Biedl Syndrome Research Articles

The interplay between RPGR, PDEδ and Arl2/3 regulate the ciliary targeting of farnesylated cargo

Defects in primary cilia result in human diseases known as ciliopathies. The retinitis pigmentosa GTPase regulator (RPGR), mutated in the most severe form of the eye disease, is located at the transition zone of the ciliary organelle. The RPGR-interacting partner PDEδ is involved in trafficking of farnesylated ciliary cargo, but the significance of this interaction is unknown. The crystal structure of the propeller domain of RPGR shows the location of patient mutations and how they perturb the structure. The RPGR·PDEδ complex structure shows PDEδ on a highly conserved surface patch of RPGR. Biochemical experiments and structural considerations show that RPGR can bind with high affinity to cargo-loaded PDEδ and exposes the Arl2/Arl3-binding site on PDEδ. On the basis of these results, we propose a model where RPGR is acting as a scaffold protein recruiting cargo-loaded PDEδ and Arl3 to release lipidated cargo into cilia.

The endocrine and metabolic characteristics of a large Bardet[ndash]Biedl syndrome clinic population

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

A novel homozygous 10 nucleotide deletion in BBS10 causes Bardet–Biedl syndrome in a Pakistani family

Bardet–Biedl Syndrome is a multisystem autosomal recessive disorder characterized by central obesity, polydactyly, hypogonadism, learning difficulties, rod-cone dystrophy and renal dysplasia. Bardet–Biedl Syndrome has a prevalence rate ranging from 1 in 100,000 to 1 in 160,000 births although there are communities where Bardet–Biedl Syndrome is found at a higher frequency due to consanguinity. We report here a Pakistani consanguineous family with two affected sons with typical clinical features of Bardet–Biedl Syndrome, in addition to abnormal liver functioning and bilateral basal ganglia calcification, the latter feature being typical of Fahr's disease. Homozygous regions obtained from SNP array depicted three known genes BBS10, BBS14 and BBS2. Bidirectional sequencing of all coding exons by traditional sequencing of all these three genes showed a homozygous deletion of 10 nucleotides (c.1958_1967del), in BBS10 in both affected brothers. The segregation analysis revealed that the parents, paternal grandfather, maternal grandmother and an unaffected sister were heterozygous for the deletion. Such a large deletion in BBS10 has not been reported previously in any population and is likely to be contributing to the phenotype of Bardet–Biedl Syndrome in this family.

RABL-regulated pathways: a new tale in sperm function

RABL-regulated pathways: a new tale in sperm function

Novel homozygous mutations in the genes ARL6 and BBS10 underlying Bardet–Biedl syndrome

Bardet–Biedl syndrome (BBS) is an autosomal recessive disorder resulting from structural and functional defects in numerous organs. Frequent manifestations reported in the syndrome include obesity, renal dysplasia, cognitive impairment, postaxial polydactyly, pigmentary retinal degeneration and hypogonadism. To date, 17 genes causing BBS have been identified. Two of these BBS1 and BBS10 are the most frequently mutated genes.The present report describes two consanguineous families (A, B) with clinical manifestations of BBS. Linkage in the family A was established to ARL6 on chromosome 3q11.2, while family B showed linkage to BBS10 on chromosome 12q21.2. Sequence analysis revealed a novel homozygous missense mutation (c.281T>C, p.Ile94Thr) in the gene ARL6 in family A and a nonsense mutation (c.1075C>T, p.Gln359*) in the gene BBS10 in family B. Mutations identified in the present study extend the body of evidence implicating the genes ARL6 and BBS10 in causing Bardet–Biedl syndrome.

