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Human CLP1 Mutations Alter tRNA Biogenesis, Affecting Both Peripheral and Central Nervous System Function

CLP1 is a RNA kinase involved in tRNA splicing. Recently, CLP1 kinase-dead mice were shown to display a neuromuscular disorder with loss of motor neurons and muscle paralysis. Human genome analyses now identified a CLP1 homozygous missense mutation (p.R140H) in five unrelated families, leading to a loss of CLP1 interaction with the tRNA splicing endonuclease (TSEN) complex, largely reduced pre-tRNA cleavage activity, and accumulation of linear tRNA introns. The affected individuals develop severe motor-sensory defects, cortical dysgenesis, and microcephaly. Mice carrying kinase-dead CLP1 also displayed microcephaly and reduced cortical brain volume due to the enhanced cell death of neuronal progenitors that is associated with reduced numbers of cortical neurons. Our data elucidate a neurological syndrome defined by CLP1 mutations that impair tRNA splicing. Reduction of a founder mutation to homozygosity illustrates the importance of rare variations in disease and supports the clan genomics hypothesis.

Molecular etiology of arthrogryposis in multiple families of mostly Turkish origin

BACKGROUND Arthrogryposis, defined as congenital joint contractures in 2 or more body areas, is a clinical sign rather than a specific disease diagnosis. To date, more than 400 different disorders have been described that present with arthrogryposis, and variants of more than 220 genes have been associated with these disorders; however, the underlying molecular etiology remains unknown in the considerable majority of these cases. METHODS We performed whole exome sequencing (WES) of 52 patients with clinical presentation of arthrogryposis from 48 different families. RESULTS Affected individuals from 17 families (35.4%) had variants in known arthrogryposis-associated genes, including homozygous variants of cholinergic γ nicotinic receptor (CHRNG, 6 subjects) and endothelin converting enzyme-like 1 (ECEL1, 4 subjects). Deleterious variants in candidate arthrogryposis-causing genes (fibrillin 3 [FBN3], myosin IXA [MYO9A], and pleckstrin and Sec7 domain containing 3 [PSD3]) were identified in 3 families (6.2%). Moreover, in 8 families with a homozygous mutation in an arthrogryposis-associated gene, we identified a second locus with either a homozygous or compound heterozygous variant in a candidate gene (myosin binding protein C, fast type [MYBPC2] and vacuolar protein sorting 8 [VPS8], 2 families, 4.2%) or in another disease-associated genes (6 families, 12.5%), indicating a potential mutational burden contributing to disease expression. CONCLUSION In 58.3% of families, the arthrogryposis manifestation could be explained by a molecular diagnosis; however, the molecular etiology in subjects from 20 families remained unsolved by WES. Only 5 of these 20 unrelated subjects had a clinical presentation consistent with amyoplasia; a phenotype not thought to be of genetic origin. Our results indicate that increased use of genome-wide technologies will provide opportunities to better understand genetic models for diseases and molecular mechanisms of genetically heterogeneous disorders, such as arthrogryposis. FUNDING This work was supported in part by US National Human Genome Research Institute (NHGRI)/National Heart, Lung, and Blood Institute (NHLBI) grant U54HG006542 to the Baylor-Hopkins Center for Mendelian Genomics, and US National Institute of Neurological Disorders and Stroke (NINDS) grant R01NS058529 to J.R. Lupski.

DVL3 Alleles Resulting in a −1 Frameshift of the Last Exon Mediate Autosomal-Dominant Robinow Syndrome

