Cerebral organoids in a dish: progress and prospects.

A three-dimensional culture of cortical tissues derived from pluripotent stem cells offers an opportunity to model human brain development and disorders. In a recent issue of Nature, Lancaster et al. describe a new method for generating cerebral organoids in a dish and use it to model microcephaly.

Mcph1, mutated in primary microcephaly, is also crucial for erythropoiesis.

Microcephaly is a common feature in inherited bone marrow failure syndromes, prompting investigations into shared pathways between neurogenesis and hematopoiesis. To understand this association, we studied the role of the microcephaly gene Mcph1 in hematological development. Our research revealed that Mcph1-knockout mice exhibited congenital macrocytic anemia due to impaired terminal erythroid differentiation during fetal development. Anemia's cause is a failure to complete cell division, evident from tetraploid erythroid progenitors with DNA content exceeding 4n. Gene expression profiling demonstrated activation of the p53 pathway in Mcph1-deficient erythroid precursors, leading to overexpression of Cdkn1a/p21, a major mediator of p53-dependent cell cycle arrest. Surprisingly, fetal brain analysis revealed hypertrophied binucleated neuroprogenitors overexpressing p21 in Mcph1-knockout mice, indicating a shared pathophysiological mechanism underlying both erythroid and neurological defects. However, inactivating p53 in Mcph1-/- mice failed to reverse anemia and microcephaly, suggesting that p53 activation in Mcph1-deficient cells resulted from their proliferation defect rather than causing it. These findings shed new light on Mcph1's function in fetal hematopoietic development, emphasizing the impact of disrupted cell division on neurogenesis and erythropoiesis - a common limiting pathway.

Entosis implicates a new role for P53 in microcephaly pathogenesis, beyond apoptosis.

Entosis, a form of cell cannibalism, is a newly discovered pathogenic mechanism leading to the development of small brains, termed microcephaly, in which P53 activation was found to play a major role. Microcephaly with entosis, found in Pals1 mutant mice, displays P53 activation that promotes entosis and apoptotic cell death. This previously unappreciated pathogenic mechanism represents a novel cellular dynamic in dividing cortical progenitors which is responsible for cell loss. To date, various recent models of microcephaly have bolstered the importance of P53 activation in cell death leading to microcephaly. P53 activation caused by mitotic delay or DNA damage manifests apoptotic cell death which can be suppressed by P53 removal in these animal models. Such genetic studies attest P53 activation as quality control meant to eliminate genomically unfit cells with minimal involvement in the actual function of microcephaly associated genes. In this review, we summarize the known role of P53 activation in a variety of microcephaly models and introduce a novel mechanism wherein entotic cell cannibalism in neural progenitors is triggered by P53 activation.

PhenoApt leverages clinical expertise to prioritize candidate genes via machine learning.

In recent years, exome sequencing (ES) has shown great utility in the diagnoses of Mendelian disorders. However, after rigorous filtering, a typical ES analysis still involves the interpretation of hundreds of variants, which greatly hinders the rapid identification of causative genes. Since the interpretations of ES data require comprehensive clinical analyses, taking clinical expertise into consideration can speed the molecular diagnoses of Mendelian disorders. To leverage clinical expertise to prioritize candidate genes, we developed PhenoApt, a phenotype-driven gene prioritization tool that allows users to assign a customized weight to each phenotype, via a machine-learning algorithm. Using the ability to rank causative genes in top-10 lists as an evaluation metric, baseline analysis demonstrated that PhenoApt outperformed previous phenotype-driven gene prioritization tools by a relative increase of 22.7%-140.0% in three independent, real-world, multi-center cohorts (cohort 1, n = 185; cohort 2, n = 784; and cohort 3, n = 208). Additional trials showed that, by adding weights to clinical indications, which should be explained by the causative gene, PhenoApt performance was improved by a relative increase of 37.3% in cohort 2 (n = 471) and 21.4% in cohort 3 (n = 208). Moreover, PhenoApt could assign an intrinsic weight to each phenotype based on the likelihood of its being a Mendelian trait using term frequency-inverse document frequency techniques. When clinical indications were assigned with intrinsic weights, PhenoApt performance was improved by a relative increase of 23.7% in cohort 2 and 15.5% in cohort 3. For the integration of PhenoApt into clinical practice, we developed a user-friendly website and a command-line tool.

