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Heymut Omran

Publications and source records attributed to Heymut Omran.

At least 19 recordsLinked to original sources
PubMed2007

Genetic defects in ciliary structure and function.

Cilia, hair-like structures extending from the cell membrane, perform diverse biological functions. Primary (genetic) defects in the structure and function of sensory and motile cilia result in multiple ciliopathies. The most prominent genetic abnormality involving motile cilia (and the respiratory tract) is primary ciliary dyskinesia (PCD). PCD is a rare, usually autosomal recessive, genetically heterogeneous disorder characterized by sino-pulmonary disease, laterality defects, and male infertility. Ciliary ultrastructural defects are identified in approximately 90% of PCD patients and involve the outer dynein arms, inner dynein arms, or both. Diagnosing PCD is challenging and requires a compatible clinical phenotype together with tests such as ciliary ultrastructural analysis, immunofluorescent staining, ciliary beat assessment, and/or nasal nitric oxide measurements. Recent mutational analysis demonstrated that 38% of PCD patients carry mutations of the dynein genes DNAI1 and DNAH5. Increased understanding of the pathogenesis will aid in better diagnosis and treatment of PCD.

Animals↗
PubMed2006

The von Hippel-Lindau tumor suppressor protein controls ciliogenesis by orienting microtubule growth.

Cilia are specialized organelles that play an important role in several biological processes, including mechanosensation, photoperception, and osmosignaling. Mutations in proteins localized to cilia have been implicated in a growing number of human diseases. In this study, we demonstrate that the von Hippel-Lindau (VHL) protein (pVHL) is a ciliary protein that controls ciliogenesis in kidney cells. Knockdown of pVHL impeded the formation of cilia in mouse inner medullary collecting duct 3 kidney cells, whereas the expression of pVHL in VHL-negative renal cancer cells rescued the ciliogenesis defect. Using green fluorescent protein-tagged end-binding protein 1 to label microtubule plus ends, we found that pVHL does not affect the microtubule growth rate but is needed to orient the growth of microtubules toward the cell periphery, a prerequisite for the formation of cilia. Furthermore, pVHL interacts with the Par3-Par6-atypical PKC complex, suggesting a mechanism for linking polarity pathways to microtubule capture and ciliogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Nephrocystin specifically localizes to the transition zone of renal and respiratory cilia and photoreceptor connecting cilia.

Nephronophthisis (NPHP) is a hereditary cystic kidney disorder that causes renal failure in children and young adults and can be associated with various extrarenal disorders, including retinitis pigmentosa. Six NPHP genes, whose functions are disrupted by autosomal recessive mutations in patients with NPHP, have been identified. The majority of patients with NPHP carry homozygous deletions of NPHP1 encoding nephrocystin. Previous data indicate that nephrocystin forms a complex at cell junctions and focal adhesions. Here, it is shown that nephrocystin specifically localizes at the ciliary base to the transition zone of renal and respiratory cilia and to photoreceptor connecting cilia. During in vitro ciliogenesis of primary human respiratory epithelial cells, nephrocystin can be detected first with a diffuse cytoplasmic localization as soon as cell polarization starts, and translocates to the transition zone when cilia are formed. In columnar respiratory cells, nephrocystin is attached tightly to the axonemal structure of the transition zone at a region that contains the calcium-sensitive cilia autotomy site. In patients with homozygous NPHP1 deletions, nephrocystin is absent from the entire respiratory cell, including the transition zone, which might be of interest for future diagnostic approaches. Cilia formation is not altered in primary nephrocystin-deficient respiratory cells, which is consistent with previous findings obtained for the Caenorhabditis elegans ortholog. In addition, it is shown that the localization pattern of intraflagellar transport proteins and nephrocystin differs, suggesting distinct functional roles. In conclusion, nephrocystin deficiency or dysfunction at the transition zone of renal monocilia and the photoreceptor connecting cilium might explain renal failure and retinal degeneration that are observed in patients with NPHP1.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Mutations of DNAI1 in primary ciliary dyskinesia: evidence of founder effect in a common mutation.

