Reassessing the association: Evaluation of a polyalanine deletion variant of RUNX2 in non-syndromic sagittal and metopic craniosynostosis.

The RUNT-related transcription factor RUNX2 plays a critical role in osteoblast differentiation, and alterations to gene dosage cause distinct craniofacial anomalies. Uniquely amongst the RUNT-related family, vertebrate RUNX2 encodes a polyglutamine/polyalanine repeat (Gln23-Glu-Ala17 in humans), with the length of the polyalanine component completely conserved in great apes. Surprisingly, a frequent 6-amino acid deletion polymorphism, p.(Ala84_Ala89)del, occurs in humans (termed 11A allele), and a previous association study (Cuellar et al. Bone 137:115395;2020) reported that the 11A variant was significantly more frequent in non-syndromic sagittal craniosynostosis (nsSag; allele frequency [AF] = 0.156; 95% confidence interval [CI] 0.126-0.189) compared to non-syndromic metopic craniosynostosis (nsMet; AF = 0.068; 95% CI 0.045-0.098). However, the gnomAD v.2.1.1 control population used by Cuellar et al. did not display Hardy-Weinberg equilibrium, hampering interpretation. To re-examine this association, we genotyped the RUNX2 11A polymorphism in 225 individuals with sporadic nsSag as parent-child trios and 164 singletons with sporadic nsMet, restricting our analysis to individuals of European ancestry. We compared observed allele frequencies to the non-transmitted alleles in the parent-child trios, and to the genome sequencing data from gnomAD v.4, which display Hardy-Weinberg equilibrium. Observed AFs (and 95% CI) were 0.076 (0.053-0.104) in nsSag and 0.082 (0.055-0.118) in nsMet, compared with 0.062 (0.042-0.089) in non-transmitted parental alleles and 0.065 (0.063-0.067) in gnomAD v.4.0.0 non-Finnish European control genomes. In summary, we observed a non-significant excess, compared to gnomAD data, of 11A alleles in both nsSag (relative risk 1.18, 95% CI 0.83-1.67) and nsMet (relative risk 1.29, 95% CI 0.87-1.92), but we did not replicate the much higher excess of RUNX2 11A alleles in nsSag previously reported (p = 0.0001).

Germline pathogenic variants in HNRNPU are associated with alterations in blood methylome.

HNRNPU encodes a multifunctional RNA-binding protein that plays critical roles in regulating pre-mRNA splicing, mRNA stability, and translation. Aberrant expression and dysregulation of HNRNPU have been implicated in various human diseases, including cancers and neurological disorders. We applied a next generation sequencing based assay (EPIC-NGS) to investigate genome-wide methylation profiling for >2 M CpGs for 7 individuals with a neurodevelopmental disorder associated with HNRNPU germline pathogenic loss-of-function variants. Compared to healthy individuals, 227 HNRNPU-associated differentially methylated positions were detected. Both hyper- and hypomethylation alterations were identified but the former predominated. The identification of a methylation episignature for HNRNPU-associated neurodevelopmental disorder (NDD) implicates HNPRNPU-related chromatin alterations in the aetiopathogenesis of this disorder and suggests that episignature profiling should have clinical utility as a predictor for the pathogenicity of HNRNPU variants of uncertain significance. The detection of a methylation episignaure for HNRNPU-associated NDD is consistent with a recent report of a methylation episignature for HNRNPK-associated NDD.

Heterozygous rare variants in NR2F2 cause a recognizable multiple congenital anomaly syndrome with developmental delays.

