SETBP1 accumulation induces P53 inhibition and genotoxic stress in neural progenitors underlying neurodegeneration in Schinzel-Giedion syndrome.

The investigation of genetic forms of juvenile neurodegeneration could shed light on the causative mechanisms of neuronal loss. Schinzel-Giedion syndrome (SGS) is a fatal developmental syndrome caused by mutations in the SETBP1 gene, inducing the accumulation of its protein product. SGS features multi-organ involvement with severe intellectual and physical deficits due, at least in part, to early neurodegeneration. Here we introduce a human SGS model that displays disease-relevant phenotypes. We show that SGS neural progenitors exhibit aberrant proliferation, deregulation of oncogenes and suppressors, unresolved DNA damage, and resistance to apoptosis. Mechanistically, we demonstrate that high SETBP1 levels inhibit P53 function through the stabilization of SET, which in turn hinders P53 acetylation. We find that the inheritance of unresolved DNA damage in SGS neurons triggers the neurodegenerative process that can be alleviated either by PARP-1 inhibition or by NAD + supplementation. These results implicate that neuronal death in SGS originates from developmental alterations mainly in safeguarding cell identity and homeostasis.

Chromatin remodeler Arid1a regulates subplate neuron identity and wiring of cortical connectivity.

Loss-of-function mutations in chromatin remodeler gene ARID1A are a cause of Coffin-Siris syndrome, a developmental disorder characterized by dysgenesis of corpus callosum. Here, we characterize Arid1a function during cortical development and find unexpectedly selective roles for Arid1a in subplate neurons (SPNs). SPNs, strategically positioned at the interface of cortical gray and white matter, orchestrate multiple developmental processes indispensable for neural circuit wiring. We find that pancortical deletion of Arid1a leads to extensive mistargeting of intracortical axons and agenesis of corpus callosum. Sparse Arid1a deletion, however, does not autonomously misroute callosal axons, implicating noncell-autonomous Arid1a functions in axon guidance. Supporting this possibility, the ascending axons of thalamocortical neurons, which are not autonomously affected by cortical Arid1a deletion, are also disrupted in their pathfinding into cortex and innervation of whisker barrels. Coincident with these miswiring phenotypes, which are reminiscent of subplate ablation, we unbiasedly find a selective loss of SPN gene expression following Arid1a deletion. In addition, multiple characteristics of SPNs crucial to their wiring functions, including subplate organization, subplate axon-thalamocortical axon cofasciculation ("handshake"), and extracellular matrix, are severely disrupted. To empirically test Arid1a sufficiency in subplate, we generate a cortical plate deletion of Arid1a that spares SPNs. In this model, subplate Arid1a expression is sufficient for subplate organization, subplate axon-thalamocortical axon cofasciculation, and subplate extracellular matrix. Consistent with these wiring functions, subplate Arid1a sufficiently enables normal callosum formation, thalamocortical axon targeting, and whisker barrel development. Thus, Arid1a is a multifunctional regulator of subplate-dependent guidance mechanisms essential to cortical circuit wiring.

PIGF deficiency causes a phenotype overlapping with DOORS syndrome.

DOORS syndrome is characterized by deafness, onychodystrophy, osteodystrophy, intellectual disability, and seizures. In this study, we report two unrelated individuals with DOORS syndrome without deafness. Exome sequencing revealed a homozygous missense variant in PIGF (NM_173074.3:c.515C>G, p.Pro172Arg) in both. We demonstrate impaired glycosylphosphatidylinositol (GPI) biosynthesis through flow cytometry analysis. We thus describe the causal role of a novel disease gene, PIGF, in DOORS syndrome and highlight the overlap between this condition and GPI deficiency disorders. For each gene implicated in DOORS syndrome and/or inherited GPI deficiencies, there is considerable clinical variability so a high index of suspicion is warranted even though not all features are noted.

The first two Chinese Myhre syndrome patients with the recurrent SMAD4 pathogenic variants: Functional consequences and clinical diversity.

