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Richard Webster

Publications and source records attributed to Richard Webster.

11 recordsLinked to original sources
PubMed2026

Expanding the genotypic and phenotypic spectrum of PGAP1 deficiency: clinical and functional insights from 15 patients.

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) are essential for neuronal development, synaptic organization and signaling. Defects in GPI-anchor biosynthesis or remodeling cause rare neurodevelopmental disorders, including post-GPI attachment to proteins 1 (PGAP1) deficiency. PGAP1 encodes an inositol deacylase required for GPI-anchor remodeling and appropriate trafficking and membrane localization of GPI-APs. Loss of PGAP1 function disrupts GPI-AP processing, but the clinical spectrum remains incompletely defined because reported cohorts are small. We report 15 individuals with biallelic PGAP1 variants from 11 unrelated families identified through international collaboration. Clinical information was collected using a standardized phenotyping questionnaire and review of available clinical records. The most frequently recorded features were developmental delay or intellectual disability, motor developmental delay, speech impairment, facial dysmorphism, hypotonia and seizures. Independent walking was clearly recorded in a minority of individuals, while feeding, ophthalmological, musculoskeletal and neuroimaging findings were recorded in subsets of the cohort. Clinical investigations were performed as part of routine care and were not uniform across sites. Accordingly, source-dependent assessments including MRI, EEG, EMG/NCS, formal ophthalmology, hearing assessment, systemic imaging, IQ/DQ testing, MRC scoring and anthropometric Z-scores are reported descriptively or using available-data denominators. Spasticity, hypertonia or possible peripheral nerve involvement was recorded in some clinical summaries; however, electrophysiological confirmation was not uniformly available, and confirmed peripheral neuropathy was not analyzed as a cohort-level prevalence outcome. Functional studies in selected patient-derived cells or model systems demonstrated PI-PLC resistance of GPI-APs, supporting impaired GPI-anchor remodeling. These findings expand the genotypic and recorded phenotypic spectrum of PGAP1 deficiency.

Journal Article↗
PubMed2006

CHRND mutation causes a congenital myasthenic syndrome by impairing co-clustering of the acetylcholine receptor with rapsyn.

The objective of this study was to analyse the mutations of the acetylcholine receptor (AChR) delta subunit gene (CHRND) in a patient with sporadic congenital myasthenic syndrome (CMS). Mutations in various genes encoding proteins expressed at the neuromuscular junction may cause CMS. Mutations of AChR subunit genes lead to end-plate AChR deficiency or to altered kinetic properties of the receptor. Mutations in the alpha, beta and delta subunits of the AChR are less frequent than mutations of the epsilon subunit; mutations in these subunits leading to AChR deficiency are often associated with a severe phenotype. A sporadic patient from Germany was studied, who presented with an early onset CMS associated with feeding difficulties, ptosis, a moderate general weakness responsive to anticholinesterase treatment and recurrent episodes of respiratory insufficiency provoked by infections. The CHRND gene was screened for mutations by RFLP, long-range PCR and sequence analysis. Subsequently, we conducted functional studies of AChR mutants co-transfected with rapsyn in HEK 293 cells. Heterozygously to a 2.2 kb microdeletion disrupting the CHRND gene, we identified a novel point mutation in the long cytoplasmic loop, CHRND E381K. The cytoplasmic loop of the AChR subunits is known to be essential for AChR-rapsyn co-clustering. We therefore studied the interaction of AChR containing the CHRND E381K mutation with rapsyn by evaluating expression and co-localization of rapsyn and mutated AChR subunits in co-transfected HEK 293 cells. Interestingly, the mutated receptor showed severely reduced cluster formation compared with the wild-type receptor. In contrast, the corresponding amino acid substitution in the cytoplasmic loop of the AChR epsilon (CHRNE E376K) as well as a recently reported CMS mutation affecting this domain (CHRNE N436del) had no impact on cluster formation. CHRND mutations are a rare cause for CMS but should be considered in patients with a severe, early onset disease form, clinically resembling a rapsyn phenotype with recurrent episodic apnoeas. Our results suggest that impairment of AChR-rapsyn co-clustering--a well-known molecular mechanism for rapsyn mutations--could also result from mutations in the delta subunit. Introduction of the same mutation in the epsilon subunit had no effect on AChR clustering indicating a special role of the delta subunit in AChR-rapsyn interactions.

Cell Line↗
PubMed2005

Outcomes in pediatric epilepsy: seeing through the fog.