Robinow syndrome is a rare congenital disorder characterized by mesomelic limb shortening, genital hypoplasia, and distinctive facial features. Recent reports have identified, in individuals with dominant Robinow syndrome, a specific type of variant characterized by being uniformly located in the penultimate exon of DVL1 and resulting in a -1 frameshift allele with a premature termination codon that escapes nonsense-mediated decay. Here, we studied a cohort of individuals who had been clinically diagnosed with Robinow syndrome but who had not received a molecular diagnosis from variant studies of DVL1, WNT5A, and ROR2. Because of the uniform location of frameshift variants in DVL1-mediated Robinow syndrome and the functional redundancy of DVL1, DVL2, and DVL3, we elected to pursue direct Sanger sequencing of the penultimate exon of DVL1 and its paralogs DVL2 and DVL3 to search for potential disease-associated variants. Remarkably, targeted sequencing identified five unrelated individuals harboring heterozygous, de novo frameshift variants in DVL3, including two splice acceptor mutations and three 1 bp deletions. Similar to the variants observed in DVL1-mediated Robinow syndrome, all variants in DVL3 result in a -1 frameshift, indicating that these highly specific alterations might be a common cause of dominant Robinow syndrome. Here, we review the current knowledge of these peculiar variant alleles in DVL1- and DVL3-mediated Robinow syndrome and further elucidate the phenotypic features present in subjects with DVL1 and DVL3 frameshift mutations.

Novel POC1A mutation in primordial dwarfism reveals new insights for centriole biogenesis

POC1A encodes a WD repeat protein localizing to centrioles and spindle poles and is associated with short stature, onychodysplasia, facial dysmorphism and hypotrichosis (SOFT) syndrome. These main features are related to the defect in cell proliferation of chondrocytes in growth plate. In the current study, we aimed at identifying the molecular basis of two patients with primordial dwarfism (PD) in a single family through utilization of whole-exome sequencing. A novel homozygous p.T120A missense mutation was detected in POC1A in both patients, a known causative gene of SOFT syndrome, and confirmed using Sanger sequencing. To test the pathogenicity of the detected mutation, primary fibroblast cultures obtained from the patients and a control individual were used. For evaluating the global gene expression profile of cells carrying p.T120A mutation in POC1A, we performed the gene expression array and compared their expression profiles to those of control fibroblast cells. The gene expression array analysis showed that 4800 transcript probes were significantly deregulated in cells with p.T120A mutation in comparison to the control. GO term association results showed that deregulated genes are mostly involved in the extracellular matrix and cytoskeleton. Furthermore, the p.T120A missense mutation in POC1A caused the formation of abnormal mitotic spindle structure, including supernumerary centrosomes, and changes in POC1A were accompanied by alterations in another centrosome-associated WD repeat protein p80-katanin. As a result, we identified a novel mutation in POC1A of patients with PD and showed that this mutation causes the formation of multiple numbers of centrioles and multipolar spindles with abnormal chromosome arrangement.

Poikiloderma with neutropenia: genotype-ethnic origin correlation, expanding phenotype and literature review.

Poikiloderma with neutropenia (PN), is a rare genodermatosis associated with patognomic features of poikiloderma and permanent neutropenia. Three common recurrent mutations of related gene, USB1, were considered to be associated with three different ethnic origins. The most common recurrent mutation, c.531delA, has been detected in seven Caucasian patients in the literature. In this paper, we present review of all patients from the literature and report two additional patients of Turkish ancestry with the diagnosis of PN. The diagnosis of these two PN patients were made clinically and confirmed by molecular analysis which detected the most common recurrent mutation, c.531delA. Genotype‐ethnic origin correlation hypothesis, therefore, has been strengthened with this result. Short stature in PN, is a common finding, which until now has never been treated with growth hormone (GH). One of our patients is the first patient with attempted treatment of short stature via GH administration. Finally, both of our patients had high‐pitched voice and vocal cord nodules which might be considered as additional clinical findings not associated with PN before.

WNT Signaling Perturbations Underlie the Genetic Heterogeneity of Robinow Syndrome

