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Fragile X syndrome (FXS) is a genetic condition caused by the inheritance of alleles with >200 CGG repeats in the 5' UTR of the fragile X messenger ribonucleoprotein 1 ( FMR1 ) gene. These full mutation (FM) alleles are associated with DNA methylation and gene silencing, which result in intellectual disabilities, developmental delays, and social and behavioral issues. Mosaicism for both the size of the CGG repeat tract and the extent of its methylation is commonly observed in individuals with the FM. Mosaicism has also been reported in carriers of premutation (PM) alleles, which have 55-200 CGG repeats. PM alleles confer risk for the fragile X premutation-associated conditions (FXPAC), including FXTAS, FXPOI, and FXAND, conditions thought to be due to the toxic consequences of transcripts containing large CGG-tracts. Unmethylated FM (UFM) alleles are transcriptionally and translationally active. Thus, they produce transcripts with toxic effects. These transcripts do produce some FMRP, the encoded product of the FMR1 gene, albeit with reduced translational efficiency. As a result, mosaicism can result in a complex clinical presentation. Here, we review the concept of mosaicism in both FXS and in PM carriers, including its potential clinical significance.

Lysine-specific demethylase 5C (KDM5C) has been identified as an important chromatin remodeling gene, contributing to X-linked neurodevelopmental disorders (NDDs). The KDM5C gene, located in the Xp22 chromosomal region, encodes the H3K4me3-me2 eraser involved in neuronal plasticity and dendritic growth. Here we report 30 individuals carrying 13 novel and one previously identified KDM5C variants. Our cohort includes the first reported case of somatic mosaicism in a male carrying a KDM5C nucleotide substitution, and a dual molecular finding in a female carrying a homozygous truncating FUCA1 alteration together with a de novo KDM5C variant. With the use of next generation sequencing strategies, we detected 1 frameshift, 1 stop codon, 2 splice-site and 10 missense variants, which pathogenic role was carefully investigated by a thorough bioinformatic analysis. The pattern of X-chromosome inactivation was found to have an impact on KDM5C phenotypic expression in females of our cohort. The affected individuals of our case series manifested a neurodevelopmental condition characterized by psychomotor delay, intellectual disability with speech disorders, and behavioral features with particular disturbed sleep pattern; other observed clinical manifestations were short stature, obesity and hypertrichosis. Collectively, these findings expand the current knowledge about the pathogenic mechanisms leading to dysfunction of this important chromatin remodeling gene and contribute to a refinement of the KDM5C phenotypic spectrum., (© 2022. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

SETBP1 mutations are associated with the Schinzel-Giedion syndrome (SGS), characterized by profound neurodevelopmental delay, typical facial features, and multiple congenital malformations (OMIM 269150). Refractory epilepsy is a common feature of SGS. Loss of function mutations have been typically associated with a distinct and milder phenotype characterized by intellectual disability and expressive speech impairment. Here we report three variants of SETBP1 , two novel de novo truncating mutations, identified by NGS analysis of an Intellectual Disability gene panel in 600 subjects with non-specific neurodevelopmental disorders, and one missense identified by a developmental epilepsy gene panel tested in 56 pediatric epileptic cases. The three individuals carrying the identified SETBP1 variants presented mild to severe developmental delay and lacked the cardinal features of classical SGS. One of these subjects, carrying the c.1765C>T (p.Arg589 * ) mutation, had mild Intellectual Disability with speech delay; the second one carrying the c.2199_2203del (p.Glu734Alafs19 * ) mutation had generalized epilepsy, responsive to treatment, and moderate Intellectual Disability; the third patient showed a severe cognitive defects and had a history of drug resistant epilepsy with West syndrome evolved into a Lennox-Gastaut syndrome. This latter subject carries the missense c.2572G>A (p.Glu858Lys) variant, which is absent from the control population, reported as de novo in a subject with ASD, and located close to the SETBP1 hot spot for SGS-associated mutations. Our findings contribute to further characterizing the associated phenotypes and suggest inclusion of SETBP1 in the list of prioritized genes for the genetic diagnosis of overlapping phenotypes ranging from non-specific neurodevelopmental disorders to "developmental and epileptic encephalopathy" (DEE)., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Leonardi, Bettella, Pelizza, Aspromonte, Polli, Boniver, Sartori, Milani and Murgia.)

