Jenneke van den Ende

Minimum prevalence, birth incidence and cause of death for Prader–Willi syndrome in Flanders

The identification of all people with a diagnosis of Prader–Willi syndrome (PWS) confirmed by DNA methylation analysis living in Flanders was attempted through contact with the four genetic centres and the PWS Association. The birth incidence for the period 1993–2001 was 1:26 676, the minimum prevalence at 31 December 2001 was 1:76 574. A decreasing number of cases with age was found, which can be explained by a number of missing cases in the older population, a higher neonatal mortality in the past and an increasing mortality with age. Childhood death is usually sudden and associated with respiratory infection and high temperature, while the cause of death in adults is considered to be circulatory or respiratory in origin.

Fourteen new cases contribute to the characterization of the 7q11.23 microduplication syndrome.

Interstitial deletions of 7q11.23 cause Williams-Beuren syndrome, one of the best characterized microdeletion syndromes. The clinical phenotype associated with the reciprocal duplication however is not well defined, though speech delay is often mentioned. We present 14 new 7q11.23 patients with the reciprocal duplication of the Williams-Beuren syndrome critical region, nine familial and five de novo. These were identified by either array-based MLPA or by array-CGH/oligonucleotide analysis in a series of patients with idiopathic mental retardation with an estimated population frequency of 1:13,000-1:20,000. Variable speech delay is a constant finding in our patient group, confirming previous reports. Cognitive abilities range from normal to moderate mental retardation. The association with autism is present in five patients and in one father who also carries the duplication. There is an increased incidence of hypotonia and congenital anomalies: heart defects (PDA), diaphragmatic hernia, cryptorchidism and non-specific brain abnormalities on MRI. Specific dysmorphic features were noted in our patients, including a short philtrum, thin lips and straight eyebrows. Our patient collection demonstrates that the 7q11.23 microduplication not only causes language delay, but is also associated with congenital anomalies and a recognizable face.

A SWI/SNF-related autism syndrome caused by de novo mutations in ADNP

Despite the high heritability of autism spectrum disorders (ASD), characterized by persistent deficits in social communication and interaction and restricted, repetitive patterns of behavior, interests or activities, a genetic diagnosis can be established in only a minority of patients. Known genetic causes include chromosomal aberrations, such as the duplication of the 15q11-13 region, and monogenic causes, as in Rett and fragile-X syndromes. The genetic heterogeneity within ASD is striking, with even the most frequent causes responsible for only 1% of cases at the most. Even with the recent developments in next-generation sequencing, for the large majority of cases no molecular diagnosis can be established. Here, we report ten patients with ASD and other shared clinical characteristics, including intellectual disability and facial dysmorphisms caused by a mutation in ADNP, a transcription factor involved in the SWI/SNF remodeling complex. We estimate this gene to be mutated in at least 0.17% of ASD cases, making it one of the most frequent ASD-associated genes known to date.

Localization of the gene for sclerosteosis to the van Buchem Disease-gene region on chromosome 17q12-q21

Sclerosteosis is an uncommon, autosomal recessive, progressive, sclerosing, bone dysplasia characterized by generalized osteosclerosis and hyperostosis of the skeleton, affecting mainly the skull and mandible. In most patients this causes facial paralysis and hearing loss. Other features are gigantism and hand abnormalities. In the present study, linkage analysis in two consanguineous families with sclerosteosis resulted in the assignment of the sclerosteosis gene to chromosome 17q12-q21. This region was analyzed because of the recent assignment to this chromosomal region of the gene causing van Buchem disease, a rare autosomal recessive condition with a hyperostosis similar to sclerosteosis. Because of the clinical similarities between sclerosteosis and van Buchem disease, it has previously been suggested that both conditions might be caused by mutations in the same gene. Our study now provides genetic evidence for this hypothesis.

A New Autosomal Recessive Form of Stickler Syndrome Is Caused by a Mutation in the COL9A1 Gene

Stickler syndrome is characterized by ophthalmic, articular, orofacial, and auditory manifestations. It has an autosomal dominant inheritance pattern and is caused by mutations in COL2A1, COL11A1, and COL11A2. We describe a family of Moroccan origin that consists of four children with Stickler syndrome, six unaffected children, and two unaffected parents who are distant relatives (fifth degree). All family members were clinically investigated for ear, nose, and throat; ophthalmologic; and radiological abnormalities. Four children showed symptoms characteristic of Stickler syndrome, including moderate-to-severe sensorineural hearing loss, moderate-to-high myopia with vitreoretinopathy, and epiphyseal dysplasia. We considered the COL9A1 gene, located on chromosome 6q13, to be a candidate gene on the basis of the structural association with collagen types II and XI and because of the high expression in the human inner ear indicated by cDNA microarray. Mutation analysis of the coding region of the COL9A1 gene showed a homozygous R295X mutation in the four affected children. The parents and four unaffected children were heterozygous carriers of the R295X mutation. Two unaffected children were homozygous for the wild-type allele. None of the family members except the homozygous R295X carriers had any signs of Stickler syndrome. Therefore, COL9A1 is the fourth identified gene that can cause Stickler syndrome. In contrast to the three previously reported Stickler syndrome-causing genes, this gene causes a form of Stickler syndrome with an autosomal recessive inheritance pattern. This finding will have a major impact on the genetic counseling of patients with Stickler syndrome and on the understanding of the pathophysiology of collagens. Mutation analysis of this gene is recommended in patients with Stickler syndrome with possible autosomal recessive inheritance.

