Mitochondrial dysfunction and oxidative stress contribute to cognitive and motor impairment in FOXP1 syndrome.

FOXP1 syndrome caused by haploinsufficiency of the forkhead box protein P1 (FOXP1) gene is a neurodevelopmental disorder that manifests motor dysfunction, intellectual disability, autism, and language impairment. In this study, we used a Foxp1+/- mouse model to address whether cognitive and motor deficits in FOXP1 syndrome are associated with mitochondrial dysfunction and oxidative stress. Here, we show that genes with a role in mitochondrial biogenesis and dynamics (e.g., Foxo1, Pgc-1α, Tfam, Opa1, and Drp1) were dysregulated in the striatum of Foxp1+/- mice at different postnatal stages. Furthermore, these animals exhibit a reduced mitochondrial membrane potential and complex I activity, as well as decreased expression of the antioxidants superoxide dismutase 2 (Sod2) and glutathione (GSH), resulting in increased oxidative stress and lipid peroxidation. These features can explain the reduced neurite branching, learning and memory, endurance, and motor coordination that we observed in these animals. Taken together, we provide strong evidence of mitochondrial dysfunction in Foxp1+/- mice, suggesting that insufficient energy supply and excessive oxidative stress underlie the cognitive and motor impairment in FOXP1 deficiency.

A complementary study approach unravels novel players in the pathoetiology of Hirschsprung disease.

Hirschsprung disease (HSCR, OMIM 142623) involves congenital intestinal obstruction caused by dysfunction of neural crest cells and their progeny during enteric nervous system (ENS) development. HSCR is a multifactorial disorder; pathogenetic variants accounting for disease phenotype are identified only in a minority of cases, and the identification of novel disease-relevant genes remains challenging. In order to identify and to validate a potential disease-causing relevance of novel HSCR candidate genes, we established a complementary study approach, combining whole exome sequencing (WES) with transcriptome analysis of murine embryonic ENS-related tissues, literature and database searches, in silico network analyses, and functional readouts using candidate gene-specific genome-edited cell clones. WES datasets of two patients with HSCR and their non-affected parents were analysed, and four novel HSCR candidate genes could be identified: ATP7A, SREBF1, ABCD1 and PIAS2. Further rare variants in these genes were identified in additional HSCR patients, suggesting disease relevance. Transcriptomics revealed that these genes are expressed in embryonic and fetal gastrointestinal tissues. Knockout of these genes in neuronal cells demonstrated impaired cell differentiation, proliferation and/or survival. Our approach identified and validated candidate HSCR genes and provided further insight into the underlying pathomechanisms of HSCR.

Imbalanced post- and extrasynaptic SHANK2A functions during development affect social behavior in SHANK2-mediated neuropsychiatric disorders.

Mutations in SHANK genes play an undisputed role in neuropsychiatric disorders. Until now, research has focused on the postsynaptic function of SHANKs, and prominent postsynaptic alterations in glutamatergic signal transmission have been reported in Shank KO mouse models. Recent studies have also suggested a possible presynaptic function of SHANK proteins, but these remain poorly defined. In this study, we examined how SHANK2 can mediate electrophysiological, molecular, and behavioral effects by conditionally overexpressing either wild-type SHANK2A or the extrasynaptic SHANK2A(R462X) variant. SHANK2A overexpression affected pre- and postsynaptic targets and revealed a reversible, development-dependent autism spectrum disorder-like behavior. SHANK2A also mediated redistribution of Ca2+-permeable AMPA receptors between apical and basal hippocampal CA1 dendrites, leading to impaired synaptic plasticity in the basal dendrites. Moreover, SHANK2A overexpression reduced social interaction and increased the excitatory noise in the olfactory cortex during odor processing. In contrast, overexpression of the extrasynaptic SHANK2A(R462X) variant did not impair hippocampal synaptic plasticity, but still altered the expression of presynaptic/axonal signaling proteins. We also observed an attention-deficit/hyperactivity-like behavior and improved social interaction along with enhanced signal-to-noise ratio in cortical odor processing. Our results suggest that the disruption of pre- and postsynaptic SHANK2 functions caused by SHANK2 mutations has a strong impact on social behavior. These findings indicate that pre- and postsynaptic SHANK2 actions cooperate for normal neuronal function, and that an imbalance between these functions may lead to different neuropsychiatric disorders.

Foxp1 expression is essential for sex-specific murine neonatal ultrasonic vocalization.

