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Pathogenic bi-allelic variants in the SPG11 gene result in rare motor neuron disorders such as Hereditary Spastic Paraplegia type 11, Charcot-Marie Tooth, and Juvenile Amyotrophic Lateral Sclerosis-5. The main challenge in SPG11-linked disease research is the lack of antibodies against SPG11 encoded spatacsin. Here, we describe the CRISPR/Cas9 mediated generation and validation of an endogenously tagged SPG11- human iPSC line that contains an HA tag at the C-terminus of SPG11. The line exhibits multi-lineage differentiation potential and holds promise for studying the role of spatacsin and for the elucidation of SPG11-associated pathogenesis. Resource Table., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)

Purpose: We describe a novel neurobehavioral phenotype of autism spectrum disorder (ASD), intellectual disability, and/or attention-deficit/hyperactivity disorder (ADHD) associated with de novo or inherited deleterious variants in members of the RFX family of genes. RFX genes are evolutionarily conserved transcription factors that act as master regulators of central nervous system development and ciliogenesis., Methods: We assembled a cohort of 38 individuals (from 33 unrelated families) with de novo variants in RFX3, RFX4, and RFX7. We describe their common clinical phenotypes and present bioinformatic analyses of expression patterns and downstream targets of these genes as they relate to other neurodevelopmental risk genes., Results: These individuals share neurobehavioral features including ASD, intellectual disability, and/or ADHD; other frequent features include hypersensitivity to sensory stimuli and sleep problems. RFX3, RFX4, and RFX7 are strongly expressed in developing and adult human brain, and X-box binding motifs as well as RFX ChIP-seq peaks are enriched in the cis-regulatory regions of known ASD risk genes., Conclusion: These results establish a likely role of deleterious variation in RFX3, RFX4, and RFX7 in cases of monogenic intellectual disability, ADHD and ASD, and position these genes as potentially critical transcriptional regulators of neurobiological pathways associated with neurodevelopmental disease pathogenesis.

Purpose: A few de novo missense variants in the cytoplasmic FMRP-interacting protein 2 (CYFIP2) gene have recently been described as a novel cause of severe intellectual disability, seizures, and hypotonia in 18 individuals, with p.Arg87 substitutions in the majority., Methods: We assembled data from 19 newly identified and all 18 previously published individuals with CYFIP2 variants. By structural modeling and investigation of WAVE-regulatory complex (WRC)-mediated actin polymerization in six patient fibroblast lines we assessed the impact of CYFIP2 variants on the WRC., Results: Sixteen of 19 individuals harbor two previously described and 11 novel (likely) disease-associated missense variants. We report p.Asp724 as second mutational hotspot (4/19 cases). Genotype-phenotype correlation confirms a consistently severe phenotype in p.Arg87 patients but a more variable phenotype in p.Asp724 and other substitutions. Three individuals with milder phenotypes carry putative loss-of-function variants, which remain of unclear pathogenicity. Structural modeling predicted missense variants to disturb interactions within the WRC or impair CYFIP2 stability. Consistent with its role in WRC-mediated actin polymerization we substantiate aberrant regulation of the actin cytoskeleton in patient fibroblasts., Conclusion: Our study expands the clinical and molecular spectrum of CYFIP2-related neurodevelopmental disorder and provides evidence for aberrant WRC-mediated actin dynamics as contributing cellular pathomechanism.

Purpose: Microcephaly is a sign of many genetic conditions but has been rarely systematically evaluated. We therefore comprehensively studied the clinical and genetic landscape of an unselected cohort of patients with microcephaly., Methods: We performed clinical assessment, high-resolution chromosomal microarray analysis, exome sequencing, and functional studies in 62 patients (58% with primary microcephaly [PM], 27% with secondary microcephaly [SM], and 15% of unknown onset)., Results: We found severity of developmental delay/intellectual disability correlating with severity of microcephaly in PM, but not SM. We detected causative variants in 48.4% of patients and found divergent inheritance and variant pattern for PM (mainly recessive and likely gene-disrupting [LGD]) versus SM (all dominant de novo and evenly LGD or missense). While centrosome-related pathways were solely identified in PM, transcriptional regulation was the most frequently affected pathway in both SM and PM. Unexpectedly, we found causative variants in different mitochondria-related genes accounting for ~5% of patients, which emphasizes their role even in syndromic PM. Additionally, we delineated novel candidate genes involved in centrosome-related pathway (SPAG5, TEDC1), Wnt signaling (VPS26A, ZNRF3), and RNA trafficking (DDX1)., Conclusion: Our findings enable improved evaluation and genetic counseling of PM and SM patients and further elucidate microcephaly pathways.

A decade after the designation of MED13L as a gene and its link to intellectual disability (ID) and dextro-looped transposition of great arteries in 2003, we previously described a recognizable syndrome due to MED13L haploinsufficiency. Subsequent reports of 22 further patients diagnosed by genome-wide testing further delineated the syndrome with expansion of the phenotypic spectrum and showed reduced penetrance for congenital heart defects. We now report two novel patients identified by whole exome sequencing, one with a de novo MED13L truncating mutation and the other with a de novo missense mutation. The first patient indicates some facial resemblance to Kleefstra syndrome as a novel differential diagnosis, and the second patient shows, for the first time, recurrence of a MED13L missense mutation (p.(Asp860Gly)). Notably, our in silico modelling predicted this missense mutation to decrease the stability of an alpha-helix and thereby affecting the MED13L secondary structure, while the majority of published missense mutations remain variants of uncertain significance. Review of the reported patients with MED13L haploinsufficiency indicates moderate to severe ID and facial anomalies in all patients, as well as severe speech delay and muscular hypotonia in the majority. Further common signs include abnormal MRI findings of myelination defects and abnormal corpus callosum, ataxia and coordination problems, autistic features, seizures/abnormal EEG, or congenital heart defects, present in about 20-50% of the patients. With reference to facial anomalies, the majority of patients were reported to show broad/prominent forehead, low set ears, bitemporal narrowing, upslanting palpebral fissures, depressed/flat nasal bridge, bulbous nose, and abnormal chin, but macroglossia and horizontal eyebrows were also observed in ∼30%. The latter are especially important in the differential diagnosis of 1p36 deletion and Kleefstra syndromes, while the more common facial gestalt shows some resemblance to 22q11.2 deletion syndrome. Despite the fact that MED13L was found to be one of the most common ID genes in the Deciphering Developmental Disorders Study, further detailed patient descriptions are needed to explore the full clinical spectrum, potential genotype-phenotype correlations, as well as the role of missense mutations and potential mutational hotspots along the gene., (Copyright © 2017 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)