Etiologic and Audiologic Evaluations After Universal Neonatal Hearing Screening: Analysis of 170 Referred Neonates

OBJECTIVE. The goal was to clarify the audiologic aspects and causes of congenital hearing loss in children who failed universal neonatal hearing screening. METHODS. A prospective analysis of 170 consecutive records of neonates referred to a tertiary center after universal neonatal hearing screening failure, between 1998 and 2006, was performed. The data presented here represent the equivalent of ∼87000 screened newborns. The screening results were validated with a clinical ear, nose, and throat examination and electrophysiological testing, including diagnostic auditory brainstem response, automated steady state response, and/or behavioral testing. A diagnostic evaluation protocol for identification of the cause of the hearing loss was also implemented, in collaboration with the departments of genetics and pediatrics. RESULTS. Permanent hearing loss was confirmed in 116 children (68.2%). Bilateral hearing loss was diagnosed in 68 infants (58.6%) and unilateral hearing loss in 48 infants (41.4%). Median thresholds for the neonates with confirmed hearing loss were severe in both unilateral and bilateral cases, at 70 dB nHL and 80 dB nHL, respectively. In 55.8% of those cases, no risk factors for hearing loss were found. In 60.4%, the initial automated auditory brainstem response diagnosis was totally in agreement with the audiologic evaluation results. In 8.3% of the cases, however, a unilateral refer result was finally classified as bilateral hearing loss. An etiologic factor could be identified in 55.2% of the cases. Of the causes identified, a genetic mechanism was present in 60.4% of the cases, peripartal problems in 20.8%, and congenital cytomegalovirus infection in 18.8%. CONCLUSIONS. An etiologic factor could be identified for nearly one half of the children with confirmed congenital hearing loss referred through a universal hearing screening program.

Stickler syndrome caused by COL2A1 mutations: Genotype-phenotype correlation in a series of 100 patients

Stickler syndrome is an autosomal dominant connective tissue disorder caused by mutations in different collagen genes. The aim of our study was to define more precisely the phenotype and genotype of Stickler syndrome type 1 by investigating a large series of patients with a heterozygous mutation in COL2A1. In 188 probands with the clinical diagnosis of Stickler syndrome, the COL2A1 gene was analyzed by either a mutation scanning technique or bidirectional fluorescent DNA sequencing. The effect of splice site alterations was investigated by analyzing mRNA. Multiplex ligation-dependent amplification analysis was used for the detection of intragenic deletions. We identified 77 different COL2A1 mutations in 100 affected individuals. Analysis of the splice site mutations showed unusual RNA isoforms, most of which contained a premature stop codon. Vitreous anomalies and retinal detachments were found more frequently in patients with a COL2A1 mutation compared with the mutation-negative group (P<0.01). Overall, 20 of 23 sporadic patients with a COL2A1 mutation had either a cleft palate or retinal detachment with vitreous anomalies. The presence of vitreous anomalies, retinal tears or detachments, cleft palate and a positive family history were shown to be good indicators for a COL2A1 defect. In conclusion, we confirm that Stickler syndrome type 1 is predominantly caused by loss-of-function mutations in the COL2A1 gene as >90% of the mutations were predicted to result in nonsense-mediated decay. On the basis of binary regression analysis, we developed a scoring system that may be useful when evaluating patients with Stickler syndrome.