Non-syndromic hearing loss (NSHL) is characterized by a vast genetic heterogeneity; some syndromic forms as Usher syndrome (USH) have onset as isolated deafness and then evolve later in life. We developed an NGS targeted gene-panel containing 59 genes and a customized bioinformatic pipeline for the analysis of DNA samples from clinically highly selected subjects with sensorineural hearing loss, previously resulted negative for GJB2 mutations/GJB6 deletions. Among the 217 tested subjects, 24 (11.1%) were found to carry mutations in genes involved both in NSHL and USH. For 6 out of 24 patients a diagnosis of USH was performed. Eleven subjects out of 24 had hearing loss without vestibular or ocular dysfunction and, due to their young age, it was not possible to establish whether their phenotype could be NSHL or USH. Seven subjects were diagnosed with NSHL, due to their age and phenotype. A total of 41 likely pathogenic/pathogenic mutations were identified, among which 17 novel ones. We report a high frequency of mutations in genes involved both in NSHL and in USH in a cohort of individuals tested for seemingly isolated deafness. Our data also highlight a wider than expected phenotypic variability in the USH phenotype.

WAC (WW Domain Containing Adaptor With Coiled-Coil) mutations have been reported in only 20 individuals presenting a neurodevelopmental disorder characterized by intellectual disability, neonatal hypotonia, behavioral problems, and mildly dysmorphic features. Using targeted deep sequencing, we screened a cohort of 630 individuals with variable degrees of intellectual disability and identified five WAC rare variants: two variants were inherited from healthy parents; two previously reported de novo mutations, c.1661_1664del (p.Ser554*) and c.374C>A (p.Ser125*); and a novel c.381+2T>C variant causing the skipping of exon 4 of the gene, inherited from a reportedly asymptomatic father with somatic mosaicism. A phenotypic evaluation of this individual evidenced areas of cognitive and behavioral deficits. The patient carrying the novel splicing mutation had a clinical history of encephalopathy related to status epilepticus during slow sleep (ESES), recently reported in another WAC individual. This first report of a WAC somatic mosaic remarks the contribution of mosaicism in the etiology of neurodevelopmental and neuropsychiatric disorders. We summarized the clinical data of reported individuals with WAC pathogenic mutations, which together with our findings, allowed for the expansion of the phenotypic spectrum of WAC-related disorders., Competing Interests: The authors declare no conflicts of interest.

Postsynaptic density (PSD) proteins have been implicated in the pathophysiology of neurodevelopmental and psychiatric disorders. Here, we present detailed clinical and genetic data for 20 patients with likely gene-disrupting mutations in TANC2-whose protein product interacts with multiple PSD proteins. Pediatric patients with disruptive mutations present with autism, intellectual disability, and delayed language and motor development. In addition to a variable degree of epilepsy and facial dysmorphism, we observe a pattern of more complex psychiatric dysfunction or behavioral problems in adult probands or carrier parents. Although this observation requires replication to establish statistical significance, it also suggests that mutations in this gene are associated with a variety of neuropsychiatric disorders consistent with its postsynaptic function. We find that TANC2 is expressed broadly in the human developing brain, especially in excitatory neurons and glial cells, but shows a more restricted pattern in Drosophila glial cells where its disruption affects behavioral outcomes.

Intellectual disability (ID) and autism spectrum disorder (ASD) are clinically and genetically heterogeneous diseases. Recent whole exome sequencing studies indicated that genes associated with different neurological diseases are shared across disorders and converge on common functional pathways. Using the Ion Torrent platform, we developed a low-cost next-generation sequencing gene panel that has been transferred into clinical practice, replacing single disease-gene analyses for the early diagnosis of individuals with ID/ASD. The gene panel was designed using an innovative in silico approach based on disease networks and mining data from public resources to score disease-gene associations. We analyzed 150 unrelated individuals with ID and/or ASD and a confident diagnosis has been reached in 26 cases (17%). Likely pathogenic mutations have been identified in another 15 patients, reaching a total diagnostic yield of 27%. Our data also support the pathogenic role of genes recently proposed to be involved in ASD. Although many of the identified variants need further investigation to be considered disease-causing, our results indicate the efficiency of the targeted gene panel on the identification of novel and rare variants in patients with ID and ASD., (© 2019 Wiley Periodicals, Inc.)

