SOX11 variants cause a neurodevelopmental disorder with infrequent ocular malformations and hypogonadotropic hypogonadism and with distinct DNA methylation profile.

PURPOSE: This study aimed to undertake a multidisciplinary characterization of the phenotype associated with SOX11 variants. METHODS: Individuals with protein altering variants in SOX11 were identified through exome and genome sequencing and international data sharing. Deep clinical phenotyping was undertaken by referring clinicians. Blood DNA methylation was assessed using Infinium MethylationEPIC array. The expression pattern of SOX11 in developing human brain was defined using RNAscope. RESULTS: We reported 38 new patients with SOX11 variants. Idiopathic hypogonadotropic hypogonadism was confirmed as a feature of SOX11 syndrome. A distinctive pattern of blood DNA methylation was identified in SOX11 syndrome, separating SOX11 syndrome from other BAFopathies. CONCLUSION: SOX11 syndrome is a distinct clinical entity with characteristic clinical features and episignature differentiating it from BAFopathies.

Divergent variant patterns among 19 patients with Rubinstein-Taybi syndrome uncovered by comprehensive genetic analysis including whole genome sequencing.

Rubinstein-Taybi syndrome (RSTS) is characterized by dysmorphic facial features, broad thumbs, and intellectual disability. CREB-binding protein (CREBBP) or E1A-binding protein P300 (EP300) are causative genes. To elucidate the underlying genetic and genomic architecture related to the RSTS phenotype, we performed comprehensive genetic analysis targeting CREBBP and/or EP300 in 22 clinically diagnosed patients. During the 11-year study period, we used several analysis methods including high-resolution melting, array-based comparative genomic hybridization, panel-based exome sequencing, whole exome sequencing, and whole genome sequencing (WGS). We identified the causative variants in 19 patients (86.3%), but they were variable and complex, so we must combine multiple analysis methods. Notably, we found genetic alterations in the non-coding regions of two patients (10.5%, 2/19): scattered deletions including a partial 5'-untranslated region of CREBBP in one patient (all coding exons were intact), and a deep 229-bp intronic deletion in another patient, resulting in a splicing error. Furthermore, we identified rare clinical findings: two patients with an EP300 variant showed abnormal development of the neural tube, and one patient with a CREBBP variant had anorectal atresia with a cloaca. Our findings expand the allelic heterogeneity of RSTS, underscore the utility of comprehensive genetic analysis, and suggest that WGS may be a practical diagnostic strategy.

Further delineation of SET-related intellectual disability syndrome.

A loss-of-function mutation of SET causes nonsyndromic intellectual disability, often associated with mild facial dysmorphic features, including plagiocephaly, facial asymmetry, broad and high forehead, a wide mouth, and a prominent mandible. We report a male individual with a 2.0 Mb deletion within 9q34.11, involving SET and SPTAN1, but not STXBP1. Among the genes with a high probability of being loss-of-function intolerant in the deletion interval, only SPTAN1 and SET had haploinsufficiency score (%HI) <10, indicating a high likelihood of haploinsufficiency. Pathogenic variants in SPTAN1 are responsible for early-onset epileptic encephalopathy by exerting a dominant-negative effect. However, whether haploinsufficiency of SPTAN1 alone also causes the severe phenotype remained unknown. SET is a regulator of cell differentiation in early human development and a component of the inhibitor of histone acetyltransferases complex. Therefore, combining the previously reported patients, our patient delineated the phenotypic spectrum of SET-related nonsyndromic intellectual disability with mild facial dysmorphism.

De novo variants in CELF2 that disrupt the nuclear localization signal cause developmental and epileptic encephalopathy.