RATIONALE: Primary ciliary dyskinesia (PCD) is a rare, usually autosomal recessive, genetic disorder characterized by ciliary dysfunction, sino-pulmonary disease, and situs inversus. Disease-causing mutations have been reported in DNAI1 and DNAH5 encoding outer dynein arm (ODA) proteins of cilia. OBJECTIVES: We analyzed DNAI1 to identify disease-causing mutations in PCD and to determine if the previously reported IVS1+2_3insT (219+3insT) mutation represents a "founder" or "hot spot" mutation. METHODS: Patients with PCD from 179 unrelated families were studied. Exclusion mapping showed no linkage to DNAI1 for 13 families; the entire coding region was sequenced in a patient from the remaining 166 families. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed on nasal epithelial RNA in 14 families. RESULTS: Mutations in DNAI1 including 12 novel mutations were identified in 16 of 179 (9%) families; 14 harbored biallelic mutations. Deep intronic splice mutations were not identified by reverse transcriptase-polymerase chain reaction. The prevalence of mutations in families with defined ODA defect was 13%; no mutations were found in patients without a defined ODA defect. The previously reported IVS1+2_3insT mutation accounted for 57% (17/30) of mutant alleles, and marker analysis indicates a common founder for this mutation. Seven mutations occurred in three exons (13, 16, and 17); taken together with previous reports, these three exons are emerging as mutation clusters harboring 29% (12/42) of mutant alleles. CONCLUSIONS: A total of 10% of patients with PCD are estimated to harbor mutations in DNAI1; most occur as a common founder IVS1+2_3insT or in exons 13, 16, and 17. This information is useful for establishing a clinical molecular genetic test for PCD.

Adolescent↗
PubMed2006

A novel X-linked recessive mental retardation syndrome comprising macrocephaly and ciliary dysfunction is allelic to oral-facial-digital type I syndrome.

We report on a large family in which a novel X-linked recessive mental retardation (XLMR) syndrome comprising macrocephaly and ciliary dysfunction co-segregates with a frameshift mutation in the OFD1 gene. Mutations of OFD1 have been associated with oral-facial-digital type 1 syndrome (OFD1S) that is characterized by X-chromosomal dominant inheritance and lethality in males. In contrast, the carrier females of our family were clinically inconspicuous, and the affected males suffered from severe mental retardation, recurrent respiratory tract infections and macrocephaly. All but one of the affected males died from respiratory problems in infancy; and impaired ciliary motility was confirmed in the index patient by high-speed video microscopy examination of nasal epithelium. This family broadens the phenotypic spectrum of OFD1 mutations in an unexpected way and sheds light on the complexity of the underlying disease mechanisms.

Alleles↗
PubMed2006

DNAH5 mutations are a common cause of primary ciliary dyskinesia with outer dynein arm defects.

RATIONALE: Primary ciliary dyskinesia (PCD) is characterized by recurrent airway infections and randomization of left-right body asymmetry. To date, autosomal recessive mutations have only been identified in a small number of patients involving DNAI1 and DNAH5, which encode outer dynein arm components. METHODS: We screened 109 white PCD families originating from Europe and North America for presence of DNAH5 mutations by haplotype analyses and/or sequencing. RESULTS: Haplotype analyses excluded linkage in 26 families. In 30 PCD families, we identified 33 novel (12 nonsense, 8 frameshift, 5 splicing, and 8 missense mutations) and two known DNAH5 mutations. We observed clustering of mutations within five exons harboring 27 mutant alleles (52%) of the 52 detected mutant alleles. Interestingly, 6 (32%) of 19 PCD families with DNAH5 mutations from North America carry the novel founder mutation 10815delT. Electron microscopic analyses in 22 patients with PCD with mutations invariably detected outer dynein arm ciliary defects. High-resolution immunofluorescence imaging of respiratory epithelial cells from eight patients with DNAH5 mutations showed mislocalization of mutant DNAH5 and accumulation at the microtubule organizing centers. Mutant DNAH5 was absent throughout the ciliary axoneme in seven patients and remained detectable in the proximal ciliary axoneme in one patient carrying compound heterozygous splicing mutations at the 3'-end (IVS75-2A>T, IVS76+5G>A). In a preselected subpopulation with documented outer dynein arm defects (n = 47), DNAH5 mutations were identified in 53% of patients. CONCLUSIONS: DNAH5 is frequently mutated in patients with PCD exhibiting outer dynein arm defects and mutations cluster in five exons.

