De novo missense variants in exon 9 of SEPHS1 cause a neurodevelopmental condition with developmental delay, poor growth, hypotonia, and dysmorphic features.

Selenophosphate synthetase (SEPHS) plays an essential role in selenium metabolism. Two mammalian SEPHS paralogues, SEPHS1 and SEPHS2, share high sequence identity and structural homology with SEPHS. Here, we report nine individuals from eight families with developmental delay, growth and feeding problems, hypotonia, and dysmorphic features, all with heterozygous missense variants in SEPHS1. Eight of these individuals had a recurrent variant at amino acid position 371 of SEPHS1 (p.Arg371Trp, p.Arg371Gln, and p.Arg371Gly); seven of these variants were known to be de novo. Structural modeling and biochemical assays were used to understand the effect of these variants on SEPHS1 function. We found that a variant at residue Trp352 results in local structural changes of the C-terminal region of SEPHS1 that decrease the overall thermal stability of the enzyme. In contrast, variants of a solvent-exposed residue Arg371 do not impact enzyme stability and folding but could modulate direct protein-protein interactions of SEPSH1 with cellular factors in promoting cell proliferation and development. In neuronal SH-SY5Y cells, we assessed the impact of SEPHS1 variants on cell proliferation and ROS production and investigated the mRNA expression levels of genes encoding stress-related selenoproteins. Our findings provided evidence that the identified SEPHS1 variants enhance cell proliferation by modulating ROS homeostasis. Our study supports the hypothesis that SEPHS1 plays a critical role during human development and provides a basis for further investigation into the molecular mechanisms employed by SEPHS1. Furthermore, our data suggest that variants in SEPHS1 are associated with a neurodevelopmental disorder.

De novo variants in FRYL are associated with developmental delay, intellectual disability, and dysmorphic features.

FRY-like transcription coactivator (FRYL) belongs to a Furry protein family that is evolutionarily conserved from yeast to humans. The functions of FRYL in mammals are largely unknown, and variants in FRYL have not previously been associated with a Mendelian disease. Here, we report fourteen individuals with heterozygous variants in FRYL who present with developmental delay, intellectual disability, dysmorphic features, and other congenital anomalies in multiple systems. The variants are confirmed de novo in all individuals except one. Human genetic data suggest that FRYL is intolerant to loss of function (LoF). We find that the fly FRYL ortholog, furry (fry), is expressed in multiple tissues, including the central nervous system where it is present in neurons but not in glia. Homozygous fry LoF mutation is lethal at various developmental stages, and loss of fry in mutant clones causes defects in wings and compound eyes. We next modeled four out of the five missense variants found in affected individuals using fry knockin alleles. One variant behaves as a severe LoF variant, whereas two others behave as partial LoF variants. One variant does not cause any observable defect in flies, and the corresponding human variant is not confirmed to be de novo, suggesting that this is a variant of uncertain significance. In summary, our findings support that fry is required for proper development in flies and that the LoF variants in FRYL cause a dominant disorder with developmental and neurological symptoms due to haploinsufficiency.

Unraveling the genetic architecture of congenital vertebral malformation with reference to the developing spine.

Congenital vertebral malformation, affecting 0.13-0.50 per 1000 live births, has an immense locus heterogeneity and complex genetic architecture. In this study, we analyze exome/genome sequencing data from 873 probands with congenital vertebral malformation and 3794 control individuals. Clinical interpretation identifies Mendelian etiologies in 12.0% of the probands and reveals a muscle-related disease mechanism. Gene-based burden test of ultra-rare variants identifies risk genes with large effect sizes (ITPR2, TBX6, TPO, H6PD, and SEC24B). To further investigate the biological relevance of the genetic association signals, we perform single-nucleus RNAseq on human embryonic spines. The burden test signals are enriched in the notochord at early developmental stages and myoblast/myocytes at late stages, highlighting their critical roles in the developing spine. Our work provides insights into the developmental biology of the human spine and the pathogenesis of spine malformation.

Immune skeletal dysplasia with neurodevelopmental abnormalities caused by a novel variant of EXTL3 gene in a Chinese family.

