[Show abstract][Hide abstract] ABSTRACT: Filamin A, the filamentous protein encoded by the X-linked gene FLNA, cross-links cytoskeletal actin into three-dimensional networks, facilitating its role as a signalling scaffold and a mechanosensor of extrinsic shear forces. Central to these functions is the ability of FLNA to form V-shaped homodimers through its C-terminal located filamin repeat 24. Additionally, many proteins that interact with FLNA have a binding site that includes the C-terminus of the protein. Here, a cohort of patients with mutations affecting this region of the protein is studied, with particular emphasis on the phenotype of male hemizygotes. Seven unrelated families are reported, with five exhibiting a typical female presentation of periventricular heterotopia (PH), a neuronal migration disorder typically caused by loss-of-function mutations in FLNA. One male presents with widespread PH consistent with previous male phenotypes attributable to hypomorphic mutations in FLNA. In stark contrast, two brothers are described with a mild PH presentation, due to a missense mutation (p.Gly2593Glu) inserting a large negatively charged amino acid into the hydrophobic dimerisation interface of FLNA. Co-immunoprecipitation, in vitro cross-linking studies and gel filtration chromatography all demonstrated that homodimerisation of isolated FLNA repeat 24 is abolished by this p.Gly2593Glu substitution but that extended FLNA(Gly2593Glu) repeat 16-24 constructs exhibit dimerisation. These observations imply that other interactions apart from those mediated by the canonical repeat 24 dimerisation interface contribute to FLNA homodimerisation and that mutations affecting this region of the protein can have broad phenotypic effects.
Full-text · Article · Feb 2015 · Journal of Molecular Medicine
[Show abstract][Hide abstract] ABSTRACT: Despite three decades of successful, predominantly phenotype-driven discovery of the genetic causes of monogenic disorders, up to half of children with severe developmental disorders of probable genetic origin remain without a genetic diagnosis. Particularly challenging are those disorders rare enough to have eluded recognition as a discrete clinical entity, those with highly variable clinical manifestations, and those that are difficult to distinguish from other, very similar, disorders. Here we demonstrate the power of using an unbiased genotype-driven approach to identify subsets of patients with similar disorders. By studying 1,133 children with severe, undiagnosed developmental disorders, and their parents, using a combination of exome sequencing and array-based detection of chromosomal rearrangements, we discovered 12 novel genes associated with developmental disorders. These newly implicated genes increase by 10% (from 28% to 31%) the proportion of children that could be diagnosed. Clustering of missense mutations in six of these newly implicated genes suggests that normal development is being perturbed by an activating or dominant-negative mechanism. Our findings demonstrate the value of adopting a comprehensive strategy, both genome-wide and nationwide, to elucidate the underlying causes of rare genetic disorders.
[Show abstract][Hide abstract] ABSTRACT: Array-comparative genomic hybridisation (array-CGH) is a relatively new test that permits close scrutiny of chromosomal structure to detect genomic microdeletions and microduplications that are invisible in a conventional karyotype. Array-CGH is now the 'first-line' genetic test in the investigation of early developmental impairments and learning difficulties, especially if the clinical picture includes dysmorphism, abnormal growth, congenital anomalies, epilepsy and autism, alone or in combination. However, due to the array-CGH report's technical content and the uncertain clinical significance of many genomic findings, the results of array-CGH studies need careful interpretation. Array-CGH trebles the frequency of diagnosis compared with conventional karyotyping, but collaborative working, involving paediatricians, clinical geneticists and clinical scientists, is most important for interpretation of the results of new genomic investigations in everyday clinical practice.
Preview · Article · Sep 2014 · Archives of Disease in Childhood - Education and Practice
[Show abstract][Hide abstract] ABSTRACT: Background:
Cornelia de Lange syndrome (CdLS) is a multisystem disorder with distinctive facial appearance, intellectual disability and growth failure as prominent features. Most individuals with typical CdLS have de novo heterozygous loss-of-function mutations in NIPBL with mosaic individuals representing a significant proportion. Mutations in other cohesin components, SMC1A, SMC3, HDAC8 and RAD21 cause less typical CdLS.