Locus heterogeneity characterizes a variety of skeletal dysplasias often due to interacting or overlapping signaling pathways. Robinow syndrome is a skeletal disorder historically refractory to molecular diagnosis, potentially stemming from substantial genetic heterogeneity. All current known pathogenic variants reside in genes within the noncanonical Wnt signaling pathway including ROR2, WNT5A, and more recently, DVL1 and DVL3. However, ∼70% of autosomal-dominant Robinow syndrome cases remain molecularly unsolved. To investigate this missing heritability, we recruited 21 families with at least one family member clinically diagnosed with Robinow or Robinow-like phenotypes and performed genetic and genomic studies. In total, four families with variants in FZD2 were identified as well as three individuals from two families with biallelic variants in NXN that co-segregate with the phenotype. Importantly, both FZD2 and NXN are relevant protein partners in the WNT5A interactome, supporting their role in skeletal development. In addition to confirming that clustered -1 frameshifting variants in DVL1 and DVL3 are the main contributors to dominant Robinow syndrome, we also found likely pathogenic variants in candidate genes GPC4 and RAC3, both linked to the Wnt signaling pathway. These data support an initial hypothesis that Robinow syndrome results from perturbation of the Wnt/PCP pathway, suggest specific relevant domains of the proteins involved, and reveal key contributors in this signaling cascade during human embryonic development. Contrary to the view that non-allelic genetic heterogeneity hampers gene discovery, this study demonstrates the utility of rare disease genomic studies to parse gene function in human developmental pathways.

Circumferential skin folds and multiple anomalies: confirmation of a distinct autosomal recessive Michelin tire baby syndrome

Department of Medical Genetics, Cerrahpasa Medical School of Istanbul University, Department of Pediatrics, Medical School of Bezmi Alem University, Istanbul and Department of Medical Genetics, Medical School of Osmangazi University, Eskisehir, Turkey Correspondence to Hakan Ulucan MD, PhD, Department of Medical Genetics, Cerrahpasa Medical School of Istanbul University, Istanbul 34098, Turkey Tel: + 90 212 414 30 00 x22 996; fax: + 90 212 414 31 84; e-mail: hulucan@istanbul.edu.tr

A novel EFNB1 mutation in a patient with craniofrontonasal syndrome and right hallux duplication

Craniofrontonasal syndrome (CFNS, MIM #304110) is a rare X-linked dominant developmental disorder that shows paradoxically greater severity in affected females than in affected males. Our female patient with frontonasal dysplasia, craniosynostosis and additional malformations was consistent with CFNS. EFNB1, which encodes a member of the ephrin family of transmembrane ligands for Eph receptor tyrosine kinases, is the only gene in which mutation is known to cause CFNS. Here, we describe 402T>C, a novel de novo mutation on EFNB1. This mutation results in substitution of highly conserved isoleucine at 134th residue to threonine.

A novel case of autosomal dominant cutis laxa in a consanguineous family: report and literature review

Autosomal dominant cutis laxa (ADCL, OMIM #123700) is a rare connective tissue disorder characterized by loose, redundant skin folds that may be apparent form birth or appear later in life. Most severely affected areas are the neck, axillar regions, trunk, and groin. Typically, patients present with characteristic facial features including a premature aged appearance, long philtrum, a high forehead, large ears, and a beaked nose. Cardiovascular and pulmonary complications include bicuspid aortic valves, aortic root dilatation, and emphysema. Sporadically, these complications have been documented to cause premature death. Several rare findings including urogenital anomalies and gastroesophageal problems can be also occur. Most patients harbor a frameshift mutation in one of the five last exons of the ELN gene (ADCL1, OMIM #123700), whereas one patient was described to have a tandem duplication in the FBLN5 gene (ADCL2, OMIM #614434). Here, we present a female ADCL patient, from a consanguineous family, with a novel mutation in ELN and review 39 previously reported ADCL patients. All patients have various skin findings, whereas cardiovascular, pulmonary findings, and multiple hernia were present in 61, 28, and 38% of patients, respectively. Strabismus, urogenital anomalies, gastroesophageal problems, and scoliosis may rarely be present. A clear definition of the ADCL syndrome can enable more accurate genetic counseling.

Report of a family with craniofrontonasal syndrome.

Craniofrontonasal syndrome (CFNS, OMIM 304110) paradoxically presents a severe phenotype in heterozygous females and a mild or a normal phenotype in hemizygous males. Hypertelorism is seen in almost all of the female CFNS patients; craniosynostosis, facial asymmetry, and bifid nose are the other major clinical features. Most of the males are mildly affected, frequently only with hypertelorism. Here, we report a family with a G151S mutation in the EFNB1 gene. The mutation was identified in two severely affected sisters and paradoxically in their clinically unaffected father. The father on whom we report is the first male patient genetically proved to carry a CFNS-causing mutation and not presenting any signs nor symptoms of CFNS.