suggestive of an inherited metabolic disease, while the patient awaits consultation with a metabolic physician. Exome sequencing or a comprehensive gene panel is recommended as a second-tier test for patients with GDD or ID. Genetic testing is not recommended for patients with NDDs in the absence of GDD, ID or ASD, unless accompanied by clinical features suggestive of a syndromic aetiology or inherited metabolic disease.

[11C]PK11195-PET Brain Imaging of the Mitochondrial Translocator Protein in Mitochondrial Disease

OBJECTIVE

To explore the possibilities of radioligands against the mitochondrial outer membrane translocator protein (TSPO) as biomarkers for mitochondrial disease, we performed brain PET-MRI with [11C]PK11195 in 14 patients with genetically confirmed mitochondrial disease and 33 matched controls.

METHODS

Case-control study of brain PET-MRI with the TSPO radioligand [11C]PK11195.

RESULTS

Forty-six percent of symptomatic patients had volumes of abnormal radiotracer binding greater than the 95th percentile in controls. [11C]PK11195 binding was generally greater in gray matter and significantly decreased in white matter. This was most striking in patients with nuclear TYMP or mitochondrial m.3243A>G MT-TL1 mutations, in keeping with differences in mitochondrial density seen postmortem. Some regional binding patterns corresponded to clinical presentation and underlying mutation, even in the absence of structural changes on MRI. This was most obvious for the cerebellum, where patients with ataxia had decreased binding in the cerebellar cortex, but not necessarily volume loss. Overall, there was a positive correlation between aberrant [11C]PK11195 binding and clinical severity.

CONCLUSION

These findings endorse the use of PET imaging with TSPO radioligands as a noninvasive in vivo biomarker of mitochondrial pathology.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that brain PET-MRI with TSPO radioligands identifies mitochondrial pathology.

Genetic and metabolic investigations for individuals with neurodevelopmental disorders: A survey of Canadian geneticists' practices

Neurodevelopmental disorders (NDDs) are genetically heterogeneous. There are many possible etiological investigations for NDDs, and a lack of clear and current guidelines for such testing. Here we characterize the practices of genetic and metabolic physicians in Canada as it pertains to etiological investigation of patients with NDDs, by means of an online questionnaire. The survey response rate was 30% (n = 46). The most commonly ordered first-line tests for patients with non-syndromic NDDs are chromosomal microarray (98%) and Fragile X testing (85%). The most commonly ordered second-line test for non-syndromic NDDs is a multi-gene panel (78%) or exome sequencing (29%). Biochemical screening is ordered as a first line test by 33% of respondents, second line by 31%, and rarely or never by 36% of respondents. Those respondents with metabolics fellowship training were more likely to order biochemical screening than those without. The number of years of clinical experience generally did not affect the types of tests ordered. For patients with NDDs, test-ordering practice among Canadian clinical geneticists is highly variable, in particular with respect to biochemical screening and use of next-generation sequencing technologies. Evidence-based guidelines should be developed to facilitate best practices in Canada.

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.

The Feasibility and Outcomes of Genetic Testing for Autism and Neurodevelopmental Disorders on an Inpatient Child and Adolescent Psychiatry Service

Diagnostic genetic testing is recommended for children with autism spectrum disorder and other neurodevelopmental disorders. One approach to improve access to genetic testing is to offer it on the inpatient child and adolescent psychiatry (CAP) service. We provided medical genetics education to CAP fellows and retrospectively compared the genetic testing rates and diagnostic yield pre- and post-education. We compared demographics to similar patients who received testing on other clinical services and assessed rates of outpatient genetics follow-up post-discharge. The genetic testing rate on the inpatient CAP service was 1.6% before the educational intervention and 10.7% afterward. Genetic risk factors were identified in 4.3% of inpatients. However, 34.8% had variants of unknown significance. 39.1% of patients who received genetic testing while inpatients were underrepresented minorities, compared to 7.7% of inpatients who received genetic testing from other clinical services. 43.5% of patients were lost to outpatient genetics follow-up. We have demonstrated that it is feasible to provide medical genetics education to CAP fellows on an inpatient service, which may improve genetic testing rates. This preliminary evidence also suggests that genetic testing for inpatients may identify variants of unknown significance instead of well-known neurodevelopmental disorder risk variants. Genetic testing on an inpatient CAP service may also improve access to genetic services for underrepresented minorities, but assuring outpatient follow-up can be challenging. LAY SUMMARY: Genetic testing is recommended for children with autism and related developmental conditions. We provided genetic testing to a group of these children who were in a psychiatric hospital by teaching their doctors how it can be helpful. We identified a genetic risk factor in a small percentage of children and a possible genetic risk factor in a large percentage of children. However, many children did not end up receiving their genetic test results once they left the hospital. These results tell us that the psychiatric hospital may be a good place for children with autism and behavioral problems to get genetic testing, but that it is really important that doctors assure follow-up is feasible for all patients to receive their genetic test results once they leave the hospital. Autism Res 2020, 13: 1450-1464. © 2020 International Society for Autism Research, Wiley Periodicals, Inc.