Nuclear receptor subfamily 2 group F member 2 (NR2F2 or COUP-TF2) encodes a transcription factor which is expressed at high levels during mammalian development. Rare heterozygous Mendelian variants in NR2F2 were initially identified in individuals with congenital heart disease (CHD), then subsequently in cohorts of congenital diaphragmatic hernia (CDH) and 46,XX ovotesticular disorders/differences of sexual development (DSD); however, the phenotypic spectrum associated with pathogenic variants in NR2F2 remains poorly characterized. Currently, less than 40 individuals with heterozygous pathogenic variants in NR2F2 have been reported. Here, we review the clinical and molecular details of 17 previously unreported individuals with rare heterozygous NR2F2 variants, the majority of which were de novo. Clinical features were variable, including intrauterine growth restriction (IUGR), CHD, CDH, genital anomalies, DSD, developmental delays, hypotonia, feeding difficulties, failure to thrive, congenital and acquired microcephaly, dysmorphic facial features, renal failure, hearing loss, strabismus, asplenia, and vascular malformations, thus expanding the phenotypic spectrum associated with NR2F2 variants. The variants seen were predicted loss of function, including a nonsense variant inherited from a mildly affected mosaic mother, missense and a large deletion including the NR2F2 gene. Our study presents evidence for rare, heterozygous NR2F2 variants causing a highly variable syndrome of congenital anomalies, commonly associated with heart defects, developmental delays/intellectual disability, dysmorphic features, feeding difficulties, hypotonia, and genital anomalies. Based on the new and previous cases, we provide clinical recommendations for evaluating individuals diagnosed with an NR2F2-associated disorder.

Pathogenic variants in the paired-related homeobox 1 gene (PRRX1) cause craniosynostosis with incomplete penetrance.

PURPOSE: Studies have previously implicated PRRX1 in craniofacial development, including demonstration of murine Prrx1 expression in the preosteogenic cells of the cranial sutures. We investigated the role of heterozygous missense and loss-of-function (LoF) variants in PRRX1 associated with craniosynostosis. METHODS: Trio-based genome, exome, or targeted sequencing were used to screen PRRX1 in patients with craniosynostosis; immunofluorescence analyses were used to assess nuclear localization of wild-type and mutant proteins. RESULTS: Genome sequencing identified 2 of 9 sporadically affected individuals with syndromic/multisuture craniosynostosis, who were heterozygous for rare/undescribed variants in PRRX1. Exome or targeted sequencing of PRRX1 revealed a further 9 of 1449 patients with craniosynostosis harboring deletions or rare heterozygous variants within the homeodomain. By collaboration, 7 additional individuals (4 families) were identified with putatively pathogenic PRRX1 variants. Immunofluorescence analyses showed that missense variants within the PRRX1 homeodomain cause abnormal nuclear localization. Of patients with variants considered likely pathogenic, bicoronal or other multisuture synostosis was present in 11 of 17 cases (65%). Pathogenic variants were inherited from unaffected relatives in many instances, yielding a 12.5% penetrance estimate for craniosynostosis. CONCLUSION: This work supports a key role for PRRX1 in cranial suture development and shows that haploinsufficiency of PRRX1 is a relatively frequent cause of craniosynostosis.

Personalized recurrence risk assessment following the birth of a child with a pathogenic de novo mutation.

Following the diagnosis of a paediatric disorder caused by an apparently de novo mutation, a recurrence risk of 1-2% is frequently quoted due to the possibility of parental germline mosaicism; but for any specific couple, this figure is usually incorrect. We present a systematic approach to providing individualized recurrence risk. By combining locus-specific sequencing of multiple tissues to detect occult mosaicism with long-read sequencing to determine the parent-of-origin of the mutation, we show that we can stratify the majority of couples into one of seven discrete categories associated with substantially different risks to future offspring. Among 58 families with a single affected offspring (representing 59 de novo mutations in 49 genes), the recurrence risk for 35 (59%) was decreased below 0.1%, but increased owing to parental mixed mosaicism for 5 (9%)-that could be quantified in semen for paternal cases (recurrence risks of 5.6-12.1%). Implementation of this strategy offers the prospect of driving a major transformation in the practice of genetic counselling.

Erratum: Variants in PHF8 cause a spectrum of X-linked neurodevelopmental disorders and facial dysmorphology.

[This corrects the article DOI: 10.1016/j.xhgg.2022.100102.].

Identifying phenotypic expansions for congenital diaphragmatic hernia plus (CDH+) using DECIPHER data.