Myhre syndrome is a rare autosomal dominant multi-organ disorder characterized by growth retardation, skeletal anomalies, muscular hypertrophy, joint stiffness, facial dysmorphism, deafness, cardiovascular disease, and abnormal sexual development. Here we described the first two Chinese Myhre syndrome patients diagnosed by whole-exome sequencing. They both had de novo c.1498A > G (p.Ile500Val) variant in SMAD4 and presented with key characteristics of Myhre syndrome but also revealed uncommon features (polydactyly in the girl and precocious puberty in the boy). We performed functional analysis on four previously reported SMAD4 pathogenic variants in Myhre syndrome patients using dual-luciferase assay. Our results revealed that the pathogenic variants resulted in a variable degree of increased transcription activity of target genes that contain the minimal SMAD binding elements in their promoter regions. The boy responded to the recombinant human growth hormone treatment with improved height but also led to hyperinsulinemia and advanced bone age. Because of his precocious puberty, we subsequently combined the recombinant human growth hormone and gonadotrophin-releasing hormone agonist treatments, which resulted in overall improved height. We reviewed the sexual features of reported Myhre syndrome cases and discussed the possible mechanism of SMAD4 variants in Myhre syndrome that lead to the abnormal hypothalamic-pituitary-gonadal axis.

Monogenic Forms of Hypertension.

Essential hypertension is a highly prevalent disease in the general population. Secondary hypertension is characterized by a specific and potentially reversible cause of increased blood pressure levels. Some secondary endocrine forms of hypertension are common (caused by uncontrolled cortisol, aldosterone, or catecholamines production). This article describes rare monogenic forms of hypertension, characterized by electrolyte disorders and suppressed renin-aldosterone axis. They represent simple models for the physiology of renal control of sodium levels and plasma volume, thus reaching a high scientific interest. Furthermore, they could explain some features closer to the essential phenotype of hypertension, suggesting a mechanistically driven personalized treatment.

A novel human stem cell model for Coffin-Siris syndrome-like syndrome reveals the importance of SOX11 dosage for neuronal differentiation and survival.

The SOXC transcription factors Sox4, Sox11 and Sox12, are critical neurodevelopmental regulators that are thought to function in a highly redundant fashion. Surprisingly, heterozygous missense mutations or deletions of SOX11 were recently detected in patients with Coffin-Siris syndrome-like syndrome (CSSLS), a neurodevelopmental disorder associated with intellectual disability, demonstrating that in humans SOX11 haploinsufficiency cannot be compensated and raising the question of the function of SOX11 in human neurodevelopment. Here, we describe the generation of SOX11+/- heterozygous human embryonic stem cell (hESC) lines by CRISPR/Cas9 genome engineering. SOX11 haploinsufficiency impaired the generation of neurons and resulted in a proliferation/differentiation imbalance of neural precursor cells and enhanced neuronal cell death. Using the SOX11+/- hESC model we provide for the first time experimental evidence that SOX11 haploinsufficiency is sufficient to impair key processes of human neurodevelopment, giving a first insight into the pathophysiology of CSSLS and SOX11 function in human neurodevelopment.

A novel dominant-negative FGFR1 variant causes Hartsfield syndrome by deregulating RAS/ERK1/2 pathway.

Hartsfield syndrome (HS) is an ultrarare developmental disorder mainly featuring holoprosencephaly and ectrodactyly. It is caused by heterozygous or biallelic variants in FGFR1. Recently, a dominant-negative effect was suggested for FGFR1 variants associated with HS. Here, exome sequencing analysis in a 12-year-old boy with HS disclosed a novel de novo heterozygous variant c.1934C>T in FGFR1 predicted to cause the p.(Ala645Val) amino-acid substitution. In order to evaluate whether the variant, changing a highly conserved residue of the kinase domain, affects FGFR1 function, biochemical studies were employed. We measured the FGFR1 receptor activity in FGF2-treated cell lines exogenously expressing wild-type or Ala645Val FGFR1 by monitoring the activation status of FGF2/FGFR1 downstream pathways. Our analysis highlighted that RAS/ERK1/2 signaling was significantly perturbed in cells expressing mutated FGFR1, in comparison with control cells. We also provided preliminary evidence showing a modulation of the autophagic process in cells expressing mutated FGFR1. This study expands the FGFR1 mutational spectrum associated with HS, provides functional evidence further supporting a dominant-negative effect of this category of FGFR1 variants and offers initial insights on dysregulation of autophagy in HS.

A Novel Splice-Site Mutation in VEGFC Is Associated with Congenital Primary Lymphoedema of Gordon.