Background: The ALDH7A1 gene is known to be responsible for autosomal recessive pyridoxine-dependent epilepsy (OMIM 266100). The phenotypic spectrum of ALDH7A1 mutations is very heterogeneous ranging from refractory epilepsy and neurodevelopmental delay, to multisystem neonatal disorder., Aim: The present study aims at describing the phenotype associated with a novel homozygous ALDH7A1 mutation and the spectrum of brain malformations associated with pyridoxine-dependent epilepsy., Methods: We conducted a literature review on the Internet database Pubmed (up to November 2017) searching for ALDH7A1 mutations associated with brain malformations and brain MRI findings., Results: We present the case of two siblings, children of related parents. The proband presented neonatal focal seizures not responding to conventional antiepileptic drugs. Electroencephalography showed a suppression burst pattern and several multifocal ictal patterns, responsive to pyridoxine. Brain MRI was normal. Molecular analysis by targeted next-generation sequencing panel for epileptic encephalopathy disclosed a homozygous missense mutation of ALDH7A1. The same mutation was then found in a stored sample of DNA from peripheral blood of an older sister dead 3 years earlier. This girl presented a complex brain malformation diagnosed with a foetal MRI and had neonatal refractory seizures with suppression burst pattern. She died at 6 months of age., Literature Review: The brain abnormalities most frequently reported in pyridoxine-dependent epilepsy include: agenesia/hypoplasia of the corpus callosum, not specific white matter abnormalities, large cisterna magna, ventriculomegaly, haemorrhages, cerebellum hypoplasia/dysplasia, and, more rarely, dysplasia of the brainstem and hydrocephalus., Discussion and Conclusions: ALDH7A1 mutations have been associated to different brain abnormalities, documented by MRI only in few cases. The study cases expand the clinical spectrum of ALDH7A1 associated conditions, suggesting to look for ALDH7A1 mutations not only in classical phenotypes but also in patients with brain malformations, mainly if there is a response to a pyridoxine trial., (Copyright © 2018 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.)

Objectives: This work was aimed at establishing the molecular etiology of hearing loss in a 9-year old girl with post-lingual non-syndromic mild sensorineural hearing loss with a complex family history of clinically heterogeneous deafness., Methods: The proband's DNA was subjected to NGS analysis of a 59-targeted gene panel, with the use of the Ion Torrent PGM platform. Conventional Sanger sequencing was used for segregation analysis in all the affected relatives. The proband and all the other hearing impaired members of the family underwent a thorough clinical and audiological evaluation., Results: A new likely pathogenic mutation in the EYA4 gene (c.1154C > T; p.Ser385Leu) was identified in the proband and in her 42-year-old father with post-lingual non-syndromic profound sensorineural hearing loss. The EYA4 mutation was also found in the proband's grandfather and uncle, both showing clinical features of Waardenburg syndrome type 1. A novel pathogenic splice-site mutation (c.321+1G > A) of the PAX3 gene was found to co-segregate with the EYA4 mutation in these two subjects., Conclusion: The identified novel EYA4 mutation can be considered responsible of the hearing loss observed in the proband and her father, while a dual molecular diagnosis was reached in the relatives co-segregating the EYA4 and the PAX3 mutations. In these two subjects the DFNA10 phenotype was masked by Waardenburg syndrome. The use of NGS targeted gene-panel, in combination with an extensive clinical and audiological examination led us to identify the genetic cause of the hearing loss in members of a family in which different forms of autosomal dominant deafness segregate. These results provide precise and especially important prognostic and follow-up information for the future audiologic management in the youngest affected member., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The PCDH19 gene encodes protocadherin-19, a transmembrane protein with six cadherin (EC) domains, containing adhesive interfaces likely to be involved in neuronal connection. Over a hundred mostly private mutations have been identified in girls with epilepsy, with or without intellectual disability (ID). Furthermore, transmitting hemizygous males are devoid of seizures or ID, making it difficult to establish the pathogenic nature of newly identified variants. Here, we describe an integrated approach to evaluate the pathogenicity of four novel PCDH19 mutations. Segregation analysis has been complemented with an in silico analysis of mutation effects at the protein level. Using sequence information, we compared different computational prediction methods. We used homology modeling to build structural models of two PCDH19 EC-domains, and compared wild-type and mutant models to identify differences in residue interactions or biochemical properties of the model surfaces. Our analysis suggests different molecular effects of the novel mutations in exerting their pathogenic role. Two of them interfere with or alter functional residues predicted to mediate ligand or protein binding, one alters the EC-domain folding stability; the frame-shift mutation produces a truncated protein lacking the intracellular domain. Interestingly, the girl carrying the putative loss of function mutation presents the most severe phenotype., (© 2014 John Wiley & Sons Ltd/University College London.)