Autism and speech and language deficits are predominantly found in boys, however the causative mechanisms for this sex bias are unknown. Human FOXP1 is associated with autism, intellectual disability and speech and language deficits. Its closely related family member FOXP2 is involved in speech and language disorder and Foxp2 deficient mice have demonstrated an absence of ultrasonic vocalizations (USVs). Since Foxp1 and Foxp2 form heterodimers for transcriptional regulation, we investigated USV in neonatal brain-specific Foxp1 KO mice. Foxp1 KO pups had strongly reduced USV and lacked the sex-specific call rate from WT pups, indicating that Foxp1 is essential for normal USV. As expression differences of Foxp1 or Foxp2 could explain the sex-dimorphic vocalization in WT animals, we quantified both proteins in the striatum and cortex at P7.5 and detected a sex-specific expression of Foxp2 in the striatum. We further analyzed Foxp1 and Foxp2 expression in the striatum and cortex of CD1 mice at different embryonic and postnatal stages and observed sex differences in both genes at E17.5 and P7.5. Sex hormones, especially androgens are known to play a crucial role in the sexual differentiation of vocalizations in many vertebrates. We show that Foxp1 and the androgen receptor are co-expressed in striatal medium spiny neurons and that brain-specific androgen receptor KO (ArNesCre) mice exhibit reduced Foxp1 expression in the striatum at E17.5 and P7.5 and an increased Foxp2 level in the cortex at P7.5. Thus, androgens may contribute to sex-specific differences in Foxp1 and Foxp2 expression and USV.

Identification and functional characterization of de novo FOXP1 variants provides novel insights into the etiology of neurodevelopmental disorder.

De novo disruptions of the neural transcription factor FOXP1 are a recently discovered, rare cause of sporadic intellectual disability (ID). We report three new cases of FOXP1-related disorder identified through clinical whole-exome sequencing. Detailed phenotypic assessment confirmed that global developmental delay, autistic features, speech/language deficits, hypotonia and mild dysmorphic features are core features of the disorder. We expand the phenotypic spectrum to include sensory integration disorder and hypertelorism. Notably, the etiological variants in these cases include two missense variants within the DNA-binding domain of FOXP1. Only one such variant has been reported previously. The third patient carries a stop-gain variant. We performed functional characterization of the three missense variants alongside our stop-gain and two previously described truncating/frameshift variants. All variants severely disrupted multiple aspects of protein function. Strikingly, the missense variants had similarly severe effects on protein function as the truncating/frameshift variants. Our findings indicate that a loss of transcriptional repression activity of FOXP1 underlies the neurodevelopmental phenotype in FOXP1-related disorder. Interestingly, the three novel variants retained the ability to interact with wild-type FOXP1, suggesting these variants could exert a dominant-negative effect by interfering with the normal FOXP1 protein. These variants also retained the ability to interact with FOXP2, a paralogous transcription factor disrupted in rare cases of speech and language disorder. Thus, speech/language deficits in these individuals might be worsened through deleterious effects on FOXP2 function. Our findings highlight that de novo FOXP1 variants are a cause of sporadic ID and emphasize the importance of this transcription factor in neurodevelopment.

Identification of SLC20A1 and SLC15A4 among other genes as potential risk factors for combined pituitary hormone deficiency.

PURPOSE: Combined pituitary hormone deficiency (CPHD) is characterized by a malformed or underdeveloped pituitary gland resulting in an impaired pituitary hormone secretion. Several transcription factors have been described in its etiology, but defects in known genes account for only a small proportion of cases. METHODS: To identify novel genetic causes for congenital hypopituitarism, we performed exome-sequencing studies on 10 patients with CPHD and their unaffected parents. Two candidate genes were sequenced in further 200 patients. Genotype data of known hypopituitary genes are reviewed. RESULTS: We discovered 51 likely damaging variants in 38 genes; 12 of the 51 variants represent de novo events (24%); 11 of the 38 genes (29%) were present in the E12.5/E14.5 pituitary transcriptome. Targeted sequencing of two candidate genes, SLC20A1 and SLC15A4, of the solute carrier membrane transport protein family in 200 additional patients demonstrated two further variants predicted as damaging. We also found combinations of de novo (SLC20A1/SLC15A4) and transmitted variants (GLI2/LHX3) in the same individuals, leading to the full-blown CPHD phenotype. CONCLUSION: These data expand the pituitary target genes repertoire for diagnostics and further functional studies. Exome sequencing has identified a combination of rare variants in different genes that might explain incomplete penetrance in CPHD.