We screened 163 affected individuals for coding region mutations in the known genes, 90 for genomic rearrangements, 19 for deep intronic variants in NIPBL and 5 had whole-exome sequencing.
Pathogenic mutations [including mosaic changes] were identified in: NIPBL 46  (28.2%); SMC1A 5  (3.1%); SMC3 5  (3.1%); HDAC8 6  (3.6%) and RAD21 1  (0.6%). One individual had a de novo 1.3 Mb deletion of 1p36.3. Another had a 520 kb duplication of 12q13.13 encompassing ESPL1, encoding separase, an enzyme that cleaves the cohesin ring. Three de novo mutations were identified in ANKRD11 demonstrating a phenotypic overlap with KBG syndrome. To estimate the number of undetected mosaic cases we used recursive partitioning to identify discriminating features in the NIPBL-positive subgroup. Filtering of the mutation-negative group on these features classified at least 18% as 'NIPBL-like'. A computer composition of the average face of this NIPBL-like subgroup was also more typical in appearance than that of all others in the mutation-negative group supporting the existence of undetected mosaic cases.
Future diagnostic testing in 'mutation-negative' CdLS thus merits deeper sequencing of multiple DNA samples derived from different tissues.
Full-text · Article · Aug 2014 · Journal of Medical Genetics
[Show abstract][Hide abstract] ABSTRACT: In 2007, the DYSCERNE pilot project funded by the European Commission Public Health Executive Agency (EU DG Sanco) aimed at setting up a network of expertise for patients with rare dysmorphic disorders. As part of DYSCERNE, a Dysmorphology Diagnostic System (DDS) was set up to enable clinicians throughout the EU to submit cases electronically for diagnosis using a secure, web-based interface, hosted at specified access points (Submitting nodes), in 26 different European countries. We report the outcome of this service for 200 cases submitted consecutively between January 2010 and 2012. Each case was reviewed by an average of five expert reviewers. An average of three possible syndromic diagnoses was suggested per case. In 22.5% of the cases, a consensus clinical diagnosis was reached. Genetic testing was suggested in 70.5% of the cases, whereas other laboratory investigations and diagnostic imaging were recommended in 35.5 and 26% of the cases, respectively. Further specialized opinions were suggested in 23.5% of the cases. Overall, a total of 181 very rare or extremely rare genetic syndromes were considered in the differential diagnosis of the 200 cases. In two cases, the reviewers suggested that the findings represented a new syndrome, and in one of these syndromes the underlying genetic cause was subsequently identified. Other benefits of the submission process included the possibility of directing the case submitters to specific centres for diagnostic testing or participation in research and educational benefit derived for both case submitters and reviewers.European Journal of Human Genetics advance online publication, 10 July 2013; doi:10.1038/ejhg.2013.137.
Full-text · Article · Mar 2014 · European Journal of HumanGenetics
[Show abstract][Hide abstract] ABSTRACT: Myhre syndrome is characterized by short stature, brachydactyly, facial features, pseudomuscular hypertrophy, joint limitation and hearing loss. We identified SMAD4 mutations as the cause of Myhre syndrome. SMAD4 mutations have also been identified in laryngotracheal stenosis, arthropathy, prognathism and short stature syndrome (LAPS). This study aimed to review the features of Myhre and LAPS patients to define the clinical spectrum of SMAD4 mutations. We included 17 females and 15 males ranging in age from 8 to 48 years. Thirty were diagnosed with Myhre syndrome and two with LAPS. SMAD4 coding sequence was analyzed by Sanger sequencing. Clinical and radiological features were collected from a questionnaire completed by the referring physicians. All patients displayed a typical facial gestalt, thickened skin, joint limitation and muscular pseudohypertrophy. Growth retardation was common (68.7%) and was variable in severity (from -5.5 to -2 SD), as was mild-to-moderate intellectual deficiency (87.5%) with additional behavioral problems in 56.2% of the patients. Significant health concerns like obesity, arterial hypertension, bronchopulmonary insufficiency, laryngotracheal stenosis, pericarditis and early death occurred in four. Twenty-nine patients had a de novo heterozygous SMAD4 mutation, including both patients with LAPS. In 27 cases mutation affected Ile500 and in two cases Arg496. The three patients without SMAD4 mutations had typical findings of Myhre syndrome. Myhre-LAPS syndrome is a clinically homogenous condition with life threatening complications in the course of the disease. Our identification of SMAD4 mutations in 29/32 cases confirms that SMAD4 is the major gene responsible for Myhre syndrome.European Journal of Human Genetics advance online publication, 15 January 2014; doi:10.1038/ejhg.2013.288.