Chromosome 16p11.2 microdeletion syndrome with microcephaly and Dandy-Walker malformation spectrum: expanding the known phenotype.

BACKGROUND: Chromosome 16p11.2 deletions and duplications were found to be the second most common copy number variation (CNV) reported in cases with clinical presentation suggestive of chromosomal syndromes. Chromosome 16p11.2 deletion syndrome shows remarkable phenotypic heterogeneity with a wide variability of presentation extending from normal development and cognition to severe phenotypes. The clinical spectrum ranges from neurocognitive and global developmental delay (GDD), intellectual disability, and language defects (dysarthria /apraxia) to neuropsychiatric and autism spectrum disorders. Other presentations include dysmorphic features, congenital malformations, insulin resistance, and a tendency for obesity. Our study aims to narrow the gap of knowledge in Saudi Arabia and the Middle Eastern and Northern African (MENA) region about genetic disorders, particularly CNV-associated disorders. Despite their rarity, genetic studies in the MENA region revealed high potential with remarkable genetic and phenotypic novelty. RESULTS: We identified a heterozygous de novo recurrent proximal chromosome 16p11.2 microdeletion by microarray (arr[GRCh38]16p11.2(29555974_30166595)x1) [(arr[GRCh37]16p11.2(29567295_30177916)x1)] and confirmed by whole exome sequencing (arr[GRCh37]16p11.2(29635211_30199850)x1). We report a Saudi girl with severe motor and cognitive disability, myoclonic epilepsy, deafness, and visual impairment carrying the above-described deletion. Our study broadens the known phenotypic spectrum associated with recurrent proximal 16p11.2 microdeletion syndrome to include developmental dysplasia of the hip, optic atrophy, and a flat retina. Notably, the patient exhibited a rare combination of microcephaly, features consistent with the Dandy-Walker spectrum, and a thin corpus callosum (TCC), which are extremely infrequent presentations in patients with the 16p11.2 microdeletion. Additionally, the patient displayed areas of skin and hair hypopigmentation, attributed to a homozygous hypomorphic allele in the TYR gene. CONCLUSION: This report expands on the clinical phenotype associated with proximal 16p11.2 microdeletion syndrome, highlighting the potential of genetic research in Saudi Arabia and the MENA region. It underscores the importance of similar future studies.

Biallelic null variants in PNPLA8 cause microcephaly by reducing the number of basal radial glia.

Patatin-like phospholipase domain-containing lipase 8 (PNPLA8), one of the calcium-independent phospholipase A2 enzymes, is involved in various physiological processes through the maintenance of membrane phospholipids. Biallelic variants in PNPLA8 have been associated with a range of paediatric neurodegenerative disorders. However, the phenotypic spectrum, genotype-phenotype correlations and the underlying mechanisms are poorly understood. Here, we newly identified 14 individuals from 12 unrelated families with biallelic ultra-rare variants in PNPLA8 presenting with a wide phenotypic spectrum of clinical features. Analysis of the clinical features of current and previously reported individuals (25 affected individuals across 20 families) showed that PNPLA8-related neurological diseases manifest as a continuum ranging from variable developmental and/or degenerative epileptic-dyskinetic encephalopathy to childhood-onset neurodegeneration. We found that complete loss of PNPLA8 was associated with the more profound end of the spectrum, with congenital microcephaly. Using cerebral organoids generated from human induced pluripotent stem cells, we found that loss of PNPLA8 led to developmental defects by reducing the number of basal radial glial cells and upper-layer neurons. Spatial transcriptomics revealed that loss of PNPLA8 altered the fate specification of apical radial glial cells, as reflected by the enrichment of gene sets related to the cell cycle, basal radial glial cells and neural differentiation. Neural progenitor cells lacking PNPLA8 showed a reduced amount of lysophosphatidic acid, lysophosphatidylethanolamine and phosphatidic acid. The reduced number of basal radial glial cells in patient-derived cerebral organoids was rescued, in part, by the addition of lysophosphatidic acid. Our data suggest that PNPLA8 is crucial to meet phospholipid synthetic needs and to produce abundant basal radial glial cells in human brain development.

IER3IP1-mutations cause microcephaly by selective inhibition of ER-Golgi transport.