To identify clinical and predictive features of outcome in cryptogenic epilepsy in pediatric neurology practice, the medical records of all patients with cryptogenic epilepsy (as defined by the International League Against Epilepsy) in a single pediatric neurology practice over a 12-year interval with at least 2 years of follow-up were systematically and retrospectively reviewed. Review revealed 60 children with cryptogenic epilepsy: 32 (53.3%) males, 11 (18.3%) prior febrile seizure, 9 (15.0%) developmental delay at onset, and 38 (63.3%) placement in regular classes. Twenty-two (35.7%) had generalized seizures. Mean follow-up after initiating antiepileptic medication was 53 months (range 24-128 months). Four (6.7%) were intractable; 4 (6.7%) had very poor outcomes; 8 (13.3%) had poor outcomes; 44 (73.3%) were well controlled. Sixteen (26.7%) and 31 (51.7%) had seizure recurrence within the last 12 and 24 months, respectively. Twenty-nine (48.3%) were seizure-free for at least 24 months. Factors associated with a poor outcome include seizure recurrence in the 6- to 12-month interval after therapy initiation (P = 0.006) and developmental delay at onset (P = 0.023). This case series suggests that children with cryptogenic epilepsy tend to have a favorable outcome. Seizure recurrence in the first months after therapy initiation and developmental delay apparent at onset are predictive of poor outcome.

Adolescent↗
PubMed2005

Developmental and functional outcomes in children with global developmental delay or developmental language impairment.

Preschool children diagnosed with either global developmental delay (GDD) or developmental language impairment (DLI) were reassessed during their early school years with standardized developmental (Battelle Developmental Inventory [BDI]) and functional (Vineland Adaptive Behavior Scale [VABS]) outcome measures. Of an original cohort of 99 children with GDD and 70 children with DLI assessed and diagnosed at a mean age of 3 years 5 months (SD 1.1) and 3 years 7 months (SD 0.7) respectively, 48 children (34 [71%] males) with GDD and 43 children (36 [84%] males) with DLI were reassessed at a mean age of 7 years 4 months (SD 0.9) and 7 years 5 months (SD 0.7) respectively. The overall total mean BDI score for children with GDD was 66.4 (SD 4.3) versus 71.9 (SD 8.2) for children with DLI (p=0.002). On each subdomain of the BDI, except communication, mean scores for the GDD group were significantly lower than for the DLI group (p<0.05). Similarly, the VABS total score for the GDD group was significantly lower than for the DLI group (p<0.001). For each subdomain of the VABS, the GDD group scored significantly lower than the DLI group (p<0.001). The proportion of children falling below meaningful cut-offs on the outcome measures selected was significantly higher for those initially diagnosed with GDD. Preschool diagnosis of either GDD or DLI has later prognostic validity with regard to persisting developmental and functional deficits.

Child↗
PubMed2005

Developmental and functional outcomes at school age of preschool children with global developmental delay.

The later developmental trajectory of young children diagnosed early with global developmental delay was determined. Using a prospective study, preschool children diagnosed with global developmental delay were systematically reassessed during the early school years with standardized developmental and functional outcome measures (Battelle Developmental Inventory and Vineland Adaptive Behavior Scale). Of an original cohort of 99 children assessed and diagnosed at a mean age of 3.4 +/- 1.1 years, 48 were reassessed at a mean age of 7.3 +/- 0.9 years. Group performance on the Battelle Developmental Inventory overall was 66.4 +/- 4.3 (mean 100 +/- 15). Between 75% and 100% of the cohort performed at least 1.5 SD below the normative mean on the individual domains of the Battelle Developmental Inventory. Similarly, the group mean on the Vineland Adaptive Behavior Scale overall was 63.5 +/- 20.8 (mean 100 +/- 15), with between 61% and 76% of the cohort scoring more than 1.5 SD below the mean on each of the domains. Univariate and multivariate analyses on potential predictor variables identified a lack of an underlying etiology as predictive of poorer performance on the Battelle Developmental Inventory fine motor and motor domains and increasing severity of initial delay as predictive of poorer performance on the Vineland Adaptive Behavior Scale communication domain and overall score. Similarly, maternal employment and paternal postsecondary education improved Vineland Adaptive Behavior Scale communication scores, whereas paternal postsecondary education alone predicted better socialization and total scores on the Vineland Adaptive Behavior Scale. Children with early global developmental delay demonstrate persistent and consistently poor performance across all developmental and functional domains. Few variables are apparent at intake to predict later performance.

Child↗
PubMed2004

A mouse model of AChR deficiency syndrome with a phenotype reflecting the human condition.