No preview · Article · Jan 2014 · European journal of human genetics: EJHG
[Show abstract][Hide abstract] ABSTRACT: Myhre syndrome (MS, MIM 139210) is a connective tissue disorder that presents with short stature, short hands and feet, facial dysmorphic features, muscle hypertrophy, thickened skin, and deafness. Recurrent missense mutations in SMAD4 encoding for a transducer mediating transforming growth factor β (TGF-β) signaling are responsible for MS. We found that MS fibroblasts showed increased SMAD4 protein levels, impaired matrix deposition, and altered expression of genes encoding matrix metalloproteinases and related inhibitors. Increased TGF-β signaling and progression of aortic root dilation in Marfan syndrome can be prevented by the antihypertensive drug losartan, a TGF-β antagonists and angiotensin-II type 1 receptor blocker. Herein, we showed that losartan normalizes metalloproteinase and related inhibitor transcript levels and corrects the extracellular matrix deposition defect in fibroblasts from MS patients. The results of this study may pave the way toward therapeutic applications of losartan in MS.European Journal of Human Genetics advance online publication, 8 January 2014; doi:10.1038/ejhg.2013.283.
Full-text · Article · Jan 2014 · European journal of human genetics: EJHG
[Show abstract][Hide abstract] ABSTRACT: Submicroscopic duplications along the long arm of the X-chromosome with known phenotypic consequences are relatively rare events. The clinical features resulting from such duplications are various, though they often include intellectual disability, microcephaly, short stature, hypotonia, hypogonadism and feeding difficulties. Female carriers are often phenotypically normal or show a similar but milder phenotype, as in most cases the X-chromosome harbouring the duplication is subject to inactivation. Xq28, which includes MECP2 is the major locus for submicroscopic X-chromosome duplications, whereas duplications in Xq25 and Xq26 have been reported in only a few cases. Using genome-wide array platforms we identified overlapping interstitial Xq25q26 duplications ranging from 0.2 to 4.76 Mb in eight unrelated families with in total five affected males and seven affected females. All affected males shared a common phenotype with intrauterine- and postnatal growth retardation and feeding difficulties in childhood. Three had microcephaly and two out of five suffered from epilepsy. In addition, three males had a distinct facial appearance with congenital bilateral ptosis and large protruding ears and two of them showed a cleft palate. The affected females had various clinical symptoms similar to that of the males with congenital bilateral ptosis in three families as most remarkable feature. Comparison of the gene content of the individual duplications with the respective phenotypes suggested three critical regions with candidate genes (AIFM1,
RAB33A, GPC3 and IGSF1) for the common phenotypes, including candidate loci for congenital bilateral ptosis, small head circumference, short stature, genital and digital defects.
