M. J. van den Boogaard

LDL Receptor-Related Protein 5 (LRP5) Affects Bone Accrual and Eye Development

In humans, low peak bone mass is a significant risk factor for osteoporosis. We report that LRP5, encoding the low-density lipoprotein receptor-related protein 5, affects bone mass accrual during growth. Mutations in LRP5 cause the autosomal recessive disorder osteoporosis-pseudoglioma syndrome (OPPG). We find that OPPG carriers have reduced bone mass when compared to age- and gender-matched controls. We demonstrate LRP5 expression by osteoblasts in situ and show that LRP5 can transduce Wnt signaling in vitro via the canonical pathway. We further show that a mutant-secreted form of LRP5 can reduce bone thickness in mouse calvarial explant cultures. These data indicate that Wnt-mediated signaling via LRP5 affects bone accrual during growth and is important for the establishment of peak bone mass.

MSX1 mutation is associated with orofacial clefting and tooth agenesis in humans

A Dutch family with tooth agenesis and various combinations of cleft palate only and cleft lip and cleft palate showed a nonsense mutation (Ser104stop) in exon 1 of MSX1. The mutant phenotype of the family is similar to that of the Msx1-mutant mouse.

Clinical Spectrum of SIX3-Associated Mutations in Holoprosencephaly: Correlation between Genotype, Phenotype, and Function.

Background: Holoprosencephaly (HPE) is the most common structural malformation of the human forebrain. There are several important HPE mutational target genes, including the transcription factor SIX3, which encodes an early regulator of Shh, Wnt, Bmp and Nodal signalling expressed in the developing forebrain and eyes of all vertebrates. Objective: To characterise genetic and clinical findings in patients with SIX3 mutations. Methods: Patients with HPE and their family members were tested for mutations in HPE-associated genes and the genetic and clinical findings, including those for additional cases found in the literature, were analysed. The results were correlated with a mutation-specific functional assay in zebrafish. Results: In a cohort of patients (n = 800) with HPE, SIX3 mutations were found in 4.7% of probands and additional cases were found through testing of relatives. In total, 138 cases of HPE were identified, 59 of whom had not previously been clinically presented. Mutations in SIX3 result in more severe HPE than in other cases of non-chromosomal, non-syndromic HPE. An over-representation of severe HPE was found in patients whose mutations confer greater loss of function, as measured by the functional zebrafish assay. The gender ratio in this combined set of patients was 1.5:1 (F:M) and maternal inheritance was almost twice as common as paternal. About 14% of SIX3 mutations in probands occur de novo. There is a wide intrafamilial clinical range of features and classical penetrance is estimated to be at least 62%. Conclusions: Our data suggest that SIX3 mutations result in relatively severe HPE and that there is a genotype–phenotype correlation, as shown by functional studies using animal models.

Copy number changes of the microcephalin 1 gene (MCPH1) in patients with autism spectrum disorders

Autism spectrum disorder (ASD) represents a set of neurodevelopmental disorders with a strong genetic aetiology. Chromosomal rearrangements have been detected in 5–10% of the patients with ASD, and recent applications of array comparative genomic hybridisation (aCGH) are identifying further candidate regions and genes. In this study, we present four patients who implicate microcephalin 1 (MCPH1) in band 8p23.1 as an ASD susceptibility gene. Patient 1 was a girl with a syndromic form of autistic disorder satisfying the Autism Diagnostic Interview‐Revised (ADI‐R), Autism Diagnostic Observation Schedule (ADOS) and Diagnostic and Statistical Manual of Mental Disorders (DSM‐IV) criteria. Oligonucleotide aCGH (oaCGH) showed that she had a classic inv dup del(8)(qter‐> p23.1::p23.1‐> p21.2) containing at least three candidate genes; MCPH1 and DLGAP2 within the 6.9‐Mb terminal deletion and NEF3 within the concomitant 14.1‐Mb duplication. Three further patients with MCPH1 copy number changes were found using single‐nucleotide polymorphism (SNP) array analysis in a cohort of 54 families with ASD patients. Our results show that ASD can be a component of the classical inv dup del(8) phenotype and identify changes in copy number of MCPH1 as a susceptibility factor for ASD in the distal short arm of chromosome 8.

Delayed diagnosis and underreporting of congenital anomalies associated with oral clefts in the Netherlands: A national validation study

OBJECTIVE Since 1997, the 15 Dutch cleft palate teams have reported their patients with oral clefts to the national oral cleft registry (NVSCA). During the first visit of the patient to the team - which is usually within the first year of life - the oral cleft and associated congenital anomalies are recorded through a unique recording form by a plastic surgeon/orthodontist/paediatrician. In this study, we evaluated the quality of data on congenital anomalies associated with clefts. METHODS We drew a random sample of 250 cases registered in the national database with oral clefts from 1997 through 2003; of these, 13 were excluded. Using two independent reregisters derived from two-phased medical data review, we analysed whether associated anomalies were correctly diagnosed and recorded. RESULTS The agreement on associated anomalies between the NVSCA and medical data ranged from moderate to poor (kappa 0.59 to 0). Seventy-seven percent of the craniofacial anomalies were underreported in the NVSCA: 30% due to delayed diagnosis and 47% due to deficient recording. Additionally, 80% of the associated anomalies of other organ systems were underreported: 52% due to delayed diagnosis and 28% due to deficient recording. The reporting of final diagnoses was somewhat better; however, 54% were still underreported (24% delayed diagnosis and 30% deficient recording). The rate of overreporting was 1.6% or lower. CONCLUSION Congenital anomalies associated with clefts are underreported in the NVSCA because they are under diagnosed and deficiently recorded during the first consultations with the cleft palate teams. Our results emphasise the need for routine and thorough examination of patients with clefts. Team members should be more focussed on co-occurring anomalies, and early genetic counselling seems warranted in most cases. Additionally, our findings underline the need for postnatal follow-up and ongoing registration of associated anomalies; reregistration in the NVSCA at a later age is recommended.