The two subtypes of mammalian muscle nicotinic acetylcholine receptors (AChR) are generated by the substitution of the epsilon (adult) subunit for the gamma (fetal) subunit within the AChR pentamer. Null mutations of the adult AChR epsilon-subunit gene are the most common cause of the AChR deficiency syndrome. This is a disorder of neuromuscular transmission characterized by non-progressive fatigable muscle weakness present throughout life. In contrast with the human disorder, mice with AChR epsilon-subunit null mutations die between 10 and 14 weeks of age. We generated transgenic mice that constitutively express the human AChR gamma-subunit in an AChR epsilon-subunit 'knock-out' background. These mice, in which neuromuscular transmission is mediated by fetal AChR, live well into adult life but show striking similarities to human AChR deficiency syndrome. They display fatigable muscle weakness, reduced miniature endplate potentials and endplate potentials, reduced motor endplate AChR number and altered endplate morphology. Our results illustrate how species differences in the control of ion-channel gene expression may affect disease phenotype, demonstrate that expression of adult AChR subtype is not essential for long-term survival, and suggest that in patients with AChR deficiency syndrome, up-regulation of the gamma-subunit could be a beneficial therapeutic strategy.

Animals↗
PubMed2004

Sequence selective binding of bis-daunorubicin WP631 to DNA.

We have used footprinting techniques on a wide range of natural and synthetic footprinting substrates to examine the sequence-selective interaction of the bis-daunorubicin antibiotic WP631 with DNA. The ligand produces clear DNase I footprints that are very different from those seen with other anthracycline antibiotics such as daunorubicin and nogalamycin. Footprints are found in a diverse range of sequences, many of which are rich in GT (AC) or GA (TC) residues. As expected, the ligand binds well to the sequences CGTACG and CGATCG, but clear footprints are also found at hexanucleotide sequences such GCATGC and GCTAGC. The various footprints do not contain any particular unique di-, tri- or tetranucleotide sequences, but are frequently contain the sequence (G/C)(A/T)(A/T)(G/C). All sequences with this composition are protected by the ligand, though it can also bind to some sites that differ from this consensus by one base pair.

Antibiotics, Antineoplastic↗
PubMed2004

Speech and language deterioration in benign rolandic epilepsy.

A 5-year-old boy presented with typical clinical and electrophysiologic features of benign rolandic epilepsy. His neurodevelopment, language, and behavior prior to the onset of epilepsy were appropriately normal. He demonstrated marked deterioration of language and cognitive function during the course to a mild and then a moderate disability range. Serial sleep electroencephalographic recordings initially showed continuous and bilateral rolandic discharges with evolution to localized left rolandic spikes. Language and cognitive improvements were subsequently seen. Educational support and evolution of the electroencephalogram to a localized focus could have been contributory. It is anticipated, however, that he will have significant long-term problems in complex language.

Anomia↗
PubMed2003

Structural abnormalities of the AChR caused by mutations underlying congenital myasthenic syndromes.

The objective was to define the molecular mechanisms underlying congenital myasthenic syndromes (CMS) by studying mutations within genes encoding the acetylcholine receptor (AChR) and related proteins at the neuromuscular junction. It was found that mutations within muscle AChRs are the most common cause of CMS. The majority are located within the epsilon-subunit gene and result in AChR deficiency.

Alleles↗
PubMed2002

Mutations in congenital myasthenic syndromes reveal an epsilon subunit C-terminal cysteine, C470, crucial for maturation and surface expression of adult AChR.

Many congenital myasthenic syndromes (CMS) are associated with mutations in the genes encoding the acetylcholine receptor (AChR), an oligomeric protein with the structure alpha(2)betadelta epsilon. AChR deficiency is frequently due to homozygous or heteroallelic mutations in the AChR epsilon subunit, most of which cause truncation of the polypeptide chain and loss of surface expression of AChR. Here we identified mutations epsilon 1369delG and epsilon Y458X, located in the 18 amino acid epsilon subunit C-terminus that lies extracellular to the M4 transmembrane domain. We then incorporated green fluorescent protein (GFP) into the intracellular loop between M3 and M4 of mutant or wild-type epsilon subunits and expressed the AChRs in RD or HEK 293 cells. AChR containing wild-type GFP-tagged epsilon subunits were incorporated into the surface membrane, whereas the GFP-tagged AChR mutant epsilon subunits co-localized with an endoplasmic reticulum (ER) marker and were not expressed on the cell surface. In addition, mutant AChRs did not reach the cell surface, as measured by labelling of intact cells with (125)I-alpha-bungarotoxin and precipitation with an epsilon-subunit-specific antiserum. Mutagenesis studies showed that cysteine 470, located four amino acids from the C-terminus, is essential for alpha/epsilon assembly and surface expression of adult AChR. Replacement of cysteine 470 by serine does not restore alpha/epsilon assembly or surface expression. Our results provide the first use of GFP-tagged AChR as a tool for investigation of CMS and demonstrate a previously undetermined role for a disulphide-bonded cystine in the epsilon subunit C-terminus, which plays a crucial role in expression of the adult AChR.

Cysteine↗