Objective Clinical genetic sequencing is frequently utilized to diagnose individuals with neurodevelopmental disorders (NDDs). Here we perform a meta‐analysis and systematic review of the success rate (diagnostic yield) of clinical sequencing through next‐generation sequencing (NGS) across NDDs. We compare the genetic testing yield across NDD subtypes and sequencing technology. Methods We performed a systematic review of the PubMed literature until May 2020. We included clinical sequencing studies that utilized NGS in individuals with epilepsy, autism spectrum disorder (ASD), or intellectual disability (ID). Data were extracted, reviewed, and categorized according to the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines. Two investigators performed clinical evaluation and grouping following the International League Against Epilepsy (ILAE) guidelines. Pooled rates of the diagnostic yield and 95% confidence intervals were estimated with a random‐effects model. Results We identified 103 studies (epilepsy, N = 72; ASD, N = 14; ID, N = 21) across 32,331 individuals. Targeted gene panel sequencing was used in 73, and exome sequencing in 36 cohorts. Given highly selected patient cohorts, the diagnostic yield was 17.1% for ASD, 24% for epilepsy, and 28.2% for ID (23.7% overall). The highest diagnostic yield for epilepsy subtypes was observed in individuals with ID (27.9%) and early onset seizures (36.8%). The diagnostic yield for exome sequencing was higher than for panel sequencing, even though not statistically significant (27.2% vs 22.6%, P = .071). We observed that clinical sequencing studies are performed predominantly in countries with a high Inequality‐adjusted Human Development Index (IHDI) (countries with sequencing studies: IHDI median = 0.84, interquartile range [IQR] = 0.09 vs countries without sequencing studies: IHDI median = 0.56, IQR = 0.3). No studies from Africa, India, or Latin America were identified, indicating potential barriers to genetic testing. Significance This meta‐analysis and systematic review provides a comprehensive overview of clinical sequencing studies of NDDs and will help guide policymaking and steer decision‐making in patient management.

Objective Forced normalization (FN) is an intriguing phenomenon characterized by the emergence of psychiatric disturbances following the establishment of seizure control or reduction in the epileptic activity in a patient with previous uncontrolled epilepsy. We aim to describe the clinical characteristics of the condition. Methods We conducted a systematic review on MEDLINE, EMBASE, Cochrane, and Scielo from January 1953 to January 2018. Clinical, electrographic, and imaging data were gathered. We considered all outcomes in children and adults. We performed no meta‐analyses due to the limited available data. Results Of 2606 abstracts identified, 36 fulfilled the FN diagnostic criteria; 193 FN episodes were evaluated and 77 of them were analyzed extensively. Sixty percent of cases were female. Mean age ± standard deviation (SD) was 28.3 ± 14.2 years. The majority of patients had focal (80%) symptomatic (44%) epilepsy. Most patients reported a high ictal frequency (58%) and were on polytherapy (51%). Patients presented psychosis (86.4%), mood disorders (25.8%), and dissociation (4.5%) as the main manifestations. In the psychosis group, persecutory (52.6%) and reference (47.3%) delusions were frequent. FN was provoked by an antiepileptic drug (AED) (48.5%) mainly levetiracetam, epilepsy surgery (31.8%), or vagus nerve stimulation (13.6%). Treatment was homogeneous including anticonvulsant withdrawal (47%) or taper (25%); antipsychotics were initiated in the majority of cases (73%). Psychiatric symptoms were partially controlled in 35%, with complete resolution of symptoms in the remaining 65% of cases. The majority of patients (87%) with AED trigger and withdrawal presented complete resolution of symptoms in comparison to 28.5% of patients triggered by surgery. Significance Forced normalization is an entity whose pathophysiology remains uncertain. Antipsychotic drug use does not predict complete resolution of psychiatric symptoms in comparison with AED withdrawal. Although there is a positive response to treatment in patients with FN triggered by drugs, the prognosis is obscure in patients with surgery triggered FN.

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