Mutations in SRCAP, encoding SNF2-related CREBBP activator protein, cause Floating-Harbor syndrome

[Floating-Harbor syndrome: a case report and literature review]

Floating-Harbor syndrome (FHS) is an autosomal dominant genetic disease caused by SRCAP mutation. This article reports the clinical features of a boy with FHS. The boy, aged 11 years and 7 months, attended the hospital due to short stature for more than 8 years and had the clinical manifestations of unusual facial features (triangularly shaped face, thin lips and long eyelashes), skeletal dysplasia (curvature finger), expressive language disorder, and retardation of bone age. Genetic detection revealed a novel heterozygous mutation, c.7330 C>T(p.R2444X), in the SRCAP gene. The boy was diagnosed with FHS based on these clinical manifestations and gene detection results. FHS is rare in clinical practice, which may lead to missed diagnosis and misdiagnosis, and gene detection may help with the clinical diagnosis of FHS in children.

Hallermann-Streiff syndrome: A missing molecular link for a highly recognizable syndrome

The use of modern next-generation sequencing-based approaches for gene identification has tremendously improved our understanding of the molecular pathogenesis of the great majority of well-known syndromes, whereas only a few remain to be elucidated. Hallermann-Streiff syndrome is such a disorder for which the molecular basis is still unknown although it represents a highly recognizable phenotype. Clinically, patients with Hallermann-Streiff syndrome show typical craniofacial dysmorphism, eye malformations, a distinctive facial appearance, abnormalities of hair and skin, short stature, and, interestingly, they might also present with aspects of premature aging. The clinical diagnosis is mainly given by the very typical facial gestalt of patients. In this review, we (a) summarize the current knowledge on the phenotypic traits, focusing on described classic cases, (b) discuss the missing molecular link, and (c) present innovative future strategies for gene identification.

Intracranial vascular pathology in two further patients with Floating-Harbor syndrome: Proposals for cerebrovascular disease risk management

Floating-Harbor syndrome (FHS) is a rare, heritable disorder caused by variants in the SRCAP gene. Most individuals with FHS have characteristic facial features, short stature, and speech and language impairment. Although FHS has been likely under-diagnosed due to a combination of lack of recognition of the clinical phenotype and limited access to genomic testing, it is a rare condition with around 100 individuals reported in the medical literature. Case series have been biased towards younger individuals (vast majority <20 years of age) meaning that it has been challenging to provide accurate medical advice for affected individuals in adulthood. We report two young adults with FHS who presented with intracranial haemorrhage likely secondary to cerebrovascular aneurysms, with devastating consequences, making a total of four FHS patients reported with significant cerebrovascular abnormalities. Three of four patients had hypertension, at least one in conjunction with normal renal structure. We consider possible relationships between hypertension, renal pathology and aneurysms in the context of FHS, and consider mechanisms through which disruption of the SRCAP protein may lead to vascular pathology. We recommend that clinicians should have a low threshold to investigate symptoms suggestive of cerebrovascular disease in FHS. We advise that patients with FHS should have annual blood pressure monitoring from adolescence, renal ultrasound at diagnosis repeated in adulthood, and timely investigation of any neurological symptoms. For patients with FHS, particularly with hypertension, we advise that clinicians should consider at least one MRA (Magnetic Resonance Imaging with Angiography) to check for cerebral aneurysms.

The Face of Chromatin Variants

A developmental program affecting human face shape is shown by Greenberg et al. (2019) to hinge on the ability to distinguish a single methyl group between two histone variant isoforms and the action of the chromatin-remodeling enzyme SRCAP. This challenges researchers to link atomic structure to a morphological defect.

Case Report of Floating-Harbor Syndrome With Bilateral Cleft Lip

Floating-Harbor syndrome (FHS) is a rare genetic disorder caused by heterozygous mutations in the Snf2-related CREBBP activator protein (SRCAP) gene. The syndrome is characterized by proportional short stature, delayed bone maturation, delayed speech development, and facial dysmorphism. Submucous cleft palate and cleft lip have been reported in FHS, but to our knowledge orofacial clefting in this condition has not been assessed in detail. Here, we report on a case of bilateral cleft lip in a patient with FHS confirmed by exome sequencing.

Novel genotypes and phenotypes among Chinese patients with Floating-Harbor syndrome

Background

Floating-Harbor syndrome (FHS) is a rare syndromic short stature disorder caused by truncating variants in SRCAP. Few Chinese FHS patients had been reported so far and limited knowledge regarding the benefit of growth hormone treatment existed.

Methods

We ascertained 12 short stature patients with molecularly confirmed diagnosis of FHS by whole exome sequencing. We performed a comprehensive clinical evaluation for all patients and assessed the responsiveness of growth hormone treatment in a subset of the patients.

Results

Five distinct pathogenic/likely pathogenic variants were identified in 12 independent FHS patients including two previously reported variants (c.7303C > T/p.Arg2435Ter and c.7330C > T/p.Arg2444Ter) and three novel variants (c.7189G > T/p.Glu2397Ter, c.7245_7246delAT/p.Ser2416ArgfsTer26 and c.7466C > G/p.Ser2489Ter). The c.7303C > T/p.Arg2435Ter mutation appears more common in Chinese FHS patients. The clinical presentations of Chinese FHS patients are very similar to those of previously reported patients of different ethnicities. Yet we noticed micropenis and ear abnormalities in multiple patients, suggesting that these may be novel phenotypes of Floating-Harbor syndrome. Eight patients (one with GH deficiency, one with undetermined GH level, six without GH deficiency) underwent growth hormone treatment, 3 patients had good responses, one with modest and two with poor responses.