Axonemal Dyneins↗
PubMed2006

Novel tools to unravel molecular mechanisms in cilia-related disorders.

Cilia are hair-like organelles extending from the cell surface that execute motile (e.g. respiratory cilia) and/or sensory functions (e.g. renal monocilia). The basic ultrastructure of cilia and flagella has been well established by electron microscopy. Several recent reports have now provided intriguing new insights into the complex molecular composition of cilia and flagella. These data from genome, proteome and transcriptome analyses will facilitate the systematic discovery and understanding of genes responsible for human cilia-related diseases, such as primary ciliary dyskinesia, polycystic kidney disease and male sterility.

Animals↗
PubMed2006

Mutations in antiquitin in individuals with pyridoxine-dependent seizures.

We show here that children with pyridoxine-dependent seizures (PDS) have mutations in the ALDH7A1 gene, which encodes antiquitin; these mutations abolish the activity of antiquitin as a delta1-piperideine-6-carboxylate (P6C)-alpha-aminoadipic semialdehyde (alpha-AASA) dehydrogenase. The accumulating P6C inactivates pyridoxal 5'-phosphate (PLP) by forming a Knoevenagel condensation product. Measurement of urinary alpha-AASA provides a simple way of confirming the diagnosis of PDS and ALDH7A1 gene analysis provides a means for prenatal diagnosis.

Aldehyde Dehydrogenase↗
PubMed2006

Mutations in ACY1, the gene encoding aminoacylase 1, cause a novel inborn error of metabolism.

N-terminal acetylation of proteins is a widespread and highly conserved process. Aminoacylase 1 (ACY1; EC 3.5.14) is the most abundant of the aminoacylases, a class of enzymes involved in hydrolysis of N-acetylated proteins. Here, we present four children with genetic deficiency of ACY1. They were identified through organic acid analyses using gas chromatography-mass spectrometry, revealing increased urinary excretion of several N-acetylated amino acids, including the derivatives of methionine, glutamic acid, alanine, leucine, glycine, valine, and isoleucine. Nuclear magnetic resonance spectroscopy analysis of urine samples detected a distinct pattern of N-acetylated metabolites, consistent with ACY1 dysfunction. Functional analyses of patients' lymphoblasts demonstrated ACY1 deficiency. Mutation analysis uncovered recessive loss-of-function or missense ACY1 mutations in all four individuals affected. We conclude that ACY1 mutations in these children led to functional ACY1 deficiency and excretion of N-acetylated amino acids. Questions remain, however, as to the clinical significance of ACY1 deficiency. The ACY1-deficient individuals were ascertained through urine metabolic screening because of unspecific psychomotor delay (one subject), psychomotor delay with atrophy of the vermis and syringomyelia (one subject), marked muscular hypotonia (one subject), and follow-up for early treated biotinidase deficiency and normal clinical findings (one subject). Because ACY1 is evolutionarily conserved in fish, frog, mouse, and human and is expressed in the central nervous system (CNS) in human, a role in CNS function or development is conceivable but has yet to be demonstrated. Thus, at this point, we cannot state whether ACY1 deficiency has pathogenic significance with pleiotropic clinical expression or is simply a biochemical variant. Awareness of this new genetic entity may help both in delineating its clinical significance and in avoiding erroneous diagnoses.

