Genomic analyses in Cornelia de Lange Syndrome and related diagnoses: Novel candidate genes, genotype-phenotype correlations and common mechanisms.

Cornelia de Lange Syndrome (CdLS) is a rare, dominantly inherited multisystem developmental disorder characterized by highly variable manifestations of growth and developmental delays, upper limb involvement, hypertrichosis, cardiac, gastrointestinal, craniofacial, and other systemic features. Pathogenic variants in genes encoding cohesin complex structural subunits and regulatory proteins (NIPBL, SMC1A, SMC3, HDAC8, and RAD21) are the major pathogenic contributors to CdLS. Heterozygous or hemizygous variants in the genes encoding these five proteins have been found to be contributory to CdLS, with variants in NIPBL accounting for the majority (>60%) of cases, and the only gene identified to date that results in the severe or classic form of CdLS when mutated. Pathogenic variants in cohesin genes other than NIPBL tend to result in a less severe phenotype. Causative variants in additional genes, such as ANKRD11, EP300, AFF4, TAF1, and BRD4, can cause a CdLS-like phenotype. The common role that these genes, and others, play as critical regulators of developmental transcriptional control has led to the conditions they cause being referred to as disorders of transcriptional regulation (or "DTRs"). Here, we report the results of a comprehensive molecular analysis in a cohort of 716 probands with typical and atypical CdLS in order to delineate the genetic contribution of causative variants in cohesin complex genes as well as novel candidate genes, genotype-phenotype correlations, and the utility of genome sequencing in understanding the mutational landscape in this population.

Overcoming chemotherapy drug resistance by targeting inhibitors of apoptosis proteins (IAPs).

Inhibitors of apoptosis (IAPs) are a family of proteins that play a significant role in the control of programmed cell death (PCD). PCD is essential to maintain healthy cell turnover within tissue but also to fight disease or infection. Uninhibited, IAPs can suppress apoptosis and promote cell cycle progression. Therefore, it is unsurprising that cancer cells demonstrate significantly elevated expression levels of IAPs, resulting in improved cell survival, enhanced tumor growth and subsequent metastasis. Therapies to target IAPs in cancer has garnered substantial scientific interest and as resistance to anti-cancer agents becomes more prevalent, targeting IAPs has become an increasingly attractive strategy to re-sensitize cancer cells to chemotherapies, antibody based-therapies and TRAIL therapy. Antagonism strategies to modulate the actions of XIAP, cIAP1/2 and survivin are the central focus of current research and this review highlights advances within this field with particular emphasis upon the development and specificity of second mitochondria-derived activator of caspase (SMAC) mimetics (synthetic analogs of endogenously expressed inhibitors of IAPs SMAC/DIABLO). While we highlight the potential of SMAC mimetics as effective single agent or combinatory therapies to treat cancer we also discuss the likely clinical implications of resistance to SMAC mimetic therapy, occasionally observed in cancer cell lines.

Calcium-regulatory proteins as modulators of chemotherapy in human neuroblastoma.

Neuroblastoma (NB) is a pediatric cancer treated with poly-chemotherapy including platinum complexes (e.g. cisplatin (CDDP), carboplatin), DNA alkylating agents, and topoisomerase I inhibitors (e.g. topotecan (TOPO)). Despite aggressive treatment, NB may become resistant to chemotherapy. We investigated whether CDDP and TOPO treatment of NB cells interacts with the expression and function of proteins involved in regulating calcium signaling. Human neuroblastoma cell lines SH-SY5Y, IMR-32 and NLF were used to investigate the effects of CDDP and TOPO on cell viability, apoptosis, calcium homeostasis, and expression of selected proteins regulating intracellular calcium concentration ([Ca2+]i). In addition, the impact of pharmacological inhibition of [Ca2+]i-regulating proteins on neuroblastoma cell survival was studied. Treatment of neuroblastoma cells with increasing concentrations of CDDP (0.1-10 µM) or TOPO (0.1 nM-1 µM) induced cytotoxicity and increased apoptosis in a concentration- and time-dependent manner. Both drugs increased [Ca2+]i over time. Treatment with CDDP or TOPO also modified mRNA expression of selected genes encoding [Ca2+]i-regulating proteins. Differentially regulated genes included S100A6, ITPR1, ITPR3, RYR1 and RYR3. With FACS and confocal laser scanning microscopy experiments we validated their differential expression at the protein level. Importantly, treatment of neuroblastoma cells with pharmacological modulators of [Ca2+]i-regulating proteins in combination with CDDP or TOPO increased cytotoxicity. Thus, our results confirm an important role of calcium signaling in the response of neuroblastoma cells to chemotherapy and suggest [Ca2+]i modulation as a promising strategy for adjunctive treatment.