Conclusion

We described novel genotypes and phenotypes in a Chinese FHS patient cohort. We showed that about half of FHS patients exhibited modest to good response to GH treatment regardless of their respective GH deficiency status. We didn’t find any correlation between different mutations and response to GH treatment.

Electronic supplementary material

The online version of this article (10.1186/s13023-019-1111-8) contains supplementary material, which is available to authorized users.

Rubinstein-Taybi syndrome in a Saudi boy with distinct features and variants in both the CREBBP and EP300 genes: a case report

BACKGROUND

Rubinstein-Taybi syndrome (RSTS) Type 1 (OMIM 180849) is characterized by three main features: intellectual disability; broad and frequently angulated thumbs and halluces; and characteristic facial dysmorphism.

CASE PRESENTATION

We report on a Saudi boy with RSTS Type 1 and the following distinct features: a midline notch of the upper lip, a bifid tip of the tongue, a midline groove of the lower lip, plump fingers with broad / flat fingertips, and brachydactyly. The child was found to be heterozygous in the CREBBP gene for a sequence variant designated c.4963del, which is predicted to result in premature protein termination p.Leu1655Cysfs*89. The child and his father were also found to be heterozygous in the EP300 gene for a sequence variant designated c.586A > G, which is predicted to result in the amino-acid substitution p.Ile196Val.

CONCLUSION

Our report expands the clinical spectrum of RSTS to include several distinct facial and limb features. The variant of the CREBBP gene is known to be causative of RSTS Type 1. The variant in the EP300 gene is benign since the father carried the same variant and exhibited no abnormalities. However, functional studies are required to investigate if this benign EP300 variant influences the phenotype in the presence of disease-causing CREBBP gene mutations.

Renal Calculus in Floating-Harbor Syndrome: A Case Report

Floating-Harbor syndrome is a rare condition marked by short stature and delayed bone age, characteristic facial features, and speech impairment. Floating-Harbor syndrome commonly results from a sporadic genetic mutation. Renal abnormalities have rarely been encountered. We report the first patient with Floating-Harbor syndrome who spontaneously passed a renal calculus consisting of calcium oxalate monohydrate and calcium oxalate dihydrate. A renal ultrasound showed echotexture within the renal pyramids, hydronephrosis, and a cyst. Pediatric nurse practitioners should be alert to the unique features associated with Floating-Harbor syndrome and be prepared to monitor and treat the renal abnormalities that may accompany this uncommon condition.

A unique de novo gain-of-function variant in CAMK4 associated with intellectual disability and hyperkinetic movement disorder

Calcium/calmodulin-dependent protein kinases (CaMKs) are key mediators of calcium signaling and underpin neuronal health. Although widely studied, the contribution of CaMKs to Mendelian disease is rather enigmatic. Here, we describe an unusual neurodevelopmental phenotype, characterized by milestone delay, intellectual disability, autism, ataxia, and mixed hyperkinetic movement disorder including severe generalized dystonia, in a proband who remained etiologically undiagnosed despite exhaustive testing. We performed trio whole-exome sequencing to identify a de novo essential splice-site variant (c.981+1G>A) in CAMK4, encoding CaMKIV. Through in silico evaluation and cDNA analyses, we demonstrated that c.981+1G>A alters CAMK4 pre-mRNA processing and results in a stable mRNA transcript containing a 77-nt out-of-frame deletion and a premature termination codon within the last exon. The expected protein, p.Lys303Serfs*28, exhibits selective loss of the carboxy-terminal regulatory domain of CaMKIV and bears striking structural resemblance to previously reported synthetic mutants that confer constitutive CaMKIV activity. Biochemical studies in proband-derived cells confirmed an activating effect of c.981+1G>A and indicated that variant-induced excessive CaMKIV signaling is sensitive to pharmacological manipulation. Additionally, we found that variants predicted to cause selective depletion of CaMKIV's regulatory domain are unobserved in diverse catalogs of human variation, thus revealing that c.981+1G>A is a unique molecular event. We propose that our proband's phenotype is explainable by a dominant CAMK4 splice-disrupting mutation that acts through a gain-of-function mechanism. Our findings highlight the importance of CAMK4 in human neurodevelopment, provide a foundation for future clinical research of CAMK4, and suggest the CaMKIV signaling pathway as a potential drug target in neurological disease.

Floating-Harbor Syndrome: Presentation of the First Romanian Patient with a SRCAP Mutation and Review of the Literature

Floating-Harbor syndrome (FHS) is a rare autosomal dominant syndrome characterized by short stature with delayed bone age, retarded speech development, intellectual disability and dysmorphic facial features. Recently, dominant mutations almost exclusively clustered in the final exon of the Snf2-related CREBBP activator protein (SRCAP) gene were identified to cause FHS. Here, we report a boy with short stature, speech delay, mild intellectual disability, dysmorphic features, and with genetically confirmed FHS. To the best of our knowledge, this is the first molecularly confirmed case with this syndrome reported in Romania. An intensive program of cognitive and speech stimulation, as well as yearly neurological, psychological, ophthalmological, otorhinolaryngological, pediatric and endocrinological monitoring for our patient were designed. We propose a checklist of clinical features suggestive of FHS, based on the main clinical features, in order to facilitate the diagnosis and clinical management of this rare condition.