First-trimester prenatal diagnosis of Ellis–van Creveld syndrome

ObjectiveTo present the perinatal findings and first-trimester molecular and transabdominal ultrasound diagnosis of a fetus with Ellis–van Creveld (EvC) syndrome. Case ReportA 35-year-old woman was referred for genetic counseling at 13 weeks of gestation because of a family history of skeletal dysplasia. She had experienced one spontaneous abortion, and delivered one male fetus and one female fetus with EvC syndrome. During this pregnancy, a prenatal transabdominal ultrasound at 13+4 weeks of gestation revealed a nuchal translucency (NT) thickness of 2.0 mm, an endocardial cushion defect, postaxial polydactyly of bilateral hands, and mesomelic dysplasia of the long bones. Amniocentesis was performed at 13+5 weeks of gestation. Results of a cytogenetic analysis revealed a karyotype of 46,XX and that of a molecular analysis revealed compound heterozygous mutations of c.1195C>T and c.871-2_894del26 in the EVC2 gene. Prenatal ultrasound at 16 weeks of gestation showed a fetus with short limbs, an endocardial cushion defect, and postaxial polydactyly of bilateral hands. The parents decided to terminate the pregnancy, and a 116-g female fetus was delivered with a narrow thorax, shortening limbs, and postaxial polydactyly of the hands. ConclusionPrenatal diagnosis of an endocardial cushion defect with postaxial polydactyly should include a differential diagnosis of EvC syndrome in addition to short rib–polydactyly syndrome, Bardet–Biedl syndrome, orofaciodigital syndrome, Smith–Lemli–Opitz syndrome, and hydrolethalus syndrome.

Can't get there from here: cilia and hydrocephalus

Hydrocephalus describes an expansion of the cerebral ventricles that is associated with decreased cerebral volume and compromised neurological function. Although hydrocephalus mostly occurs sporadically, it is frequently associated with diseases caused by defective cilia function, including Bardet–Biedl syndrome (BBS). A new study reveals that hydrocephalus in a mouse model of BBS is related to defective proliferation and apoptosis of neural progenitor cells (NPCs) and can be rescued with lithium treatment (pages 1797–1804).

A child with obesity and polydactyly

 Bardet Biedle syndrome is a rare genetic disorder related to Laurence moon syndrome. It is characterized by obesity, hypogonadism, polydactyly, renal abnormalities, retinal pigmentation, and other features, some patients has mental retardation and other clinical findings. Situs inversus is very rarely reported as an association of this syndrome, The cause of this syndrome is genetic with multiple genes involved, it is usually inherited as autosomal recessive pattern .There is no any proved treatment for this syndrome apart from dealing with specific problems which might have been arisen. We presented a 6 years old boy patient exhibiting characteristic features of this syndrome with additional rare associated features that make the case unique and discrete. In the  setting of this case, the literature about Bardet Biedl syndrome was reviewed.

Structural defects in cilia of the choroid plexus, subfornical organ and ventricular ependyma are associated with ventriculomegaly

BackgroundHydrocephalus is a heterogeneous disorder with multiple etiologies that are not yet fully understood. Animal models have implicated dysfunctional cilia of the ependyma and choroid plexus in the development of the disorder. In this report, we sought to determine the origin of the ventriculomegaly in four Bardet Biedl syndrome (BBS) mutant mouse strains as models of a ciliopathy.MethodsEvans Blue dye was injected into the lateral ventricle of wild- type and BBS mutant mice to determine whether obstruction of intra- or extra-ventricular CSF flow contributed to ventriculomegaly. Transmission electron microscopy (TEM) was used to examine the ultrastructure of the choroid plexus, subfornical organ (SFO), subcommisural organ (SCO), and ventricular ependyma to evaluate their ultrastructure and the morphology of their primary and motile cilia.Results and discussionNo obstruction of intra- or extra-ventricular CSF flow was observed, implying a communicating form of hydrocephalus in BBS mutant mice. TEM analyses of the mutants showed no evidence of choroidal papillomas or breakdown of the blood:CSF barrier. In contrast, structural defects were observed in a subpopulation of cilia lining the choroid plexus, SFO, and ventricular ependyma. These included disruptions of the microtubular structure of the axoneme and the presence of electron-dense vesicular-like material along the ciliary shaft and at the tips of cilia.ConclusionsAbnormalities in cilia structure and function have the potential to influence ciliary intraflagellar transport (IFT), cilia maintenance, protein trafficking, and regulation of CSF production. Ciliary structural defects are the only consistent pathological features associated with CSF-related structures in BBS mutant mice. These defects are observed from an early age, and may contribute to the underlying pathophysiology of ventriculomegaly.

