Methylation Defect in Imprinted Genes Detected in Patients with an Albright's Hereditary Osteodystrophy Like Phenotype and Platelet Gs Hypofunction

Pseudohypoparathyroidism (PHP) indicates a group of heterogeneous disorders whose common feature is represented by impaired signaling of hormones that activate Gsalpha, encoded by the imprinted GNAS gene. PHP-Ib patients have isolated Parathormone (PTH) resistance and GNAS epigenetic defects while PHP-Ia cases present with hormone resistance and characteristic features jointly termed as Albright's Hereditary Osteodystrophy (AHO) due to maternally inherited GNAS mutations or similar epigenetic defects as found for PHP-Ib. Pseudopseudohypoparathyroidism (PPHP) patients with an AHO phenotype and no hormone resistance and progressive osseous heteroplasia (POH) cases have inactivating paternally inherited GNAS mutations.We here describe 17 subjects with an AHO-like phenotype that could be compatible with having PPHP but none of them carried Gsalpha mutations. Functional platelet studies however showed an obvious Gs hypofunction in the 13 patients that were available for testing. Methylation for the three differentially methylated GNAS regions was quantified via the Sequenom EpiTYPER. Patients showed significant hypermethylation of the XL amplicon compared to controls (36 ± 3 vs. 29 ± 3%; p<0.001); a pattern that is reversed to XL hypomethylation found in PHPIb. Interestingly, XL hypermethylation was associated with reduced XLalphaS protein levels in the patients' platelets. Methylation for NESP and ExonA/B was significantly different for some but not all patients, though most patients have site-specific CpG methylation abnormalities in these amplicons. Since some AHO features are present in other imprinting disorders, the methylation of IGF2, H19, SNURF and GRB10 was quantified. Surprisingly, significant IGF2 hypermethylation (20 ± 10 vs. 14 ± 7%; p<0.05) and SNURF hypomethylation (23 ± 6 vs. 32 6%; p<0.001) was found in patients vs. controls, while H19 and GRB10 methylation was normal.In conclusion, this is the first report of methylation defects including GNAS in patients with an AHO-like phenotype without endocrinological abnormalities. Additional studies are still needed to correlate the methylation defect with the clinical phenotype

De novo TBR1 variants cause a neurocognitive phenotype with ID and autistic traits:report of 25 new individuals and review of the literature

TBR1, a T-box transcription factor expressed in the cerebral cortex, regulates the expression of several candidate genes for autism spectrum disorders (ASD). Although TBR1 has been reported as a high-confidence risk gene for ASD and intellectual disability (ID) in functional and clinical reports since 2011, TBR1 has only recently been recorded as a human disease gene in the OMIM database. Currently, the neurodevelopmental disorders and structural brain anomalies associated with TBR1 variants are not well characterized. Through international data sharing, we collected data from 25 unreported individuals and compared them with data from the literature. We evaluated structural brain anomalies in seven individuals by analysis of MRI images, and compared these with anomalies observed in TBR1 mutant mice. The phenotype included ID in all individuals, associated to autistic traits in 76% of them. No recognizable facial phenotype could be identified. MRI analysis revealed a reduction of the anterior commissure and suggested new features including dysplastic hippocampus and subtle neocortical dysgenesis. This report supports the role of TBR1 in ID associated with autistic traits and suggests new structural brain malformations in humans. We hope this work will help geneticists to interpret TBR1 variants and diagnose ASD probands

Rare variants in NR2F2 cause congenital heart defects in humans

Congenital heart defects (CHDs) are the most common birth defect worldwide and are a leading cause of neonatal mortality. Nonsyndromic atrioventricular septal defects (AVSDs) are an important subtype of CHDs for which the genetic architecture is poorly understood. We performed exome sequencing in 13 parent-offspring trios and 112 unrelated individuals with nonsyndromic AVSDs and identified five rare missense variants (two of which arose de novo) in the highly conserved gene NR2F2, a very significant enrichment (p = 7.7 × 10?7) compared to 5,194 control subjects. We identified three additional CHD-affected families with other variants in NR2F2 including a de novo balanced chromosomal translocation, a de novo substitution disrupting a splice donor site, and a 3 bp duplication that cosegregated in a multiplex family. NR2F2 encodes a pleiotropic developmental transcription factor, and decreased dosage of NR2F2 in mice has been shown to result in abnormal development of atrioventricular septa. Via luciferase assays, we showed that all six coding sequence variants observed in individuals significantly alter the activity of NR2F2 on target promoters