Re-evaluating the first-tier status of fragile X testing in neurodevelopmental disorders

PURPOSE

Evaluate whether fragile X syndrome (FXS) testing should be transitioned to a second-tier test in global developmental delay, intellectual disability, and autism spectrum disorder in the absence of family history and suggestive clinical features.

METHODS

Determine the diagnostic yield of FXS testing performed by the Alberta Children's Hospital (ACH) Molecular Diagnostic Laboratory between 2012 and 2017. Retrospective chart review of FXS-positive patients to determine presence or absence of suggestive clinical features and family history.

RESULTS

Of the 2486 pediatric patients with neurodevelopmental disorders tested for FXS, 25 males and 5 females were positive. This corresponds to a 1.2% diagnostic yield of FXS testing at our center. Retrospective chart review of the FXS-positive cases revealed that 96% of FXS patients had either, if not both, clinical features or family history suggestive of FXS present at the time of testing. Only one patient had neither family history nor clinical features suggestive of FXS.

CONCLUSION

In 96% of FXS-positive cases, there was sufficient clinical suspicion raised on the basis of clinical features and/or family history to perform targeted FXS testing. We thus propose that in the absence of suggestive clinical features or family history, FXS testing should be transitioned to a second-tier test in neurodevelopmental disorders.

Overview and Introduction to Autism Spectrum Disorder (ASD)

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder generally manifesting in the first few years of life and tending to persist into adolescence and adulthood. It is characterized by deficits in communication and social interaction and restricted, repetitive patterns of behavior, interests, and activities. It is a disorder with multifactorial etiology. In this chapter, we will focus on the most important and common epidemiological studies, pathogenesis, screening, and diagnostic tools along with an explication of genetic testing in ASD.

CHRNA7 copy number gains are enriched in adolescents with major depressive and anxiety disorders

OBJECTIVE

Neuronal nicotinic acetylcholine receptors (nAChRs), specifically the α7 nAChR encoded by the gene CHRNA7, have been implicated in behavior regulation in animal models. In humans, copy number variants (CNVs) of CHRNA7 are found in a range of neuropsychiatric disorders, including mood and anxiety disorders. Here, we aimed to determine the prevalence of CHRNA7 CNVs among adolescents and young adults with major depressive disorder (MDD) and anxiety disorders.

METHODS

Twelve to 21 year-old participants with MDD and/or anxiety disorders (34% males, mean ± std age: 18.9 ± 1.8 years) were assessed for CHRNA7 copy number state using droplet digital PCR (ddPCR) and genomic quantitative PCR (qPCR). Demographic, anthropometric, and clinical data, including the Beck Anxiety Index (BAI), Beck Depression Inventory (BDI), and the Inventory of Depressive Symptoms (IDS) were collected and compared across individuals with and without a CHRNA7 CNV.

RESULTS

Of 205 individuals, five (2.4%) were found to carry a CHRNA7 gain, significantly higher than the general population. No CHRNA7 deletions were identified. Clinically, the individuals carrying CHRNA7 duplications did not differ significantly from copy neutral individuals with MDD and/or anxiety disorders.

CONCLUSIONS

CHRNA7 gains are relatively prevalent among young individuals with MDD and anxiety disorders (odds ratio = 4.032) without apparent distinguishing clinical features. Future studies should examine the therapeutic potential of α7 nAChR targeting drugs to ameliorate depressive and anxiety disorders.