Paulien A. Terhal

Hypomethylation of the H19 Gene Causes Not Only Silver-Russell Syndrome (SRS) but Also Isolated Asymmetry or an SRS-Like Phenotype

The H19 differentially methylated region (DMR) controls the allele-specific expression of both the imprinted H19 tumor-suppressor gene and the IGF2 growth factor. Hypermethylation of this DMR--and subsequently of the H19 promoter region--is a major cause of the clinical features of gigantism and/or asymmetry seen in Beckwith-Wiedemann syndrome or in isolated hemihypertrophy. Here, we report a series of patients with hypomethylation of the H19 locus. Their main clinical features of asymmetry and growth retardation are the opposite of those seen in patients with hypermethylation of this region. In addition, we show that complete hypomethylation of the H19 promoter is found in two of three patients with the full clinical spectrum of Silver-Russell syndrome. This syndrome is also characterized by growth retardation and asymmetry, among other clinical features. We conclude that patients with these clinical features should be analyzed for H19 hypomethylation.

Mutations in genes encoding the cadherin receptor-ligand pair DCHS1 and FAT4 disrupt cerebral cortical development.

The regulated proliferation and differentiation of neural stem cells before the generation and migration of neurons in the cerebral cortex are central aspects of mammalian development. Periventricular neuronal heterotopia, a specific form of mislocalization of cortical neurons, can arise from neuronal progenitors that fail to negotiate aspects of these developmental processes. Here we show that mutations in genes encoding the receptor-ligand cadherin pair DCHS1 and FAT4 lead to a recessive syndrome in humans that includes periventricular neuronal heterotopia. Reducing the expression of Dchs1 or Fat4 within mouse embryonic neuroepithelium increased progenitor cell numbers and reduced their differentiation into neurons, resulting in the heterotopic accumulation of cells below the neuronal layers in the neocortex, reminiscent of the human phenotype. These effects were countered by concurrent knockdown of Yap, a transcriptional effector of the Hippo signaling pathway. These findings implicate Dchs1 and Fat4 upstream of Yap as key regulators of mammalian neurogenesis.

Definition of a critical region on chromosome 18 for congenital aural atresia by arrayCGH

Deletions of the long arm of chromosome 18 occur in approximately 1 in 10,000 live births. Congenital aural atresia (CAA), or narrow external auditory canals, occurs in approximately 66% of all patients who have a terminal deletion 18q. The present report describes a series of 20 patients with CAA, of whom 18 had microscopically visible 18q deletions. The extent and nature of the chromosome-18 deletions were studied in detail by array-based comparative genomic hybridization (arrayCGH). High-resolution chromosome-18 profiles were obtained for all patients, and a critical region of 5 Mb that was deleted in all patients with CAA could be defined on 18q22.3-18q23. Therefore, this region can be considered as a candidate region for aural atresia. The array-based high-resolution copy-number screening enabled a refined cytogenetic diagnosis in 12 patients. Our approach appeared to be applicable to the detection of genetic mosaicisms and, in particular, to a detailed delineation of ring chromosomes. This study clearly demonstrates the power of the arrayCGH technology in high-resolution molecular karyotyping. Deletion and amplification mapping can now be performed at the submicroscopic level and will allow high-throughput definition of genomic regions harboring disease genes.

Dominant missense mutations in ABCC9 cause Cantú syndrome

Cantú syndrome is characterized by congenital hypertrichosis, distinctive facial features, osteochondrodysplasia and cardiac defects. By using family-based exome sequencing, we identified a de novo mutation in ABCC9. Subsequently, we discovered novel dominant missense mutations in ABCC9 in 14 of the 16 individuals with Cantú syndrome examined. The ABCC9 protein is part of an ATP-dependent potassium (KATP) channel that couples the metabolic state of a cell with its electrical activity. All mutations altered amino acids in or close to the transmembrane domains of ABCC9. Using electrophysiological measurements, we show that mutations in ABCC9 reduce the ATP-mediated potassium channel inhibition, resulting in channel opening. Moreover, similarities between the phenotype of individuals with Cantú syndrome and side effects from the KATP channel agonist minoxidil indicate that the mutations in ABCC9 result in channel opening. Given the availability of ABCC9 antagonists, our findings may have direct implications for the treatment of individuals with Cantú syndrome.

Gain of glycosylation in integrin α3 causes lung disease and nephrotic syndrome

Integrins are transmembrane αβ glycoproteins that connect the extracellular matrix to the cytoskeleton. The laminin-binding integrin α3β1 is expressed at high levels in lung epithelium and in kidney podocytes. In podocytes, α3β1 associates with the tetraspanin CD151 to maintain a functional filtration barrier. Here, we report on a patient homozygous for a novel missense mutation in the human ITGA3 gene, causing fatal interstitial lung disease and congenital nephrotic syndrome. The mutation caused an alanine-to-serine substitution in the integrin α3 subunit, thereby introducing an N-glycosylation motif at amino acid position 349. We expressed this mutant form of ITGA3 in murine podocytes and found that hyperglycosylation of the α3 precursor prevented its heterodimerization with β1, whereas CD151 association with the α3 subunit occurred normally. Consequently, the β1 precursor accumulated in the ER, and the mutant α3 precursor was degraded by the ubiquitin-proteasome system. Thus, these findings uncover a gain-of-glycosylation mutation in ITGA3 that prevents the biosynthesis of functional α3β1, causing a fatal multiorgan disorder.

