Evaluation of the diagnostic accuracy of exome sequencing and its impact on diagnostic thinking for patients with rare disease in a publicly funded health care system: A prospective cohort study.

PURPOSE: To evaluate the diagnostic utility of publicly funded clinical exome sequencing (ES) for patients with suspected rare genetic diseases. METHODS: We prospectively enrolled 297 probands who met eligibility criteria and received ES across 5 sites in Ontario, Canada, and extracted data from medical records and clinician surveys. Using the Fryback and Thornbury Efficacy Framework, we assessed diagnostic accuracy by examining laboratory interpretation of results and assessed diagnostic thinking by examining the clinical interpretation of results and whether clinical-molecular diagnoses would have been achieved via alternative hypothetical molecular tests. RESULTS: Laboratories reported 105 molecular diagnoses and 165 uncertain results in known and novel genes. Of these, clinicians interpreted 102 of 105 (97%) molecular diagnoses and 6 of 165 (4%) uncertain results as clinical-molecular diagnoses. The 108 clinical-molecular diagnoses were in 104 families (35% diagnostic yield). Each eligibility criteria resulted in diagnostic yields of 30% to 40%, and higher yields were achieved when >2 eligibility criteria were met (up to 45%). Hypothetical tests would have identified 61% of clinical-molecular diagnoses. CONCLUSION: We demonstrate robustness in eligibility criteria and high clinical validity of laboratory results from ES testing. The importance of ES was highlighted by the potential 40% of patients that would have gone undiagnosed without this test.

Functional and clinical studies reveal pathophysiological complexity of CLCN4-related neurodevelopmental condition.

Missense and truncating variants in the X-chromosome-linked CLCN4 gene, resulting in reduced or complete loss-of-function (LOF) of the encoded chloride/proton exchanger ClC-4, were recently demonstrated to cause a neurocognitive phenotype in both males and females. Through international clinical matchmaking and interrogation of public variant databases we assembled a database of 90 rare CLCN4 missense variants in 90 families: 41 unique and 18 recurrent variants in 49 families. For 43 families, including 22 males and 33 females, we collated detailed clinical and segregation data. To confirm causality of variants and to obtain insight into disease mechanisms, we investigated the effect on electrophysiological properties of 59 of the variants in Xenopus oocytes using extended voltage and pH ranges. Detailed analyses revealed new pathophysiological mechanisms: 25% (15/59) of variants demonstrated LOF, characterized by a "shift" of the voltage-dependent activation to more positive voltages, and nine variants resulted in a toxic gain-of-function, associated with a disrupted gate allowing inward transport at negative voltages. Functional results were not always in line with in silico pathogenicity scores, highlighting the complexity of pathogenicity assessment for accurate genetic counselling. The complex neurocognitive and psychiatric manifestations of this condition, and hitherto under-recognized impacts on growth, gastrointestinal function, and motor control are discussed. Including published cases, we summarize features in 122 individuals from 67 families with CLCN4-related neurodevelopmental condition and suggest future research directions with the aim of improving the integrated care for individuals with this diagnosis.

Monoallelic loss-of-function BMP2 variants result in BMP2-related skeletal dysplasia spectrum.

PURPOSE: Bone morphogenic proteins (BMPs) regulate gene expression that is related to many critical developmental processes, including osteogenesis for which they are named. In addition, BMP2 is widely expressed in cells of mesenchymal origin, including bone, cartilage, skeletal and cardiac muscle, and adipose tissue. It also participates in neurodevelopment by inducing differentiation of neural stem cells. In humans, BMP2 variants result in a multiple congenital anomaly syndrome through a haploinsufficiency mechanism. We sought to expand the phenotypic spectrum and highlight phenotypes of patients harboring monoallelic missense variants in BMP2. METHODS: We used retrospective chart review to examine phenotypes from an international cohort of 18 individuals and compared these with published cases. Patient-derived missense variants were modeled in zebrafish to examine their effect on the ability of bmp2b to promote embryonic ventralization. RESULTS: The presented cases recapitulated existing descriptions of BMP2-related disorders, including craniofacial, cardiac, and skeletal anomalies and exhibit a wide phenotypic spectrum. We also identified patients with neural tube defects, structural brain anomalies, and endocrinopathies. Missense variants modeled in zebrafish resulted in loss of protein function. CONCLUSION: We use this expansion of reported phenotypes to suggest multidisciplinary medical monitoring and management of patients with BMP2-related skeletal dysplasia spectrum.