Lymphedema is characterized by chronic swelling of any body part caused by malfunctioning or obstruction in the lymphatic system. Primary lymphedema is often considered genetic in origin. VEGFC, which is a gene encoding the ligand for the vascular endothelial growth factor receptor 3 (VEGFR3/FLT4) and important for lymph vessel development during lymphangiogenesis, has been associated with a specific subtype of primary lymphedema. Through Sanger sequencing of a proband with bilateral congenital pedal edema resembling Milroy disease, we identified a novel mutation (NM_005429.2; c.361+5G>A) in VEGFC. The mutation induced skipping of exon 2 of VEGFC resulting in a frameshift and the introduction of a premature stop codon (p.Ala50ValfsTer18). The mutation leads to a loss of the entire VEGF-homology domain and the C-terminus. Expression of this Vegfc variant in the zebrafish floorplate showed that the splice-site variant significantly reduces the biological activity of the protein. Our findings confirm that the splice-site variant, c.361+5G>A, causes the primary lymphedema phenotype in the proband. We examine the mutations and clinical phenotypes of the previously reported cases to review the current knowledge in this area.

Renal sodium and magnesium reabsorption are not coupled in a mouse model of Gordon syndrome.

Active reabsorption of magnesium (Mg2+ ) in the distal convoluted tubule (DCT) of the kidney is crucial for maintaining Mg2+ homeostasis. Impaired activity of the Na+ -Cl- -cotransporter (NCC) has been associated with hypermagnesiuria and hypomagnesemia, while increased activity of NCC, as observed in patients with Gordon syndrome, is not associated with alterations in Mg2+ balance. To further elucidate the possible interrelationship between NCC activity and renal Mg2+ handling, plasma Mg2+ levels and urinary excretion of sodium (Na+ ) and Mg2+ were measured in a mouse model of Gordon syndrome. In this model, DCT1-specific expression of a constitutively active mutant form of the NCC-phosphorylating kinase, SPAK (CA-SPAK), increases NCC activity and hydrochlorothiazide (HCTZ)-sensitive Na+ reabsorption. These mice were normomagnesemic and HCTZ administration comparably reduced plasma Mg2+ levels in CA-SPAK mice and control littermates. As inferred by the initial response to HCTZ, CA-SPAK mice exhibited greater NCC-dependent Na+ reabsorption together with decreased Mg2+ reabsorption, compared to controls. Following prolonged HCTZ administration (4 days), CA-SPAK mice exhibited higher urinary Mg2+ excretion, while urinary Na+ excretion decreased to levels observed in control animals. Surprisingly, CA-SPAK mice had unaltered renal expression of Trpm6, encoding the Mg2+ -permeable channel TRPM6, or other magnesiotropic genes. In conclusion, CA-SPAK mice exhibit normomagnesemia, despite increased NCC activity and Na+ reabsorption. Thus, Mg2+ reabsorption is not coupled to increased thiazide-sensitive Na+ reabsorption, suggesting a similar process explains normomagnesemia in Gordon syndrome. Further research is required to unravel the molecular underpinnings of this phenomenon and the more pronounced Mg2+ excretion after prolonged HCTZ administration.

Allosteric Activation Dictates PRC2 Activity Independent of Its Recruitment to Chromatin.

PRC2 is a therapeutic target for several types of cancers currently undergoing clinical trials. Its activity is regulated by a positive feedback loop whereby its terminal enzymatic product, H3K27me3, is specifically recognized and bound by an aromatic cage present in its EED subunit. The ensuing allosteric activation of the complex stimulates H3K27me3 deposition on chromatin. Here we report a stepwise feedback mechanism entailing key residues within distinctive interfacing motifs of EZH2 or EED that are found to be mutated in cancers and/or Weaver syndrome. PRC2 harboring these EZH2 or EED mutants manifested little activity in vivo but, unexpectedly, exhibited similar chromatin association as wild-type PRC2, indicating an uncoupling of PRC2 activity and recruitment. With genetic and chemical tools, we demonstrated that targeting allosteric activation overrode the gain-of-function effect of EZH2Y646X oncogenic mutations. These results revealed critical implications for the regulation and biology of PRC2 and a vulnerability in tackling PRC2-addicted cancers.

SMARCA4 inactivating mutations cause concomitant Coffin-Siris syndrome, microphthalmia and small-cell carcinoma of the ovary hypercalcaemic type.