BACKGROUND: Immune skeletal dysplasia with neurodevelopmental abnormalities (ISDNA) is an extremely rare, autosomal recessive genetic disorder characterized by various skeletal abnormalities, neurodevelopmental deficits, and abnormal immune system function. ISDNA is caused by variation in the exostosin-like 3 (EXTL3) gene, located on chromosome 8p21.2, whose primary function is the biosynthesis of heparan sulfate (HS) skeleton structure. Only a few variations in the EXTL3 gene have been discovered so far. In these years of development, many pathogenic variants in genetic diseases with genetic and phenotypic heterogeneity have been investigated using whole-exome sequencing (WES) technology. METHODS: In this research, a novel EXTL3 variant was first detected in a patient using WES, which was validated from Sanger sequencing in this family. Family history and clinical information were then collected through comprehensive medical examinations and genetic counseling. In silico prediction was then utilized to confirm the pathogenicity of the variant. RESULTS: A novel homozygous variant, NM_001440: c.2015G>A (p.Arg672Gln) in the EXTL3 gene, was identified using WES, which has never been reported before. Sanger sequencing was performed to confirm that the variant segregated with the disease within the family. CONCLUSION: This research identified a novel pathogenic variant in the EXTL3 gene responsible for ISDNA in a Chinese family. It showed the potential diagnostic role of WES in ISDNA, expanded the EXTL3 gene variation spectrum, and demonstrated that the diagnosis of ISDNA using WES is feasible and effective. More comprehensive genetic counseling and precise prenatal diagnosis for the next pregnancy can also be provided to families with genetic disorders.

Molecular characterization of 13 patients with PIK3CA-related overgrowth spectrum using a targeted deep sequencing approach.

Activating variants in the PIK3CA gene cause a heterogeneous spectrum of disorders that involve congenital or early-onset segmental/focal overgrowth, now referred to as PIK3CA-related overgrowth spectrum (PROS). Historically, the clinical diagnoses of patients with PROS included a range of distinct syndromes, including CLOVES syndrome, dysplastic megalencephaly, hemimegalencephaly, focal cortical dysplasia, Klippel-Trenaunay syndrome, CLAPO syndrome, fibroadipose hyperplasia or overgrowth, hemihyperplasia multiple lipomatosis, and megalencephaly capillary malformation-polymicrogyria (MCAP) syndrome. MCAP is a sporadic overgrowth disorder that exhibits core features of progressive megalencephaly, vascular malformations, distal limb malformations, cortical brain malformations, and connective tissue dysplasia. In 2012, our research group contributed to the identification of predominantly mosaic, gain-of-function variants in PIK3CA as an underlying genetic cause of the syndrome. Mosaic variants are technically more difficult to detect and require implementation of more sensitive sequencing technologies and less stringent variant calling algorithms. In this study, we demonstrated the utility of deep sequencing using the Illumina TruSight Oncology 500 (TSO500) sequencing panel in identifying variants with low allele fractions in a series of patients with PROS and suspected mosaicism: pathogenic, mosaic PIK3CA variants were identified in all 13 individuals, including 6 positive controls. This study highlights the importance of screening for low-level mosaic variants in PROS patients. The use of targeted panels with deep sequencing in clinical genetic testing laboratories would improve diagnostic yield and accuracy within this patient population.

Biallelic loss-of-function variants in CACHD1 cause a novel neurodevelopmental syndrome with facial dysmorphism and multisystem congenital abnormalities.