Congenital diaphragmatic hernia (CDH) can occur in isolation or in conjunction with other birth defects (CDH+). A molecular etiology can only be identified in a subset of CDH cases. This is due, in part, to an incomplete understanding of the genes that contribute to diaphragm development. Here, we used clinical and molecular data from 36 individuals with CDH+ who are cataloged in the DECIPHER database to identify genes that may play a role in diaphragm development and to discover new phenotypic expansions. Among this group, we identified individuals who carried putatively deleterious sequence or copy number variants affecting CREBBP, SMARCA4, UBA2, and USP9X. The role of these genes in diaphragm development was supported by their expression in the developing mouse diaphragm, their similarity to known CDH genes using data from a previously published and validated machine learning algorithm, and/or the presence of CDH in other individuals with their associated genetic disorders. Our results demonstrate how data from DECIPHER, and other public databases, can be used to identify new phenotypic expansions and suggest that CREBBP, SMARCA4, UBA2, and USP9X play a role in diaphragm development.

Variants in PHF8 cause a spectrum of X-linked neurodevelopmental disorders and facial dysmorphology.

Loss-of-function variants in PHD Finger Protein 8 (PHF8) cause Siderius X-linked intellectual disability (ID) syndrome, hereafter called PHF8-XLID. PHF8 is a histone demethylase that is important for epigenetic regulation of gene expression. PHF8-XLID is an under-characterized disorder with only five previous reports describing different PHF8 predicted loss-of-function variants in eight individuals. Features of PHF8-XLID include ID and craniofacial dysmorphology. In this report we present 16 additional individuals with PHF8-XLID from 11 different families of diverse ancestry. We also present five individuals from four different families who have ID and a variant of unknown significance in PHF8 with no other explanatory variant in another gene. All affected individuals exhibited developmental delay and all but two had borderline to severe ID. Of the two who did not have ID, one had dyscalculia and the other had mild learning difficulties. Craniofacial findings such as hypertelorism, microcephaly, elongated face, ptosis, and mild facial asymmetry were found in some affected individuals. Orofacial clefting was seen in three individuals from our cohort, suggesting that this feature is less common than previously reported. Autism spectrum disorder and attention deficit hyperactivity disorder, which were not previously emphasized in PHF8-XLID, were frequently observed in affected individuals. This series expands the clinical phenotype of this rare ID syndrome caused by loss of PHF8 function.

Unexpected role of SIX1 variants in craniosynostosis: expanding the phenotype of SIX1-related disorders.

BACKGROUND: Pathogenic heterozygous SIX1 variants (predominantly missense) occur in branchio-otic syndrome (BOS), but an association with craniosynostosis has not been reported. METHODS: We investigated probands with craniosynostosis of unknown cause using whole exome/genome (n=628) or RNA (n=386) sequencing, and performed targeted resequencing of SIX1 in 615 additional patients. Expression of SIX1 protein in embryonic cranial sutures was examined in the Six1nLacZ/+ reporter mouse. RESULTS: From 1629 unrelated cases with craniosynostosis we identified seven different SIX1 variants (three missense, including two de novo mutations, and four nonsense, one of which was also present in an affected twin). Compared with population data, enrichment of SIX1 loss-of-function variants was highly significant (p=0.00003). All individuals with craniosynostosis had sagittal suture fusion; additionally four had bilambdoid synostosis. Associated BOS features were often attenuated; some carrier relatives appeared non-penetrant. SIX1 is expressed in a layer basal to the calvaria, likely corresponding to the dura mater, and in the mid-sagittal mesenchyme. CONCLUSION: Craniosynostosis is associated with heterozygous SIX1 variants, with possible enrichment of loss-of-function variants compared with classical BOS. We recommend screening of SIX1 in craniosynostosis, particularly when sagittal±lambdoid synostosis and/or any BOS phenotypes are present. These findings highlight the role of SIX1 in cranial suture homeostasis.

Evaluating the performance of a clinical genome sequencing program for diagnosis of rare genetic disease, seen through the lens of craniosynostosis.