SMARCA4 chromatin remodelling factor is mutated in 11% of Coffin-Siris syndrome (CSS) patients and in almost all small-cell carcinoma of the ovary hypercalcaemic type (SCCOHT) tumours. Missense mutations with gain-of-function or dominant-negative effects are associated with CSS, whereas inactivating mutations, leading to loss of SMARCA4 expression, have been exclusively found in SCCOHT. We applied whole-exome sequencing to study a 15-year-old patient with mild CSS who concomitantly developed SCCOHT at age 13 years. Interestingly, our patient also showed congenital microphthalmia, which has never previously been reported in CSS patients. We detected a de novo germline heterozygous nonsense mutation in exon 19 of SMARCA4 (c.2935C > T;p.Arg979*), and a somatic frameshift mutation in exon 6 (c.1236_1236delC;p.Gln413Argfs*88), causing complete loss of SMARCA4 immunostaining in the tumour. The immunohistochemical findings are supported by the observation that the c.2935C > T mutant transcript was detected by reverse transcription polymerase chain reaction at a much lower level than the wild-type allele in whole blood and the lymphoblastoid cell line of the proband, confirming nonsense-mediated mRNA decay. Accordingly, immunoblotting demonstrated that there was approximately half the amount of SMARCA4 protein in the proband's cells as in controls. This study suggests that SMARCA4 constitutional mutations associated with CSS are not necessarily non-truncating, and that haploinsufficiency may explain milder CSS phenotypes, as previously reported for haploinsufficient ARID1B. In addition, our case supports the dual role of chromatin remodellers in developmental disorders and cancer, as well as the involvement of SMARCA4 in microphthalmia, confirming previous findings in mouse models and the DECIPHER database. Finally, we speculate that mild CSS might be under-recognized in a proportion of SCCOHT patients harbouring SMARCA4 mutations. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Inherited Arterial Calcification Syndromes: Etiologies and Treatment Concepts.

PURPOSE OF REVIEW: We give an update on the etiology and potential treatment options of rare inherited monogenic disorders associated with arterial calcification and calcific cardiac valve disease. RECENT FINDINGS: Genetic studies of rare inherited syndromes have identified key regulators of ectopic calcification. Based on the pathogenic principles causing the diseases, these can be classified into three groups: (1) disorders of an increased extracellular inorganic phosphate/inorganic pyrophosphate ratio (generalized arterial calcification of infancy, pseudoxanthoma elasticum, arterial calcification and distal joint calcification, progeria, idiopathic basal ganglia calcification, and hyperphosphatemic familial tumoral calcinosis; (2) interferonopathies (Singleton-Merten syndrome); and (3) others, including Keutel syndrome and Gaucher disease type IIIC. Although some of the identified causative mechanisms are not easy to target for treatment, it has become clear that a disturbed serum phosphate/pyrophosphate ratio is a major force triggering arterial and cardiac valve calcification. Further studies will focus on targeting the phosphate/pyrophosphate ratio to effectively prevent and treat these calcific disease phenotypes.

EIF4A3 deficient human iPSCs and mouse models demonstrate neural crest defects that underlie Richieri-Costa-Pereira syndrome.

Biallelic loss-of-function mutations in the RNA-binding protein EIF4A3 cause Richieri-Costa-Pereira syndrome (RCPS), an autosomal recessive condition mainly characterized by craniofacial and limb malformations. However, the pathogenic cellular mechanisms responsible for this syndrome are entirely unknown. Here, we used two complementary approaches, patient-derived induced pluripotent stem cells (iPSCs) and conditional Eif4a3 mouse models, to demonstrate that defective neural crest cell (NCC) development explains RCPS craniofacial abnormalities. RCPS iNCCs have decreased migratory capacity, a distinct phenotype relative to other craniofacial disorders. Eif4a3 haploinsufficient embryos presented altered mandibular process fusion and micrognathia, thus recapitulating the most penetrant phenotypes of the syndrome. These defects were evident in either ubiquitous or NCC-specific Eif4a3 haploinsufficient animals, demonstrating an autonomous requirement of Eif4a3 in NCCs. Notably, RCPS NCC-derived mesenchymal stem-like cells (nMSCs) showed premature bone differentiation, a phenotype paralleled by premature clavicle ossification in Eif4a3 haploinsufficient embryos. Likewise, nMSCs presented compromised in vitro chondrogenesis, and Meckel's cartilage was underdeveloped in vivo. These findings indicate novel and essential requirements of EIF4A3 for NCC migration and osteochondrogenic differentiation during craniofacial development. Altogether, complementary use of iPSCs and mouse models pinpoint unique cellular mechanisms by which EIF4A3 mutation causes RCPS, and provide a paradigm to study craniofacial disorders.