The Clinician-reported Genetic testing Utility InDEx (C-GUIDE): Preliminary evidence of validity and reliability.

PURPOSE: Demonstrating the clinical utility of genetic testing is fundamental to clinical adoption and reimbursement, but standardized definitions and measurement strategies for this construct do not exist. The Clinician-reported Genetic testing Utility InDEx (C-GUIDE) offers a novel measure to fill this gap. This study assessed its validity and inter-rater reliability. METHODS: Genetics professionals completed C-GUIDE after disclosure of test results to patients. Construct validity was assessed using regression analysis to measure associations between C-GUIDE and global item scores as well as potentially explanatory variables. Inter-rater reliability was assessed by administering a vignette-based survey to genetics professionals and calculating Krippendorff's α. RESULTS: On average, a 1-point increase in the global item score was associated with an increase of 3.0 in the C-GUIDE score (P < .001). Compared with diagnostic results, partially/potentially diagnostic and nondiagnostic results were associated with a reduction in C-GUIDE score of 9.5 (P < .001) and 10.2 (P < .001), respectively. Across 19 vignettes, Krippendorff's α was 0.68 (95% CI: 0.63-0.72). CONCLUSION: C-GUIDE showed acceptable validity and inter-rater reliability. Although further evaluation is required, C-GUIDE version 1.2 can be useful as a standardized approach to assess the clinical utility of genetic testing.

Diagnostic outcomes for molecular genetic testing in children with suspected Ehlers-Danlos syndrome.

Ehlers-Danlos syndrome (EDS) is a heterogeneous group of connective tissue disorders characterized by hyperextensible skin, hypermobile joints, easy bruisability, and fragility of the connective tissues. The diagnosis is based on clinical assessment and phenotype-guided genetic testing. Most EDS subtypes can be confirmed by genetic testing except for hypermobile EDS. This study explored the utility of applying the 2017 EDS classification criteria and molecular genetic testing in establishing an EDS diagnosis in children. In this retrospective study, we reviewed 72 patients referred to a tertiary care center for evaluation of EDS who underwent one or more forms of genetic testing. Eighteen patients (18/72, 25%) met the clinical criteria for one of the EDS subtypes and of these, 15 (15/18, 83%) were confirmed molecularly. Fifty-four patients (54/72, 75%) had features that overlapped EDS and other syndromes associated with joint hypermobility but did not fully meet clinical criteria. Twelve of them (12/54, 22%) were later shown to have a positive molecular genetic diagnosis of EDS. Different molecular genetic tests were performed on the cohort of 72 patients (EDS panel, n = 44; microarray, n = 25; whole exome sequencing [WES], n = 9; single gene sequencing, n = 3; familial variant testing, n = 10; other genetic panels n = 3). EDS panel was completed in 44 patients (61%), and a molecular diagnosis was confirmed in nine of the patients who satisfied criteria for one of the EDS subtypes (9/12, 75%) and in nine of the patients who did not fully meet criteria (9/32, 28%). We observed a correlation between generalized joint hypermobility, poor healing, easy bruising, atrophic scars, skin hyperextensibility, and developmental dysplasia of the hip with a positive molecular result. This study provides guidance for the use of molecular genetic testing in combination with the 2017 clinical diagnostic criteria in children presenting with EDS characteristics.

Phagocytosis of Erythrocytes from Gaucher Patients Induces Phenotypic Modifications in Macrophages, Driving Them toward Gaucher Cells.