[Show abstract][Hide abstract] ABSTRACT: Many neurological conditions are caused by immensely heterogeneous gene mutations. The diagnostic process is often long and complex with most patients undergoing multiple invasive and costly investigations without ever reaching a conclusive molecular diagnosis. The advent of massively parallel, next-generation sequencing promises to revolutionize genetic testing and shorten the 'diagnostic odyssey' for many of these patients. We performed a pilot study using heterogeneous ataxias as a model neurogenetic disorder to assess the introduction of next-generation sequencing into clinical practice. We captured 58 known human ataxia genes followed by Illumina Next-Generation Sequencing in 50 highly heterogeneous patients with ataxia who had been extensively investigated and were refractory to diagnosis. All cases had been tested for spinocerebellar ataxia 1-3, 6, 7 and Friedrich's ataxia and had multiple other biochemical, genetic and invasive tests. In those cases where we identified the genetic mutation, we determined the time to diagnosis. Pathogenicity was assessed using a bioinformatics pipeline and novel variants were validated using functional experiments. The overall detection rate in our heterogeneous cohort was 18% and varied from 8.3% in those with an adult onset progressive disorder to 40% in those with a childhood or adolescent onset progressive disorder. The highest detection rate was in those with an adolescent onset and a family history (75%). The majority of cases with detectable mutations had a childhood onset but most are now adults, reflecting the long delay in diagnosis. The delays were primarily related to lack of easily available clinical testing, but other factors included the presence of atypical phenotypes and the use of indirect testing. In the cases where we made an eventual diagnosis, the delay was 3-35 years (mean 18.1 years). Alignment and coverage metrics indicated that the capture and sequencing was highly efficient and the consumable cost was ∼£400 (€460 or US$620). Our pathogenicity interpretation pathway predicted 13 different mutations in eight different genes: PRKCG, TTBK2, SETX, SPTBN2, SACS, MRE11, KCNC3 and DARS2 of which nine were novel including one causing a newly described recessive ataxia syndrome. Genetic testing using targeted capture followed by next-generation sequencing was efficient, cost-effective, and enabled a molecular diagnosis in many refractory cases. A specific challenge of next-generation sequencing data is pathogenicity interpretation, but functional analysis confirmed the pathogenicity of novel variants showing that the pipeline was robust. Our results have broad implications for clinical neurology practice and the approach to diagnostic testing.
[Show abstract][Hide abstract] ABSTRACT: Kabuki syndrome (KS) is a rare multi-system disorder that can result in a variety of congenital malformations, typical dysmorphism and variable learning disability. It is caused by MLL2 point mutations in the majority of the cases and, rarely by deletions involving KDM6A. Nearly one third of cases remain unsolved. Here, we expand the known genetic basis of KS by presenting five typical patients with the condition, all of whom have novel MLL2 mutation types- two patients with mosaic small deletions, one with a mosaic whole-gene deletion, one with a multi-exon deletion and one with an intragenic multi-exon duplication. We recommend MLL2 dosage studies for all patients with typical KS, where traditional Sanger sequencing fails to identify mutations. The prevalence of such MLL2 mutations in KS may be comparable with deletions involving KDM6A. These findings may be helpful in understanding the mutational mechanism of MLL2 and the disease mechanism of KS.
No preview · Article · Aug 2012 · Clinical Genetics
[Show abstract][Hide abstract] ABSTRACT: McGowan R, Challoner BR, Ross S, Holloway S, Joss S, Wilcox D, Holden ST, Tolmie J, Longman C. Results of Duchenne muscular dystrophy family screening in practice: leaks rather than cascades?
Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by mutations in the gene that encodes the protein dystrophin. Approximately 2 of 3 affected boys inherit their mutation from their carrier mother whereupon other female relatives are at risk of carrying the mutation. Female carriers are also at risk of developing cardiomyopathy and regular cardiac screening is recommended. Clinical genetics services offer genetic counselling and carrier tests for consenting relatives of DMD patients known as ‘cascade screening’. We retrospectively analysed data from two genetics centres, West of Scotland and South East Thames where the latter centre operated a computer-held DMD register. Over the period, 1971–2008, a total of 843 potential carriers, in 195 West of Scotland families, were tested: 16% of 1st degree relatives and 48% of 2nd degree and more distant relatives were not tested. In South East Thames, a total of 1223 potential carriers in 349 families were tested: 49% of 1st degree and 65% of 2nd degree and more distant relatives were not tested. These data are similar to Becker muscular dystrophy/DMD carrier screening results recently reported from the Netherlands. Retrospective results from three countries indicate that despite efforts to offer extended cascade screening, significant numbers of potential carriers of DMD remain unaware of their reproductive and health risks.