PURPOSE: We established the genetic etiology of a syndromic neurodevelopmental condition characterized by variable cognitive impairment, recognizable facial dysmorphism, and a constellation of extra-neurological manifestations. METHODS: We performed phenotypic characterization of 6 participants from 4 unrelated families presenting with a neurodevelopmental syndrome and used exome sequencing to investigate the underlying genetic cause. To probe relevance to the neurodevelopmental phenotype and craniofacial dysmorphism, we established two- and three-dimensional human stem cell-derived neural models and generated a stable cachd1 zebrafish mutant on a transgenic cartilage reporter line. RESULTS: Affected individuals showed mild cognitive impairment, dysmorphism featuring oculo-auriculo abnormalities, and developmental defects involving genitourinary and digestive tracts. Exome sequencing revealed biallelic putative loss-of-function variants in CACHD1 segregating with disease in all pedigrees. RNA sequencing in CACHD1-depleted neural progenitors revealed abnormal expression of genes with key roles in Wnt signaling, neurodevelopment, and organ morphogenesis. CACHD1 depletion in neural progenitors resulted in reduced percentages of post-mitotic neurons and enlargement of 3D neurospheres. Homozygous cachd1 mutant larvae showed mandibular patterning defects mimicking human facial dysmorphism. CONCLUSION: Our findings support the role of loss-of-function variants in CACHD1 as the cause of a rare neurodevelopmental syndrome with facial dysmorphism and multisystem abnormalities.

Craniofacial dysmorphism, skeletal anomalies, and impaired intellectual development syndrome-1 in two new patients with the same homozygous TMCO1 variant and review of the literature.

Craniofacial dysmorphism, skeletal anomalies, and impaired intellectual development syndrome-1 (CFSMR1; OMIM#213980) is a rare autosomal recessive disorder characterized by the clinical triad of developmental delay and/or intellectual disability, a typical facial gestalt with brachycephaly, highly-arched bushy eyebrows, synophrys, hypertelorism, wide nasal bridge, and short nose, as well as multiple vertebrae and rib malformations, such as bifid and fused ribs and abnormal vertebral segmentation and fusion. Biallelic loss-of-function variants in TMCO1 cause CFSMR1. We report on two unrelated Egyptian patients with a phenotype suggestive of CFSMR. Single whole-exome sequencing in patient 1 and Sanger sequencing of TMCO1 in patient 2 revealed the same homozygous TMCO1 nonsense variant c.187C > T/p.(Arg63*) in both affected individuals; patients' healthy parents were heterozygous carriers of the variant. Congenital hearing loss in patients 1 and 2 is an occasional finding in individuals affected by CFSMR. Camptodactyly and syndactyly, which were noted in patient 2, have not or rarely been reported in CFSMR. Review of the literature revealed a total of 30 individuals with the clinically recognizable and unique phenotype of CFSMR1, including the patients reported here, who all carried biallelic TMCO1 variants. Six different TMCO1 variants have been reported in the 30 patients from 14 families, comprising three nonsense, two 2-bp deletions, and a splice donor site variant. All disease-associated TMCO1 variants likely represent null alleles resulting in absence of the encoded protein. TMCO1 has been proposed to act as a Ca2+ channel, while other data revealed TMCO1 as a mitochondrial protein and a component of the translocon at the endoplasmic reticulum, a cellular machinery important for the biogenesis of multi-pass membrane proteins. RAB5IF/C20orf24 has recently been identified as causative gene for craniofacial dysmorphism, skeletal anomalies, and impaired intellectual development syndrome-2 (CFSMR2; OMIM#616994). Heterodimerization of RAB5IF/C20orf24 and TMCO1 and their interdependence may suggest a pathophysiological role of ER-mitochondria interaction underlying CFSMR.

PIK3CA Mutational Analysis in Patients With Macrodactyly.

BACKGROUND: Somatic mosaicism for PIK3CA mutations causes various types of growth disorders, which have been summarized under the term PROS (PIK3CA related overgrowth spectrum). Targeted therapy with PI3K inhibitors seems to be a promising alternative for severe PROS cases. Therefore, PIK3CA testing may become more relevant in the future. METHODS: We report on 14 PROS patients, who had surgery for macrodactyly in the majority of cases. Clinical data were retrieved from the patient's records. Macroscopic and microscopic findings were retrospectively reviewed. Mutational analysis was performed on formalin-fixed paraffin-embedded (FFPE) material. RESULTS: Patient age ranged from 7 months to 35 years. Five patients showed additional anomalies. One patient had CLOVES syndrome. The majority of the specimens were ray resections characterized by hypertrophic fat tissue. Overall, microscopy was subtle. The abnormal adipose tissue showed lobules exhibiting at least focally fibrous septa. In each case, we could detect a PIK3CA mutation. CONCLUSION: Histology of affected fat tissue in PROS patients is overall nonspecific. Therefore, mutational analysis represents the key to the diagnosis, especially in unclear clinical cases. We demonstrated that FFPE material is suitable for PIK3CA testing, which can be considered as basis for targeted therapy with PI3K inhibitors.