Further delineation of the clinical spectrum of de novo TRIM8 truncating mutations

De novo mutations of the TRIM8 gene, which codes for a tripartite motif protein, have been identified using whole exome sequencing (WES) in two patients with epileptic encephalopathy (EE), but these reports were not sufficient to conclude that TRIM8 was a novel gene responsible for EE. Here we report four additional patients presenting with EE and de novo truncating mutations of TRIM8 detected by WES, and give further details of the patient previously reported by the Epi4K consortium. Epilepsy of variable severity was diagnosed in children aged 2 months to 3.5 years of age. All patients had developmental delay of variable severity with no or very limited language, often associated with behavioral anomalies and unspecific facial features or MRI brain abnormalities. The phenotypic variability observed in these patients appeared related to the severity of the epilepsy. One patient presented pharmacoresistant EE with regression, recurrent infections and nephrotic syndrome, compatible with the brain and kidney expression of TRIM8. Interestingly, all mutations were located at the highly conserved C-terminus section of TRIM8. This collaborative study confirms that TRIM8 is a novel gene responsible for EE, possibly associated with nephrotic syndrome. This report brings new evidence on the pathogenicity of TRIM8 mutations and highlights the value of data-sharing to delineate the phenotypic characteristics and biological basis of extremely rare disorders.

The first Korean case with Floating-Harbor syndrome with a novel SRCAP mutation diagnosed by targeted exome sequencing

Floating-Harbor syndrome is a rare autosomal dominant genetic disorder associated with SRCAP mutation. To date, approximately 50 cases of Floating-Harbor syndrome have been reported, but none have been reported in Korea yet. Floating-Harbor syndrome is characterized by delayed bony maturation, unique facial features, and language impairment. Here, we present a 6-year-old boy with a triangular face, deep-set protruding eyes, low-set ears, wide nose with narrow nasal bridge, short philtrum, long thin lips, clinodactyly, and developmental delay that was transferred to our pediatric clinic for genetic evaluation. He showed progressive delay in the area of language and cognition-adaption as he grew. He had previously undergone chromosomal analysis at another hospital due to his language delay, but his karyotype was normal. We performed targeted exome sequencing, considering several syndromes with similar phenotypes. Library preparation was performed with the TruSight One sequencing panel, which enriches the sample for about 4,800 genes of clinical relevance. Massively parallel sequencing was conducted with NextSeq. An identified variant was confirmed by Sanger sequencing of the patient and his parents. Finally, the patient was confirmed as the first Korean case of Floating-Harbor syndrome with a novel SRCAP (Snf2 related CREBBP activator protein) mutation (c.7732dupT, p.Ser2578Phefs*6), resulting in early termination of the protein; it was not found in either of his healthy parents or a control population. To our knowledge, this is the first study to describe a boy with Floating-Harbor syndrome with a novel SRCAP mutation diagnosed by targeted exome sequencing in Korea.

De Novo Truncating Mutations in WASF1 Cause Intellectual Disability with Seizures

Next-generation sequencing has been invaluable in the elucidation of the genetic etiology of many subtypes of intellectual disability in recent years. Here, using exome sequencing and whole-genome sequencing, we identified three de novo truncating mutations in WAS protein family member 1 (WASF1) in five unrelated individuals with moderate to profound intellectual disability with autistic features and seizures. WASF1, also known as WAVE1, is part of the WAVE complex and acts as a mediator between Rac-GTPase and actin to induce actin polymerization. The three mutations connected by Matchmaker Exchange were c.1516C>T (p.Arg506Ter), which occurs in three unrelated individuals, c.1558C>T (p.Gln520Ter), and c.1482delinsGCCAGG (p.Ile494MetfsTer23). All three variants are predicted to partially or fully disrupt the C-terminal actin-binding WCA domain. Functional studies using fibroblast cells from two affected individuals with the c.1516C>T mutation showed a truncated WASF1 and a defect in actin remodeling. This study provides evidence that de novo heterozygous mutations in WASF1 cause a rare form of intellectual disability.

LncKdm2b controls self-renewal of embryonic stem cells via activating expression of transcription factor Zbtb3

Divergent long noncoding RNAs (lncRNAs) represent a major lncRNA biotype in mouse and human genomes. The biological and molecular functions of the divergent lncRNAs remain largely unknown. Here, we show that lncKdm2b, a divergent lncRNA for Kdm2b gene, is conserved among five mammalian species and highly expressed in embryonic stem cells (ESCs) and early embryos. LncKdm2b knockout impairs ESC self-renewal and causes early embryonic lethality. LncKdm2b can activate Zbtb3 by promoting the assembly and ATPase activity of Snf2-related CREBBP activator protein (SRCAP) complex in trans Zbtb3 potentiates the ESC self-renewal in a Nanog-dependent manner. Finally, Zbtb3 deficiency impairs the ESC self-renewal and early embryonic development. Therefore, our findings reveal that lncRNAs may represent an additional layer of the regulation of ESC self-renewal and early embryogenesis.