Characterization of CCDC28B reveals its role in ciliogenesis and provides insight to understand its modifier effect on Bardet–Biedl syndrome

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder that is generally inherited in an autosomal recessive fashion. However, in some families, trans mutant alleles interact with the primary causal locus to modulate the penetrance and/or the expressivity of the phenotype. CCDC28B (MGC1203) was identified as a second site modifier of BBS encoding a protein of unknown function. Here we report the first functional characterization of this protein and show it affects ciliogenesis both in cultured cells and in vivo in zebrafish. Consistent with this biological role, our in silico analysis shows that the presence of CCDC28B homologous sequences is restricted to ciliated metazoa. Depletion of Ccdc28b in zebrafish results in defective ciliogenesis and consequently causes a number of phenotypes that are characteristic of BBS and other ciliopathy mutants including hydrocephalus, left-right axis determination defects and renal function impairment. Thus, this work reports CCDC28B as a novel protein involved in the process of ciliogenesis whilst providing functional insight into the cellular basis of its modifier effect in BBS patients.

A systematic analysis of small supernumerary marker chromosomes using array CGH exposes unexpected complexity

A small supernumerary marker chromosome is often seen in patients with developmental disorders. Prior to array-based comparative genomic hybridization markers were rarely genotyped end to end. In this study, a valid genotype-to-phenotype correlation was possible because the supernumerary marker chromosomes were fully characterized by array-based comparative genomic hybridization in a genome-wide analysis. Ten consecutive de novo small supernumerary marker chromosome cases were systematically genotyped using G-banding, C-banding, AgNOR staining, whole-genome array-based comparative genomic hybridization, and fluorescence in situ hybridization. Among 10 small supernumerary marker chromosome cases studied, 4 (40%) were not identified by array-based comparative genomic hybridization because of low-level mosaicism or because they lacked euchromatin. One case (10%) was a simple pericentromeric marker extending from 5p13.3 to 5q11.2. Five (50%) markers showed unexpected complexity. Two cases had markers that were derivative acrocentric (AgNOR+) chromosomes with the euchromatin from chromosomes 18p or 19p. Each of the other three cases with complex markers had unusual characteristics including a marker from noncontiguous segments of chromosome 19q, a highly complex rearrangement involving a chromosome 20 homolog as well as the small supernumerary marker chromosome, and a mosaic duplication of a proximal 8p marker. Small supernumerary marker chromosomes are frequently complex on the basis of our small sample. Whole-genome array-based comparative genomic hybridization characterization of the small supernumerary marker chromosome provided informed genetic counseling.

Phenotypic expression of Bardet–Biedl syndrome in patients homozygous for the common M390R mutation in the BBS1 gene

PurposeTo characterize the phenotype of Bardet–Biedl syndrome (BBS) patients homozygous for the BBS1 M390R mutation. MethodsThree patients [PT1, F, 27years old (yo) at last examination, 14-year follow-up (F/U) PT2, F, 15-yo PT3, M, 15-yo, both 1-year F/U] underwent eye exams, Goldmann visual fields (GVFs), dark- (DA) and light-adapted (LA) electroretinograms (ERGs), spectral domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF). Vision and systemic history were also collected. ResultsAll patients had night blindness, hyperopic astigmatism, ptosis or mild blepharospasm, foot polydactyly, 5th finger clinodactyly, history of headaches, and variable, diet-responsive obesity. Two had asthma, PT1 was developmentally delayed, PT2 had Asperger-like symptoms, and PT3 had normal cognition. At age 14, acuity was 20/100 in PT1, who had nystagmus since age 2, 20/40 in PT2 and 20/30 in PT3. By 27yo PT1 progressed to 20/320, by 15yo PT2 was 20/60 and PT3 remained stable. PT1 had well preserved peripheral GVFs, with minimal progression over 10years of F/U. PT2 and PT3 presented with ring scotomas and I4e<5°. All patients had severe generalized visual sensitivity depression. ERGs were consistently recordable (also rod ERG in PT3 after 60min DA), but progressed to non-recordable in PT1. Mixed DA ERGs exhibited electronegativity. In PT3, this was partly due to a bleaching effect during bright-flash DA averaging, partly to ON≫OFF LA response compromise. PT2 and 3 had, on SD-OCTs, generalized macular thinning, normal retinal lamination, and widespread photoreceptor outer/inner segment attenuation except foveally, and multiple rings of abnormal FAF configuring a complex bull’s eye-pattern. PT1 had macular atrophy. All patients also had peripapillary nerve fiber layer thickening. ConclusionsThe observed phenotype matches very closely that reported in patients by Azari et al. (IOVS 2006) and in the Bbs1-M390R knock-in mouse model, and expands it to the characterization of important ERG response characteristics that provide insight in the pathogenesis of retinopathy in these patients. Our findings confirm the consistent pathogenicity of the BBS1 M390R mutation.