Identifying patients with EVEN-plus syndrome using exome sequencing and clinical feature analysis: A case report.

BACKGROUND: The EVEN-plus syndrome (epiphyseal-vertebral-ear-nose dysplasia plus associated findings) is an extremely rare autosomal recessive inherited disease characterised by specific facial features and skeletal dysplasia. It has a prenatal onset due to defects in the HSPA9 gene. The syndrome has not been reported previously in China. METHODS: This study reported the characteristics, examination results, diagnosis and treatment of a female case aged 3 years and 3 months. RESULTS: The patient had global developmental delay and specific facial features, including a prominent forehead, a bilateral auricle deformity, a collapsed nose, a high palatine arch, a short neck and other appearance abnormalities. Her hip joint magnetic resonance imaging (MRI) results showed bilateral femoral head epiphyseal dysplasia with a fork-shaped malformation at the distal end, and her brain MRI showed white matter myelin dysplasia. HSPA9 compound heterozygous variants c.882_c.883delAG and c.613A>G were identified by exome sequencing. CONCLUSIONS: This finding expands the spectra of EVEN-plus syndrome phenotype and pathogenic variants and suggests that c.882_c.883delAG may have a higher distribution frequency in East Asian populations.

Expanding the phenotype of PIK3C2A related syndrome: Report of two siblings with novel features and genotype.

A pair of siblings was ascertained due to multiple congenital anomalies, including strikingly similar facial, skeletal, and ocular abnormalities. Exome sequencing of both the children and their mother revealed two novel PIK3C2A variants in the siblings, c.4381delC (p.Arg1461Glufs*31) and c.1555C > T (p.Arg519Ter). PIK3C2A belongs to the Class IIa family of Phosphatidylinositol-3-kinases, which create second messenger lipids that regulate a wide range of downstream signaling pathways involved in cell growth, survival and migration. Tiosano et al. (2019) identified the first monogenic disorder associated with biallelic PIK3C2A loss-of-function variants (oculoskeletodental syndrome). The novel syndrome was characterized by short stature, coarse facial features, ocular and skeletal abnormalities. This report describes two additional siblings affected by the PIK3C2A-related syndrome, confirms core clinical features, establishes intrafamilial variability and expands the phenotype to include proteinuria.

Genotype-phenotype spectrum and correlations in Xia-Gibbs syndrome: Report of five novel cases and literature review.

BACKGROUND: Xia-Gibbs syndrome (XGS) is a rare neurodevelopmental disorder caused by pathogenic variants in the AT-hook DNA-binding motif-containing 1 gene (AHDC1), encoding a protein with a crucial role in transcription and epigenetic regulation, axonogenesis, brain function, and neurodevelopment. AHDC1 variants possibly act through a dominant-negative mechanism and may interfere with DNA repair processes, leading to genome instability and impaired DNA translesion repair. Variants affecting residues closer to the N-terminal are thought to determine a milder phenotype with better cognitive performances. However, clean-cut genotype-phenotype correlations are still lacking. CASES: In this study, we investigated five subjects with XGS in whom exome sequencing led to the identification of five novel de novo pathogenic variants in AHDC1. All variants were extremely rare and predicted to cause a loss of protein function. The phenotype of the reported patients included developmental delay, hypotonia, and distinctive facial dysmorphisms. Additionally, uncommon clinical features were observed, including congenital hypothyroidism and peculiar skeletal abnormalities. CONCLUSIONS: In this study, we report uncommon XGS features associated with five novel truncating variants in AHDC, thus expanding the genotype and phenotypic spectrum of this complex condition. We also compared our cases to previously reported cases, discussing the current status of genotype-phenotype correlations in XGS.