Nervous system development and disease: A focus on trithorax related proteins and chromatin remodelers

The nervous system comprises many different cell types including neurons, glia, macrophages, and immune cells, each of which is defined by specific patterns of gene expression, morphology, function, and anatomical location. Establishment of these complex and highly regulated cell fates requires spatial and temporal coordination of gene transcription. Open chromatin (euchromatin) allows transcription factors to interact with gene promoters and activate lineage specific genes, whereas closed chromatin (heterochromatin) remains inaccessible to transcriptional activation. Changes in the genome-wide distribution of euchromatin accompany transcriptional plasticity that allows the diversity of mature cell fates to be generated during development. In the past 20years, many new genes and gene families have been identified to participate in regulation of chromatin accessibility. These genes include chromatin remodelers that interact with Trithorax group (TrxG) and Polycomb group (PcG) proteins to activate or repress transcription, respectively. Here we review the role of TrxG proteins in neurodevelopment and disease.

Perthes disease: A new finding in Floating-Harbor syndrome

Floating-Harbor Syndrome (FHS; OMIM #136140) is an ultra-rare autosomal dominant genetic condition characterized by expressive language delay, short stature with delayed bone mineralization, a triangular face with a prominent nose, and deep-set eyes, and hand anomalies. First reported in 1973, FHS is associated with mutations in the SRCAP gene, which encodes SNF2-related CREBBP activator protein. Mutations in the CREBBP gene cause Rubinstein-Taybi Syndrome (RSTS; OMIM #180849, #613684), another rare disease characterized by broad thumbs and halluces, facial dysmorphisms, short stature, and intellectual disability, which has a phenotypic overlap with FHS. We describe a case of FHS associated with a novel SRCAP mutation and characterized by Perthes disease, a skeletal anomaly described in approximately 3% of patients with RSTS. Thus Perthes disease can be added to the list of clinical features that overlap between FHS and RSTS.

Genomic DNA Methylation Signatures Enable Concurrent Diagnosis and Clinical Genetic Variant Classification in Neurodevelopmental Syndromes

Pediatric developmental syndromes present with systemic, complex, and often overlapping clinical features that are not infrequently a consequence of Mendelian inheritance of mutations in genes involved in DNA methylation, establishment of histone modifications, and chromatin remodeling (the "epigenetic machinery"). The mechanistic cross-talk between histone modification and DNA methylation suggests that these syndromes might be expected to display specific DNA methylation signatures that are a reflection of those primary errors associated with chromatin dysregulation. Given the interrelated functions of these chromatin regulatory proteins, we sought to identify DNA methylation epi-signatures that could provide syndrome-specific biomarkers to complement standard clinical diagnostics. In the present study, we examined peripheral blood samples from a large cohort of individuals encompassing 14 Mendelian disorders displaying mutations in the genes encoding proteins of the epigenetic machinery. We demonstrated that specific but partially overlapping DNA methylation signatures are associated with many of these conditions. The degree of overlap among these epi-signatures is minimal, further suggesting that, consistent with the initial event, the downstream changes are unique to every syndrome. In addition, by combining these epi-signatures, we have demonstrated that a machine learning tool can be built to concurrently screen for multiple syndromes with high sensitivity and specificity, and we highlight the utility of this tool in solving ambiguous case subjects presenting with variants of unknown significance, along with its ability to generate accurate predictions for subjects presenting with the overlapping clinical and molecular features associated with the disruption of the epigenetic machinery.

The role of ISWI chromatin remodeling complexes in brain development and neurodevelopmental disorders

The mammalian ISWI (Imitation Switch) genes SMARCA1 and SMARCA5 encode the ATP-dependent chromatin remodeling proteins SNF2L and SNF2H. The ISWI proteins interact with BAZ (bromodomain adjacent to PHD zinc finger) domain containing proteins to generate eight distinct remodeling complexes. ISWI complex-mediated nucleosome positioning within genes and gene regulatory elements is proving important for the transition from a committed progenitor state to a differentiated cell state. Genetic studies have implicated the involvement of many ATP-dependent chromatin remodeling proteins in neurodevelopmental disorders (NDDs), including SMARCA1. Here we review the characterization of mice inactivated for ISWI and their interacting proteins, as it pertains to brain development and disease. A better understanding of chromatin dynamics during neural development is a prerequisite to understanding disease pathologies and the development of therapeutics for these complex disorders.

ACTB Loss-of-Function Mutations Result in a Pleiotropic Developmental Disorder

ACTB encodes β-actin, an abundant cytoskeletal housekeeping protein. In humans, postulated gain-of-function missense mutations cause Baraitser-Winter syndrome (BRWS), characterized by intellectual disability, cortical malformations, coloboma, sensorineural deafness, and typical facial features. To date, the consequences of loss-of-function ACTB mutations have not been proven conclusively. We describe heterozygous ACTB deletions and nonsense and frameshift mutations in 33 individuals with developmental delay, apparent intellectual disability, increased frequency of internal organ malformations (including those of the heart and the renal tract), growth retardation, and a recognizable facial gestalt (interrupted wavy eyebrows, dense eyelashes, wide nose, wide mouth, and a prominent chin) that is distinct from characteristics of individuals with BRWS. Strikingly, this spectrum overlaps with that of several chromatin-remodeling developmental disorders. In wild-type mouse embryos, β-actin expression was prominent in the kidney, heart, and brain. ACTB mRNA expression levels in lymphoblastic lines and fibroblasts derived from affected individuals were decreased in comparison to those in control cells. Fibroblasts derived from an affected individual and ACTB siRNA knockdown in wild-type fibroblasts showed altered cell shape and migration, consistent with known roles of cytoplasmic β-actin. We also demonstrate that ACTB haploinsufficiency leads to reduced cell proliferation, altered expression of cell-cycle genes, and decreased amounts of nuclear, but not cytoplasmic, β-actin. In conclusion, we show that heterozygous loss-of-function ACTB mutations cause a distinct pleiotropic malformation syndrome with intellectual disability. Our biological studies suggest that a critically reduced amount of this protein alters cell shape, migration, proliferation, and gene expression to the detriment of brain, heart, and kidney development.