We report heterozygous CELF2 (NM_006561.3) variants in five unrelated individuals: Individuals 1-4 exhibited developmental and epileptic encephalopathy (DEE) and Individual 5 had intellectual disability and autistic features. CELF2 encodes a nucleocytoplasmic shuttling RNA-binding protein that has multiple roles in RNA processing and is involved in the embryonic development of the central nervous system and heart. Whole-exome sequencing identified the following CELF2 variants: two missense variants [c.1558C>T:p.(Pro520Ser) in unrelated Individuals 1 and 2, and c.1516C>G:p.(Arg506Gly) in Individual 3], one frameshift variant in Individual 4 that removed the last amino acid of CELF2 c.1562dup:p.(Tyr521Ter), possibly resulting in escape from nonsense-mediated mRNA decay (NMD), and one canonical splice site variant, c.272-1G>C in Individual 5, also probably leading to NMD. The identified variants in Individuals 1, 2, 4, and 5 were de novo, while the variant in Individual 3 was inherited from her mosaic mother. Notably, all identified variants, except for c.272-1G>C, were clustered within 20 amino acid residues of the C-terminus, which might be a nuclear localization signal. We demonstrated the extranuclear mislocalization of mutant CELF2 protein in cells transfected with mutant CELF2 complementary DNA plasmids. Our findings indicate that CELF2 variants that disrupt its nuclear localization are associated with DEE.

A novel method for isolating lymphatic endothelial cells from lymphatic malformations and detecting PIK3CA somatic mutation in these isolated cells.

PURPOSE: Tissue disaggregation and the cell sorting technique by surface markers has played an important role in isolating lymphatic endothelial cells (LECs) from lymphatic malformation (LM). However, this technique may have the drawback of impurities or result in isolation failure because it is dependent on surface marker expressions, the heterogeneity of which has been found in the lymphatic system. We developed a novel method for isolating LM-LECs without using whole tissue disaggregation. METHODS: Seven LM surgical specimens were collected from seven patients with LMs. LM-LECs were detached from the LM cyst wall by "lumen digestion" and irrigating the cystic cavity with trypsin, and maintained in culture. RESULTS: The cells formed a monolayer with a cobblestone-like appearance. Immunohistochemistry and quantitative RT-PCR of these cells revealed high expression of lymphatic-specific genes, confirming their identity as LM-LECs. The whole-exome sequencing and PIK3CA sequencing of these cells revealed somatic mutations in PIK3CA in all cases. CONCLUSIONS: We established a novel technique for isolating LM-LECs from LM tissue by "lumen digestion" without whole-tissue disaggregation. The limited incorporation of non-LM LECs in the isolate in our method could make it an important tool for investigating the heterogeneity of gene expression as well as mutations in LM-LECs.

Biallelic Mutations in MYPN, Encoding Myopalladin, Are Associated with Childhood-Onset, Slowly Progressive Nemaline Myopathy.

Nemaline myopathy (NM) is a common form of congenital nondystrophic skeletal muscle disease characterized by muscular weakness of proximal dominance, hypotonia, and respiratory insufficiency but typically not cardiac dysfunction. Wide variation in severity has been reported. Intranuclear rod myopathy is a subtype of NM in which rod-like bodies are seen in the nucleus, and it often manifests as a severe phenotype. Although ten mutant genes are currently known to be associated with NM, only ACTA1 is associated with intranuclear rod myopathy. In addition, the genetic cause remains unclear in approximately 25%-30% of individuals with NM. We performed whole-exome sequencing on individuals with histologically confirmed but genetically unsolved NM. Our study included individuals with milder, later-onset NM and identified biallelic loss-of-function mutations in myopalladin (MYPN) in four families. Encoded MYPN is a sarcomeric protein exclusively localized in striated muscle in humans. Individuals with identified MYPN mutations in all four of these families have relatively mild, childhood- to adult-onset NM with slowly progressive muscle weakness. Walking difficulties were recognized around their forties. Decreased respiratory function, cardiac involvement, and intranuclear rods in biopsied muscle were observed in two individuals. MYPN was localized at the Z-line in control skeletal muscles but was absent from affected individuals. Homozygous knockin mice with a nonsense mutation in Mypn showed Z-streaming and nemaline-like bodies adjacent to a disorganized Z-line on electron microscopy, recapitulating the disease. Our results suggest that MYPN screening should be considered in individuals with mild NM, especially when cardiac problems or intranuclear rods are present.