Mutations in the IER3IP1 (Immediate Early Response-3 Interacting Protein 1) gene can give rise to MEDS1 (Microcephaly with Simplified Gyral Pattern, Epilepsy, and Permanent Neonatal Diabetes Syndrome-1), a severe condition leading to early childhood mortality. The small endoplasmic reticulum (ER)-membrane protein IER3IP1 plays a non-essential role in ER-Golgi transport. Here, we employed secretome and cell-surface proteomics to demonstrate that the absence of IER3IP1 results in the mistrafficking of proteins crucial for neuronal development and survival, including FGFR3, UNC5B and SEMA4D. This phenomenon correlates with the distension of ER membranes and increased lysosomal activity. Notably, the trafficking of cargo receptor ERGIC53 and KDEL-receptor 2 are compromised, with the latter leading to the anomalous secretion of ER-localized chaperones. Our investigation extended to in-utero knock-down of Ier3ip1 in mouse embryo brains, revealing a morphological phenotype in newborn neurons. In summary, our findings provide insights into how the loss or mutation of a 10 kDa small ER-membrane protein can cause a fatal syndrome.

HiPSC-derived 3D neural models reveal neurodevelopmental pathomechanisms of the Cockayne Syndrome B.

Cockayne Syndrome B (CSB) is a hereditary multiorgan syndrome which-through largely unknown mechanisms-can affect the brain where it clinically presents with microcephaly, intellectual disability and demyelination. Using human induced pluripotent stem cell (hiPSC)-derived neural 3D models generated from CSB patient-derived and isogenic control lines, we here provide explanations for these three major neuropathological phenotypes. In our models, CSB deficiency is associated with (i) impaired cellular migration due to defective autophagy as an explanation for clinical microcephaly; (ii) altered neuronal network functionality and neurotransmitter GABA levels, which is suggestive of a disturbed GABA switch that likely impairs brain circuit formation and ultimately causes intellectual disability; and (iii) impaired oligodendrocyte maturation as a possible cause of the demyelination observed in children with CSB. Of note, the impaired migration and oligodendrocyte maturation could both be partially rescued by pharmacological HDAC inhibition.

Complex structural variation and nonsense variant in trans cause VPS50-related disorder.

Homozygous VPS50 variants have been previously described in two unrelated patients with a neurodevelopmental disorder with microcephaly, seizures and neonatal cholestasis. VPS50 encodes a subunit that is unique to the heterotetrameric endosome-associated recycling protein (EARP) complex. The other subunits of the EARP complex, such as VPS51, VPS52 and VPS53, are also shared by the Golgi-associated retrograde protein complex. We report on an 18-month-old female patient with biallelic VPS50 variants. She carried a paternally inherited heterozygous nonsense c.13A>T; p.(Lys5*) variant. By long-read genome sequencing, we characterised a structural variant with a 4.3 Mb inversion flanked by deletions at both breakpoints on the maternal allele. The ~428 kb deletion at the telomeric inversion breakpoint encompasses the entire VPS50 gene. We demonstrated a deficiency of VPS50 in patient-derived fibroblasts, confirming the loss-of-function nature of both VPS50 variants. VPS53 and VPS52 protein levels were significantly reduced and absent, respectively, in fibroblasts of the patient. These data show that VPS50 and/or EARP deficiency and the associated functional defects underlie the phenotype in patients with VPS50 pathogenic variants. The VPS50-related core phenotype comprises severe developmental delay, postnatal microcephaly, hypoplastic corpus callosum, neonatal low gamma-glutamyl transpeptidase cholestasis and failure to thrive. The disease is potentially fatal in early childhood.

Genetic evidence for splicing-dependent structural and functional plasticity in CASK protein.

BACKGROUND: Pontocerebellar hypoplasia (PCH) may present with supratentorial phenotypes and is often accompanied by microcephaly. Damaging mutations in the X-linked gene CASK produce self-limiting microcephaly with PCH in females but are often lethal in males. CASK deficiency leads to early degeneration of cerebellar granule cells but its role in other regions of the brain remains uncertain. METHOD: We generated a conditional Cask knockout mice and deleted Cask ubiquitously after birth at different times. We examined the clinical features in several subjects with damaging mutations clustered in the central part of the CASK protein. We have performed phylogenetic analysis and RT-PCR to assess the splicing pattern within the same protein region and performed in silico structural analysis to examine the effect of splicing on the CASK's structure. RESULT: We demonstrate that deletion of murine Cask after adulthood does not affect survival but leads to cerebellar degeneration and ataxia over time. Intriguingly, damaging hemizygous CASK mutations in boys who display microcephaly and cerebral dysfunction but without PCH are known. These mutations are present in two vertebrate-specific CASK exons. These exons are subject to alternative splicing both in forebrain and hindbrain. Inclusion of these exons differentially affects the molecular structure and hence possibly the function/s of the CASK C-terminus. CONCLUSION: Loss of CASK function disproportionately affects the cerebellum. Clinical data, however, suggest that CASK may have additional vertebrate-specific function/s that play a role in the mammalian forebrain. Thus, CASK has an ancient function shared between invertebrates and vertebrates as well as novel vertebrate-specific function/s.