A novel finding of oligodontia and ankyloglossia in a 14-year-old with Floating-Harbor syndrome

Floating-Harbor syndrome (FHS) is a rare genetic condition characterized by distinct facial features, short stature and delayed skeletal development. Here we present case of a 14-year-old boy with short stature, typical facial features, impaired voice quality, clinodactyly, cryptorchidism and unilateral agenesis of kidney. In addition he had oligodontia and ankyloglossia with features suggestive of FHS. Treatment rendered was restoration of caries, application of pit and fissure sealants followed by frenectomy. The purpose of this report is to highlight the oral developmental anomalies and the management of a patient with FHS and to add to the current knowledge of the literature on this syndrome.

Suppression of SRCAP chromatin remodelling complex and restriction of lymphoid lineage commitment by Pcid2

Lymphoid lineage commitment is an important process in haematopoiesis, which forms the immune system to protect the host from pathogen invasion. However, how multipotent progenitors (MPP) switch into common lymphoid progenitors (CLP) or common myeloid progenitors (CMP) during this process remains elusive. Here we show that PCI domain-containing protein 2 (Pcid2) is highly expressed in MPPs. Pcid2 deletion in the haematopoietic system causes skewed lymphoid lineage specification. In MPPs, Pcid2 interacts with the Zinc finger HIT-type containing 1 (ZNHIT1) to block Snf2-related CREBBP activator protein (SRCAP) activity and prevents the deposition of histone variant H2A.Z and transcription factor PU.1 to key lymphoid fate regulator genes. Furthermore, Znhit1 deletion also abrogates H2A/H2A.Z exchange in MPPs. Thus Pcid2 controls lymphoid lineage commitment through the regulation of SRCAP remodelling activity.

Genetics of Short Stature

Short stature is a common and heterogeneous condition that is often genetic in etiology. For most children with genetic short stature, the specific molecular causes remain unknown; but with advances in exome/genome sequencing and bioinformatics approaches, new genetic causes of growth disorders have been identified, contributing to the understanding of the underlying molecular mechanisms of longitudinal bone growth and growth failure. Identifying new genetic causes of growth disorders has the potential to improve diagnosis, prognostic accuracy, and individualized management, and help avoid unnecessary testing for endocrine and other disorders.

Constitutional Epi/Genetic Conditions: Genetic, Epigenetic, and Environmental Factors

There are more than 4,000 phenotypes for which the molecular basis is at least partly known. Though defects in primary DNA structure constitute a major cause of these disorders, epigenetic disruption is emerging as an important alternative mechanism in the etiology of a broad range of congenital and developmental conditions. These include epigenetic defects caused by either localized (in cis) genetic alterations or more distant (in trans) genetic events but can also include environmental effects. Emerging evidence suggests interplay between genetic and environmental factors in the epigenetic etiology of several constitutional "epi/genetic" conditions. This review summarizes our broadening understanding of how epigenetics contributes to pediatric disease by exploring different classes of epigenomic disorders. It further challenges the simplistic dogma of "DNA encodes RNA encodes protein" to best understand the spectrum of factors that can influence genetic traits in a pediatric population.

The defining DNA methylation signature of Floating-Harbor Syndrome

Floating-Harbor syndrome (FHS) is an autosomal dominant genetic condition characterized by short stature, delayed osseous maturation, expressive language impairment, and unique facial dysmorphology. We previously identified mutations in the chromatin remodeling protein SRCAP (SNF2-related CBP Activator Protein) as the cause of FHS. SRCAP has multiple roles in chromatin and transcriptional regulation; however, specific epigenetic consequences of SRCAP mutations remain to be described. Using high resolution genome-wide DNA methylation analysis, we identified a unique and highly specific DNA methylation "epi-signature" in the peripheral blood of individuals with FHS. Both hyper and hypomethylated loci are distributed across the genome, preferentially occurring in CpG islands. Clonal bisulfite sequencing of two hypermethylated (FIGN and STPG2) and two hypomethylated (MYO1F and RASIP1) genes confirmed these findings. The identification of a unique methylation signature in FHS provides further insight into the biological function of SRCAP and provides a unique biomarker for this disorder.

Loss of the arginine methyltranserase PRMT7 causes syndromic intellectual disability with microcephaly and brachydactyly

Post-translational protein modifications exponentially expand the functional complement of proteins encoded by the human genome. One such modification is the covalent addition of a methyl group to arginine or lysine residues, which is used to regulate a substantial proportion of the proteome. Arginine and lysine methylation are catalyzed by protein arginine methyltransferase (PRMTs) and protein lysine methyltransferase proteins (PKMTs), respectively; each methyltransferase has a specific set of target substrates. Here, we report a male with severe intellectual disability, facial dysmorphism, microcephaly, short stature, brachydactyly, cryptorchidism and seizures who was found to have a homozygous 15,309 bp deletion encompassing the transcription start site of PRMT7, which we confirmed is functionally a null allele. We show that the patient's cells have decreased levels of protein arginine methylation, and that affected proteins include the essential histones, H2B and H4. Finally, we demonstrate that patient cells have altered Wnt signaling, which may have contributed to the skeletal abnormalities. Our findings confirm the recent disease association of PRMT7, expand the phenotypic manifestations of this disorder and provide insight into the molecular pathogenesis of this new condition.