Update of the genotype and phenotype of KMT2D and KDM6A by genetic screening of 100 patients with clinically suspected Kabuki syndrome.

Kabuki syndrome is characterized by a variable degree of intellectual disability, characteristic facial features, and complications in various organs. Many variants have been identified in two causative genes, that is, lysine methyltransferase 2D (KMT2D) and lysine demethylase 6A (KDM6A). In this study, we present the results of genetic screening of 100 patients with a suspected diagnosis of Kabuki syndrome in our center from July 2010 to June 2018. We identified 76 variants (43 novel) in KMT2D and 4 variants (3 novel) in KDM6A as pathogenic or likely pathogenic. Rare variants included a deep splicing variant (c.14000-8C>G) confirmed by RNA sequencing and an 18% mosaicism level for a KMT2D mutation. We also characterized a case with a blended phenotype consisting of Kabuki syndrome, osteogenesis imperfecta, and 16p13.11 microdeletion. We summarized the clinical phenotypes of 44 patients including a patient who developed cervical cancer of unknown origin at 16 years of age. This study presents important details of patients with Kabuki syndrome including rare clinical cases and expands our genetic understanding of this syndrome, which will help clinicians and researchers better manage and understand patients with Kabuki syndrome they may encounter.

An efficient genetic test flow for multiple congenital anomalies and intellectual disability.

BACKGROUND: Genetic testing has enabled the diagnosis of multiple congenital anomalies and/or intellectual disabilities. However, because of the phenotypic variability in these disorders, selection of an appropriate genetic test can be difficult and complex. For clinical examination, particularly in clinical facilities, a simple and standardized system is needed. METHODS: We compared microarray comparative genomic hybridization and clinical exome sequencing with regard to diagnostic yield, cost, and time required to reach a definitive diagnosis. After first performing G-banding for 200 patients with multiple congenital anomalies and/or intellectual disability, as a subsequent genetic test, microarray and clinical exome sequencing were compared with regard to diagnostic yield, cost, and time required. RESULTS: There was no obvious difference in the diagnostic rate between the two methods; however, clinical exome sequencing was superior in terms of cost and time. In addition, clinical exome sequencing could sufficiently identify copy number variants, and even smaller copy number variants could be identified. CONCLUSIONS: Clinical exome sequencing should be implemented earlier as a genetic test for undiagnosed patients with multiple congenital anomalies and/or intellectual disabilities. Our results can be used to establish inspection methods in clinical facilities.

RNA sequencing solved the most common but unrecognized NEB pathogenic variant in Japanese nemaline myopathy.

PURPOSE: The diagnostic rate for Mendelian diseases by exome sequencing (ES) is typically 20-40%. The low rate is partly because ES misses deep-intronic or synonymous variants leading to aberrant splicing. In this study, we aimed to apply RNA sequencing (RNA-seq) to efficiently detect the aberrant splicings and their related variants. METHODS: Aberrant splicing in biopsied muscles from six nemaline myopathy (NM) cases unresolved by ES were analyzed with RNA-seq. Variants related to detected aberrant splicing events were analyzed with Sanger sequencing. Detected variants were screened in NM patients unresolved by ES. RESULTS: We identified a novel deep-intronic NEB pathogenic variant, c.1569+339A>G in one case, and another novel synonymous NEB pathogenic variant, c.24684G>C (p.Ser8228Ser) in three cases. The c.24684G>C variant was observed to be the most frequent among all NEB pathogenic variants in normal Japanese populations with a frequency of 1 in 178 (20 alleles in 3552 individuals), but was previously unrecognized. Expanded screening of the variant identified it in a further four previously unsolved nemaline myopathy cases. CONCLUSION: These results indicated that RNA-seq may be able to solve a large proportion of previously undiagnosed muscle diseases.

Genetic abnormalities in a large cohort of Coffin-Siris syndrome patients.