Homozygous missense mutation in the LMAN2L gene segregates with intellectual disability in a large consanguineous Pakistani family.

BACKGROUND: Intellectual disability (ID) is a neurodevelopmental disorder affecting 1%-3% of the population worldwide. It is characterised by high phenotypic and genetic heterogeneity and in most cases the underlying cause of the disorder is unknown. In our study we investigated a large consanguineous family from Baluchistan, Pakistan, comprising seven affected individuals with a severe form of autosomal recessive ID (ARID) and epilepsy, to elucidate a putative genetic cause. METHODS AND RESULTS: Whole exome sequencing (WES) of a trio, including a child with ID and epilepsy and its healthy parents that were part of this large family, revealed a homozygous missense variant p.R53Q in the lectin mannose-binding 2-like (LMAN2L) gene. This homozygous variant was co-segregating in the family with the phenotype of severe ID and infantile epilepsy; unaffected family members were heterozygous variant carriers. The variant was predicted to be pathogenic by five different in silico programmes and further three-dimensional structure modelling of the protein suggests that variant p.R53Q may impair protein-protein interaction. LMAN2L (OMIM: 609552) encodes for the lectin, mannose-binding 2-like protein which is a cargo receptor in the endoplasmic reticulum important for glycoprotein transport. Genome-wide association studies have identified an association of LMAN2L to different neuropsychiatric disorders. CONCLUSION: This is the first report linking LMAN2L to a phenotype of severe ARID and seizures, indicating that the deleterious homozygous p.R53Q variant very likely causes the disorder.

Meta-analysis of SHANK Mutations in Autism Spectrum Disorders: a gradient of severity in cognitive impairments.

SHANK genes code for scaffold proteins located at the post-synaptic density of glutamatergic synapses. In neurons, SHANK2 and SHANK3 have a positive effect on the induction and maturation of dendritic spines, whereas SHANK1 induces the enlargement of spine heads. Mutations in SHANK genes have been associated with autism spectrum disorders (ASD), but their prevalence and clinical relevance remain to be determined. Here, we performed a new screen and a meta-analysis of SHANK copy-number and coding-sequence variants in ASD. Copy-number variants were analyzed in 5,657 patients and 19,163 controls, coding-sequence variants were ascertained in 760 to 2,147 patients and 492 to 1,090 controls (depending on the gene), and, individuals carrying de novo or truncating SHANK mutations underwent an extensive clinical investigation. Copy-number variants and truncating mutations in SHANK genes were present in ∼1% of patients with ASD: mutations in SHANK1 were rare (0.04%) and present in males with normal IQ and autism; mutations in SHANK2 were present in 0.17% of patients with ASD and mild intellectual disability; mutations in SHANK3 were present in 0.69% of patients with ASD and up to 2.12% of the cases with moderate to profound intellectual disability. In summary, mutations of the SHANK genes were detected in the whole spectrum of autism with a gradient of severity in cognitive impairment. Given the rare frequency of SHANK1 and SHANK2 deleterious mutations, the clinical relevance of these genes remains to be ascertained. In contrast, the frequency and the penetrance of SHANK3 mutations in individuals with ASD and intellectual disability-more than 1 in 50-warrant its consideration for mutation screening in clinical practice.

Investigation of SHANK3 in schizophrenia.

The postsynaptic scaffolding protein SHANK3 is essential for the normal function of glutamatergic synapses in the brain. Emerging evidence suggests that impaired plasticity of glutamatergic synapses contributes to the pathology of schizophrenia (SCZ). To investigate whether variants in the SHANK3 gene contribute to the etiology of SCZ, we sequenced SHANK3 in 500 affected individuals (cohort C1). In total, we identified 48 variants and compared them to European controls from the 1000 Genomes Project and the Exome Variant Server. Five variants showed significant differences in frequencies between patients and controls. We were able to follow three of them up in an independent cohort (C2) comprising 993 SCZ patients and 932 German controls. We could not confirm an association for three of these variants (rs140201628, rs1557620, and rs61729471). Two rare variants with predicted functional relevance were identified in further SCZ individuals of cohort C1: c.3032G>T (p.G1011V) and c.*27C>T. The latter variant was found in one additional SCZ individual and the p.G1011V variant was identified in two additional SCZ individuals from cohort C2. The p.G1011V variant was the most interesting variant in our study; together with previous studies this variant has been identified in 4 out of 1,524 SCZ patients and in 4 out of 2,147 individuals with autism spectrum disorder (ASD), but not in 2468 European Sanger-sequenced controls. Therefore, we consider this variant a promising candidate variant for follow-up studies in larger samples and functional investigations. © 2017 Wiley Periodicals, Inc.