Chiari I malformation as part of the Floating-Harbor syndrome?

We report the first case of a patient diagnosed with Floating-Harbor syndrome (FHS) and Chiari I malformation. The 3-year-old girl was of proportional short stature, had delay of language development, conductive hearing loss and a high threshold of pain. Diagnosis of Chiari I malformation may be difficult in FHS patients who present with communication problems. Clinicians following patients with FHS should be aware of a possible relation between FHS and Chiari I malformation.

The Matchmaker Exchange API: automating patient matching through the exchange of structured phenotypic and genotypic profiles

Despite the increasing prevalence of clinical sequencing, the difficulty of identifying additional affected families is a key obstacle to solving many rare diseases. There may only be a handful of similar patients worldwide, and their data may be stored in diverse clinical and research databases. Computational methods are necessary to enable finding similar patients across the growing number of patient repositories and registries. We present the Matchmaker Exchange Application Programming Interface (MME API), a protocol and data format for exchanging phenotype and genotype profiles to enable matchmaking among patient databases, facilitate the identification of additional cohorts, and increase the rate with which rare diseases can be researched and diagnosed. We designed the API to be straightforward and flexible in order to simplify its adoption on a large number of data types and workflows. We also provide a public test data set, curated from the literature, to facilitate implementation of the API and development of new matching algorithms. The initial version of the API has been successfully implemented by three members of the Matchmaker Exchange and was immediately able to reproduce previously identified matches and generate several new leads currently being validated. The API is available at https://github.com/ga4gh/mme-apis.

DNA End Resection: Facts and Mechanisms

DNA double-strand breaks (DSBs), which arise following exposure to a number of endogenous and exogenous agents, can be repaired by either the homologous recombination (HR) or non-homologous end-joining (NHEJ) pathways in eukaryotic cells. A vital step in HR repair is DNA end resection, which generates a long 3′ single-stranded DNA (ssDNA) tail that can invade the homologous DNA strand. The generation of 3′ ssDNA is not only essential for HR repair, but also promotes activation of the ataxia telangiectasia and Rad3-related protein (ATR). Multiple factors, including the MRN/X complex, C-terminal-binding protein interacting protein (CtIP)/Sae2, exonuclease 1 (EXO1), Bloom syndrome protein (BLM)/Sgs1, DNA2 nuclease/helicase, and several chromatin remodelers, cooperate to complete the process of end resection. Here we review the basic machinery involved in DNA end resection in eukaryotic cells.

De Novo and Rare Variants at Multiple Loci Support the Oligogenic Origins of Atrioventricular Septal Heart Defects

Congenital heart disease (CHD) has a complex genetic etiology, and recent studies suggest that high penetrance de novo mutations may account for only a small fraction of disease. In a multi-institutional cohort surveyed by exome sequencing, combining analysis of 987 individuals (discovery cohort of 59 affected trios and 59 control trios, and a replication cohort of 100 affected singletons and 533 unaffected singletons) we observe variation at novel and known loci related to a specific cardiac malformation the atrioventricular septal defect (AVSD). In a primary analysis, by combining developmental coexpression networks with inheritance modeling, we identify a de novo mutation in the DNA binding domain of NR1D2 (p.R175W). We show that p.R175W changes the transcriptional activity of Nr1d2 using an in vitro transactivation model in HUVEC cells. Finally, we demonstrate previously unrecognized cardiovascular malformations in the Nr1d2tm1-Dgen knockout mouse. In secondary analyses we map genetic variation to protein-interaction networks suggesting a role for two collagen genes in AVSD, which we corroborate by burden testing in a second replication cohort of 100 AVSDs and 533 controls (p = 8.37e-08). Finally, we apply a rare-disease inheritance model to identify variation in genes previously associated with CHD (ZFPM2, NSD1, NOTCH1, VCAN, and MYH6), cardiac malformations in mouse models (ADAM17, CHRD, IFT140, PTPRJ, RYR1 and ATE1), and hypomorphic alleles of genes causing syndromic CHD (EHMT1, SRCAP, BBS2, NOTCH2, and KMT2D) in 14 of 59 trios, greatly exceeding variation in control trios without CHD (p = 9.60e-06). In total, 32% of trios carried at least one putatively disease-associated variant across 19 loci,suggesting that inherited and de novo variation across a heterogeneous group of loci may contribute to disease risk.