Gaucher disease (GD) is caused by glucocerebrosidase deficiency leading to the accumulation of sphingolipids in macrophages named "Gaucher's Cells". These cells are characterized by deregulated expression of cell surface markers, abnormal secretion of inflammatory cytokines, and iron sequestration. These cells are known to infiltrate tissues resulting in hematological manifestations, splenomegaly, and bone diseases. We have already demonstrated that Gaucher red blood cells exhibit altered properties suggesting their key role in GD clinical manifestations. We hypothesized that Gaucher's erythrocytes could be prone to premature destruction by macrophages contributing to the formation of altered macrophages and Gaucher-like cells. We conducted in vitro experiments of erythrophagocytosis using erythrocytes from Gaucher's patients or healthy donors. Our results showed an enhanced erythrophagocytosis of Gaucher red blood cells compared to healthy red blood cells, which is related to erythrocyte sphingolipids overload and reduced deformability. Importantly, we showed elevated expression of the antigen-presenting molecules CD1d and MHC-II and of the iron-regulator hepcidin in macrophages, as well as enhanced secretion of the pro-inflammatory cytokine IL-1ß after phagocytosis of GD erythrocytes. These results strongly suggested that erythrophagocytosis in GD contribute to phenotypic modifications in macrophages. This present study shows that erythrocytes-macrophages interactions may be crucial in GD pathophysiology and pathogenesis.

New cases that expand the genotypic and phenotypic spectrum of Congenital NAD Deficiency Disorder.

Nicotinamide adenine dinucleotide (NAD) is an essential coenzyme involved in over 400 cellular reactions. During embryogenesis, mammals synthesize NAD de novo from dietary l -tryptophan via the kynurenine pathway. Biallelic, inactivating variants in three genes encoding enzymes of this biosynthesis pathway (KYNU, HAAO, and NADSYN1) disrupt NAD synthesis and have been identified in patients with multiple malformations of the heart, kidney, vertebrae, and limbs; these patients have Congenital NAD Deficiency Disorder HAAO and four families with biallelic variants in KYNU. These patients present similarly with multiple malformations of the heart, kidney, vertebrae, and limbs, of variable severity. We show that each variant identified in these patients results in loss-of-function, revealed by a significant reduction in NAD levels via yeast genetic complementation assays. For the first time, missense mutations are identified as a cause of malformation and shown to disrupt enzyme function. These missense and frameshift variants cause moderate to severe NAD deficiency in yeast, analogous to insufficient synthesized NAD in patients. We hereby expand the genotypic and corresponding phenotypic spectrum of Congenital NAD Deficiency Disorder.

Functional Dysregulation of CDC42 Causes Diverse Developmental Phenotypes.

Exome sequencing has markedly enhanced the discovery of genes implicated in Mendelian disorders, particularly for individuals in whom a known clinical entity could not be assigned. This has led to the recognition that phenotypic heterogeneity resulting from allelic mutations occurs more commonly than previously appreciated. Here, we report that missense variants in CDC42, a gene encoding a small GTPase functioning as an intracellular signaling node, underlie a clinically heterogeneous group of phenotypes characterized by variable growth dysregulation, facial dysmorphism, and neurodevelopmental, immunological, and hematological anomalies, including a phenotype resembling Noonan syndrome, a developmental disorder caused by dysregulated RAS signaling. In silico, in vitro, and in vivo analyses demonstrate that mutations variably perturb CDC42 function by altering the switch between the active and inactive states of the GTPase and/or affecting CDC42 interaction with effectors, and differentially disturb cellular and developmental processes. These findings reveal the remarkably variable impact that dominantly acting CDC42 mutations have on cell function and development, creating challenges in syndrome definition, and exemplify the importance of functional profiling for syndrome recognition and delineation.

The phenotypic spectrum of AMER1-related osteopathia striata with cranial sclerosis: The first Canadian cohort.