Acetylation↗
PubMed2006

Axonemal localization of the dynein component DNAH5 is not altered in secondary ciliary dyskinesia.

Primary ciliary dyskinesia (PCD) is a heterogeneous genetic disorder characterized by recurrent airway infections and situs inversus in half of affected individuals. Diagnosis currently relies on demonstration of abnormal ciliary ultrastructure or altered ciliary beat. Alterations encountered in secondary ciliary dyskinesia (SCD) caused by inflammation often complicate the diagnostic workup. We have recently shown that in respiratory epithelial cells from PCD patients with outer dynein arm defects the dynein protein DNAH5 is mislocalized and either completely or partially absent from the ciliary axoneme. In this study, we addressed the question whether SCD might affect axonemal DNAH5 localization in respiratory cells. To induce SCD in vitro, we treated primary human respiratory epithelial cell cultures with interleukin-13 (IL-13). Ciliary function and ultrastructure were assessed by high-speed videomicroscopy and transmission electron microscopy, respectively. For in vivo localization of DNAH5, we performed nasal brushing biopsies in patients with evidence of SCD. Expression of DNAH5 was analyzed by immunofluorescence microscopy. IL-13-treated cells showed evidence of SCD. Ciliary beat frequency was significantly reduced and ultrastructural analyses showed axonemal disorganization compared with control cells. High-resolution immunofluorescence studies of respiratory epithelial cells with SCD identified in vitro and in vivo normal axonemal DNAH5 localization. DNAH5 localization is not altered by SCD, indicating a high potential for immunofluorescence analysis as a novel diagnostic tool in PCD.

Axonemal Dyneins↗
PubMed2005

Surgical treatment of hemangioblastomas of the central nervous system in pediatric patients.

OBJECTIVE: Hemangioblastomas are histologically benign lesions that occur sporadically or as a manifestation of von Hippel-Lindau disease (VHL). The treatment strategy of these neoplasms is complicated by their unpredictable growth patterns and the often irreversible neurological deficits they may cause. This study aims to outline the neurosurgical treatment options and to address the ongoing debate of surgical timing in pediatric patients with VHL. PATIENTS AND METHODS: Thirteen consecutive pediatric patients (mean age 15.1 years) who were surgically treated for intracranial (n=8) or spinal hemangioblastomas (n=5) were included in this study (range of clinical follow up 12-86 months). Ten patients were affected by von Hippel-Lindau and three were with sporadic tumors. Serial examinations, preoperative MRI studies, and operative findings were reviewed. RESULTS: Patients with cerebellar and intramedullary hemangioblastomas did not develop additional neurological deficits postoperatively. Two patients with brainstem tumors exhibited transient hemiparesis and caudal nerve palsy, respectively. Both patients recovered completely from their postoperative deficits. Preoperatively symptomatic patients with spinal tumors did not deteriorate nor improve after surgery. During the observed follow-up periods, no tumor recurrences were observed. CONCLUSION: Central nervous system (CNS) hemangioblastomas in pediatric patients can be surgically treated with low morbidity. Based on our experience, we recommend considering also the surgical removal of asymptomatic hemangioblastomas with proven radiological progression to prevent the development of permanent neurological deficits. Molecular screening of every pediatric patient and family is mandatory to enable the detection of extraneurological tumors and the development of an efficient therapeutic strategy.

Adolescent↗
PubMed2005

Phosphorylation by casein kinase 2 induces PACS-1 binding of nephrocystin and targeting to cilia.