MECHANISMS IN ENDOCRINOLOGY: Novel genetic causes of short stature

The fast technological development, particularly single nucleotide polymorphism array, array-comparative genomic hybridization, and whole exome sequencing, has led to the discovery of many novel genetic causes of growth failure. In this review we discuss a selection of these, according to a diagnostic classification centred on the epiphyseal growth plate. We successively discuss disorders in hormone signalling, paracrine factors, matrix molecules, intracellular pathways, and fundamental cellular processes, followed by chromosomal aberrations including copy number variants (CNVs) and imprinting disorders associated with short stature. Many novel causes of GH deficiency (GHD) as part of combined pituitary hormone deficiency have been uncovered. The most frequent genetic causes of isolated GHD are GH1 and GHRHR defects, but several novel causes have recently been found, such as GHSR, RNPC3, and IFT172 mutations. Besides well-defined causes of GH insensitivity (GHR, STAT5B, IGFALS, IGF1 defects), disorders of NFκB signalling, STAT3 and IGF2 have recently been discovered. Heterozygous IGF1R defects are a relatively frequent cause of prenatal and postnatal growth retardation. TRHA mutations cause a syndromic form of short stature with elevated T3/T4 ratio. Disorders of signalling of various paracrine factors (FGFs, BMPs, WNTs, PTHrP/IHH, and CNP/NPR2) or genetic defects affecting cartilage extracellular matrix usually cause disproportionate short stature. Heterozygous NPR2 or SHOX defects may be found in ∼3% of short children, and also rasopathies (e.g., Noonan syndrome) can be found in children without clear syndromic appearance. Numerous other syndromes associated with short stature are caused by genetic defects in fundamental cellular processes, chromosomal abnormalities, CNVs, and imprinting disorders.

Do short, frequent DNA sequence motifs mould the epigenome?

'Epigenome' refers to the panoply of chemical modifications borne by DNA and its associated proteins that locally affect genome function. Epigenomic patterns are thought to be determined by external constraints resulting from development, disease and the environment, but DNA sequence is also a potential influence. We propose that domains of relatively uniform DNA base composition may modulate the epigenome through cell type-specific proteins that recognize short, frequent sequence motifs. Differential recruitment of epigenomic modifiers may adjust gene expression in multigene blocks as an alternative to tuning the activity of each gene separately, thus simplifying gene expression programming.

Network-Informed Gene Ranking Tackles Genetic Heterogeneity in Exome-Sequencing Studies of Monogenic Disease

Genetic heterogeneity presents a significant challenge for the identification of monogenic disease genes. Whole-exome sequencing generates a large number of candidate disease-causing variants and typical analyses rely on deleterious variants being observed in the same gene across several unrelated affected individuals. This is less likely to occur for genetically heterogeneous diseases, making more advanced analysis methods necessary. To address this need, we present HetRank, a flexible gene-ranking method that incorporates interaction network data. We first show that different genes underlying the same monogenic disease are frequently connected in protein interaction networks. This motivates the central premise of HetRank: those genes carrying potentially pathogenic variants and whose network neighbors do so in other affected individuals are strong candidates for follow-up study. By simulating 1,000 exome sequencing studies (20,000 exomes in total), we model varying degrees of genetic heterogeneity and show that HetRank consistently prioritizes more disease-causing genes than existing analysis methods. We also demonstrate a proof-of-principle application of the method to prioritize genes causing Adams-Oliver syndrome, a genetically heterogeneous rare disease. An implementation of HetRank in R is available via the Website http://sourceforge.net/p/hetrank/.

Ultra-Rare Syndromes: The Example of Rubinstein-Taybi Syndrome

Rubinstein-Taybi syndrome (RSTS) is a rare, congenital, plurimalformative, and neurodevelopmental disorder. Clinical diagnosis can be complicated by the heterogeneous clinical presentation and the lack of a consensus list of diagnostic criteria, and it is confirmed by molecular tests in approximately 55 to 78% of cases. The etiology is partially known with mutations in two functionally related genes: CREBBP and EP300. Notwithstanding the knowledge on clinical, genetic, and allelic heterogeneity, no clear genotype-phenotype correlation has yet been established. Standardized guidelines for the management of pediatric patients are available and therapy for RSTS patients is currently only symptomatic. In this article, several clinic and genetic aspects of RSTS are critically reviewed.

Epigenetic factors in intellectual disability: the Rubinstein-Taybi syndrome as a paradigm of neurodevelopmental disorder with epigenetic origin

The number of genetic syndromes associated with intellectual disability that are caused by mutations in genes encoding chromatin-modifying enzymes has sharply risen in the last decade. We discuss here a neurodevelopmental disorder, the Rubinstein-Taybi syndrome (RSTS), originated by mutations in the genes encoding the lysine acetyltransferases CBP and p300. We first describe clinical and genetic aspects of the syndrome to later focus on the insight provided by the research in animal models of this disease. These studies have not only clarified the molecular etiology of RSTS and helped to dissect the developmental and adult components of the syndrome but also contributed to outline some important connections between epigenetics and cognition. We finally discuss how this body of research has opened new venues for the therapeutic intervention of this currently untreatable disease and present some of the outstanding questions in the field. We believe that the progress in the understanding of this rare disorder also has important implications for other intellectual disability disorders that share an epigenetic origin.

GeneMatcher aids in the identification of a new malformation syndrome with intellectual disability, unique facial dysmorphisms, and skeletal and connective tissue abnormalities caused by de novo variants in HNRNPK

We report a new syndrome due to loss-of-function variants in the heterogeneous nuclear ribonucleoprotein K gene (HNRNPK). We describe two probands: one with a de novo frameshift (NM_002140.3: c.953+1dup), and the other with a de novo splice donor site variant (NM_002140.3: c.257G>A). Both probands have intellectual disability, a shared unique craniofacial phenotype, and connective tissue and skeletal abnormalities. The identification of this syndrome was made possible by a new online tool, GeneMatcher, which facilitates connections between clinicians and researchers based on shared interest in candidate genes. This report demonstrates that new Web-based approaches can be effective in helping investigators solve exome sequencing projects, and also highlights the newer paradigm of "reverse phenotyping," where characterization of syndromic features follows the identification of genetic variants.