Osteopathia striata with cranial sclerosis (OSCS; OMIM# 300373) is a rare X-linked disorder caused by mutations of the AMER1 gene. OSCS is traditionally considered a skeletal dysplasia, characterized by cranial sclerosis and longitudinal striations in the long bone metaphyses. However, OSCS affects many body systems and varies significantly in phenotypic severity between individuals. This case series focuses on the phenotypic presentation and development of individuals with OSCS. We provide an account of 12 patients with OSCS, ranging from 5 months to 38 years of age. These patients were diagnosed with OSCS after genetic testing confirmed pathogenic mutations in AMER1. Patient consent was obtained for photos and participation. Data were collected regarding perinatal history, dysmorphic features, and review of systems. This case series documents common facial dysmorphology, as well as rare extraskeletal features of OSCS, including two patients with intestinal malrotation and two patients with pyloric stenosis. We share four apparently nonmosaic males with OSCS (one de novo and three maternal variants). We also provide a clinical update on a patient who was previously published by Chénier et al. (2012). American Journal of Medical Genetics Part A, 158, 2946-2952. More research is needed to investigate the links between genotype and phenotype and assess the long-term comorbidities and overall quality of life of individuals with OSCS.

Effects of sphingolipids overload on red blood cell properties in Gaucher disease.

Gaucher disease (GD) is a genetic disease with mutations in the GBA gene that encodes glucocerebrosidase causing complications such as anaemia and bone disease. GD is characterized by accumulation of the sphingolipids (SL) glucosylceramide (GL1), glucosylsphingosine (Lyso-GL1), sphingosine (Sph) and sphingosine-1-phosphate (S1P). These SL are increased in the plasma of GD patients and the associated complications have been attributed to the accumulation of lipids in macrophages. Our recent findings indicated that red blood cells (RBCs) and erythroid progenitors may play an important role in GD pathophysiology. RBCs abnormalities and dyserythropoiesis have been observed in GD patients. Moreover, we showed higher SL levels in the plasma and in RBCs from untreated GD patients compared with controls. In this study, we quantified SL in 16 untreated GD patients and 15 patients treated with enzyme replacement therapy. Our results showed that the treatment significantly decreases SL levels in the plasma and RBCs. The increased SL content in RBCs correlates with abnormal RBC properties and with markers of disease activity. Because RBCs lack glucocerebrosidase activity, we investigated how lipid overload could occur in these cells. Our results suggested that SL overload in RBCs occurs both during erythropoiesis and during its circulation in the plasma.

CHARGE and Kabuki Syndromes: Gene-Specific DNA Methylation Signatures Identify Epigenetic Mechanisms Linking These Clinically Overlapping Conditions.

Epigenetic dysregulation has emerged as a recurring mechanism in the etiology of neurodevelopmental disorders. Two such disorders, CHARGE and Kabuki syndromes, result from loss of function mutations in chromodomain helicase DNA-binding protein 7 (CHD7LOF) and lysine (K) methyltransferase 2D (KMT2DLOF), respectively. Although these two syndromes are clinically distinct, there is significant phenotypic overlap. We therefore expected that epigenetically driven developmental pathways regulated by CHD7 and KMT2D would overlap and that DNA methylation (DNAm) alterations downstream of the mutations in these genes would identify common target genes, elucidating a mechanistic link between these two conditions, as well as specific target genes for each disorder. Genome-wide DNAm profiles in individuals with CHARGE and Kabuki syndromes with CHD7LOF or KMT2DLOF identified distinct sets of DNAm differences in each of the disorders, which were used to generate two unique, highly specific and sensitive DNAm signatures. These DNAm signatures were able to differentiate pathogenic mutations in these two genes from controls and from each other. Analysis of the DNAm targets in each gene-specific signature identified both common gene targets, including homeobox A5 (HOXA5), which could account for some of the clinical overlap in CHARGE and Kabuki syndromes, as well as distinct gene targets. Our findings demonstrate how characterization of the epigenome can contribute to our understanding of disease pathophysiology for epigenetic disorders, paving the way for explorations of novel therapeutics.

Mutations in EXTL3 Cause Neuro-immuno-skeletal Dysplasia Syndrome.