Coffin-Siris syndrome (CSS, MIM#135900) is a congenital disorder characterized by coarse facial features, intellectual disability, and hypoplasia of the fifth digit and nails. Pathogenic variants for CSS have been found in genes encoding proteins in the BAF (BRG1-associated factor) chromatin-remodeling complex. To date, more than 150 CSS patients with pathogenic variants in nine BAF-related genes have been reported. We previously reported 71 patients of whom 39 had pathogenic variants. Since then, we have recruited an additional 182 CSS-suspected patients. We performed comprehensive genetic analysis on these 182 patients and on the previously unresolved 32 patients, targeting pathogenic single nucleotide variants, short insertions/deletions and copy number variations (CNVs). We confirmed 78 pathogenic variations in 78 patients. Pathogenic variations in ARID1B, SMARCB1, SMARCA4, ARID1A, SOX11, SMARCE1, and PHF6 were identified in 48, 8, 7, 6, 4, 1, and 1 patients, respectively. In addition, we found three CNVs including SMARCA2. Of particular note, we found a partial deletion of SMARCB1 in one CSS patient and we thoroughly investigated the resulting abnormal transcripts.

A novel gene (FAM20B encoding glycosaminoglycan xylosylkinase) for neonatal short limb dysplasia resembling Desbuquois dysplasia.

Desbuquois dysplasia (DBQD) is an autosomal recessive heterogeneous disorder characterized by joint laxity and skeletal changes, including a distinctive monkey-wrench appearance of the femora, advanced carpal ossification, and abnormal patterning of the preaxial digits. Two genes for DBQD (CANT1 encoding calcium-activated nucleotidase-1 and XYLT1 encoding xylosyltransferase-1) have been reported. We propose a novel gene for neonatal short limb dysplasia resembling DBQD, based on the phenotype and genotype of two affected siblings. The affected boy and girl died in early infancy and shortly after birth, respectively. The clinical hallmarks included mid-face hypoplasia, thoracic hypoplasia with respiratory failure, very short stature (approximately -7 SD of birth length) with mesomelic shortening of the limbs, and multiple dislocations of the large joints. Radiological examinations showed prominent lesser trochanter, flared metaphyses of the long bones, and joint dislocations. The affected boy had preaxial digital hypoplasia, and the affected girl showed overlapping and syndactyly of the preaxial digits. Molecular analyses of the girl showed compound heterozygous variants in FAM20B (NM_014864: c.174_178delTACCT p.T59Afs*19/c.1038delG p.N347Mfs*4). FAM20B encodes glycosaminoglycan xylosylkinase, which acts downstream of xylosyltransferase-1. Given the fact that FAM20B deficiency causes skeletal phenotypes in mice and zebrafish, these variants are highly probable to be pathogenic.

Homozygous splicing mutation in NUP133 causes Galloway-Mowat syndrome.

OBJECTIVE: Galloway-Mowat syndrome (GAMOS) is a neural and renal disorder, characterized by microcephaly, brain anomalies, and early onset nephrotic syndrome. Biallelic mutations in WDR73 and the 4 subunit genes of the KEOPS complex are reported to cause GAMOS. Furthermore, an identical homozygous NUP107 (nucleoporin 107kDa) mutation was identified in 4 GAMOS-like families, although biallelic NUP107 mutations were originally identified in steroid-resistant nephrotic syndrome. NUP107 and NUP133 (nucleoporin 133kDa) are interacting subunits of the nuclear pore complex in the nuclear envelope during interphase, and these proteins are also involved in centrosome positioning and spindle assembly during mitosis. METHODS: Linkage analysis and whole exome sequencing were performed in a previously reported GAMOS family with brain atrophy and steroid-resistant nephrotic syndrome. RESULTS: We identified a homozygous NUP133 mutation, c.3335-11T>A, which results in the insertion of 9bp of intronic sequence between exons 25 and 26 in the mutant transcript. NUP133 and NUP107 interaction was impaired by the NUP133 mutation based on an immunoprecipitation assay. Importantly, focal cortical dysplasia type IIa was recognized in the brain of an autopsied patient and focal segmental glomerulosclerosis was confirmed in the kidneys of the 3 examined patients. A nup133-knockdown zebrafish model exhibited microcephaly, fewer neuronal cells, underdeveloped glomeruli, and fusion of the foot processes of the podocytes, which mimicked human GAMOS features. nup133 morphants could be rescued by human wild-type NUP133 mRNA but not by mutant mRNA. INTERPRETATION: These data indicate that the biallelic NUP133 loss-of-function mutation causes GAMOS. Ann Neurol 2018;84:814-828.