A truncating mutation of Alms1 reduces the number of hypothalamic neuronal cilia in obese mice

Primary cilia are ubiquitous cellular antennae whose dysfunction collectively causes various disorders, including vision and hearing impairment, as well as renal, skeletal, and central nervous system anomalies. One ciliopathy, Alström syndrome, is closely related to Bardet-Biedl syndrome (BBS), sharing amongst other phenotypic features morbid obesity. As the cellular and molecular links between weight regulation and cilia are poorly understood, we used the obese mouse strain foz/foz, bearing a truncating mutation in the Alström syndrome protein (Alms1), to help elucidate why it develops hyperphagia, leading to early onset obesity and metabolic anomalies. Our in vivo studies reveal that Alms1 localizes at the base of cilia in hypothalamic neurons, which are implicated in the control of satiety. Alms1 is lost from this location in foz/foz mice, coinciding with a strong postnatal reduction (∼70%) in neurons displaying cilia marked with adenylyl cyclase 3 (AC3), a signaling protein implicated in obesity. Notably, the reduction in AC3-bearing cilia parallels the decrease in cilia containing two appetite-regulating proteins, Mchr1 and Sstr3, as well as another established Arl13b ciliary marker, consistent with progressive loss of cilia during development. Together, our results suggest that Alms1 maintains the function of neuronal cilia implicated in weight regulation by influencing the maintenance and/or stability of the organelle. Given that Mchr1 and Sstr3 localization to remaining cilia is maintained in foz/foz animals but known to be lost from BBS knockout mice, our findings suggest different molecular etiologies for the satiety defects associated with the Alström syndrome and BBS ciliopathies.

New topics in the skeletal dysplasias

A first glance at the Table of contents of this issue might give the impression that we have chosen a disparate group of conditions to explore. However, we feel that this selection represents several key principles of the field and genetics, as well as medicine in general: these rare disorders need careful delineation and study so as not to be mistakenly lumped and inappropriately treated, molecular origins turn out to be more intricate and beautiful than previously imagined, and only through accurate recording can we move forward. Drs. Terhal and Mortier from the Netherlands and Belgium, together with clinical partners from several countries, have studied a large series of patients with mutations in theCOL2A1 gene and elaborated new growth curves for spondylo-epiphyseal dysplasia congenital (SEDC) and related collagen 2 disorders. Development of these molecularly based growth curves is a major step forward in the nosography of collagen 2-related dysplasias, one of the largest and most important group of patients in a skeletal dysplasia clinic. Although variability remains significant and points to the multifactorial determination of height even in the presence of a single gene with a major influence, the possibility of comparing the growth chart of a single patient with that of a cohort of patients with similar mutations is a significant improvement over the past and projects us towards the future. It is hoped that similar studies will begin as soon as possible for all other major chondrodysplasia genes allowing the creation of a comprehensive database. In the best of worlds, such a database would include also data on morbidity and complications. The data presented by Drs. Terhal, Mortier and coworkers will undoubtedly constitute an important reference for years to come. The so-called enchondromatoses have been difficult to deal with in many a revision of the Nosology. Are they really ‘‘anarchic’’ development of bone or are they a special type of dysplasia? Andwhat about their inheritance, so many cases being sporadic? Drs. SupertiFurga, Nishimura and Spranger have tried to tackle these questions with the help of recent results that have revealed unexpected molecular mechanisms. They suggest that enchondromas are useful but nonspecific findings and that the molecular bases include both homeostatic defects of bone resorption as well as true dysregulation of cell proliferation. In the latter group, the role of somatic mutations gives a novel twist to the story. The newly proposed classification and the presentation of reference images from molecularly proven individuals will prove to be a helpful companion for the clinician and radiologist. The Paris group led by Dr. Valerie Cormier-Daire contributes two articles illustrating the contribution of the study of genetic disorders to our understanding of skeletal biology and of human growth. In the article on ‘‘ciliary’’ disorders, Drs. Huber and Cormier take us into the world of monocilia, fascinating structures that stand like tall poles on the surface ofmost cells, including chondrocytes, receiving and transmitting signals—much like the antennas of cellular phones that today line the highways of modern countries—or, like in photoreceptors, carry large stacks of sensory molecules. The high morphologic and functional specialization of cilia is based on a complex transport and assembly apparatus (the intraflagellary transport system, IFT) and mutations in components of this apparatus affect proliferation and differentiation of cells. Based on the current state of knowledge in the skeletal dysplasias and in other ciliary disorders such as the Bardet–Biedl syndrome and the genetic nephropathies, Le Goff and Cormier predict that mutations in many more ciliary genes will be uncovered, and that genotype– DEDICATION To the memory of