EXTL3 regulates the biosynthesis of heparan sulfate (HS), important for both skeletal development and hematopoiesis, through the formation of HS proteoglycans (HSPGs). By whole-exome sequencing, we identified homozygous missense mutations c.1382C>T, c.1537C>T, c.1970A>G, and c.2008T>G in EXTL3 in nine affected individuals from five unrelated families. Notably, we found the identical homozygous missense mutation c.1382C>T (p.Pro461Leu) in four affected individuals from two unrelated families. Affected individuals presented with variable skeletal abnormalities and neurodevelopmental defects. Severe combined immunodeficiency (SCID) with a complete absence of T cells was observed in three families. EXTL3 was most abundant in hematopoietic stem cells and early progenitor T cells, which is in line with a SCID phenotype at the level of early T cell development in the thymus. To provide further support for the hypothesis that mutations in EXTL3 cause a neuro-immuno-skeletal dysplasia syndrome, and to gain insight into the pathogenesis of the disorder, we analyzed the localization of EXTL3 in fibroblasts derived from affected individuals and determined glycosaminoglycan concentrations in these cells as well as in urine and blood. We observed abnormal glycosaminoglycan concentrations and increased concentrations of the non-sulfated chondroitin disaccharide D0a0 and the disaccharide D0a4 in serum and urine of all analyzed affected individuals. In summary, we show that biallelic mutations in EXTL3 disturb glycosaminoglycan synthesis and thus lead to a recognizable syndrome characterized by variable expression of skeletal, neurological, and immunological abnormalities.

Semaphorin 7A: A novel marker of disease activity in Gaucher disease.

Gaucher disease (GD) is a recessively inherited lysosomal storage disorder in which sphingolipids accumulates in the macrophages that transform into Gaucher cells. A growing body of evidence indicates that red blood cells (RBCs) represent important actors in GD pathophysiology. We previously demonstrated that altered RBC properties including increased Lyso-GL1 levels, dyserythropoiesis, and iron metabolism defect in GD patients contribute to anemia and hyperferritinemia. Since RBC defects also correlated well with markers of GD severity and were normalized under enzyme replacement therapy (ERT), the identification of molecules that are deregulated in GD RBCs represents an important issue in the search of pertinent markers of the disease. Here, we found a decreased expression of the GPI-anchored cell surface protein Semaphorin 7A (Sema7A) in RBCs from untreated GD (GD UT) patients, in parallel with increased levels of the soluble form in the plasma. Sema7A plays a role in neural guidance, atherosclerosis, and inflammatory diseases and represents a promigratory cue in physiological and pathological conditions. We showed that the decreased expression of Sema7A in RBCs correlated with their abnormal properties and with markers of GD activity. Interestingly, ERT restored the level of Sema7A to normal values both in RBCs and in plasma from GD patients. We then proposed that SemaA7A represents a simple and pertinent marker of inflammation in GD. Finally, because Sema7A is known to regulate the activity of immune cells, the increased level of soluble Sema7A in GD patients could propagate inflammation in several tissues.

Novel c.G630A TCIRG1 mutation causes aberrant splicing resulting in an unusually mild form of autosomal recessive osteopetrosis.

Autosomal recessive osteopetrosis (ARO) is a severe genetic bone disease characterized by high bone density due to mutations that affect formation or function of osteoclasts. Mutations in the a3 subunit of the vacuolar-type H+ -ATPase (encoded by T-cell immune regulator 1 [TCIRG1]) are responsible for ~50% of all ARO cases. We identified a novel TCIRG1 (c.G630A) mutation responsible for an unusually mild form of the disease. To characterize this mutation, osteoclasts were differentiated using peripheral blood monocytes from the patient (c.G630A/c.G630A), male sibling (+/+), unaffected female sibling (+/c.G630A), and unaffected parent (+/c.G630A). Osteoclast formation, bone-resorbing function, TCIRG1 protein, and mRNA expression levels were assessed. The c.G630A mutation did not affect osteoclast differentiation; however, bone-resorbing function was decreased. Both TCIRG1 protein and full-length TCIRG1 mRNA expression levels were also diminished in the affected patient's sample. The c.G630A mutation replaces the last nucleotide of exon 6 and may cause splicing defects. We analyzed the TCIRG1 splicing pattern between exons 4 to 8 and detected deletions of exons 5, 6, 7, and 5-6 (ΔE56). These deletions were only observed in c.G630A/c.G630A and +/c.G630A samples, but not in +/+ controls. Among these deletions, only ΔE56 maintained the reading frame and was predicted to generate an 85 kDa protein. Exons 5-6 encode an uncharacterized portion of the cytoplasmic N-terminal domain of a3, a domain not involved in proton translocation. To investigate the effect of ΔE56 on V-ATPase function, we transformed yeast with plasmids carrying full-length or truncated Vph1p, the yeast ortholog of a3. Both proteins were expressed; however, ΔE56-Vph1p transformed yeast failed to grow on Zn2+ -containing plates, a growth assay dependent on V-ATPase-mediated vacuolar acidification. In conclusion, our results show that the ΔE56 truncated protein is not functional, suggesting that the mild ARO phenotype observed in the patient is likely due to the residual full-length protein expression.