G-Protein-Coupled Receptor 35 Mediates Human Saphenous Vein Vascular Smooth Muscle Cell Migration and Endothelial Cell Proliferation.

Vascular smooth muscle cell (VSMC) migration and proliferation is central to neointima formation in vein graft failure following coronary artery bypass. However, there are currently no pharmacological interventions that prevent vein graft failure through intimal occlusion. It is hence a therapeutic target. Here, we investigated the contribution of GPR35 to human VSMC and endothelial cell (EC) migration, using a scratch-wound assay, and also the contribution to proliferation, using MTS and BrdU assays, in in vitro models using recently characterized human GPR35 ortholog-selective small-molecule agonists and antagonists. Real-time PCR studies showed GPR35 to be robustly expressed in human VSMCs and ECs. Stimulation of GPR35, with either the human-selective agonist pamoic acid or the reference agonist zaprinast, promoted VSMC migration in the scratch-wound assay. These effects were blocked by coincubation with either of the human GPR35-specific antagonists, CID-2745687 or ML-145. These GPR35-mediated effects were produced by inducing alterations in the actin cytoskeleton via the Rho A/Rho kinase signaling axis. Additionally, the agonist ligands stimulated a proliferative response in ECs. These studies highlight the potential that small molecules that stimulate or block GPR35 activity can modulate vascular proliferation and migration. These data propose GPR35 as a translational therapeutic target in vascular remodeling.

The antiallergic mast cell stabilizers lodoxamide and bufrolin as the first high and equipotent agonists of human and rat GPR35.

Lack of high potency agonists has restricted analysis of the G protein-coupled receptor GPR35. Moreover, marked variation in potency and/or affinity of current ligands between human and rodent orthologs of GPR35 has limited their productive use in rodent models of physiology. Based on the reported modest potency of the antiasthma and antiallergic ligands cromolyn disodium and nedocromil sodium, we identified the related compounds lodoxamide and bufrolin as high potency agonists of human GPR35. Unlike previously identified high potency agonists that are highly selective for human GPR35, both lodoxamide and bufrolin displayed equivalent potency at rat GPR35. Further synthetic antiallergic ligands, either sharing features of the standard surrogate agonist zaprinast, or with lodoxamide and bufrolin, were also shown to display agonism at either human or rat GPR35. Because both lodoxamide and bufrolin are symmetric di-acids, their potential mode of binding was explored via mutagenesis based on swapping between the rat and human ortholog nonconserved arginine residues within proximity of a key conserved arginine at position 3.36. Computational modeling and ligand docking predicted the contributions of different arginine residues, other than at 3.36, in human GPR35 for these two ligands and were consistent with selective loss of potency of either bufrolin or lodoxamide at distinct arginine mutants. The computational models also suggested that bufrolin and lodoxamide would display reduced potency at a low-frequency human GPR35 single nucleotide polymorphism. This prediction was confirmed experimentally.

Novel, complex interruptions of the GAA repeat in small, expanded alleles of two affected siblings with late-onset Friedreich ataxia.

Friedreich ataxia (FA) is an autosomal recessive disorder associated with expanded GAA repeats in intron 1 of the FRDA gene. Two siblings presented with a mild form of FA at >60 years of age. Both had a large expansion (>600 repeats) and a small expansion (120 repeats) by long-range PCR. Sequence analysis of the small allele revealed multiple, complex interruptions in the GAA repeat. These 2 patients presented later than predicted from their allele size alone, when compared with a large cohort of FA patients. Accounting for the interruptions in the GAA repeat, though, did not make the age of onset consistent with that noted in other patients. Three additional patients with late onset FA and small expanded alleles also exhibited interrupted GAA repeats that were not associated with inappropriately late onset. Our observations suggest that interrupted GAA repeats do not clearly impact the age of onset in FA.

Additional clinical manifestations in children with sensorineural hearing loss and biallelic GJB2 mutations: who should be offered GJB2 testing?