Rett syndrome is a clinically defined neurodevelopmental disorder almost exclusively affecting females. Usually sporadic, Rett syndrome is caused by mutations in the X-linked MECP2 gene in ∼90-95% of classic cases and 40-60% of individuals with atypical Rett syndrome. Mutations in the CDKL5 gene have been associated with the early-onset seizure variant of Rett syndrome and mutations in FOXG1 have been associated with the congenital Rett syndrome variant. We report the clinical features and array CGH findings of three atypical Rett syndrome patients who had severe intellectual impairment, early-onset developmental delay, postnatal microcephaly and hypotonia. In addition, the females had a seizure disorder, agenesis of the corpus callosum and subtle dysmorphism. All three were found to have an interstitial deletion of 14q12. The deleted region in common included the PRKD1 gene but not the FOXG1 gene. Gene expression analysis suggested a decrease in FOXG1 levels in two of the patients. Screening of 32 atypical Rett syndrome patients did not identify any pathogenic mutations in the PRKD1 gene, although a previously reported frameshift mutation affecting FOXG1 (c.256dupC, p.Gln86ProfsX35) was identified in a patient with the congenital Rett syndrome variant. There is phenotypic overlap between congenital Rett syndrome variants with FOXG1 mutations and the clinical presentation of our three patients with this 14q12 microdeletion, not encompassing the FOXG1 gene. We propose that the primary defect in these patients is misregulation of the FOXG1 gene rather than a primary abnormality of PRKD1.

Two genes causally involved in refractory epilepsy with mental retardation, cyclin-dependent kinase-like 5 and aristaless-related homeobox, could account for at least some forms of early onset epileptic encephalopathy that still lack etiological explanation. With the aim of investigating the specific pathogenic involvement of the 2 genes, we have conducted a clinical and molecular study in 80 patients with epileptic encephalopathy of unknown etiology and onset within the first year of life, regardless of the presence of other clinical features or the definition of a precise epileptologic syndrome. A total of 8 different disease-causing mutations were detected in our population, confirming the pivotal role of these genes in the pathogenesis of the epileptic encephalopathies in infancy. Early key clinical and electroencephalographic phenotypical features identified in these patients can contribute to more precise and early diagnoses. This work provides a better phenotypic characterization and more stringent clinical indications for the molecular test.

Mutations of the cyclin-dependent kinase-like 5 gene (CDKL5), reported almost exclusively in female subjects, have been recently found to be the cause of a phenotype overlapping Rett syndrome with early-onset epileptic encephalopathy. We describe the first CDKL5 mutation detected in a male individual with 47,XXY karyotype. This previously unreported, de novo, mutation truncates the large CDKL5 COOH-terminal region, thought to be crucial for the proper sub-cellular localization of the CDKL5 protein. The resulting phenotype is characterized by a severe early-onset epileptic encephalopathy, global developmental delay, and profound intellectual and motor impairment with features reminiscent of Rett syndrome. In light of the data presented we discuss the possible phenotypic modulatory effects of the supernumerary wild type X allele and pattern of X chromosome inactivation and stress the importance of considering the causal involvement of CDKL5 in developmentally delayed males with early-onset seizures., ((c) 2009 Wiley-Liss, Inc.)