Disruption of the PTHLH regulatory landscape results in features consistent with hyperparathyroid disease.

Parathyroid hormone like hormone (PTHLH) signaling is essential for the proper formation of bone and its elevation or disruption has been directly implicated in several different skeletal dysplasias. We report a patient with a 2.802 Mb deletion upstream of the PTHLH coding sequence who presents with multiple fractures, metaphyseal changes, and overall features consistent with hyperparathyroid like disease. Analysis of the deleted region revealed the loss of putative regulatory regions adjacent to PTHLH and the possible gain of a limb enhancer. Furthermore, PTHLH expression appeared to be mis-regulated in fibroblasts derived from the patient. Altogether, we find that the disruption of the regulatory landscape of PTHLH likely results in its inappropriate expression and this novel clinical presentation.

16q22.1 microdeletion and anticipatory guidance.

The widespread availability of comparative genomic hybridization (CGH) array analysis has led to the discovery of several genomic microdeletion-associated syndromes and has identified possible genetic causes for patients with previously unexplained clinical features. We report the case of four unrelated patients who share common clinical characteristics, namely failure to thrive, developmental delay, dysmorphic features, and congenital anomalies. CGH array analysis revealed that all four patients had a de novo microdeletion at 16q22.1. In this case report, we describe the clinical features of these patients and offer possible explanations for how their 16q22.1 microdeletion may account for their symptoms. We also suggest guidelines for the management of 16q22.1 microdeletion based on the phenotypes seen in our patients and the function of the genes affected by this microdeletion.

Identification of a Recognizable Progressive Skeletal Dysplasia Caused by RSPRY1 Mutations.

Skeletal dysplasias are highly variable Mendelian phenotypes. Molecular diagnosis of skeletal dysplasias is complicated by their extreme clinical and genetic heterogeneity. We describe a clinically recognizable autosomal-recessive disorder in four affected siblings from a consanguineous Saudi family, comprising progressive spondyloepimetaphyseal dysplasia, short stature, facial dysmorphism, short fourth metatarsals, and intellectual disability. Combined autozygome/exome analysis identified a homozygous frameshift mutation in RSPRY1 with resulting nonsense-mediated decay. Using a gene-centric "matchmaking" system, we were able to identify a Peruvian simplex case subject whose phenotype is strikingly similar to the original Saudi family and whose exome sequencing had revealed a likely pathogenic homozygous missense variant in the same gene. RSPRY1 encodes a hypothetical RING and SPRY domain-containing protein of unknown physiological function. However, we detect strong RSPRY1 protein localization in murine embryonic osteoblasts and periosteal cells during primary endochondral ossification, consistent with a role in bone development. This study highlights the role of gene-centric matchmaking tools to establish causal links to genes, especially for rare or previously undescribed clinical entities.

Recessive osteogenesis imperfecta caused by missense mutations in SPARC.

