X-exome sequencing of 405 unresolved families identifies seven novel intellectual disability genes.

X-linked intellectual disability (XLID) is a clinically and genetically heterogeneous disorder. During the past two decades in excess of 100 X-chromosome ID genes have been identified. Yet, a large number of families mapping to the X-chromosome remained unresolved suggesting that more XLID genes or loci are yet to be identified. Here, we have investigated 405 unresolved families with XLID. We employed massively parallel sequencing of all X-chromosome exons in the index males. The majority of these males were previously tested negative for copy number variations and for mutations in a subset of known XLID genes by Sanger sequencing. In total, 745 X-chromosomal genes were screened. After stringent filtering, a total of 1297 non-recurrent exonic variants remained for prioritization. Co-segregation analysis of potential clinically relevant changes revealed that 80 families (20%) carried pathogenic variants in established XLID genes. In 19 families, we detected likely causative protein truncating and missense variants in 7 novel and validated XLID genes (CLCN4, CNKSR2, FRMPD4, KLHL15, LAS1L, RLIM and USP27X) and potentially deleterious variants in 2 novel candidate XLID genes (CDK16 and TAF1). We show that the CLCN4 and CNKSR2 variants impair protein functions as indicated by electrophysiological studies and altered differentiation of cultured primary neurons from Clcn4(-/-) mice or after mRNA knock-down. The newly identified and candidate XLID proteins belong to pathways and networks with established roles in cognitive function and intellectual disability in particular. We suggest that systematic sequencing of all X-chromosomal genes in a cohort of patients with genetic evidence for X-chromosome locus involvement may resolve up to 58% of Fragile X-negative cases.

Wrong-site nerve blocks: 10 yr experience in a large multihospital health-care system.

INTRODUCTION: Although wrong-site surgery has garnered extensive scrutiny, the incidence of wrong-site blocks remains unknown. Our study thus sought to quantify the incidence of wrong-site blocks and examine some of their associated risk factors in our multihospital health-care system. METHODS: Using quality-improvement and billing data, we quantified the total number of blocks and wrong-site blocks occurring between July 1, 2002 and June 30, 2012 within the University of Pittsburgh Medical Center Health System. The incidence of wrong-site block was determined by block type, hospital, and type of service involved in performing the block. The incidence of wrong-site block was compared with that of wrong-site surgery. Fisher's exact tests were performed to determine associations between the incidence of wrong-site block and any of the aforementioned variables. A root-cause analysis was performed to determine the source of wrong-site blocks after the implementation of a timeout policy. RESULTS: Of the 85 915 patients receiving blocks, 70 441 received only unilateral blocks, yielding an overall incidence of wrong-site block of 1.28 (95% confidence interval 0.43-2.13) per 10 000 patients receiving unilateral blocks. The incidence of wrong-site block was highest with femoral blocks, and differed from the incidence of wrong-site surgery. All occurrences of wrong-site block after the implementation of the timeout policy involved policy violations. CONCLUSIONS: Our study provides the first incidence data on wrong-site block in a large patient population and can help hospitals to develop policies based on these data. It is yet to be determined whether active intervention can eliminate this adverse event.

Emerging major synaptic signaling pathways involved in intellectual disability.

Genetic causes of intellectual disability (ID) include mutations in proteins with various functions. However, many of these proteins are enriched in synapses and recent investigations point out their crucial role in the subtle regulation of synaptic activity and dendritic spine morphogenesis. Moreover, in addition to genetic data, functional and animal model studies are providing compelling evidence that supports the emerging unifying synapse-based theory for cognitive deficit. In this review, we highlight ID-related gene products involved in synaptic morphogenesis and function, with a particular focus on the emergent signaling pathways involved in synaptic plasticity whose disruption results in cognitive deficit.

Isolation of a candidate gene for Menkes disease that encodes a potential heavy metal binding protein.