Biallelic THOC6 pathogenic variants: Prenatal phenotype and review of the literature.

BACKGROUND: The THOC6 protein is a component of the THO complex. It is involved in mRNA transcription, processing and nuclear export. Interestingly molecular biallelic loss-of-function variants of the THOC6 gene were identified in the Beaulieu-Boycott-Innes syndrome (BBIS- OMIM # 613680). This condition was described in 17 patients and is characterized by a moderate to severe intellectual disability, facial dysmorphic features and severe birth defects such as heart, skeletal, ano-genital and renal congenital malformations. METHODS: In the present study, we report on a new family with two affected sibs. The 6-year-old female had severe intellectual disability with autistic features, feeding difficulties, growth delay, facial dysmorphic, and congenital malformations (hand, skeletal and cardiac anomalies). The male fetus presented antenatally with a cystic hygroma associated with severe aortic and left ventricular hypoplasia. Autopsy, after termination of pregnancy at 15 weeks of gestation, showed facial dysmorphic, short right thumb and hypospadias. RESULTS: Exome sequencing detected in both sibs compound heterozygous variants of the THOC6 gene (NM_024339.3, GRCh37): the already reported c.[298T>A;700G>T;824G>A] haplotype and a novel variant c.977T>G, p.(Val326Gly). DISCUSSION: We made a review of the literature of 17 BBIS reported patients including our two siblings. Severe to moderate ID and congenital malformations were constant. Prenatal and postnatal failure to thrive were frequent. Brain MRI were not specific. Prenatal findings were reported in 40% of cases but we described the first case of cystic hygroma. The present study reports extends the prenatal delineation of the phenotypic features observed in association with the presence of THOC6 variants. In addition, it underscores the intrafamilial phenotypic variability observed in BBIS.

The fibrillinopathies: New insights with focus on the paradigm of opposing phenotypes for both FBN1 and FBN2.

Different pathogenic variants in the fibrillin-1 gene (FBN1) cause Marfan syndrome and acromelic dysplasias. Whereas the musculoskeletal features of Marfan syndrome involve tall stature, arachnodactyly, joint hypermobility, and muscle hypoplasia, acromelic dysplasia patients present with short stature, brachydactyly, stiff joints, and hypermuscularity. Similarly, pathogenic variants in the fibrillin-2 gene (FBN2) cause either a Marfanoid congenital contractural arachnodactyly or a FBN2-related acromelic dysplasia that most prominently presents with brachydactyly. The phenotypic and molecular resemblances between both the FBN1 and FBN2-related disorders suggest that reciprocal pathomechanistic lessons can be learned. In this review, we provide an updated overview and comparison of the phenotypic and mutational spectra of both the "tall" and "short" fibrillinopathies. The future parallel functional study of both FBN1/2-related disorders will reveal new insights into how pathogenic fibrillin variants differently affect the fibrillin microfibril network and/or growth factor homeostasis in clinically opposite syndromes. This knowledge may eventually be translated into new therapeutic approaches by targeting or modulating the fibrillin microfibril network and/or the signaling pathways under its control.

Bruck syndrome in 13 new patients: Identification of five novel FKBP10 and PLOD2 variants and further expansion of the phenotypic spectrum.

Bruck Syndrome (BS) is a very rare disorder characterized by osteogenesis imperfecta (OI) associated with congenital contractures and is caused by mutations in FKBP10 or PLOD2 genes. Herein, we describe 13 patients from 9 unrelated Egyptian families with BS. All patients had white sclerae, recurrent fractures, kyphoscoliosis and osteoporosis with variable degrees of severity. Large joint contractures were seen in 11 patients, one patient had contractures of small interphalangeal joints, and one patient had no contractures. Unusual findings noted in individual patients included microcephaly, dental malocclusion, enamel hypoplasia, unilateral congenital dislocation of knee joint, prominent tailbone, and myopathy. Nine different variants were identified in FKBP10 and PLOD2 including five novel ones. FKBP10 variants were found in six families (67%) while PLOD2 variants were identified in three families (33%). The four families, with two affected sibs each, showed inter- and intrafamilial phenotypic variability. In conclusion, we report five novel variants in FKBP10 and PLOD2 thus, expanding the mutational spectrum of BS. In addition, our results expand the phenotypic spectrum, describe newly associated orodental findings, and further illustrate the phenotypic overlap between OI and Bruck syndrome supporting the suggestion of considering BS as a variant of OI rather than a separate entity.