SHOX triggers the lysosomal pathway of apoptosis via oxidative stress.

The SHOX gene encodes for a transcription factor important for normal bone development. Mutations in the gene are associated with idiopathic short stature and are responsible for the growth failure and skeletal defects found in the majority of patients with Léri-Weill dyschondrosteosis (LWD) and Langer mesomelic dysplasia. SHOX is expressed in growth plate chondrocytes where it is supposed to modulate the proliferation, differentiation and cell death of these cells. Supporting this hypothesis, in vitro studies have shown that SHOX expression induces cell cycle arrest and apoptosis in both transformed and primary cells. In this study, we further characterized the cell death mechanisms triggered by SHOX and compared them with the effects induced by one clinically relevant mutant form of SHOX, detected in LWD patients (SHOX R153L) and a SHOX C-terminally truncated version (L185X). We show that SHOX expression in U2OS osteosarcoma cells leads to oxidative stress that, in turn, induces lysosomal membrane rupture with release of active cathepsin B to the cytosol and subsequent activation of the intrinsic apoptotic pathway characterized by mitochondrial membrane permeabilization and caspase activation. Importantly, cells expressing SHOX R153L or L185X did not display any of these features. Given the fact that many of the events observed in SHOX-expressing cells also characterize the complex cell death process occurring in the growth plate during endochondral ossification, our findings further support the hypothesis that SHOX may play a central role in the regulation of the cell death pathways activated during long bone development.

Coding and non-coding variants in the SHOX2 gene in patients with early-onset atrial fibrillation.

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia with a strong genetic component. Molecular pathways involving the homeodomain transcription factor Shox2 control the development and function of the cardiac conduction system in mouse and zebrafish. Here we report the analysis of human SHOX2 as a potential susceptibility gene for early-onset AF. To identify causal variants and define the underlying mechanisms, results from 378 patients with early-onset AF before the age of 60 years were analyzed and compared to 1870 controls or reference datasets. We identified two missense mutations (p.G81E, p.H283Q), that were predicted as damaging. Transactivation studies using SHOX2 targets and phenotypic rescue experiments in zebrafish demonstrated that the p.H283Q mutation severely affects SHOX2 pacemaker function. We also demonstrate an association between a 3'UTR variant c.*28T>C of SHOX2 and AF (p = 0.00515). Patients carrying this variant present significantly longer PR intervals. Mechanistically, this variant creates a functional binding site for hsa-miR-92b-5p. Circulating hsa-miR-92b-5p plasma levels were significantly altered in AF patients carrying the 3'UTR variant (p = 0.0095). Finally, we demonstrate significantly reduced SHOX2 expression levels in right atrial appendages of AF patients compared to patients with sinus rhythm. Together, these results suggest a genetic contribution of SHOX2 in early-onset AF.

Mutations in the genes for thyroglobulin and thyroid peroxidase cause thyroid dyshormonogenesis and autosomal-recessive intellectual disability.

We have used single-nucleotide polymorphism microarray genotyping and homozygosity-by-descent (HBD) mapping followed by Sanger sequencing or whole-exome sequencing (WES) to identify causative mutations in three consanguineous families with intellectual disability (ID) related to thyroid dyshormonogenesis (TDH). One family was found to have a shared HBD region of 12.1 Mb on 8q24.21-q24.23 containing 36 coding genes, including the thyroglobulin gene, TG. Sanger sequencing of TG identified a homozygous nonsense mutation Arg2336*, which segregated with the phenotype in the family. A second family showed several HBD regions, including 6.0 Mb on 2p25.3-p25.2. WES identified a homozygous nonsense mutation, Glu596*, in the thyroid peroxidase gene, TPO. WES of a mother/father/proband trio from a third family revealed a homozygous missense mutation, Arg412His, in TPO. Mutations in TG and TPO are very rarely associated with ID, mainly because TDH is generally detectable and treatable. However, in populations where resources for screening and detection are limited, and especially where consanguineous marriages are common, mutations in genes involved in thyroid function may also be causes of ID, and as TPO and TG mutations are the most common genetic causes of TDH, these are also likely to be relatively common causes of ID.