Menkes disease is a lethal-X linked recessive disorder associated with copper metabolism disturbance. We have recently mapped two chromosome breakpoints related to this disease in a 1 megabase yeast artificial chromosome contig at Xq13.3. We now report the construction of a phage contig and the isolation of candidate partial cDNAs for the Menkes disease gene. The candidate gene expresses an 8 kb message in all investigated tissues, and deletions were detected in 16% of 100 unrelated Menkes patients. The deduced partial protein sequence shared the GMTCXXC motif with bacterial metal resistance operons, suggesting a potential heavy metal binding protein. These findings should lead to more accurate prenatal diagnosis of this severe disease and a better understanding of the cellular homeostasis of essential heavy metals.

Mutations in ARHGEF6, encoding a guanine nucleotide exchange factor for Rho GTPases, in patients with X-linked mental retardation.

X-linked forms of mental retardation (XLMR) include a variety of different disorders and may account for up to 25% of all inherited cases of mental retardation. So far, seven X-chromosomal genes mutated in nonspecific mental retardation (MRX) have been identified: FMR2, GDI1, RPS6KA3, IL1RAPL, TM4SF2, OPHN1 and PAK3 (refs 2-9). The products of the latter two have been implicated in regulation of neural plasticity by controlling the activity of small GTPases of the Rho family. Here we report the identification of a new MRX gene, ARHGEF6 (also known as alphaPIX or Cool-2), encoding a protein with homology to guanine nucleotide exchange factors for Rho GTPases (Rho GEF). Molecular analysis of a reciprocal X/21 translocation in a male with mental retardation showed that this gene in Xq26 was disrupted by the rearrangement. Mutation screening of 119 patients with nonspecific mental retardation revealed a mutation in the first intron of ARHGEF6 (IVS1-11T-->C) in all affected males in a large Dutch family. The mutation resulted in preferential skipping of exon 2, predicting a protein lacking 28 amino acids. ARHGEF6 is the eighth MRX gene identified so far and the third such gene to encode a protein that interacts with Rho GTPases.

Mutations in GDI1 are responsible for X-linked non-specific mental retardation.

Rab GDP-dissociation inhibitors (GDI) are evolutionarily conserved proteins that play an essential role in the recycling of Rab GTPases required for vesicular transport through the secretory pathway. We have found mutations in the GDI1 gene (which encodes uGDI) in two families affected with X-linked non-specific mental retardation. One of the mutations caused a non-conservative substitution (L92P) which reduced binding and recycling of RAB3A, the second was a null mutation. Our results show that both functional and developmental alterations in the neuron may account for the severe impairment of learning abilities as a consequence of mutations in GDI1, emphasizing its critical role in development of human intellectual and learning abilities.

A new gene involved in X-linked mental retardation identified by analysis of an X;2 balanced translocation.

X-linked forms of mental retardation (MR) affect approximately 1 in 600 males and are likely to be highly heterogeneous. They can be categorized into syndromic (MRXS) and nonspecific (MRX) forms. In MRX forms, affected patients have no distinctive clinical or biochemical features. At least five MRX genes have been identified by positional cloning, but each accounts for only 0.5%-1.0% of MRX cases. Here we show that the gene TM4SF2 at Xp11.4 is inactivated by the X breakpoint of an X;2 balanced translocation in a patient with MR. Further investigation led to identification of TM4SF2 mutations in 2 of 33 other MRX families. RNA in situ hybridization showed that TM4SF2 is highly expressed in the central nervous system, including the cerebral cortex and hippocampus. TM4SF2 encodes a member of the tetraspanin family of proteins, which are known to contribute in molecular complexes including beta-1 integrins. We speculate that through this interaction, TM4SF2 might have a role in the control of neurite outgrowth.

A new member of the IL-1 receptor family highly expressed in hippocampus and involved in X-linked mental retardation.