Christianson syndrome across the lifespan: genetic mutations and longitudinal study in children, adolescents, and adults.

OBJECTIVES: Mutations in the X-linked endosomal Na+/H+ exchanger 6 (NHE6) cause Christianson syndrome (CS). Here, in the largest study to date, we examine genetic diversity and clinical progression in CS into adulthood. METHOD: Data were collected as part of the International Christianson Syndrome and NHE6 (SLC9A6) Gene Network Study. 44 individuals with 31 unique NHE6 mutations, age 2-32 years, were followed prospectively, herein reporting baseline, 1 year follow-up and retrospective natural history. RESULTS: We present data on the CS phenotype with regard to physical growth and adaptive and motor regression across the lifespan including information on mortality. Longitudinal data on body weight and height were examined using a linear mixed model. The rate of growth across development was slow and resulted in prominently decreased age-normed height and weight by adulthood. Adaptive functioning was longitudinally examined; a majority of adult participants (18+ years) lost gross and fine motor skills over a 1 year follow-up. Previously defined core diagnostic criteria for CS (present in>85%)-namely non-verbal status, intellectual disability, epilepsy, postnatal microcephaly, ataxia, hyperkinesia-were universally present in age 6-16; however, an additional core feature of high pain tolerance was added (present in 91%). While neurologic examinations were consistent with cerebellar dysfunction, importantly, a majority of individuals (>50% older than 10) also had corticospinal tract abnormalities. Three participants died during the period of the study. CONCLUSIONS: In this large and longitudinal study of CS, we begin to define the trajectory of symptoms and the adult phenotype thereby identifying critical targets for treatment.

How does Zika virus cause microcephaly?

The re-emergence of Zika virus (ZIKV), a mosquito-borne and sexually transmitted flavivirus circulating in >70 countries and territories, poses a significant global threat to public health due to its ability to cause severe developmental defects in the human brain, such as microcephaly. Since the World Health Organization declared the ZIKV outbreak a Public Health Emergency of International Concern, remarkable progress has been made to gain insight into cellular targets, pathogenesis, and underlying biological mechanisms of ZIKV infection. Here we review the current knowledge and progress in understanding the impact of ZIKV exposure on the mammalian brain development and discuss potential underlying mechanisms.

CIAO1 and MMS19 deficiency: A lethal neurodegenerative phenotype caused by cytosolic Fe-S cluster protein assembly disorders.

PURPOSE: The functionality of many cellular proteins depends on cofactors; yet, they have only been implicated in a minority of Mendelian diseases. Here, we describe the first 2 inherited disorders of the cytosolic iron-sulfur protein assembly system. METHODS: Genetic testing via genome sequencing was applied to identify the underlying disease cause in 3 patients with microcephaly, congenital brain malformations, progressive developmental and neurologic impairments, recurrent infections, and a fatal outcome. Studies in patient-derived skin fibroblasts and zebrafish models were performed to investigate the biochemical and cellular consequences. RESULTS: Metabolic analysis showed elevated uracil and thymine levels in body fluids but no pathogenic variants in DPYD, encoding dihydropyrimidine dehydrogenase. Genome sequencing identified compound heterozygosity in 2 patients for missense variants in CIAO1, encoding cytosolic iron-sulfur assembly component 1, and homozygosity for an in-frame 3-nucleotide deletion in MMS19, encoding the MMS19 homolog, cytosolic iron-sulfur assembly component, in the third patient. Profound alterations in the proteome, metabolome, and lipidome were observed in patient-derived fibroblasts. We confirmed the detrimental effect of deficiencies in CIAO1 and MMS19 in zebrafish models. CONCLUSION: A general failure of cytosolic and nuclear iron-sulfur protein maturation caused pleiotropic effects. The critical function of the cytosolic iron-sulfur protein assembly machinery for antiviral host defense may well explain the recurrent severe infections occurring in our patients.