Sensorineural hearing loss (SNHL), the most common sensory impairment noted at birth, occurs in 3 out of every 1,000 births live births. At least half of congenital SNHL is genetic in origin, with nonsyndromic, or isolated hearing loss, accounting for approximately 70% of the total genetic causes. Syndromic hearing loss (hearing loss associated with other clinical findings) makes up the remaining 30%. Worldwide, mutations in the gap junction beta 2 (GJB2) gene, encoding the connexin 26 (Cx26) protein, are responsible for approximately 30% of all cases of childhood SNHL. GJB2 mutations have been primarily associated with nonsyndromic forms of bilateral SNHL although rare syndromic forms involving dermatologic manifestations have also been reported. In general, unless skin findings are present, children with bilateral SNHL and other structural or developmental abnormalities are not generally thought of as candidates for GJB2 testing. We evaluated 163 individuals with biallelic GJB2 mutations and SNHL for the presence of other clinical findings. Twenty-nine of the 163 (18%) were found to have structural and/or developmental abnormalities in addition to the SNHL and four subjects had diagnoses that were felt to account for their hearing loss prior to being screened for GJB2 mutations. Although the GJB2 mutations are likely not responsible for these additional clinical manifestations, this study underscores the importance of considering GJB2 mutational analysis in individuals with more than just isolated SNHL given the high prevalence of GJB2-related hearing loss.

Ophthalmologic findings in Cornelia de Lange syndrome: a genotype-phenotype correlation study.

OBJECTIVE: To evaluate individuals with Cornelia de Lange syndrome previously screened for mutations in the NIPBL gene for genotype-phenotype correlations with regard to severity of ophthalmologic findings. METHODS: Fifty-four patients with Cornelia de Lange syndrome (26 mutation positive and 28 mutation negative) with varying extent and severity of ophthalmologic findings participated in the study. We conducted a retrospective analysis of ophthalmologic data obtained through survey responses and medical records. The severity of nasolacrimal duct obstruction, myopia, ptosis, and strabismus was classified. The severity of eye findings was compared relative to the presence vs the absence of mutations in the coding region of NIPBL and relative to mutations predicted to result in a truncated protein (nonsense and frameshift mutations) vs missense mutations. Fisher exact test was used to determine the significance of these correlations. RESULTS: A trend toward increased ptosis severity was found among individuals with truncating (nonsense and frameshift) mutations compared with individuals with missense mutations (P = .07). CONCLUSION: NIPBL may be directly involved in ptosis pathogenesis. CLINICAL RELEVANCE: Elucidating the pathogenetic mechanisms of ophthalmologic morbidities in patients with de Lange syndrome may lead to more effective treatment.

Outcomes of clinical examination and genetic testing of 500 individuals with hearing loss evaluated through a genetics of hearing loss clinic.

Hearing loss (HL) occurs in approximately 2 out of every 1,000 births and is genetic in origin in approximately 50% of cases. This high incidence coupled with the increasing number of genes implicated in HL and the trend toward universal newborn screening led to the establishment of the Genetics of Hearing Loss Clinic at The Children's Hospital of Philadelphia to manage the diagnosis, genetic screening, and counseling of families with an affected child. To date 500 individuals have been evaluated from 1999 to 2004. To determine the cause of their HL and screen for syndromic forms of HL, individuals were offered a panel of tests. Depending on the type and severity of the HL, recommendations included GJB2 mutation analysis, renal and thyroid function studies, a CT scan of the temporal bones, an ophthalmology evaluation, an EKG, and, at times, additional genetic tests. Of the 500 patients evaluated 70 (14%) had a syndromic etiology for their HL. Twenty-eight different syndromic etiologies were identified. Enlarged vestibular aqueducts (EVAs) and/or Mondini malformations were seen in 18% of individuals with HL who had a CT or MRI of the temporal bones. Genetic testing of the GJB2 gene was completed for 310 of the 377 patients with bilateral sensorineural HL (82.2%). Nineteen different variants were identified in the GJB2 gene. Through GJB2 mutational analysis, clinical examination, and laboratory testing, a definitive etiologic diagnosis was established in 110/500 (22%) of patients.

Precocious sister chromatid separation (PSCS) in Cornelia de Lange syndrome.