Secreted protein, acidic, cysteine-rich (SPARC) is a glycoprotein that binds to collagen type I and other proteins in the extracellular matrix. Using whole-exome sequencing to identify the molecular defect in two unrelated girls with severe bone fragility and a clinical diagnosis of osteogenesis imperfecta type IV, we identified two homozygous variants in SPARC (GenBank: NM_003118.3; c.497G>A [p.Arg166His] in individual 1; c.787G>A [p.Glu263Lys] in individual 2). Published modeling and site-directed mutagenesis studies had previously shown that the residues substituted by these mutations form an intramolecular salt bridge in SPARC and are essential for the binding of SPARC to collagen type I. The amount of SPARC secreted by skin fibroblasts was reduced in individual 1 but appeared normal in individual 2. The migration of collagen type I alpha chains produced by these fibroblasts was mildly delayed on SDS-PAGE gel, suggesting some overmodification of collagen during triple helical formation. Pulse-chase experiments showed that collagen type I secretion was mildly delayed in skin fibroblasts from both individuals. Analysis of an iliac bone sample from individual 2 showed that trabecular bone was hypermineralized on the material level. In conclusion, these observations show that homozygous mutations in SPARC can give rise to severe bone fragility in humans.

Mutations Preventing Regulated Exon Skipping in MET Cause Osteofibrous Dysplasia.

The periosteum contributes to bone repair and maintenance of cortical bone mass. In contrast to the understanding of bone development within the epiphyseal growth plate, factors that regulate periosteal osteogenesis have not been studied as intensively. Osteofibrous dysplasia (OFD) is a congenital disorder of osteogenesis and is typically sporadic and characterized by radiolucent lesions affecting the cortical bone immediately under the periosteum of the tibia and fibula. We identified germline mutations in MET, encoding a receptor tyrosine kinase, that segregate with an autosomal-dominant form of OFD in three families and a mutation in a fourth affected subject from a simplex family and with bilateral disease. Mutations identified in all families with dominant inheritance and in the one simplex subject with bilateral disease abolished the splice inclusion of exon 14 in MET transcripts, which resulted in a MET receptor (MET(Δ14)) lacking a cytoplasmic juxtamembrane domain. Splice exclusion of this domain occurs during normal embryonic development, and forced induction of this exon-exclusion event retarded osteoblastic differentiation in vitro and inhibited bone-matrix mineralization. In an additional subject with unilateral OFD, we identified a somatic MET mutation, also affecting exon 14, that substituted a tyrosine residue critical for MET receptor turnover and, as in the case of the MET(Δ14) mutations, had a stabilizing effect on the mature protein. Taken together, these data show that aberrant MET regulation via the juxtamembrane domain subverts core MET receptor functions that regulate osteogenesis within cortical diaphyseal bone.

The genetic landscape of familial congenital hydrocephalus.

OBJECTIVE: Congenital hydrocephalus is an important birth defect, the genetics of which remains incompletely understood. To date, only 4 genes are known to cause Mendelian diseases in which congenital hydrocephalus is the main or sole clinical feature, 2 X-linked (L1CAM and AP1S2) and 2 autosomal recessive (CCDC88C and MPDZ). In this study, we aimed to determine the genetic etiology of familial congenital hydrocephalus with the assumption that these cases represent Mendelian forms of the disease. METHODS: Exome sequencing combined, where applicable, with positional mapping. RESULTS: We identified a likely causal mutation in the majority of these families (21 of 27, 78%), spanning 16 genes, none of which is X-linked. Ciliopathies and dystroglycanopathies were the most common etiologies of congenital hydrocephalus in our cohort (19% and 26%, respectively). In 1 family with 4 affected members, we identified a homozygous truncating variant in EML1, which we propose as a novel cause of congenital hydrocephalus in addition to its suggested role in cortical malformation. Similarly, we show that recessive mutations in WDR81, previously linked to cerebellar ataxia, mental retardation, and disequilibrium syndrome 2, cause severe congenital hydrocephalus. Furthermore, we confirm the previously reported candidacy of MPDZ by presenting a phenotypic spectrum of congenital hydrocephalus associated with 5 recessive alleles. INTERPRETATION: Our study highlights the importance of recessive mutations in familial congenital hydrocephalus and expands the locus heterogeneity of this condition. Ann Neurol 2017;81:890-897.