Full-text · Article · Mar 2012 · Clinical Genetics
[Show abstract][Hide abstract] ABSTRACT: Myhre syndrome (MIM 139210) is a developmental disorder characterized by short stature, short hands and feet, facial dysmorphism, muscular hypertrophy, deafness and cognitive delay. Using exome sequencing of individuals with Myhre syndrome, we identified SMAD4 as a candidate gene that contributes to this syndrome on the basis of its pivotal role in the bone morphogenetic pathway (BMP) and transforming growth factor (TGF)-β signaling. We identified three distinct heterozygous missense SMAD4 mutations affecting the codon for Ile500 in 11 individuals with Myhre syndrome. All three mutations are located in the region of SMAD4 encoding the Mad homology 2 (MH2) domain near the site of monoubiquitination at Lys519, and we found a defect in SMAD4 ubiquitination in fibroblasts from affected individuals. We also observed decreased expression of downstream TGF-β target genes, supporting the idea of impaired TGF-β-mediated transcriptional control in individuals with Myhre syndrome.
[Show abstract][Hide abstract] ABSTRACT: MLL2 mutations are detected in 55 to 80% of patients with Kabuki syndrome (KS). In 20 to 45% patients with KS, the genetic basis remains unknown, suggesting possible genetic heterogeneity. Here, we present the largest yet reported cohort of 116 patients with KS. We identified MLL2 variants in 74 patients, of which 47 are novel and a majority are truncating. We show that pathogenic missense mutations were commonly located in exon 48. We undertook a systematic facial KS morphology study of patients with KS at our regional dysmorphology meeting. Our data suggest that nearly all patients with typical KS facial features have pathogenic MLL2 mutations, although KS can be phenotypically variable. Furthermore, we show that MLL2 mutation-positive KS patients are more likely to have feeding problems, kidney anomalies, early breast bud development, joint dislocations and palatal malformations in comparison with MLL2 mutation-negative patients. Our work expands the mutation spectrum of MLL2 that may help in better understanding of this molecule, which is important in gene expression, epigenetic control of active chromatin states, embryonic development and cancer. Our analyses of the phenotype indicates that MLL2 mutation-positive and -negative patients differ systematically, and genetic heterogeneity of KS is not as extensive as previously suggested. Moreover, phenotypic variability of KS suggests that MLL2 testing should be considered even in atypical patients.
Full-text · Article · Nov 2011 · European journal of human genetics: EJHG
[Show abstract][Hide abstract] ABSTRACT: Autosomal recessive renal tubular dysgenesis (RTD) is a severe disorder of renal tubular development characterized by early onset and persistent fetal anuria leading to oligohydramnios and the Potter sequence, associated with skull ossification defects. Early death occurs in most cases from anuria, pulmonary hypoplasia, and refractory arterial hypotension. The disease is linked to mutations in the genes encoding several components of the renin-angiotensin system (RAS): AGT (angiotensinogen), REN (renin), ACE (angiotensin-converting enzyme), and AGTR1 (angiotensin II receptor type 1). Here, we review the series of 54 distinct mutations identified in 48 unrelated families. Most of them are novel and ACE mutations are the most frequent, observed in two-thirds of families (64.6%). The severity of the clinical course was similar whatever the mutated gene, which underlines the importance of a functional RAS in the maintenance of blood pressure and renal blood flow during the life of a human fetus. Renal hypoperfusion, whether genetic or secondary to a variety of diseases, precludes the normal development/ differentiation of proximal tubules. The identification of the disease on the basis of precise clinical and histological analyses and the characterization of the genetic defects allow genetic counseling and early prenatal diagnosis.
[Show abstract][Hide abstract] ABSTRACT: We describe the clinical characteristics of 4 singleton cases, 3 males and 1 female, with Myhre Syndrome (OMIM 139210), who were born to non-consanguineous parents. Three cases had no family history of similarly affected individuals but 1 male's mother had short stature, some facial features suggestive of Myhre syndrome and evidence of skewed X-chromosome inactivation in her blood DNA. Short stature, deafness, learning difficulties, skeletal anomalies and facial dysmorphisms were evident in all cases. Arthralgia and stiff joints with limited movement were also present. The facial appearance, thickened skin, a 'muscular' habitus are memorable features. The female patient was least affected: this patient and one affected male displayed streaky skin with areas of patchy thickening, suggestive of genetic mosaicism. One patient developed sleep apnoea, a restrictive ventilatory defect and died following a choking episode. Another affected male developed recurrent, progressive, proximal, tracheal stenosis requiring partial tracheal resection, laser treatment and eventually tracheotomy. Review of Myhre syndrome patients in the literature and syndromes in the differential diagnosis, suggests heterogeneity in Myhre syndrome and clinical overlap with Laryngotracheal stenosis, Arthropathy, Prognathism and Short stature syndrome.