Biallelic loss-of-function variants of ZFTRAF1 cause neurodevelopmental disorder with microcephaly and hypotonia.

PURPOSE: Neurodevelopmental disorders exhibit clinical and genetic heterogeneity, ergo manifest dysfunction in components of diverse cellular pathways; the precise pathomechanism for the majority remains elusive. METHODS: We studied 5 affected individuals from 3 unrelated families manifesting global developmental delay, postnatal microcephaly, and hypotonia. We used exome sequencing and prioritized variants that were subsequently characterized using immunofluorescence, immunoblotting, pulldown assays, and RNA sequencing. RESULTS: We identified biallelic variants in ZFTRAF1, encoding a protein of yet unknown function. Four affected individuals from 2 unrelated families segregated 2 homozygous frameshift variants in ZFTRAF1, whereas, in the third family, an intronic splice site variant was detected. We investigated ZFTRAF1 at the cellular level and signified it as a nucleocytoplasmic protein in different human cell lines. ZFTRAF1 was completely absent in the fibroblasts of 2 affected individuals. We also identified 110 interacting proteins enriched in mRNA processing and autophagy-related pathways. Based on profiling of autophagy markers, patient-derived fibroblasts show irregularities in the protein degradation process. CONCLUSION: Thus, our findings suggest that biallelic variants of ZFTRAF1 cause a severe neurodevelopmental disorder.

B-cell immune deficiency in twin sisters expands the phenotype of MOPDI.

Microcephalic osteodysplastic primordial dwarfism type I (MOPDI) is a very rare and severe autosomal recessive disorder characterized by marked intrauterine growth retardation, skeletal dysplasia, microcephaly and brain malformations. MOPDI is caused by biallelic mutations in RNU4ATAC, a non-coding gene involved in U12-type splicing of 1% of the introns in the genome, which are recognized by their specific splicing consensus sequences. Here, we describe a unique observation of immunodeficiency in twin sisters with mild MOPDI, who harbor a novel n.108_126del mutation, encompassing part of the U4atac snRNA 3' stem-loop and Sm protein binding site, and the previously reported n.111G>A mutation. Interestingly, both twin sisters show mild B-cell anomalies, including low naive B-cell counts and increased memory B-cell and plasmablasts counts, suggesting partial and transitory blockage of B-cell maturation and/or excessive activation of naive B-cells. Hence, the localization of a mutation in stem II of U4atac snRNA, as observed in another RNU4ATAC-opathy with immunodeficiency, that is, Roifman syndrome (RFMN), is not required for the occurrence of an immune deficiency. Finally, we emphasize the importance of considering immunodeficiency in MOPDI management to reduce the risk of serious infectious episodes.

Dissecting CASK: Novel splice site variant associated with male MICPCH phenotype.

CASK (MIM#300172), encoding a calcium/calmodulin-dependent serine protein kinase, is crucial for synaptic transmission and gene regulation during neural development. Pathogenic variants of CASK are known to cause several neurodevelopmental disorders, including X-linked intellectual disability and microcephaly with pontine and cerebellar hypoplasia (MICPCH). This study introduces a novel, de novo synonymous CASK variant (NM_001367721.1: c.1737G>A, p.(Glu579=)), discovered in a male patient diagnosed with MICPCH, characterized by microcephaly, developmental delay, visual impairment, and myoclonic seizures. The variant disrupts a donor splice-site at the end of exon 18. Transcriptomic analysis of blood identified 12 different CASK transcripts secondary to the synonymous variant. Nearly one third of these transcripts were predicted to result in nonsense mediated decay or protein degradation. Protein modeling revealed structural alterations in the PDZ functional domain of CASK, due to exon 18 deletion. Our findings highlight the utility of transcriptomic analysis in demonstrating the underlying disease mechanism in neurodevelopmental disorders.

A novel KNL1 intronic splicing variant likely destabilizes the KMN complex, causing primary microcephaly.