SHANK1 Deletions in Males with Autism Spectrum Disorder.

Recent studies have highlighted the involvement of rare (<1% frequency) copy-number variations and point mutations in the genetic etiology of autism spectrum disorder (ASD); these variants particularly affect genes involved in the neuronal synaptic complex. The SHANK gene family consists of three members (SHANK1, SHANK2, and SHANK3), which encode scaffolding proteins required for the proper formation and function of neuronal synapses. Although SHANK2 and SHANK3 mutations have been implicated in ASD and intellectual disability, the involvement of SHANK1 is unknown. Here, we assess microarray data from 1,158 Canadian and 456 European individuals with ASD to discover microdeletions at the SHANK1 locus on chromosome 19. We identify a hemizygous SHANK1 deletion that segregates in a four-generation family in which male carriers--but not female carriers--have ASD with higher functioning. A de novo SHANK1 deletion was also detected in an unrelated male individual with ASD with higher functioning, and no equivalent SHANK1 mutations were found in >15,000 controls (p = 0.009). The discovery of apparent reduced penetrance of ASD in females bearing inherited autosomal SHANK1 deletions provides a possible contributory model for the male gender bias in autism. The data are also informative for clinical-genetics interpretations of both inherited and sporadic forms of ASD involving SHANK1.

Tbx4 interacts with the short stature homeobox gene Shox2 in limb development.

BACKGROUND: The short stature homeodomain transcription factors SHOX and SHOX2 play key roles in limb formation. To gain more insight into genes regulated by Shox2 during limb development, we analyzed expression profiles of WT and Shox2-/- mouse embryonic limbs and identified the T-Box transcription factor Tbx4 as a potential downstream target. Tbx4 is known to exert essential functions in skeletal and muscular hindlimb development. In humans, haploinsufficiency of TBX4 causes small patella syndrome, a skeletal dysplasia characterized by anomalies of the knee, pelvis, and foot. RESULTS: Here, we demonstrate an inhibitory regulatory effect of Shox2 on Tbx4 specifically in the forelimbs. We also show that Tbx4 activates Shox2 expression in fore- and hindlimbs, suggesting Shox2 as a feedback modulator of Tbx4. Using EMSA studies, we find that Tbx4/TBX4 is able to bind to distinct T-box binding sites within the mouse and human Shox2/SHOX2 promoter. CONCLUSIONS: Our data identifies Tbx4 as a novel transcriptional activator of Shox2 during murine fore- and hindlimb development. Tbx4 is also regulated by Shox2 specifically in the forelimb bud possibly via a feedback mechanism. These data extend our understanding of the role and regulation of Tbx4 and Shox2 in limb development and limb associated diseases.

Biallelic variants in CSMD1 are implicated in a neurodevelopmental disorder with intellectual disability and variable cortical malformations.

CSMD1 (Cub and Sushi Multiple Domains 1) is a well-recognized regulator of the complement cascade, an important component of the innate immune response. CSMD1 is highly expressed in the central nervous system (CNS) where emergent functions of the complement pathway modulate neural development and synaptic activity. While a genetic risk factor for neuropsychiatric disorders, the role of CSMD1 in neurodevelopmental disorders is unclear. Through international variant sharing, we identified inherited biallelic CSMD1 variants in eight individuals from six families of diverse ancestry who present with global developmental delay, intellectual disability, microcephaly, and polymicrogyria. We modeled CSMD1 loss-of-function (LOF) pathogenesis in early-stage forebrain organoids differentiated from CSMD1 knockout human embryonic stem cells (hESCs). We show that CSMD1 is necessary for neuroepithelial cytoarchitecture and synchronous differentiation. In summary, we identified a critical role for CSMD1 in brain development and biallelic CSMD1 variants as the molecular basis of a previously undefined neurodevelopmental disorder.

Generation of two homozygous SHOX2 knock-out human induced pluripotent stem cell lines using CRISPR/Cas9.

SHOX2 is a homeobox transcription factor associated with atrial fibrillation (AF) and sinus node dysfunction. Here, we generated two homozygous SHOX2 knock-out hiPSC lines from a healthy control line and a corrected AF patient line (disease-specific SHOX2 mutation corrected to WT) using CRISPR/Cas9. These cell lines maintained pluripotency, an ability to differentiate into all three germlayers and a normal karyotype, presenting a valuable tool to investigate the impact of a full SHOX2 knock-out with respect to arrhythmogenic diseases on a cellular level.