16p11.2 de novo microdeletion encompassing SRCAP gene in a patient with speech impairment, global developmental delay and behavioural problems

We describe a patient with speech impairment, global developmental delay, behavioural problems and a 186 kb de novo microdeletion on 16p11.2. There are four OMIM Phenotypes entries partially overlapping with the deleted region and related to recurrent microdeletions/microduplications in 16p11.2. A detailed review of published data shows that microdeletions/microduplications' boundaries do not include genes that are deleted in the case here reported. The deletion encompasses 9 RefSeq genes and includes SRCAP (Snf2-related CREBBP activator protein, OMIM*611421), a disease causing gene. Recently, truncating mutations in the SRCAP gene have been shown to cause Floating-Harbor syndrome (FHS, OMIM#136140), a rare disorder characterized by peculiar facial features, short stature with delayed osseous maturation and speech impairment. The patient reported here shows few subtle phenotypic features resembling that of FHS, but she does not have sufficient signs and symptoms for the clinical diagnosis and a clinical classification based on facial gestalt is not possible. This is the first report of a 16p11.2 deletion completely removing one copy of SRCAP, suggesting that haploinsufficiency of this gene could be associated to speech impairment, global developmental delay, behavioural problems and few subtle phenotypic features resembling FHS. However, further evidence for the putative causative role of SRCAP isolated deletion is needed.

Mendelian disorders of the epigenetic machinery: tipping the balance of chromatin states

Mendelian disorders of the epigenetic machinery are a newly delineated group of multiple congenital anomaly and intellectual disability syndromes resulting from mutations in genes encoding components of the epigenetic machinery. The gene products affected in these inherited conditions act in trans and are expected to have widespread epigenetic consequences. Many of these syndromes demonstrate phenotypic overlap with classical imprinting disorders and with one another. The various writer and eraser systems involve opposing players, which we propose must maintain a balance between open and closed chromatin states in any given cell. An imbalance might lead to disrupted expression of disease-relevant target genes. We suggest that classifying disorders based on predicted effects on this balance would be informative regarding pathogenesis. Furthermore, strategies targeted at restoring this balance might offer novel therapeutic avenues, taking advantage of available agents such as histone deacetylase inhibitors and histone acetylation antagonists.

Whole-exome sequencing in undiagnosed genetic diseases: interpreting 119 trios

Purpose:

Despite the recognized clinical value of exome-based diagnostics, methods for comprehensive genomic interpretation remain immature. Diagnoses are based on known or presumed pathogenic variants in genes already associated with a similar phenotype. Here, we extend this paradigm by evaluating novel bioinformatics approaches to aid identification of new gene–disease associations.

Genet Med17 10, 774–781.

Methods:

We analyzed 119 trios to identify both diagnostic genotypes in known genes and candidate genotypes in novel genes. We considered qualifying genotypes based on their population frequency and in silico predicted effects we also characterized the patterns of genotypes enriched among this collection of patients.

Genet Med17 10, 774–781.

Results:

We obtained a genetic diagnosis for 29 (24%) of our patients. We showed that patients carried an excess of damaging de novo mutations in intolerant genes, particularly those shown to be essential in mice (P = 3.4 × 10⁻⁸). This enrichment is only partially explained by mutations found in known disease-causing genes.

Genet Med17 10, 774–781.

Conclusion:

This work indicates that the application of appropriate bioinformatics analyses to clinical sequence data can also help implicate novel disease genes and suggest expanded phenotypes for known disease genes. These analyses further suggest that some cases resolved by whole-exome sequencing will have direct therapeutic implications.

Genet Med17 10, 774–781.

Global transcriptional disturbances underlie Cornelia de Lange syndrome and related phenotypes

Cornelia de Lange syndrome (CdLS) is a genetically heterogeneous disorder that presents with extensive phenotypic variability, including facial dysmorphism, developmental delay/intellectual disability (DD/ID), abnormal extremities, and hirsutism. About 65% of patients harbor mutations in genes that encode subunits or regulators of the cohesin complex, including NIPBL, SMC1A, SMC3, RAD21, and HDAC8. Wiedemann-Steiner syndrome (WDSTS), which shares CdLS phenotypic features, is caused by mutations in lysine-specific methyltransferase 2A (KMT2A). Here, we performed whole-exome sequencing (WES) of 2 male siblings clinically diagnosed with WDSTS; this revealed a hemizygous, missense mutation in SMC1A that was predicted to be deleterious. Extensive clinical evaluation and WES of 32 Turkish patients clinically diagnosed with CdLS revealed the presence of a de novo heterozygous nonsense KMT2A mutation in 1 patient without characteristic WDSTS features. We also identified de novo heterozygous mutations in SMC3 or SMC1A that affected RNA splicing in 2 independent patients with combined CdLS and WDSTS features. Furthermore, in families from 2 separate world populations segregating an autosomal-recessive disorder with CdLS-like features, we identified homozygous mutations in TAF6, which encodes a core transcriptional regulatory pathway component. Together, our data, along with recent transcriptome studies, suggest that CdLS and related phenotypes may be "transcriptomopathies" rather than cohesinopathies.