Clinical utility gene card for: DiGeorge syndrome, velocardiofacial syndrome, Shprintzen syndrome, chromosome 22q11.2 deletion syndrome (22q11.2, TBX1)

status: publishe

Radiotracer Studies of the Fluorine Bond Lability of Some Binary Fluorides

Fluorine bond lability with respect to exchange is an important chemical property of binary fluorides. This can be useful in predicting new synthetic routes for derivatives of fluorine compounds or elucidating the mechanisms of processes taking place at fluorinated surfaces. In the present study fluorine bond lability with respect to exchange of some fluoroanions namely, boron, phosphorus, arsenic, antimony, niobium and tantalum has been investigated during their interaction with [18F]-labelled hexafluorides of molybdenum, tungsten and uranium in acetonitrile. Two distinct types of exchange behaviour are identified among the fluoroanions. It is firmly established that the M-F bond (M = B,P, Nb and Ta) in BF4-, PF6-, NbF6 and TaF6- is labile with respect to exchange whereas the As-F and Sb-F bonds in AsF6- and SbF6- are inert although AsF6- is found to exchange in the presence of UF5 18F under the same conditions. The latter result is consistent with the higher fluoride ion affinity of UF6 as compared with that of MoF6 or WF6. An associative mechanism is used to account for the fluorine exchange of BF4-, PF6- NbF6-, TaF6- and AsF6- although a dissociative mechanism can not be ruled out. The difference in the fluoride bond lability among the fluoroanions under investigation is consistent with the difference in the Lewis acidity order of their parent fluorides. Evidence for the existence of the heptafluoromolybdate(VI) ion in solution has been obtained for the first time in this study by reaction between CsF and MoF5 18F in MeCN. The existence of the heptafluorotungstate(VI) ion in solution is confirmed by reaction between CsF and WF5 18F in MeCN. Both ions are assigned in the symmetry. The fluorine bond lability with respect to exchange of MoF7- and WF7- has been investigated both under homogeneous (MeCN) and heterogeneous (gas plus solid) conditions in the presence of MF5 18F (M = Mo, W or U). The WF7- ion has been used as its copper(II), thallium(I), nitrosonium and caesium salts whereas MoF7- ion has been used as its caesium salt only. All systems are found to undergo rapid and complete [18F]-fluorine exchange with MF518F (M = Mo or W) in MeCN at room temperature and below (253K). The nature of the cation does not have any effect on the exchange behaviour of the systems. However under heterogeneous conditions the same systems undergo partial exchange in the presence of MF5 18F (M = Mo, W or U). In MeCN the experimental observations are consistent with, but do not prove, a displacement mechanism for the exchange and an associative mechanism can not be ruled out. Under hetero- geneous conditions fluorine exchange is best accounted for by an associative mechanism. The partial exchange of [ 18F]-fluorine is ascribed to the anion-cation interaction. The reaction between activated caesium fluoride and MF5-18F (M = Mo, W and U) results in the formation of more than one species, MoF7- , WF7- and UF8 2- being the major ones. The formation of more than one species is ascribed to the lack of uniformity of the surface reactions. The amount of hexa- fluoroacetone used during the activation of CsF is found to have a direct effect on its reactivity and most probably its surface area. [ 18F]-Fluorine exchange is observed only when uptakes of MF6 are considerable. The exchange is shown to take place between the adsorbed species and free hexafluorides. An associative mechanism similar to that between MF7- (M = Mo or W) and MF518F (M= Mo,W or U)under heterogeneous conditions is used to account for the exchange between adsorbed species and free MF518F (M = Mo, W). The interaction of MF518F (M = Mo, W and U) with CuF2 and T1F under heterogeneous conditions results in a smaller uptake and [18F]-fluorine exchange in the case of CuF2 as compared with T1F. In neither case has it been possible to determine the nature of the adsorbed species. The difference in affinity for the hexafluorides between T1F and CuF2 is consistent with the difference in the Lewis acidity of T1+ and Cu2+. The reaction between tris(dimethylamino)sulphonium difluorotrimethylsilicate, TAS+F , and MF6 (M = Mo and W) in MeCN yields a brown viscous liquid thought to be due to either the formation of MF7- or MF5NMe2 (M = Mo and W) species. It is shown that the reaction between TAS+F- and BF3 or PF5 results in the formation of colourless crystalline TAS+BF4- or TAS+PF6- salts respectively. Complete [18F]-fluorine exchange between TAS +F- and [18F]-labelled Me3SiF is found to take place in MeCN most probably via an associative mechanism

Mutations in LRP2, which encodes the multiligand receptor megalin, cause Donnai-Barrow and facio-oculo-acoustico-renal syndromes

Donnai-Barrow syndrome is associated with agenesis of the corpus callosum, congenital diaphragmatic hernia, facial dysmorphology, ocular anomalies, sensorineural hearing loss and developmental delay. By studying multiplex families, we mapped this disorder to chromosome 2q23.3–31.1 and identified LRP2 mutations in six families with Donnai-Barrow syndrome and one family with facio-oculo-acoustico-renal syndrome. LRP2 encodes megalin, a multiligand uptake receptor that regulates levels of diverse circulating compounds. This work implicates a pathway with potential pharmacological therapeutic targets