PURPOSE: Genome sequencing (GS) for diagnosis of rare genetic disease is being introduced into the clinic, but the complexity of the data poses challenges for developing pipelines with high diagnostic sensitivity. We evaluated the performance of the Genomics England 100,000 Genomes Project (100kGP) panel-based pipelines, using craniosynostosis as a test disease. METHODS: GS data from 114 probands with craniosynostosis and their relatives (314 samples), negative on routine genetic testing, were scrutinized by a specialized research team, and diagnoses compared with those made by 100kGP. RESULTS: Sixteen likely pathogenic/pathogenic variants were identified by 100kGP. Eighteen additional likely pathogenic/pathogenic variants were identified by the research team, indicating that for craniosynostosis, 100kGP panels had a diagnostic sensitivity of only 47%. Measures that could have augmented diagnoses were improved calling of existing panel genes (+18% sensitivity), review of updated panels (+12%), comprehensive analysis of de novo small variants (+29%), and copy-number/structural variants (+9%). Recent NHS England recommendations that partially incorporate these measures should achieve 85% overall sensitivity (+38%). CONCLUSION: GS identified likely pathogenic/pathogenic variants in 29.8% of previously undiagnosed patients with craniosynostosis. This demonstrates the value of research analysis and the importance of continually improving algorithms to maximize the potential of clinical GS.

Non-coding region variants upstream of MEF2C cause severe developmental disorder through three distinct loss-of-function mechanisms.

Clinical genetic testing of protein-coding regions identifies a likely causative variant in only around half of developmental disorder (DD) cases. The contribution of regulatory variation in non-coding regions to rare disease, including DD, remains very poorly understood. We screened 9,858 probands from the Deciphering Developmental Disorders (DDD) study for de novo mutations in the 5' untranslated regions (5' UTRs) of genes within which variants have previously been shown to cause DD through a dominant haploinsufficient mechanism. We identified four single-nucleotide variants and two copy-number variants upstream of MEF2C in a total of ten individual probands. We developed multiple bespoke and orthogonal experimental approaches to demonstrate that these variants cause DD through three distinct loss-of-function mechanisms, disrupting transcription, translation, and/or protein function. These non-coding region variants represent 23% of likely diagnoses identified in MEF2C in the DDD cohort, but these would all be missed in standard clinical genetics approaches. Nonetheless, these variants are readily detectable in exome sequence data, with 30.7% of 5' UTR bases across all genes well covered in the DDD dataset. Our analyses show that non-coding variants upstream of genes within which coding variants are known to cause DD are an important cause of severe disease and demonstrate that analyzing 5' UTRs can increase diagnostic yield. We also show how non-coding variants can help inform both the disease-causing mechanism underlying protein-coding variants and dosage tolerance of the gene.

Dissection of contiguous gene effects for deletions around ERF on chromosome 19.

Heterozygous intragenic loss-of-function mutations of ERF, encoding an ETS transcription factor, were previously reported to cause a novel craniosynostosis syndrome, suggesting that ERF is haploinsufficient. We describe six families harboring heterozygous deletions including, or near to, ERF, of which four were characterized by whole-genome sequencing and two by chromosomal microarray. Based on the severity of associated intellectual disability (ID), we identify three categories of ERF-associated deletions. The smallest (32 kb) and only inherited deletion included two additional centromeric genes and was not associated with ID. Three larger deletions (264-314 kb) that included at least five further centromeric genes were associated with moderate ID, suggesting that deletion of one or more of these five genes causes ID. The individual with the most severe ID had a more telomerically extending deletion, including CIC, a known ID gene. Children found to harbor ERF deletions should be referred for craniofacial assessment, to exclude occult raised intracranial pressure.

DLG4-related synaptopathy: a new rare brain disorder.

PURPOSE: Postsynaptic density protein-95 (PSD-95), encoded by DLG4, regulates excitatory synaptic function in the brain. Here we present the clinical and genetic features of 53 patients (42 previously unpublished) with DLG4 variants. METHODS: The clinical and genetic information were collected through GeneMatcher collaboration. All the individuals were investigated by local clinicians and the gene variants were identified by clinical exome/genome sequencing. RESULTS: The clinical picture was predominated by early onset global developmental delay, intellectual disability, autism spectrum disorder, and attention deficit-hyperactivity disorder, all of which point to a brain disorder. Marfanoid habitus, which was previously suggested to be a characteristic feature of DLG4-related phenotypes, was found in only nine individuals and despite some overlapping features, a distinct facial dysmorphism could not be established. Of the 45 different DLG4 variants, 39 were predicted to lead to loss of protein function and the majority occurred de novo (four with unknown origin). The six missense variants identified were suggested to lead to structural or functional changes by protein modeling studies. CONCLUSION: The present study shows that clinical manifestations associated with DLG4 overlap with those found in other neurodevelopmental disorders of synaptic dysfunction; thus, we designate this group of disorders as DLG4-related synaptopathy.