An unusual case of Bardet–Biedl syndrome presenting with type 1 diabetes mellitus

An unusual case of Bardet–Biedl syndrome presenting with type 1 diabetes mellitus

Extended mutation spectrum of Usher syndrome in Finland

The Finnish distribution of clinical Usher syndrome (USH) types is 40% USH3, 34% USH1 and 12% USH2. All patients with USH3 carry the founder mutation in clarin 1 (CLRN1), whereas we recently reported three novel myosin VIIA (MYO7A) mutations in two unrelated patients with USH1. This study was carried out to further investigate the USH mutation spectrum in Finnish patients. We analysed samples from nine unrelated USH patients/families without known mutations and two USH3 families with atypically severe phenotype. The Asper Ophthalmics USH mutation chip was used to screen for known mutations and to evaluate the chip in molecular diagnostics of Finnish patients. The chip revealed a heterozygous usherin (USH2A) mutation, p.N346H, in one patient. Sequencing of MYO7A and/or USH2A in three index patients revealed two novel heterozygous mutations, p.R873W in MYO7A and c.14343+2T>C in USH2A. We did not identify definite pathogenic second mutations in the patients, but identified several probably nonpathogenic variations that may modify the disease phenotype. Possible digenism could not be excluded in two families segregating genomic variations in both MYO7A and USH2A, and two families with CLRN1 and USH2A. We conclude that there is considerable genetic heterogeneity of USH1 and USH2 in Finland, making molecular diagnostics and genetic counselling of patients and families challenging.

Obesity in patients with Bardet–Biedl syndrome: influence of appetite-regulating hormones

Bardet-Biedl syndrome (BBS) is a genetic disorder with obesity as one of the major phenotypic criterion, which is proposed to be of neuroendocrine origin. Therefore, disturbances in appetite-regulating hormones have been considered as causative factors. Acyl ghrelin is an orexigenic hormone, whereas its desacylated form, obestatin, and leptin have the opposite functions. Ghrelin is negatively regulated in relation to nutritional status. The aim of this study was to evaluate the impact of hormone alterations on obesity development in BBS patients. Total and acylated ghrelin, obestatin, leptin and adiponectin were measured in eight children with BBS. The results were analyzed in relation to auxological parameters [body mass index (BMI), height]. The mean BMI was significantly increased in BBS patients compared to the controls. Plasma levels of acylated ghrelin, total ghrelin and obestatin were slightly elevated in BBS patients compared to controls, as was the acyl/total ghrelin ratio. Leptin levels were significantly elevated in BBS patients. BBS patients lack the negative regulatory mechanisms of appetite-regulating hormones with respect to nutritional status and exhibit resistance to anorexigenic leptin. This results in a shift towards the orexigenic effects of this self-regulating system. These alterations may in part be responsible for the disturbed appetite regulation in BBS patients.