We demonstrate here the importance of interleukin signalling pathways in cognitive function and the normal physiology of the CNS. Thorough investigation of an MRX critical region in Xp22.1-21.3 enabled us to identify a new gene expressed in brain that is responsible for a non-specific form of X-linked mental retardation. This gene encodes a 696 amino acid protein that has homology to IL-1 receptor accessory proteins. Non-overlapping deletions and a nonsense mutation in this gene were identified in patients with cognitive impairment only. Its high level of expression in post-natal brain structures involved in the hippocampal memory system suggests a specialized role for this new gene in the physiological processes underlying memory and learning abilities.

Unravelling the etiology of sporadic late-onset cerebellar ataxia in a cohort of 205 patients: a prospective study.

BACKGROUND: Despite recent progress in the field of genetics, sporadic late-onset (> 40 years) cerebellar ataxia (SLOCA) etiology remains frequently elusive, while the optimal diagnostic workup still needs to be determined. We aimed to comprehensively describe the causes of SLOCA and to discuss the relevance of the investigations. METHODS: We included 205 consecutive patients with SLOCA seen in our referral center. Patients were prospectively investigated using exhaustive clinical assessment, biochemical, genetic, electrophysiological, and imaging explorations. RESULTS: We established a diagnosis in 135 (66%) patients and reported 26 different causes for SLOCA, the most frequent being multiple system atrophy cerebellar type (MSA-C) (41%). Fifty-one patients (25%) had various causes of SLOCA including immune-mediated diseases such as multiple sclerosis or anti-GAD antibody-mediated ataxia; and other causes, such as alcoholic cerebellar degeneration, superficial siderosis, or Creutzfeldt-Jakob disease. We also identified 11 genetic causes in 20 patients, including SPG7 (n = 4), RFC1-associated CANVAS (n = 3), SLC20A2 (n = 3), very-late-onset Friedreich's ataxia (n = 2), FXTAS (n = 2), SCA3 (n = 1), SCA17 (n = 1), DRPLA (n = 1), MYORG (n = 1), MELAS (n = 1), and a mitochondriopathy (n = 1) that were less severe than MSA-C (p < 0.001). Remaining patients (34%) had idiopathic late-onset cerebellar ataxia which was less severe than MSA-C (p < 0.01). CONCLUSION: Our prospective study provides an exhaustive picture of the etiology of SLOCA and clues regarding yield of investigations and diagnostic workup. Based on our observations, we established a diagnostic algorithm for SLOCA.

Mutations of the UPF3B gene, which encodes a protein widely expressed in neurons, are associated with nonspecific mental retardation with or without autism.

Mutations in the UPF3B gene, which encodes a protein involved in nonsense-mediated mRNA decay, have recently been described in four families with specific (Lujan-Fryns and FG syndromes), nonspecific X-linked mental retardation (XLMR) and autism. To further elucidate the contribution of UPF3B to mental retardation (MR), we screened its coding sequence in 397 families collected by the EuroMRX consortium. We identified one nonsense mutation, c.1081C>T/p.Arg361(*), in a family with nonspecific MR (MRX62) and two amino-acid substitutions in two other, unrelated families with MR and/or autism (c.1136G>A/p.Arg379His and c.1103G>A/p.Arg368Gln). Functional studies using lymphoblastoid cell lines from affected patients revealed that c.1081C>T mutation resulted in UPF3B mRNA degradation and consequent absence of the UPF3B protein. We also studied the subcellular localization of the wild-type and mutated UPF3B proteins in mouse primary hippocampal neurons. We did not detect any obvious difference in the localization between the wild-type UPF3B and the proteins carrying the two missense changes identified. However, we show that UPF3B is widely expressed in neurons and also presents in dendritic spines, which are essential structures for proper neurotransmission and thus learning and memory processes. Our results demonstrate that in addition to Lujan-Fryns and FG syndromes, UPF3B protein truncation mutations can cause also nonspecific XLMR. We also identify comorbidity of MR and autism in another family with UPF3B mutation. The neuronal localization pattern of the UPF3B protein and its function in mRNA surveillance suggests a potential function in the regulation of the expression and degradation of various mRNAs present at the synapse.

Cell cloning-based transcriptome analysis in Rett patients: relevance to the pathogenesis of Rett syndrome of new human MeCP2 target genes.