Mutations in proteins localized to cilia and basal bodies have been implicated in a growing number of human diseases. Access of these proteins to the ciliary compartment requires targeting to the base of the cilia. However, the mechanisms involved in transport of cilia proteins to this transitional zone are elusive. Here we show that nephrocystin, a ciliary protein mutated in the most prevalent form of cystic kidney disease in childhood, is expressed in respiratory epithelial cells and accumulates at the base of cilia, overlapping with markers of the basal body area and the transition zone. Nephrocystin interacts with the phosphofurin acidic cluster sorting protein (PACS)-1. Casein kinase 2 (CK2)-mediated phosphorylation of three critical serine residues within a cluster of acidic amino acids in nephrocystin mediates PACS-1 binding, and is essential for colocalization of nephrocystin with PACS-1 at the base of cilia. Inhibition of CK2 activity abrogates this interaction and results in the loss of correct nephrocystin targeting. These data suggest that CK2-dependent transport processes represent a novel pathway of targeting proteins to the cilia.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Identification and analysis of axonemal dynein light chain 1 in primary ciliary dyskinesia patients.

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder characterized by chronic infections of the upper and lower airways, randomization of left/right body asymmetry, and reduced fertility. The phenotype results from dysfunction of motile cilia of the respiratory epithelium, at the embryonic node and of sperm flagella. Ultrastructural defects often involve outer dynein arms (ODAs), that are composed of several light (LCs), intermediate, and heavy (HCs) dynein chains. We recently showed that recessive mutations of DNAH5, the human ortholog of the biflagellate Chlamydomonas ODA gamma-HC, cause PCD. In Chlamydomonas, motor protein activity of the gamma-ODA-HC is regulated by binding of the axonemal LC1. We report the identification of the human (DNAL1) and murine (Dnal1) orthologs of the Chlamydomonas LC1-gene. Northern blot and in situ hybridization analyses revealed specific expression in testis, embryonic node, respiratory epithelium, and ependyma, resembling the DNAH5 expression pattern. In silico protein analysis showed complete conservation of the LC1/gamma-HC binding motif in DNAL1. Protein interaction studies demonstrated binding of DNAL1 and DNAH5. Based on these findings, we considered DNAL1 a candidate for PCD and sequenced all exons of DNAL1 in 86 patients. Mutational analysis was negative, excluding a major role of DNAL1 in the pathogenesis of PCD.

Amino Acid Motifs↗
PubMed2005

Far lateral supracerebellar infratentorial approach for the treatment of upper brainstem gliomas: clinical experience with pediatric patients.

OBJECTIVE: Surgical exposure of intrinsic lesions located lateral to the brainstem still represents a challenging task. The aim of this study was to assess the feasibility of the extracerebral far lateral supracerebellar infratentorial (FLSI) approach for the treatment of gliomas located in the upper brainstem in the pediatric population. METHODS AND RESULTS: Between 1992 and 2002, seven patients (mean age 8.7 years) with tumors of glial origin (WHO I-IV) located mainly in the pontomesencephalic region were operated with the FLSI approach in a sitting position. Satisfactory extent of resection without additional morbidity was achieved. CONCLUSION: In a carefully selected pediatric patient population, the FLSI approach proved to be a feasible and effective surgical route for the treatment of upper brainstem gliomas.

Adolescent↗
PubMed2005

Mislocalization of DNAH5 and DNAH9 in respiratory cells from patients with primary ciliary dyskinesia.

RATIONALE: Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder characterized by recurrent infections of the airways and situs inversus in half of the affected offspring. The most frequent genetic defects comprise recessive mutations of DNAH5 and DNAI1, which encode outer dynein arm (ODA) components. Diagnosis of PCD usually relies on electron microscopy, which is technically demanding and sometimes difficult to interpret. METHODS: Using specific antibodies, we determined the subcellular localization of the ODA heavy chains DNAH5 and DNAH9 in human respiratory epithelial and sperm cells of patients with PCD and control subjects by high-resolution immunofluorescence imaging. We also assessed cilia and sperm tail function by high-speed video microscopy. RESULTS: In normal ciliated airway epithelium, DNAH5 and DNAH9 show a specific regional distribution along the ciliary axoneme, indicating the existence of at least two distinct ODA types. DNAH5 was completely or only distally absent from the respiratory ciliary axoneme in patients with PCD with DNAH5- (n = 3) or DNAI1- (n = 1) mutations, respectively, and instead accumulated at the microtubule-organizing centers. In contrast to respiratory cilia, sperm tails from a patient with DNAH5 mutations had normal ODA heavy chain distribution, suggesting different modes of ODA generation in these cell types. Blinded investigation of a large cohort of patients with PCD and control subjects identified DNAH5 mislocalization in all patients diagnosed with ODA defects by electron microscopy (n = 16). Cilia with complete axonemal DNAH5 deficiency were immotile, whereas cilia with distal DNAH5 deficiency showed residual motility. CONCLUSIONS: Immunofluorescence staining can detect ODA defects, which will possibly aid PCD diagnosis.