The genetic basis of DOORS syndrome: an exome-sequencing study

Summary Background Deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures (DOORS) syndrome is a rare autosomal recessive disorder of unknown cause. We aimed to identify the genetic basis of this syndrome by sequencing most coding exons in affected individuals. Methods Through a search of available case studies and communication with collaborators, we identified families that included at least one individual with at least three of the five main features of the DOORS syndrome: deafness, onychodystrophy, osteodystrophy, intellectual disability, and seizures. Participants were recruited from 26 centres in 17 countries. Families described in this study were enrolled between Dec 1, 2010, and March 1, 2013. Collaborating physicians enrolling participants obtained clinical information and DNA samples from the affected child and both parents if possible. We did whole-exome sequencing in affected individuals as they were enrolled, until we identified a candidate gene, and Sanger sequencing to confirm mutations. We did expression studies in human fibroblasts from one individual by real-time PCR and western blot analysis, and in mouse tissues by immunohistochemistry and real-time PCR. Findings 26 families were included in the study. We did exome sequencing in the first 17 enrolled families; we screened for TBC1D24 by Sanger sequencing in subsequent families. We identified TBC1D24 mutations in 11 individuals from nine families (by exome sequencing in seven families, and Sanger sequencing in two families). 18 families had individuals with all five main features of DOORS syndrome, and TBC1D24 mutations were identified in half of these families. The seizure types in individuals with TBC1D24 mutations included generalised tonic-clonic, complex partial, focal clonic, and infantile spasms. Of the 18 individuals with DOORS syndrome from 17 families without TBC1D24 mutations, eight did not have seizures and three did not have deafness. In expression studies, some mutations abrogated TBC1D24 mRNA stability. We also detected Tbc1d24 expression in mouse phalangeal chondrocytes and calvaria, which suggests a role of TBC1D24 in skeletogenesis. Interpretation Our findings suggest that mutations in TBC1D24 seem to be an important cause of DOORS syndrome and can cause diverse phenotypes. Thus, individuals with DOORS syndrome without deafness and seizures but with the other features should still be screened for TBC1D24 mutations. More information is needed to understand the cellular roles of TBC1D24 and identify the genes responsible for DOORS phenotypes in individuals who do not have a mutation in TBC1D24. Funding US National Institutes of Health, the CIHR (Canada), the NIHR (UK), the Wellcome Trust, the Henry Smith Charity, and Action Medical Research.

Phenotypic Spectrum of Simpson–Golabi–Behmel Syndrome in a Series of 42 Cases With a Mutation in GPC3 and Review of the Literature

Simpson–Golabi–Behmel syndrome (SGBS) is a rare X‐linked multiple congenital abnormality/intellectual disability syndrome characterized by pre‐ and post‐natal overgrowth, distinctive craniofacial features, macrocephaly, variable congenital malformations, organomegaly, increased risk of tumor and mild/moderate intellectual deficiency. In 1996, Glypican 3 (GPC3) was identified as the major gene causing SGBS but the mutation detection rate was only 28–70%, suggesting either genetic heterogeneity or that some patients could have alternative diagnoses. This was particularly suggested by some reports of atypical cases with more severe prognoses. In the family reported by Golabi and Rosen, a duplication of GPC4 was recently identified, suggesting that GPC4 could be the second gene for SGBS but no point mutations within GPC4 have yet been reported. In the genetics laboratory in Tours Hospital, GPC3 molecular testing over more than a decade has detected pathogenic mutations in only 8.7% of individuals with SGBS. In addition, GPC4 mutations have not been identified thus raising the question of frequent misdiagnosis. In order to better delineate the phenotypic spectrum of SGBS caused by GPC3 mutations, and to try to define specific clinical criteria for GPC3 molecular testing, we reviewed the clinical features of all male cases with a GPC3 mutation identified in the two molecular laboratories providing this test in France (Tours and Paris). We present here the results of the analysis of 42 patients belonging to 31 families and including five fetuses and three deceased neonates.

Waardenburg Syndrome: Clinical Differentiation Between Types I and II

Here we present the results of a study performed on 59 patients affected by Waardenburg syndrome (WS), 30 with the I variant, 21 having the type II, and 8 of them being isolated cases without telecanthus. These patients belong to 37 families; the main contributions and conclusions are based on the detailed study of 25 of these families, examined using standard procedures. All patients were examined as to the presence of eight cardinal signs important for the diagnosis of the condition; from each patient, from many of his/her normal relatives, and from a control sample of 300 normal individuals stratified by age and sex, 23 different craniofacial measurements were obtained. We also estimated, using our own data as well those collected from the literature, the frequencies of the cardinal signs, based on a total sample of 461 affected individuals with WSI and 121 with WSII. In order to originate discriminant functions to separate individuals affected by one of the two variants, both metric (from craniofacial measurements) as well as categoric data (based on the frequencies of the cardinal signs or symptoms) were used. Discriminant analysis based on the frequency of the eight cardinal signs can improve the separation of WSI patients without telecanthus from those presenting the variant II. We present also a Table with the conditional probabilities favoring the diagnosis of WSI for suspect subjects without telecanthus and any combination of the other seven signs/symptoms. The discriminant function based on the four ocular measurements (inner and outer intercanthal, interpupillary, and inferior lacrymal distances), on the other side, perfectly classifies patients affected by one of the variants of WS, the same taking place when the average values of the W index of all affected individuals per family are used. The discriminant function based solely in the individual W index values of patients correctly classifies 93% of WSII subjects, but only 60% of the patients with the I variant of WS.