The Cornelia de Lange syndrome (CdLS) (OMIM# 122470) is a dominantly inherited multisystem developmental disorder. The phenotype consists of characteristic facial features, hirsutism, abnormalities of the upper extremities ranging from subtle changes in the phalanges and metacarpal bones to oligodactyly and phocomelia, gastroesophageal dysfunction, growth retardation, and neurodevelopmental delay. Prevalence is estimated to be as high as 1 in 10,000. Recently, mutations in NIPBL were identified in sporadic and familial CdLS cases. To date, mutations in this gene have been identified in over 45% of individuals with CdLS. NIPBL is the human homolog of the Drosophila Nipped-B gene. Although its function in mammalian systems has not yet been elucidated, sequence homologs of Nipped-B in yeast (Scc2 and Mis4) are required for sister chromatid cohesion during mitosis, and a similar role was recently demonstrated for Nipped-B in Drosophila. In order to evaluate NIPBL role in sister chromatid cohesion in humans, metaphase spreads on 90 probands (40 NIPBL mutation positive and 50 NIPBL mutation negative) with CdLS were evaluated for evidence of precocious sister chromatid separation (PSCS). We screened 50 metaphases from each proband and found evidence of PSCS in 41% (compared to 9% in control samples). These studies indicate that NIPBL may play a role in sister chromatid cohesion in humans as has been reported for its homologs in Drosophila and yeast.

NIPBL mutational analysis in 120 individuals with Cornelia de Lange syndrome and evaluation of genotype-phenotype correlations.

The Cornelia de Lange syndrome (CdLS) is a multisystem developmental disorder characterized by facial dysmorphia, upper-extremity malformations, hirsutism, cardiac defects, growth and cognitive retardation, and gastrointestinal abnormalities. Both missense and protein-truncating mutations in NIPBL, the human homolog of the Drosophila melanogaster Nipped-B gene, have recently been reported to cause CdLS. The function of NIPBL in mammals is unknown. The Drosophila Nipped-B protein facilitates long-range enhancer-promoter interactions and plays a role in Notch signaling and other developmental pathways, as well as being involved in mitotic sister-chromatid cohesion. We report the spectrum and distribution of NIPBL mutations in a large well-characterized cohort of individuals with CdLS. Mutations were found in 56 (47%) of 120 unrelated individuals with sporadic or familial CdLS. Statistically significant phenotypic differences between mutation-positive and mutation-negative individuals were identified. Analysis also suggested a trend toward a milder phenotype in individuals with missense mutations than in those with other types of mutations.

Subunit-specific regulation of NMDA receptor endocytosis.

At excitatory synapses, both NMDA and AMPA receptors are localized to the postsynaptic density (PSD). However, unlike AMPA receptors, synaptic NMDA receptors are stable components of the PSD. Even so, surface-expressed NMDA receptors undergo endocytosis, which is more robust early in development and declines during synaptic development. We investigated the subunit-specific contributions to NMDA receptor endocytosis, specifically defining the endocytic motifs and endocytic pathways preferred by the NR2A and NR2B subunits. We find that NR2A and NR2B have distinct endocytic motifs encoded in their distal C termini and that these interact with clathrin adaptor complexes with differing affinities. We also find that NR2A and NR2B sort into different intracellular pathways after endocytosis, with NR2B preferentially trafficking through recycling endosomes. In mature cultures, we find that NR2B undergoes more robust endocytosis than NR2A, consistent with previous studies showing that NR2A is more highly expressed at stable synaptic sites. Our findings demonstrate fundamental differences between NR2A and NR2B that help clarify developmental changes in NMDA receptor trafficking and surface expression.

Cornelia de Lange syndrome is caused by mutations in NIPBL, the human homolog of Drosophila melanogaster Nipped-B.

Cornelia de Lange syndrome (CdLS; OMIM 122470) is a dominantly inherited multisystem developmental disorder characterized by growth and cognitive retardation; abnormalities of the upper limbs; gastroesophageal dysfunction; cardiac, ophthalmologic and genitourinary anomalies; hirsutism; and characteristic facial features. Genital anomalies, pyloric stenosis, congenital diaphragmatic hernias, cardiac septal defects, hearing loss and autistic and self-injurious tendencies also frequently occur. Prevalence is estimated to be as high as 1 in 10,000 (ref. 4). We carried out genome-wide linkage exclusion analysis in 12 families with CdLS and identified four candidate regions, of which chromosome 5p13.1 gave the highest multipoint lod score of 2.7. This information, together with the previous identification of a child with CdLS with a de novo t(5;13)(p13.1;q12.1) translocation, allowed delineation of a 1.1-Mb critical region on chromosome 5 for the gene mutated in CdLS. We identified mutations in one gene in this region, which we named NIPBL, in four sporadic and two familial cases of CdLS. We characterized the genomic structure of NIPBL and found that it is widely expressed in fetal and adult tissues. The fly homolog of NIPBL, Nipped-B, facilitates enhancer-promoter communication and regulates Notch signaling and other developmental pathways in Drosophila melanogaster.