De novo hotspot variants in CYFIP2 cause early-onset epileptic encephalopathy.

OBJECTIVE: The cytoplasmic fragile X mental retardation 1 interacting proteins 2 (CYFIP2) is a component of the WASP-family verprolin-homologous protein (WAVE) regulatory complex, which is involved in actin dynamics. An obvious association of CYFIP2 variants with human neurological disorders has never been reported. Here, we identified de novo hotspot CYFIP2 variants in neurodevelopmental disorders and explore the possible involvement of the CYFIP2 mutants in the WAVE signaling pathway. METHODS: We performed trio-based whole-exome sequencing (WES) in 210 families and case-only WES in 489 individuals with epileptic encephalopathies. The functional effect of CYFIP2 variants on WAVE signaling was evaluated by computational structural analysis and in vitro transfection experiments. RESULTS: We identified three de novo CYFIP2 variants at the Arg87 residue in 4 unrelated individuals with early-onset epileptic encephalopathy. Structural analysis indicated that the Arg87 residue is buried at an interface between CYFIP2 and WAVE1, and the Arg87 variant may disrupt hydrogen bonding, leading to structural instability and aberrant activation of the WAVE regulatory complex. All mutant CYFIP2 showed comparatively weaker interactions to the VCA domain than wild-type CYFIP2. Immunofluorescence revealed that ectopic speckled accumulation of actin and CYFIP2 was significantly increased in cells transfected with mutant CYFIP2. INTERPRETATION: Our findings suggest that de novo Arg87 variants in CYFIP2 have gain-of-function effects on the WAVE signaling pathway and are associated with severe neurological disorders. Ann Neurol 2018;83:794-806.

Biallelic Mutations in Nuclear Pore Complex Subunit NUP107 Cause Early-Childhood-Onset Steroid-Resistant Nephrotic Syndrome.

The nuclear pore complex (NPC) is a huge protein complex embedded in the nuclear envelope. It has central functions in nucleocytoplasmic transport, nuclear framework, and gene regulation. Nucleoporin 107 kDa (NUP107) is a component of the NPC central scaffold and is an essential protein in all eukaryotic cells. Here, we report on biallelic NUP107 mutations in nine affected individuals who are from five unrelated families and show early-onset steroid-resistant nephrotic syndrome (SRNS). These individuals have pathologically focal segmental glomerulosclerosis, a condition that leads to end-stage renal disease with high frequency. NUP107 is ubiquitously expressed, including in glomerular podocytes. Three of four NUP107 mutations detected in the affected individuals hamper NUP107 binding to NUP133 (nucleoporin 133 kDa) and NUP107 incorporation into NPCs in vitro. Zebrafish with nup107 knockdown generated by morpholino oligonucleotides displayed hypoplastic glomerulus structures and abnormal podocyte foot processes, thereby mimicking the pathological changes seen in the kidneys of the SRNS individuals with NUP107 mutations. Considering the unique properties of the podocyte (highly differentiated foot-process architecture and slit membrane and the inability to regenerate), we propose a "podocyte-injury model" as the pathomechanism for SRNS due to biallelic NUP107 mutations.

Cerebellar ataxia-dominant phenotype in patients with ERCC4 mutations.