More than 90% of Rett syndrome (RTT) patients have heterozygous mutations in the X-linked methyl-CpG binding protein 2 (MECP2) gene that encodes the methyl-CpG-binding protein 2, a transcriptional modulator. Because MECP2 is subjected to X chromosome inactivation (XCI), girls with RTT either express the wild-type or mutant allele in each individual cell. To test the consequences of MECP2 mutations resulting from a genome-wide transcriptional dysregulation and to identify its target genes in a system that circumvents the functional mosaicism resulting from XCI, we carried out gene expression profiling of clonal populations derived from fibroblast primary cultures expressing exclusively either the wild-type or the mutant MECP2 allele. Clonal cultures were obtained from skin biopsy of three RTT patients carrying either a non-sense or a frameshift MECP2 mutation. For each patient, gene expression profiles of wild-type and mutant clones were compared by oligonucleotide expression microarray analysis. Firstly, clustering analysis classified the RTT patients according to their genetic background and MECP2 mutation. Secondly, expression profiling by microarray analysis and quantitative RT-PCR indicated four up-regulated genes and five down-regulated genes significantly dysregulated in all our statistical analysis, including excellent potential candidate genes for the understanding of the pathophysiology of this neurodevelopmental disease. Thirdly, chromatin immunoprecipitation analysis confirmed MeCP2 binding to respective CpG islands in three out of four up-regulated candidate genes and sequencing of bisulphite-converted DNA indicated that MeCP2 preferentially binds to methylated-DNA sequences. Most importantly, the finding that at least two of these genes (BMCC1 and RNF182) were shown to be involved in cell survival and/or apoptosis may suggest that impaired MeCP2 function could alter the survival of neurons thus compromising brain function without inducing cell death.

Continuous peripheral nerve blocks in acute pain management.

The indications for continuous nerve blocks for the perioperative pain management in hospitalized and ambulatory patients have extended well beyond orthopaedics. These techniques are not only used to control pain in patients undergoing major upper and lower extremity surgery, but also to provide perioperative analgesia in patients undergoing abdominal, plastic, urological, gynaecological, thoracic, and trauma surgeries. Infusion regimens of local anaesthetics and supplements must take into consideration the condition of the patient before and after surgery, the nature and intensity of the surgical stress associated with the surgery, and the possible need for immediate functional recovery. Continuous nerve blocks have proved safe and effective in reducing opioid consumption and related side-effects, accelerating recovery, and in many patients reducing the length of hospital stay. Continuous nerve blocks provide a safer alternative to epidural analgesia in patients receiving thromboprophylaxis, especially with low molecular-weight heparin.

Impairment of CDKL5 nuclear localisation as a cause for severe infantile encephalopathy.

Mutations in the human X-linked cyclin-dependent kinase-like 5 (CDKL5) gene have been shown to cause infantile spasms as well as Rett syndrome-like phenotype. To date, fewer than 20 different mutations have been reported. So far, no clear genotype-phenotype correlation has been established. We screened the entire coding region of CDKL5 in 151 affected girls with a clinically heterogeneous phenotype ranging from encephalopathy with epilepsy to atypical Rett syndrome by denaturing high liquid performance chromatography and direct sequencing, and we identified three novel missense mutations located in catalytic domain (p.Ala40Val, p.Arg65Gln, p.Leu220Pro). Segregation analysis showed that p.Arg65Gln was inherited from the healthy father, which rules out the involvement of CDKL5 in the aetiology of the phenotype in this patient. However, the de novo occurrence was shown for p.Ala40Val and p.Leu220Pro. The p.Ala40Val mutation was observed in two unrelated patients and represented the first recurrent mutation in the CDKL5 gene. For the two de novo mutations, we analysed the cellular localisation of the wild-type and CDKL5 mutants by transfection experiments. We showed that the two CDKL5 mutations cause mislocalisation of the mutant CDKL5 proteins in the cytoplasm. Interestingly these missense mutations that result in a mislocalisation of the CDKL5 protein are associated with severe developmental delay which was apparent within the first months of life characterised by early and generalised hypotonia, and autistic features, and as well as early infantile spasms.