Differential binding of the AP-2 adaptor complex and PSD-95 to the C-terminus of the NMDA receptor subunit NR2B regulates surface expression.

NMDA receptor expression on the plasma membrane and at synaptic sites is tightly regulated. We have recently shown that the NMDA receptor subunit NR2B has an endocytic motif contained within its C-terminus. We now identify this motif as a consensus tyrosine-based motif (YEKL) and demonstrate that this sequence binds directly to the medium chain of the AP-2 adaptor, a protein complex that links internalized proteins to clathrin. Although the AP-2 binding site on NR2B is adjacent to the PSD-95 binding site, it is distinct, as mutation of tyrosine 1472 of the endocytic motif disrupts AP-2 binding but not binding to PSD-95. Internalization assays reveal that like PSD-95, both SAP97 and PSD-93 inhibit NR2B-mediated endocytosis. Furthermore, we find that co-expression of a PSD-95 mutant that is unable to cluster NMDA receptors also inhibits NR2B-mediated endocytosis. Together, these data demonstrate that AP-2 and PSD-95 bind to unique sites on the C-terminus of NR2B and have antagonistic functional consequences that are independent of the ability of the PSD-95 to cluster receptors on the plasma membrane.

Trafficking and surface expression of the glutamate receptor subunit, KA2.

Kainate receptors are a class of ionotropic glutamate receptors that are widely expressed in the mammalian brain, yet little is known about their physiological role or the mechanisms by which they are regulated. Kainate receptors are composed of multiple subunits (GluR5-7; KA1-2), which can combine to form homomeric or heteromeric channels. While the kainate receptor subunit KA2 can combine with GluR5-7 to form heteromeric channels, it does not form functional homomeric channels when expressed alone. In an attempt to identify the molecular mechanisms for this, we have characterized the trafficking and surface expression of KA2. We find that KA2 alone does not traffic to the plasma membrane and is retained in the endoplasmic reticulum (ER). In contrast, co-expression with GluR6 disrupts ER-retention of KA2 and allows plasma membrane expression. Using a chimeric reporter protein we have identified an ER-retention motif within the KA2 cytosolic domain. Recent studies have identified a consensus ER-retention motif (RRR) that is contained within both the NMDA receptor NR1 subunit and K(+) channels. While KA2 contains a similar stretch of amino acids within its C-terminus (RRRRR), unlike the NR1 motif, disruption of this motif with alternating glutamic acid residues does not disrupt ER-retention of KA2, suggesting a unique mechanism regulating KA2 surface expression.

Different nematocytes have different synapses in the sea anemone Aiptasia pallida (Cnidaria, Anthozoa).

Sea anemones feed by discharging nematocysts into their prey, but the pathway for control of nematocyst discharge is unknown. The purpose of this study was to investigate the ultrastructural evidence of neuro-nematocyte synapses and to determine the types of synaptic vesicles present at different kinds of nematocyst-containing cells. The tip and middle of tentacles from small specimens of Aiptasia pallida were prepared for electron microscopy and serial micrographs were examined. We found clear vesicles in synapses on mastigophore-containing nematocytes and dense-cored vesicles in synapses on basitrich-containing nematocytes and on one cnidoblast with a developing nematocyst. In addition, we found reciprocal neuro-neuronal and sequential neuro-neuro-nematocyte synapses in which dense-cored vesicles were present. It was concluded that : (1) neuro-nematocyte synapses are present in sea anemones, (2) different kinds of synaptic vesicles are present at cells containing different types of nematocysts, (3) synapses are present on cnidoblasts before the developing nematocyst can be identified and these synapses may have a trophic influence on nematocyst differentiation, and (4) both reciprocal and sequential synapses are present at the nematocyte, suggesting a complex pathway for neural control of nematocyst discharge. J. Morphol. 238:53-62, 1998. © 1998 Wiley-Liss, Inc.