No preview · Article · Jul 2011 · European journal of medical genetics
[Show abstract][Hide abstract] ABSTRACT: Using exome sequencing and a variant prioritization strategy that focuses on loss-of-function variants, we identified biallelic, loss-of-function CEP57 mutations as a cause of constitutional mosaic aneuploidies. CEP57 is a centrosomal protein and is involved in nucleating and stabilizing microtubules. Our findings indicate that these and/or additional functions of CEP57 are crucial for maintaining correct chromosomal number during cell division.
[Show abstract][Hide abstract] ABSTRACT: Ulnar Mammary syndrome (UMS) is an autosomal disorder caused by haploinsufficiency of the TBX3 gene. There is marked intrafamilial variation in expression of the syndrome. We present one three generation family in which the proband has absence of the right ulna and third, fourth and fifth rays in her right hand. Her mother and maternal grandmother have more subtle anomalies while all have a similar facial appearance with a broad nasal tip, a broad jaw, a prominent chin and a tongue frenulum. They have a single base pair insertion (c. 992dup) in TBX3. We compare faces from the handful of published UMS patients which include photographs, this family and four other cases with TBX3 mutations. All have similarities in appearance which we suggest could alert clinicians to the possibility of a TBX3 mutation if individuals present with more subtle features of UMS such as postaxial polydactyly, isolated 5th finger anomalies, delayed puberty in males, breast hypoplasia or short stature with or without growth hormone deficiency.
No preview · Article · May 2011 · European journal of medical genetics
[Show abstract][Hide abstract] ABSTRACT: Bohring-Opitz syndrome (BOS) is a rare congenital disorder of unknown etiology diagnosed on the basis of distinctive clinical features. We suggest diagnostic criteria for this condition, describe ten previously unreported patients, and update the natural history of four previously reported patients. This is the largest series reported to date, providing a unique opportunity to document the key clinical features and course through childhood. Investigations undertaken to try and elucidate the underlying pathogenesis of BOS using array comparative genomic hybridization and tandem mass spectrometry of cholesterol precursors did not show any pathogenic changes responsible.
Full-text · Article · Feb 2011 · European journal of human genetics: EJHG
[Show abstract][Hide abstract] ABSTRACT: Willemsen MH, Beunders G, Callaghan M, de Leeuw N, Nillesen WM, Yntema HG, van Hagen JM, Nieuwint AWM, Morrison N, Keijzers-Vloet STM, Hoischen A, Brunner HG, Tolmie J, Kleefstra T. Familial Kleefstra syndrome due to maternal somatic mosaicism for interstitial 9q34.3 microdeletions.
The Kleefstra syndrome (Online Mendelian Inheritance in Man 607001) is caused by a submicroscopic 9q34.3 deletion or by intragenic euchromatin histone methyl transferase 1 (EHMT1) mutations. So far only de novo occurrence of mutations has been reported, whereas 9q34.3 deletions can be either de novo or caused by complex chromosomal rearrangements or translocations. Here we give the first descriptions of affected parent-to-child transmission of Kleefstra syndrome caused by small interstitial deletions, approximately 200 kb, involving part of the EHMT1 gene. Additional genome-wide array studies in the parents showed the presence of similar deletions in both mothers who only had mild learning difficulties and minor facial characteristics suggesting either variable clinical expression or somatic mosaicism for these deletions. Further studies showed only one of the maternal deletions resulted in significantly quantitative differences in signal intensity on the array between the mother and her child. But by investigating different tissues with additional fluorescent in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA) analyses, we confirmed somatic mosaicism in both mothers. Careful clinical and cytogenetic assessments of parents of an affected proband with an (interstitial) 9q34.3 microdeletion are merited for accurate estimation of recurrence risk.
No preview · Article · Dec 2010 · Clinical Genetics