Stankiewicz-Isidor syndrome: expanding the clinical and molecular phenotype.

PURPOSE: Haploinsufficiency of PSMD12 has been reported in individuals with neurodevelopmental phenotypes, including developmental delay/intellectual disability (DD/ID), facial dysmorphism, and congenital malformations, defined as Stankiewicz-Isidor syndrome (STISS). Investigations showed that pathogenic variants in PSMD12 perturb intracellular protein homeostasis. Our objective was to further explore the clinical and molecular phenotypic spectrum of STISS. METHODS: We report 24 additional unrelated patients with STISS with various truncating single nucleotide variants or copy-number variant deletions involving PSMD12. We explore disease etiology by assessing patient cells and CRISPR/Cas9-engineered cell clones for various cellular pathways and inflammatory status. RESULTS: The expressivity of most clinical features in STISS is highly variable. In addition to previously reported DD/ID, speech delay, cardiac and renal anomalies, we also confirmed preaxial hand abnormalities as a feature of this syndrome. Of note, 2 patients also showed chilblains resembling signs observed in interferonopathy. Remarkably, our data show that STISS patient cells exhibit a profound remodeling of the mTORC1 and mitophagy pathways with an induction of type I interferon-stimulated genes. CONCLUSION: We refine the phenotype of STISS and show that it can be clinically recognizable and biochemically diagnosed by a type I interferon gene signature.

Segmental undergrowth is associated with pathogenic variants in vascular malformation genes: A retrospective case-series study.

Segmental overgrowth has been widely described in patients with congenital vascular anomalies. However, segmental undergrowth has been poorly characterized, and no large series of patients have been published. We present the clinical and molecular characteristics a cohort of 37 patients with vascular malformations and segmental undergrowth. True undergrowth was only considered when the musculoskeletal system was involved to avoid confusion with other causes of segmental reduction, as in lipodystrophy or the long-term osteopenia seen in patients with Servelle-Martorell syndrome. Deep high-throughput sequencing was performed in tissue samples from 20 patients using a custom panel. We identified three groups: undergrowth associated with (1) venous, (2) capillary-venous, and (3) lymphatic-capillary-venous malformations. Congenital or early childhood onset undergrowth can occur with or without associated overgrowth. Different likely pathogenic or pathogenic variants were detected in 13 of 20 (65%) tissue samples in the PIK3CA, TEK, GNAQ, or GNA11 genes. In conclusion, the eponymous Servelle-Martorell syndrome should not be used as a synonym for undergrowth. Segmental undergrowth should be considered a characteristic associated with vascular malformations. Patients with PIK3CA variants show all different combinations of overgrowth and undergrowth. Thus, the term PROS (PIK3CA-related overgrowth spectrum) does not cover the entire spectrum.

Cerebrofacial vascular metameric syndrome is caused by somatic pathogenic variants in PIK3CA.