Axonemal Dyneins↗
PubMed2005

Nephrocystin-5, a ciliary IQ domain protein, is mutated in Senior-Loken syndrome and interacts with RPGR and calmodulin.

Nephronophthisis (NPHP) is the most frequent genetic cause of chronic renal failure in children. Identification of four genes mutated in NPHP subtypes 1-4 (refs. 4-9) has linked the pathogenesis of NPHP to ciliary functions. Ten percent of affected individuals have retinitis pigmentosa, constituting the renal-retinal Senior-Loken syndrome (SLSN). Here we identify, by positional cloning, mutations in an evolutionarily conserved gene, IQCB1 (also called NPHP5), as the most frequent cause of SLSN. IQCB1 encodes an IQ-domain protein, nephrocystin-5. All individuals with IQCB1 mutations have retinitis pigmentosa. Hence, we examined the interaction of nephrocystin-5 with RPGR (retinitis pigmentosa GTPase regulator), which is expressed in photoreceptor cilia and associated with 10-20% of retinitis pigmentosa. We show that nephrocystin-5, RPGR and calmodulin can be coimmunoprecipitated from retinal extracts, and that these proteins localize to connecting cilia of photoreceptors and to primary cilia of renal epithelial cells. Our studies emphasize the central role of ciliary dysfunction in the pathogenesis of SLSN.

Amino Acid Sequence↗
PubMed2005

Dominant negative mutations in the C-propeptide of COL2A1 cause platyspondylic lethal skeletal dysplasia, torrance type, and define a novel subfamily within the type 2 collagenopathies.

Platyspondylic lethal skeletal dysplasia (PLSD) Torrance type (PLSD-T) is a rare skeletal dysplasia characterized by platyspondyly, brachydactyly, and metaphyseal changes. Generally a perinatally lethal disease, a few long-term survivors have been reported. Recently, mutations in the carboxy-propeptide of type II collagen have been identified in two patients with PLSD-T, indicating that PLSD-T is a type 2 collagen-associated disorder. We studied eight additional cases of PLSD-T and found that all had mutations in the C-propeptide domain of COL2A1. The mutational spectrum includes missense, stop codon and frameshift mutations. All non-sense mutations were located in the last exon, where they would escape non-sense-mediated RNA-decay. We conclude that PLSD-T is caused by mutations in the C-propeptide domain of COL2A1, which lead to biosynthesis of an altered collagen chain (as opposed to a null allele). Similar mutations have recently been found to be the cause of spondyloperipheral dysplasia, a non-lethal dominant disorder whose clinical and radiographical features overlap those of the rare long-term survivors with PLSD-T. Thus, spondyloperipheral dysplasia and PLSD-T constitute a novel subfamily within the type II collagenopathies, associated with specific mutations in the C-propeptide domain and characterized by distinctive radiological features including metaphyseal changes and brachydactyly that set them apart from other type 2 collagenopathies associated with mutations in the triple-helical domain of COL2A1. The specific phenotype of C-propeptide mutations could result from a combination of diminished collagen fibril formation, toxic effects through the accumulation of unfolded collagen chains inside the chondrocytes, and alteration of a putative signaling function of the carboxy-propeptide of type 2 collagen.

Child, Preschool↗