Rett syndrome in females with CTS hot spot deletions: a disorder profile.

From a series of 107 females with Rett syndrome (RTT), we describe the long‐term history of ten females with a deletion in the C‐terminus of the MECP2 gene. We observed that their disorder profile is clinically recognizable with time and different from other atypical and milder RTT phenotypes. In females with hot spot deletions in the C‐terminus, dystonia is present from childhood and results in a serious spine deformation in spite of preventive measures. Their adaptive behavior is surprisingly better preserved and in contrast with the typical decline in motor functioning. The delineaton of disorder profiles by long‐term clinical observation can teach us about genotype/phenotype relationships and eventually about the effect of epigenetic phenomena on the final phenotype.

Clinical features of maternal uniparental disomy 14 in patients with an epimutation and a deletion of the imprinted DLK1/GTL2 gene cluster.

Maternal uniparental disomy 14 [upd(14)mat] is associated with a recognizable phenotype that includes pre‐ and postnatal growth retardation, neonatal hypotonia, feeding problems and precocious puberty. Chromosome 14 contains an imprinted gene cluster, which is regulated by a differentially methylated region (IG‐DMR) between DLK1 and GTL2. Here we report on four patients with clinical features of upd(14)mat who show a maternal‐only methylation pattern, but biparental inheritance for chromosome 14. In three of the patients loss of paternal methylation appears to be a primary epimutation, whereas the other patient has a paternally derived deletion of −1 Mb that includes the imprinted DLK1‐GTL2 gene cluster. These findings demonstrate that the upd(14)mat phenotype is caused by altered expression of genes within this cluster. Hum Mutat 0, 1–6, 2008.

Recessive multiple epiphyseal dysplasia (rMED): phenotype delineation in eighteen homozygotes for DTDST mutation R279W

Multiple epiphyseal dysplasia (MED) is a generalised skeletal dysplasia that although relatively mild is associated with significant morbidity. Joint pain, joint deformity, waddling gait, and short stature are the main clinical signs and symptoms. In the past, the disorder was subdivided into the milder Ribbing type, usually with flattened epiphyses,1 and the more severe Fairbank type with round epiphyses,2 but many cases were not classifiable as clearly either type.3 MED can be caused by mutations in at least six separate genes: COMP ,4–7 collagen IX ( COL9A1 , COL9A2 , and COL9A3 ),8–13 matrilin 3 ( MATN3 ),15 and the sulphate transporter, DTDST ( DTDST/SLC26A2 ). We have previously reported an adult with a recessively inherited form of MED (rMED) characterised by club feet, double layered patellae, and normal stature, who was homozygous for the mutation 862c>t/R279W in the DTDST gene, previously associated with the achondrogenesis 1B-atelosteogenesis 2-diastrophic dysplasia spectrum. We now report on a group of 18 subjects who are homozygous for this point mutation, allowing a comprehensive assessment of this particular MED phenotype. Distinction of rMED is important because of its recessive inheritance (unlike other MED types) and genetic counselling implications. The frequency of the R279W mutation and the number of subjects with molecularly proven rMED identified since its description suggest that rMED may be more common than hitherto assumed. Blood or genomic DNA was sent to the Zurich centre for DTDST mutation analysis because of clinical and radiographic signs similar to the reported case of rMED,20 or because of a clinical diagnosis of MED and negative mutation analysis of COMP or collagen IX genes. Genomic DNA was extracted from blood leucocytes using standard protocols and was subjected to DTDST mutation analysis. The fragment of interest, that is, the 5′ part of exon …

Effectiveness of whole-exome sequencing and costs of the traditional diagnostic trajectory in children with intellectual disability

Purpose:This study investigated whole-exome sequencing (WES) yield in a subset of intellectually disabled patients referred to our clinical diagnostic center and calculated the total costs of these patients’ diagnostic trajectory in order to evaluate early WES implementation.Methods:We compared 17 patients’ trio-WES yield with the retrospective costs of diagnostic procedures by comprehensively examining patient records and collecting resource use information for each patient, beginning with patient admittance and concluding with WES initiation. We calculated cost savings using scenario analyses to evaluate the costs replaced by WES when used as a first diagnostic tool.Results:WES resulted in diagnostically useful outcomes in 29.4% of patients. The entire traditional diagnostic trajectory average cost was

Loss-of-Function Mutations in TBC1D20 Cause Cataracts and Male Infertility in blind sterile Mice and Warburg Micro Syndrome in Humans

16,409 per patient, substantially higher than the