Autosomal recessive cerebellar ataxias (ARCAs) are clinically and genetically heterogeneous neurological disorders. Through whole-exome sequencing of Japanese ARCA patients, we identified three index patients from unrelated families who had biallelic mutations in ERCC4. ERCC4 mutations have been known to cause xeroderma pigmentosum complementation group F (XP-F), Cockayne syndrome, and Fanconi anemia phenotypes. All of the patients described here showed very slowly progressive cerebellar ataxia and cognitive decline with choreiform involuntary movement, with young adolescent or midlife onset. Brain MRI demonstrated atrophy that included the cerebellum and brainstem. Of note, cutaneous symptoms were very mild: there was normal to very mild pigmentation of exposed skin areas and/or an equivocal history of pathological sunburn. However, an unscheduled DNA synthesis assay of fibroblasts from the patient revealed impairment of nucleotide excision repair. A similar phenotype was very recently recognized through genetic analysis of Caucasian cerebellar ataxia patients. Our results confirm that biallelic ERCC4 mutations cause a cerebellar ataxia-dominant phenotype with mild cutaneous symptoms, possibly accounting for a high proportion of the genetic causes of ARCA in Japan, where XP-F is prevalent.

ANKRD11 variants cause variable clinical features associated with KBG syndrome and Coffin-Siris-like syndrome.

KBG syndrome (KBGS) is an autosomal dominant multiple congenital anomaly-intellectual disability syndrome, characterized by developmental delay with neurological involvements, macrodontia of the upper central incisors, characteristic facial dysmorphism and skeletal anomalies. Variants in ANKRD11 cause KBGS. We present five individuals from four families with ANKRD11 variants identified by whole-exome sequencing. Four of the five were clinically affected, and their diagnoses were varied. One was typical KBGS, two were Coffin-Siris syndrome-like (CSS), and one was intellectual disability with infantile spasms. One individual showed extremely mild phenotype. All individuals fulfilled the proposed diagnostic criteria for KBGS. Phenotypic features overlap between KBGS and CSS to some extent, and characteristic dental and fifth finger/toe findings can indicate differential diagnosis. These findings indicate that patients with ANKRD11 variants occupy a wide spectrum of intellectual disability, including clinically normal individuals. This is the first report highlighting the clinical overlap between KBGS and CSS and supporting the recently proposed clinical concept, in which transcriptional machineries are disrupted.

Deletions and de novo mutations of SOX11 are associated with a neurodevelopmental disorder with features of Coffin-Siris syndrome.

BACKGROUND: SOX11 is a transcription factor proposed to play a role in brain development. The relevance of SOX11 to human developmental disorders was suggested by a recent report of SOX11 mutations in two patients with Coffin-Siris syndrome. Here we further investigate the role of SOX11 variants in neurodevelopmental disorders. METHODS: We used array based comparative genomic hybridisation and trio exome sequencing to identify children with intellectual disability who have deletions or de novo point mutations disrupting SOX11. The pathogenicity of the SOX11 mutations was assessed using an in vitro gene expression reporter system. Loss-of-function experiments were performed in xenopus by knockdown of Sox11 expression. RESULTS: We identified seven individuals with chromosome 2p25 deletions involving SOX11. Trio exome sequencing identified three de novo SOX11 variants, two missense (p.K50N; p.P120H) and one nonsense (p.C29*). The biological consequences of the missense mutations were assessed using an in vitro gene expression system. These individuals had microcephaly, developmental delay and shared dysmorphic features compatible with mild Coffin-Siris syndrome. To further investigate the function of SOX11, we knocked down the orthologous gene in xenopus. Morphants had significant reduction in head size compared with controls. This suggests that SOX11 loss of function can be associated with microcephaly. CONCLUSIONS: We thus propose that SOX11 deletion or mutation can present with a Coffin-Siris phenotype.

Detection of low-prevalence somatic TSC2 mutations in sporadic pulmonary lymphangioleiomyomatosis tissues by deep sequencing.