Overlapping SETBP1 gain-of-function mutations in Schinzel-Giedion syndrome and hematologic malignancies.

Schinzel-Giedion syndrome (SGS) is a rare developmental disorder characterized by multiple malformations, severe neurological alterations and increased risk of malignancy. SGS is caused by de novo germline mutations clustering to a 12bp hotspot in exon 4 of SETBP1. Mutations in this hotspot disrupt a degron, a signal for the regulation of protein degradation, and lead to the accumulation of SETBP1 protein. Overlapping SETBP1 hotspot mutations have been observed recurrently as somatic events in leukemia. We collected clinical information of 47 SGS patients (including 26 novel cases) with germline SETBP1 mutations and of four individuals with a milder phenotype caused by de novo germline mutations adjacent to the SETBP1 hotspot. Different mutations within and around the SETBP1 hotspot have varying effects on SETBP1 stability and protein levels in vitro and in in silico modeling. Substitutions in SETBP1 residue I871 result in a weak increase in protein levels and mutations affecting this residue are significantly more frequent in SGS than in leukemia. On the other hand, substitutions in residue D868 lead to the largest increase in protein levels. Individuals with germline mutations affecting D868 have enhanced cell proliferation in vitro and higher incidence of cancer compared to patients with other germline SETBP1 mutations. Our findings substantiate that, despite their overlap, somatic SETBP1 mutations driving malignancy are more disruptive to the degron than germline SETBP1 mutations causing SGS. Additionally, this suggests that the functional threshold for the development of cancer driven by the disruption of the SETBP1 degron is higher than for the alteration in prenatal development in SGS. Drawing on previous studies of somatic SETBP1 mutations in leukemia, our results reveal a genotype-phenotype correlation in germline SETBP1 mutations spanning a molecular, cellular and clinical phenotype.

Skywalker-TBC1D24 has a lipid-binding pocket mutated in epilepsy and required for synaptic function.

Mutations in TBC1D24 cause severe epilepsy and DOORS syndrome, but the molecular mechanisms underlying these pathologies are unresolved. We solved the crystal structure of the TBC domain of the Drosophila ortholog Skywalker, revealing an unanticipated cationic pocket conserved among TBC1D24 homologs. Cocrystallization and biochemistry showed that this pocket binds phosphoinositides phosphorylated at the 4 and 5 positions. The most prevalent patient mutations affect the phosphoinositide-binding pocket and inhibit lipid binding. Using in vivo photobleaching of Skywalker-GFP mutants, including pathogenic mutants, we showed that membrane binding via this pocket restricts Skywalker diffusion in presynaptic terminals. Additionally, the pathogenic mutations cause severe neurological defects in flies, including impaired synaptic-vesicle trafficking and seizures, and these defects are reversed by genetically increasing synaptic PI(4,5)P2 concentrations through synaptojanin mutations. Hence, we discovered that a TBC domain affected by clinical mutations directly binds phosphoinositides through a cationic pocket and that phosphoinositide binding is critical for presynaptic function.

Brothers with constrictive pericarditis - A novel mutation in a rare disease.

Familial constrictive pericarditis is extremely rare. We report a case of two brothers both suffering constrictive pericarditis along with having multiple painless joint deformities. Genetic workup confirmed the clinical diagnosis of camptodactyly-arthropathy-coxa vara-pericarditis (CACP) syndrome CACP syndrome and also revealed a rare mutation in the causative gene.

The hydrolethalus syndrome protein HYLS-1 regulates formation of the ciliary gate.

Transition fibres (TFs), together with the transition zone (TZ), are basal ciliary structures thought to be crucial for cilium biogenesis and function by acting as a ciliary gate to regulate selective protein entry and exit. Here we demonstrate that the centriolar and basal body protein HYLS-1, the C. elegans orthologue of hydrolethalus syndrome protein 1, is required for TF formation, TZ organization and ciliary gating. Loss of HYLS-1 compromises the docking and entry of intraflagellar transport (IFT) particles, ciliary gating for both membrane and soluble proteins, and axoneme assembly. Additional depletion of the TF component DYF-19 in hyls-1 mutants further exacerbates TZ anomalies and completely abrogates ciliogenesis. Our data support an important role for HYLS-1 and TFs in establishment of the ciliary gate and underline the importance of selective protein entry for cilia assembly.