Refinement of cortical dysgeneses spectrum associated with TUBA1A mutations.

OBJECTIVE: We have recently shown that de novo mutations in the TUBA1A gene are responsible for a wide spectrum of neuronal migration disorders. To better define the range of these abnormalities, we searched for additional mutations in a cohort of 100 patients with lissencephaly spectrum for whom no mutation was identified in DCX, LIS1 and ARX genes and compared these data to five previously described patients with TUBA1A mutations. RESULTS: We detected de novo TUBA1A mutations in six patients and highlight the existence of a prominent form of TUBA1A related lissencephaly. In four patients, the mutations identified, c.1190T>C (p.L397P), c.1265G>A (p.R422H), c.1264C>T (p.R422C), c.1306G>T (p.G436R), have not been reported before and in two others, the mutation corresponds to a recurrent missense mutation, c.790C>T (p.R264C), likely to be a hot spot of mutation. All together, it emerges that the TUBA1A related lissencephaly spectrum ranges from perisylvian pachygyria, in the less severe form, to posteriorly predominant pachygyria in the most severe, associated with dysgenesis of the anterior limb of the internal capsule and mild to severe cerebellar hypoplasia. When compared with a large series of lissencephaly of other origins (ILS17, ILSX or unknown origin), these features appear to be specific to TUBA1A related lissencephaly. In addition, TUBA1A mutated patients share a common clinical phenotype that consists of congenital microcephaly, mental retardation and diplegia/tetraplegia. CONCLUSIONS: Our data highlight the presence of consistent and specific abnormalities that should allow the differentiation of TUBA1A related lissencephalies from those related to LIS1, DCX and ARX genes.

Doublecortin is a developmentally regulated, microtubule-associated protein expressed in migrating and differentiating neurons.

Recently, we and others reported that the doublecortin gene is responsible for X-linked lissencephaly and subcortical laminar heterotopia. Here, we show that Doublecortin is expressed in the brain throughout the period of corticogenesis in migrating and differentiating neurons. Immunohistochemical studies show its localization in the soma and leading processes of tangentially migrating neurons, and a strong axonal labeling is observed in differentiating neurons. In cultured neurons, Doublecortin expression is highest in the distal parts of developing processes. We demonstrate by sedimentation and microscopy studies that Doublecortin is associated with microtubules (MTs) and postulate that it is a novel MAP. Our data suggest that the cortical dysgeneses associated with the loss of Doublecortin function might result from abnormal cytoskeletal dynamics in neuronal cell development.

International normalized ratio and prothrombin time values before the removal of a lumbar plexus catheter in patients receiving warfarin after total hip replacement.

BACKGROUND: There is a paucity of data regarding the coagulation status when discontinuing perineural catheters in patients receiving anticoagulant after operation. This retrospective study was designed to establish international normalized ratio (INR) and prothrombin time (PT) at the time of removal of lumbar plexus perineural catheters in patients receiving warfarin after total hip replacement. METHODS: Patients who received a continuous lumbar plexus nerve block for postoperative analgesia and received warfarin after total hip surgery between August 2002 and June 2007 were included in this retrospective study. PT and INRs were recorded before surgery and every day after operation along with any post-surgical nerve injury and bleeding related to the removal of the perineural catheter. RESULTS: Six hundred and seventy patients met the inclusion criteria. Almost all lumbar plexus catheters (89%) were removed on postoperative day 2. At the time of the perineural catheter removal, 36.2% of patients had an INR >1.4 (range: 1.5-3.9). One case of local bleeding was recorded at the time of the catheter removal with an INR of 3.0. This was managed with a direct pressure at the site. CONCLUSIONS: Although in this retrospective analysis, we demonstrated that lumbar plexus catheters were removed with an INR > or =1.5, additional data are required to confirm the safety of such an approach.