Characterization of amorphous silicon

S‐parameter positron beam measurements have been done on several kinds of a‐Si: Kr‐sputtered a‐Si, PECVD a‐Si, MeV ion beam amorphized Si and a‐Si grown in an MBE‐system at a low deposition temperature. Kr sputtered a‐Si becomes denser for higher Kr concentration. PECVD a‐Si:H contains micro‐cavities with a size depending on growth temperature. MeV ion beam amorphized Si contains 1.2 at. % small vacancies, which decreases upon annealing (relaxation) to 0.4 at. %. This effect can be mimicked by H‐implantation and subsequent annealing, showing that at least some of the dangling bonds in a‐Si are located at these vacancy‐type defects. Finally positron measurements show that MBE‐system grown a‐Si contains large open‐volume defects. The positron annihilation data are supplemented by data from some other techniques.

Deuterium diffusion in α-Si:H studied with elastic recoil detection

We have used elastic-recoil detection (ERD) with 10 MeV 28 Si ions and buried layers of deuterium-rich material to measure diffusion coefficients of deuterium in undoped PECVD a-Si:H samples deposited at temperatures between 50 and 250 o C. The results are consistent with our previous measurements of the optical bandgap during annealing. Especially for low deposition temperatures (∼50 o C) we observe that microvoid-associated defects play an important role in the trapping of hydrogen and deuterium

Structural changes in a-Si:H during annealing

Annealing experiments on undoped glow-discharge a-Si:H films deposited both from undiluted SiH4 and from a SiH4H2 mixture, show that annealing after deposition is a more effective way to improve the structure than an increase in deposition temperature, at least in cases when considerable numbers of (SiH2)n polymers are created during deposition.

De novo truncating variants in the intronless IRF2BPL are responsible for developmental epileptic encephalopathy

PurposeDevelopmental and epileptic encephalopathies (DEEs) are severe clinical conditions characterized by stagnation or decline of cognitive and behavioral abilities preceded, accompanied or followed by seizures. Because DEEs are clinically and genetically heterogeneous, next-generation sequencing, especially exome sequencing (ES), is becoming a first-tier strategy to identify the molecular etiologies of these disorders.MethodsWe combined ES analysis and international data sharing.ResultsWe identified 11 unrelated individuals with DEE and de novo heterozygous truncating variants in the interferon regulatory factor 2–binding protein-like gene (IRF2BPL). The 11 individuals allowed for delineation of a consistent neurodevelopmental disorder characterized by mostly normal initial psychomotor development followed by severe global neurological regression and epilepsy with nonspecific electroencephalogram (EEG) abnormalities and variable central nervous system (CNS) anomalies. IRF2BPL, also known as enhanced at puberty protein 1 (EAP1), encodes a transcriptional regulator containing a C-terminal RING-finger domain common to E3 ubiquitin ligases. This domain is required for its repressive and transactivating transcriptional properties. The variants identified are expected to encode a protein lacking the C-terminal RING-finger domain.ConclusionsThese data support the causative role of truncating IRF2BPL variants in pediatric neurodegeneration and expand the spectrum of transcriptional regulators identified as molecular factors implicated in genetic developmental and epileptic encephalopathies.

Further audiovestibular characterization of DFNB77, caused by deleterious variants in LOXHD1, and investigation into the involvement of Fuchs corneal dystrophy

This study focuses on further characterization of the audiovestibular phenotype and on genotype‐phenotype correlations of DFNB77, an autosomal recessive type of hearing impairment (HI). DFNB77 is associated with disease‐causing variants in LOXHD1, and is genetically and phenotypically highly heterogeneous. Heterozygous deleterious missense variants in LOXHD1 have been associated with late‐onset Fuchs corneal dystrophy (FCD). However, up to now screening for FCD of heterozygous carriers in DFNB77 families has not been reported. This study describes the genotype and audiovestibular phenotype of 9 families with DFNB77. In addition, carriers within the families were screened for FCD. Fifteen pathogenic missense and truncating variants were identified, of which 12 were novel. The hearing phenotype showed high inter‐ and intrafamilial variation in severity and progression. There was no evidence for involvement of the vestibular system. None of the carriers showed (pre‐clinical) symptoms of FCD. Our findings expand the genotypic and phenotypic spectrum of DFNB77, but a clear correlation between the type or location of the variant and the severity or progression of HI could not be established. We hypothesize that environmental factors or genetic modifiers are responsible for phenotypic differences. No association was found between heterozygous LOXHD1 variants and the occurrence of FCD in carriers.