Lymphangioleiomyomatosis (LAM) (MIM #606690) is a rare lung disorder leading to respiratory failure associated with progressive cystic destruction due to the proliferation and infiltration of abnormal smooth muscle-like cells (LAM cells). LAM can occur alone (sporadic LAM, S-LAM) or combined with tuberous sclerosis complex (TSC-LAM). TSC is caused by a germline heterozygous mutation in either TSC1 or TSC2, and TSC-LAM is thought to occur as a result of a somatic mutation (second hit) in addition to a germline mutation in TSC1 or TSC2 (first hit). S-LAM is also thought to occur under the two-hit model involving a somatic mutation and/or loss of heterozygosity in TSC2. To identify TSC1 or TSC2 changes in S-LAM patients, the two genes were analyzed by deep next-generation sequencing (NGS) using genomic DNA from blood leukocytes (n = 9), LAM tissue from lung (n = 7), LAM cultured cells (n = 4), or LAM cell clusters (n = 1). We identified nine somatic mutations in six of nine S-LAM patients (67 %) with mutant allele frequencies of 1.7-46.2 %. Three of these six patients (50 %) showed two different TSC2 mutations with allele frequencies of 1.7-28.7 %. Furthermore, at least five mutations with low prevalence (<20 % of allele frequency) were confirmed by droplet digital PCR. As LAM tissues are likely to be composed of heterogeneous cell populations, mutant allele frequencies can be low. Our results confirm the consistent finding of TSC2 mutations in LAM samples, and highlight the benefit of laser capture microdissection and in-depth allele analyses for detection, such as NGS.

De Novo mutations in GNAO1, encoding a Gαo subunit of heterotrimeric G proteins, cause epileptic encephalopathy.

Heterotrimeric G proteins, composed of α, ß, and γ subunits, can transduce a variety of signals from seven-transmembrane-type receptors to intracellular effectors. By whole-exome sequencing and subsequent mutation screening, we identified de novo heterozygous mutations in GNAO1, which encodes a Gαo subunit of heterotrimeric G proteins, in four individuals with epileptic encephalopathy. Two of the affected individuals also showed involuntary movements. Somatic mosaicism (approximately 35% to 50% of cells, distributed across multiple cell types, harbored the mutation) was shown in one individual. By mapping the mutation onto three-dimensional models of the Gα subunit in three different complexed states, we found that the three mutants (c.521A>G [p.Asp174Gly], c.836T>A [p.Ile279Asn], and c.572_592del [p.Thr191_Phe197del]) are predicted to destabilize the Gα subunit fold. A fourth mutant (c.607G>A), in which the Gly203 residue located within the highly conserved switch II region is substituted to Arg, is predicted to impair GTP binding and/or activation of downstream effectors, although the p.Gly203Arg substitution might not interfere with Gα binding to G-protein-coupled receptors. Transient-expression experiments suggested that localization to the plasma membrane was variably impaired in the three putatively destabilized mutants. Electrophysiological analysis showed that Gαo-mediated inhibition of calcium currents by norepinephrine tended to be lower in three of the four Gαo mutants. These data suggest that aberrant Gαo signaling can cause multiple neurodevelopmental phenotypes, including epileptic encephalopathy and involuntary movements.

Mutations in B3GALT6, which encodes a glycosaminoglycan linker region enzyme, cause a spectrum of skeletal and connective tissue disorders.

Proteoglycans (PGs) are a major component of the extracellular matrix in many tissues and function as structural and regulatory molecules. PGs are composed of core proteins and glycosaminoglycan (GAG) side chains. The biosynthesis of GAGs starts with the linker region that consists of four sugar residues and is followed by repeating disaccharide units. By exome sequencing, we found that B3GALT6 encoding an enzyme involved in the biosynthesis of the GAG linker region is responsible for a severe skeletal dysplasia, spondyloepimetaphyseal dysplasia with joint laxity type 1 (SEMD-JL1). B3GALT6 loss-of-function mutations were found in individuals with SEMD-JL1 from seven families. In a subsequent candidate gene study based on the phenotypic similarity, we found that B3GALT6 is also responsible for a connective tissue disease, Ehlers-Danlos syndrome (progeroid form). Recessive loss-of-function mutations in B3GALT6 result in a spectrum of disorders affecting a broad range of skeletal and connective tissues characterized by lax skin, muscle hypotonia, joint dislocation, and spinal deformity. The pleiotropic phenotypes of the disorders indicate that B3GALT6 plays a critical role in a wide range of biological processes in various tissues, including skin, bone, cartilage, tendon, and ligament.