Further delineation of BCAP31-linked intellectual disability: description of 17 new families with LoF and missense variants.

The BCAP31 gene, located at Xq28, encodes BAP31, which plays a role in ER-to-Golgi anterograde transport. To date, BCAP31 pathogenic variants have been reported in 12 male cases from seven families (six loss of function (LoF) and one missense). Patients had severe intellectual disability (ID), dystonia, deafness, and central hypomyelination, delineating a so-called deafness, dystonia and cerebral hypomyelination syndrome (DDCH). Female carriers are mostly asymptomatic but may present with deafness. BCAP31 is flanked by the SLC6A8 and ABCD1 genes. Contiguous deletions of BCAP31 and ABCD1 and/or SLC6A8 have been described in 12 patients. Patients with deletions including BCAP31 and SLC6A8 have the same phenotype as BCAP31 patients. Patients with deletions of BCAP31 and ABCD1 have contiguous ABCD1 and DXS1375E/BCAP31 deletion syndrome (CADDS), and demonstrate a more severe neurological phenotype with cholestatic liver disease and early death. We report 17 novel families, 14 with intragenic BCAP31 variants (LoF and missense) and three with a deletion of BCAP31 and adjacent genes (comprising two CADDS patients, one male and one symptomatic female). Our study confirms the phenotype reported in males with intragenic LoF variants and shows that males with missense variants exhibit a milder phenotype. Most patients with a LoF pathogenic BCAP31 variant have permanent or transient liver enzyme elevation. We further demonstrate that carrier females (n = 10) may have a phenotype comprising LD, ID, and/or deafness. The male with CADDS had a severe neurological phenotype, but no cholestatic liver disease, and the symptomatic female had moderate ID and cholestatic liver disease.

Expanding the phenotype of biallelic loss-of-function variants in the NSUN2 gene: Description of four individuals with juvenile cataract, chronic nephritis, or brain anomaly as novel complications.

The NSUN2 gene encodes a tRNA cytosine methyltransferase that functions in the maturation of leucyl tRNA (Leu) (CAA) precursors, which is crucial for the anticodon-codon pairing and correct translation of mRNA. Biallelic loss of function variants in NSUN2 are known to cause moderate to severe intellectual disability. Microcephaly, postnatal growth retardation, and dysmorphic facial features are common complications in this genetic disorder, and delayed puberty is occasionally observed. Here, we report four individuals, two sets of siblings, with biallelic loss-of-function variants in the NSUN2 gene. The first set of siblings have compound heterozygous frameshift variants: c.546_547insCT, p.Met183Leufs*13; c.1583del, p.Pro528Hisfs*19, and the other siblings carry a homozygous frameshift variant: c.1269dup, p.Val424Cysfs*14. In addition to previously reported clinical features, the first set of siblings showed novel complications of juvenile cataract and chronic nephritis. The other siblings showed hypomyelination and simplified gyral pattern in neuroimaging. NSUN2-related intellectual disability is a very rare condition, and less than 20 cases have been reported previously. Juvenile cataract, chronic nephritis, and brain anomaly shown in the present patients have not been previously described. Our report suggests clinical diversity of NSUN2-related intellectual disability.

Correction: SMAD6 variants in craniosynostosis: genotype and phenotype evaluation.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

SMAD6 variants in craniosynostosis: genotype and phenotype evaluation.