Primary microcephaly (MCPH) is an autosomal recessive disorder characterized by head circumference of at least two standard deviations below the mean. Biallelic variants in the kinetochore gene KNL1 is a known cause of MCPH4. KNL1 is the central component of the KNL1-MIS12-NSL1 (KMN) network, which acts as the signaling hub of the kinetochore and is required for correct chromosomal segregation during mitosis. We identified biallelic KNL1 variants in two siblings from a non-consanguineous family with microcephaly and intellectual disability. The two siblings carry a frameshift variant predicted to prematurely truncate the transcript and undergo nonsense mediated decay, and an intronic single nucleotide variant (SNV) predicted to disrupt splicing. An in vitro splicing assay and qPCR from blood-derived RNA confirmed that the intronic variant skips exon 23, significantly reducing levels of the canonical transcript. Protein modeling confirmed that absence of exon 23, an inframe exon, would disrupt a key interaction within the KMN network and likely destabilize the kinetochore signaling hub, disrupting mitosis. Therefore, this splicing variant is pathogenic and, in trans with a frameshift variant, causes the MCPH phenotype associated with KLN1. This finding furthers the association of splicing variants as a common pathogenic variant class for KNL1.

Novel biallelic SASS6 variants associated with primary microcephaly and fetal growth restriction.

Primary microcephaly is characterized by a head circumference prenatally or at birth that falls below three standard deviations from age-, ethnic-, and sex-specific norms. Genetic defects are one of the underlying causes of primary microcephaly. Since 2014, five variants of the SASS6 gene have been identified as the cause of MCPH 14 in three reported families. In this study, we present the genetic findings of members of a nonconsanguineous Chinese couple with a history of microcephaly and fetal growth restriction (FGR) during their first pregnancy. Utilizing trio whole-exome sequencing, we identified compound heterozygous variants involving a frameshift NM_194292.3:c.450_453del p.(Lys150AsnfsTer7) variant and a splice region NM_194292.3:c.1674+3A>G variant within the SASS6 gene in the affected fetus. Moreover, reverse transcriptase-polymerase chain reaction from RNA of the mother's peripheral blood leukocytes revealed that the c.1674+3A>G variant led to the skipping of exon 14 and an inframe deletion. To the best of our knowledge, the association between FGR and SASS6-related microcephaly has not been reported, and our findings confirm the pivotal role of SASS6 in microcephaly pathogenesis and reveal an expanded view of the phenotype and mutation spectrum associated with this gene.

Novel biallelic ZNF335 variant causing primary microcephaly: A case report and radiological review.

Biallelic pathogenic variants in ZNF335 are one of the genetic causes of microcephaly, reported only in the past decade. It regulates neural progenitor proliferation and neurogenesis by interacting with a H3K4 methyltransferase complex. Biallelic pathogenic ZNF335 variants predispose to neuronal cell death and aberrant differentiation, thus causing secondary microcephaly. These neurodevelopmental anomalies lead to imaging findings in the cortex, posterior fossa, and basal ganglia. We report an individual of Nepalese ancestry with a novel homozygous ZNF335 variant (c.3591 + 2dup) (p.?) (NM_022095.3) which on further RNA analysis confirmed a splice site variant in intron 23. The patient presented with primary microcephaly with atrophic cerebral hemispheres, oversimplification of gyri, basal ganglia, and corpus callosal atrophy. Literature review on the topic revealed a spectrum of brain abnormalities, which can present either with a primary or secondary microcephaly depending upon the underlying genetic variant.

RNA analysis and computer-aided facial phenotyping help to classify a novel TRIO splice site variant.

Pathogenic variants in TRIO, encoding the guanine nucleotide exchange factor, are associated with two distinct neurodevelopmental delay phenotypes: gain-of-function missense mutations within the spectrin repeats are causative for a severe developmental delay with macrocephaly (MIM: 618825), whereas loss-of-function missense variants in the GEF1 domain and truncating variants throughout the gene lead to a milder developmental delay and microcephaly (MIM: 617061). In three affected family members with mild intellectual disability/NDD and microcephaly, we detected a novel heterozygous TRIO variant at the last coding base of exon 31 (NM_007118.4:c.4716G>A). RNA analysis from patient-derived lymphoblastoid cells confirmed aberrant splicing resulting in the skipping of exon 31 (r.4615_4716del), leading to an in-frame deletion in the first Pleckstrin homology subdomain of the GEF1 domain: p.(Thr1539_Lys1572del). To test for a distinct gestalt, facial characteristics of the family members and 41 previously published TRIO cases were systematically evaluated via GestaltMatcher. Computational analysis of the facial gestalt suggests a distinguishable facial TRIO-phenotype not outlined in the existing literature.