Amplification of the STOML3, FREM2, and LHFP Genes Is Associated with Mesenchymal Differentiation in Gliosarcoma

Gliosarcoma is a rare glioblastoma variant characterized by a biphasic tissue pattern with alternating areas that display either glial (glial fibrillary acidic protein-positive) or mesenchymal (reticulin-positive) differentiation. Previous analyses have shown identical genetic alterations in glial and mesenchymal tumor areas, suggesting that gliosarcomas are genetically monoclonal, and mesenchymal differentiation was considered to reflect the elevated genomic instability of glioblastomas. In the present study, we compared genome-wide chromosomal imbalances using array comparative genomic hybridization in glial and mesenchymal tumor areas of 13 gliosarcomas. The patterns of gain and loss were similar, except that the gain at 13q13.3-q14.1 (log(2) ratio >3.0), containing the STOML3, FREM2, and LHFP genes, which was restricted to the mesenchymal tumor area of a gliosarcoma. Further analyses of 64 cases of gliosarcoma using quantitative PCR showed amplification of the STOML3, FREM2, and LHFP genes in 14 (22%), 10 (16%), and 7 (11%) mesenchymal tumor areas, respectively, but not in glial tumor areas. Results of IHC analysis confirmed that overexpression of STOML3 and FREM2 was more extensive in mesenchymal than in glial tumor areas. These results suggest that the mesenchymal components in a small fraction of gliosarcomas may be derived from glial cells with additional genetic alterations.

Bardet Biedl syndrome genes are required for autonomic control of the circulation

Bardet Biedl syndrome (BBS) is a pleiotropic autosomal recessive disorder with several features including hypertension and cardiovascular disease. The 16 Bbs genes identified so far have been implicated in the regulation of several physiological functions. Here, we used the knock‐in Bbs1M390R mouse model that phenocopy human BBS to test the hypothesis that Bbs genes are important for autonomic function. Baroreflex sensitivity (BRS) was examined in conscious state using the responses of renal sympathetic activity, arterial pressure and heart rate (HR) to the sequential intravenous injection of sodium nitroprusside and phenylephrine (PE). Notably, the maximum gain of the baroreflex was reduced in the Bbs1M390R mice (0.8±0.5%) vs. controls (3.3±0.9%, P&lt;0.01). Direct recording of baroreceptor activity from the aortic depressor nerve (ADN) during PE‐induced hypertension which provides another measure of BRS revealed attenuated ADN baroreflex response in Bbs1M390R mice (6±2%) vs. controls (12±3%, P&lt;0.05). Finally, analysis of the central component of the baroreflex with electrical stimulation (40 Hz) of the ADN showed an attenuated HR reflex response in Bbs1M390R mice (−47±16 bpm) vs. controls (−88±15 bpm, P&lt;0.03) indicating that the impairment in BRS in BBS mice is centrally‐mediated. Our data demonstrates that Bbs genes are critically involved in the autonomic regulation of the cardiovascular function.

In search of triallelism in Bardet–Biedl syndrome

Bardet-Biedl syndrome (BBS) is a model disease for ciliopathy in humans. The remarkable genetic heterogeneity that characterizes this disease is consistent with accumulating data on the interaction between the proteins encoded by the 14 BBS genes identified to date. Previous reports suggested that such interaction may also extend to instances of oligogenic inheritance in the form of triallelism which defies the long held view of BBS as an autosomal recessive disease. In order to investigate the magnitude of triallelism in BBS, we conducted a comprehensive analysis of all 14 BBS genes as well as the CCDC28B-modifier gene in a cohort of 29 BBS families, most of which are multiplex. Two in trans mutations in a BBS gene were identified in each of these families for a total of 20 mutations including 12 that are novel. In no instance did we observe two mutations in unaffected members of a given family, or observe the presence of a third allele that convincingly acted as a modifier of penetrance and supported the triallelic model of BBS. In addition to presenting a comprehensive genotype/phenotype overview of a large set of BBS mutations, including the occurrence of nonsyndromic retinitis pigmentosa in a family with a novel BBS9 mutation, our study argues in favor of straightforward autosomal recessive BBS in most cases.