Disorganized morphogenesis of arteries, veins, capillaries, and lymphatic vessels results in vascular malformations. Most individuals with isolated vascular malformations have postzygotic (mosaic), activating pathogenic variants in a handful of oncogenes within the PI3K-RAS-MAPK pathway (Padia et al., Laryngoscope Investig Otolaryngol 4: 170-173 [2019]). Activating pathogenic variants in the gene PIK3CA, which encodes for the catalytic subunit of phosphatidylinositol 3-kinase, are present in both lymphatic and venous malformations as well as arteriovenous malformations in other complex disorders such as CLOVES syndrome (congenital, lipomatous, overgrowth, vascular malformations, epidermal anevi, scoliosis) (Luks et al., Pediatr Dev Pathol 16: 51 [2013]; Luks et al., J Pediatr 166: 1048-1054.e1-5 [2015]; Al-Olabi et al., J Clin Invest 128: 1496-1508 [2018]). These vascular malformations are part of the PIK3CA-related overgrowth spectrum, a spectrum of entities that have regionalized disordered growth due to the presence of tissue-restricted postzygotic PIK3CA pathogenic variants (Keppler-Noreuil et al., Am J Med Genet A 167A: 287-295 [2015]). Cerebrofacial vascular metameric syndrome (CVMS; also described as cerebrofacial arteriovenous metameric syndrome, Bonnet-Dechaume-Blanc syndrome, and Wyburn-Mason syndrome) is the association of retinal, facial, and cerebral vascular malformations (Bhattacharya et al., Interv Neuroradiol 7: 5-17 [2001]; Krings et al., Neuroimaging Clin N Am 17: 245-258 [2007]). The segmental distribution, the presence of tissue overgrowth, and the absence of familial recurrence are all consistent with CVMS being caused by a postzygotic mutation, which has been hypothesized by previous authors (Brinjiki et al., Am J Neuroradiol 39: 2103-2107 [2018]). However, the genetic cause of CVMS has not yet been described. Here, we present three individuals with CVMS and mosaic activating pathogenic variants within the gene PIK3CA We propose that CVMS be recognized as part of the PIK3CA-related overgrowth spectrum, providing justification for future trials using pharmacologic PIK3CA inhibitors (e.g., alpelisib) for these difficult-to-treat patients.

STAT3 is critical for skeletal development and bone homeostasis by regulating osteogenesis.

Skeletal deformities are typical AD-HIES manifestations, which are mainly caused by heterozygous and loss-of-function mutations in Signal transducer and activator of transcription 3 (STAT3). However, the mechanism is still unclear and the treatment strategy is limited. Herein, we reported that the mice with Stat3 deletion in osteoblasts, but not in osteoclasts, induced AD-HIES-like skeletal defects, including craniofacial malformation, osteoporosis, and spontaneous bone fracture. Mechanistic analyses revealed that STAT3 in cooperation with Msh homeobox 1(MSX1) drove osteoblast differentiation by promoting Distal-less homeobox 5(Dlx5) transcription. Furthermore, pharmacological activation of STAT3 partially rescued skeletal deformities in heterozygous knockout mice, while inhibition of STAT3 aggravated bone loss. Taken together, these data show that STAT3 is critical for modulating skeletal development and maintaining bone homeostasis through STAT3-indcued osteogenesis and suggest it may be a potential target for treatments.

Ttc30a affects tubulin modifications in a model for ciliary chondrodysplasia with polycystic kidney disease.

Skeletal ciliopathies (e.g., Jeune syndrome, short rib polydactyly syndrome, and Sensenbrenner syndrome) are frequently associated with nephronophthisis-like cystic kidney disease and other organ manifestations. Despite recent progress in genetic mapping of causative loci, a common molecular mechanism of cartilage defects and cystic kidneys has remained elusive. Targeting two ciliary chondrodysplasia loci (ift80 and ift172) by CRISPR/Cas9 mutagenesis, we established models for skeletal ciliopathies in Xenopus tropicalis Froglets exhibited severe limb deformities, polydactyly, and cystic kidneys, closely matching the phenotype of affected patients. A data mining-based in silico screen found ttc30a to be related to known skeletal ciliopathy genes. CRISPR/Cas9 targeting replicated limb malformations and renal cysts identical to the models of established disease genes. Loss of Ttc30a impaired embryonic renal excretion and ciliogenesis because of altered posttranslational tubulin acetylation, glycylation, and defective axoneme compartmentalization. Ttc30a/b transcripts are enriched in chondrocytes and osteocytes of single-cell RNA-sequenced embryonic mouse limbs. We identify TTC30A/B as an essential node in the network of ciliary chondrodysplasia and nephronophthisis-like disease proteins and suggest that tubulin modifications and cilia segmentation contribute to skeletal and renal ciliopathy manifestations of ciliopathies in a cell type-specific manner. These findings have implications for potential therapeutic strategies.