PURPOSE: Enrichment of heterozygous missense and truncating SMAD6 variants was previously reported in nonsyndromic sagittal and metopic synostosis, and interaction of SMAD6 variants with a common polymorphism nearBMP2 (rs1884302) was proposed to contribute to inconsistent penetrance. We determined the occurrence of SMAD6 variants in all types of craniosynostosis, evaluated the impact of different missense variants on SMAD6 function, and tested independently whether rs1884302 genotype significantly modifies the phenotype. METHODS: We performed resequencing of SMAD6 in 795 unsolved patients with any type of craniosynostosis and genotyped rs1884302 in SMAD6-positive individuals and relatives. We examined the inhibitory activity and stability of SMAD6 missense variants. RESULTS: We found 18 (2.3%) different rare damaging SMAD6 variants, with the highest prevalence in metopic synostosis (5.8%) and an 18.3-fold enrichment of loss-of-function variants comparedwith gnomAD data (P < 10-7). Combined with eight additional variants, ≥20/26 were transmitted from an unaffected parent but rs1884302 genotype did not predict phenotype. CONCLUSION: Pathogenic SMAD6 variants substantially increase the risk of both nonsyndromic and syndromic presentations of craniosynostosis, especially metopic synostosis. Functional analysis is important to evaluate missense variants. Genotyping of rs1884302 is not clinically useful. Mechanisms to explain the remarkable diversity of phenotypes associated with SMAD6 variants remain obscure.

De Novo Variants in CNOT1, a Central Component of the CCR4-NOT Complex Involved in Gene Expression and RNA and Protein Stability, Cause Neurodevelopmental Delay.

CNOT1 is a member of the CCR4-NOT complex, which is a master regulator, orchestrating gene expression, RNA deadenylation, and protein ubiquitination. We report on 39 individuals with heterozygous de novo CNOT1 variants, including missense, splice site, and nonsense variants, who present with a clinical spectrum of intellectual disability, motor delay, speech delay, seizures, hypotonia, and behavioral problems. To link CNOT1 dysfunction to the neurodevelopmental phenotype observed, we generated variant-specific Drosophila models, which showed learning and memory defects upon CNOT1 knockdown. Introduction of human wild-type CNOT1 was able to rescue this phenotype, whereas mutants could not or only partially, supporting our hypothesis that CNOT1 impairment results in neurodevelopmental delay. Furthermore, the genetic interaction with autism-spectrum genes, such as ASH1L, DYRK1A, MED13, and SHANK3, was impaired in our Drosophila models. Molecular characterization of CNOT1 variants revealed normal CNOT1 expression levels, with both mutant and wild-type alleles expressed at similar levels. Analysis of protein-protein interactions with other members indicated that the CCR4-NOT complex remained intact. An integrated omics approach of patient-derived genomics and transcriptomics data suggested only minimal effects on endonucleolytic nonsense-mediated mRNA decay components, suggesting that de novo CNOT1 variants are likely haploinsufficient hypomorph or neomorph, rather than dominant negative. In summary, we provide strong evidence that de novo CNOT1 variants cause neurodevelopmental delay with a wide range of additional co-morbidities. Whereas the underlying pathophysiological mechanism warrants further analysis, our data demonstrate an essential and central role of the CCR4-NOT complex in human brain development.

Clinical findings of 21 previously unreported probands with HNRNPU-related syndrome and comprehensive literature review.

With advances in genetic testing and improved access to such advances, whole exome sequencing is becoming a first-line investigation in clinical work-up of children with developmental delay/intellectual disability (ID). As a result, the need to understand the importance of genetic variants and its effect on the clinical phenotype is increasing. Here, we report on the largest cohort of patients with HNRNPU variants. These 21 patients follow on from the previous study published by Yates et al. in 2017 from our group predominantly identified from the Deciphering Developmental Disorders study that reported seven patients with HNRNPU variants. All the probands reported here have a de novo loss-of-function variant. These probands have craniofacial dysmorphic features, in the majority including widely spaced teeth, microcephaly, high arched eyebrows, and palpebral fissure abnormalities. Many of the patients in the group also have moderate to severe ID and seizures that tend to start in early childhood. This series has allowed us to define a novel neurodevelopmental syndrome, with a likely mechanism of haploinsufficiency, and expand substantially on already published literature on HNRNPU-related neurodevelopmental syndrome.