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Genes Sep 2021Treacher Collins syndrome (TCS) is associated with abnormal differentiation of the first and second pharyngeal arches, occurring during fetal development. Features of... (Review)
Review
Treacher Collins syndrome (TCS) is associated with abnormal differentiation of the first and second pharyngeal arches, occurring during fetal development. Features of TCS include microtia with conductive hearing loss, slanting palpebral fissures with possibly coloboma of the lateral part of lower eyelids, midface hypoplasia, micrognathia as well as sporadically cleft palate and choanal atresia or stenosis. TCS occurs in the general population at a frequency of 1 in 50,000 live births. Four subtypes of Treacher Collins syndrome exist. TCS can be caused by pathogenic variants in the , , and genes. Genetically, the gene contains 27 exons which encodes the Treacle protein. In , over 200 pathogenic variants have been identified, of which most are deletions leading to a frame-shift, that result in the formation of a termination codon. In the presented article, we review the genetics and phenotype of TCS as well as the management and surgical procedures utilized for treatment.
Topics: Choanal Atresia; DNA-Directed RNA Polymerases; Humans; Mandibulofacial Dysostosis; Nuclear Proteins; Phosphoproteins; Syndrome
PubMed: 34573374
DOI: 10.3390/genes12091392 -
Orphanet Journal of Rare Diseases Jan 2019Freeman-Burian syndrome (FBS) is a rare congenital myopathic craniofacial syndrome. Considerable variability in severity is seen, but diagnosis requires the following:... (Review)
Review
CLINICAL DESCRIPTION
Freeman-Burian syndrome (FBS) is a rare congenital myopathic craniofacial syndrome. Considerable variability in severity is seen, but diagnosis requires the following: microstomia, whistling-face appearance (pursed lips), H or V-shaped chin defect, and prominent nasolabial folds. Some patients do not have limb malformations, but essentially all do, typically camptodactyly with ulnar deviation of the hand and talipes equinovarus. Neuro-cognitive function is not impaired.
EPIDEMIOLOGY
Population prevalence of FBS is unknown.
AETIOLOGY
Environmental and parental factors are not implicated in pathogenesis. Allelic variations in embryonic myosin heavy chain gene are associated with FBS. White fibrous tissue within histologically normal muscle fibres and complete replacement of muscle by fibrous tissue, which behaves like tendinous tissue, are observed.
MANAGEMENT
Optimal care seems best achieved through a combination of early craniofacial reconstructive surgery and intensive physiotherapy for most other problems. Much of the therapeutic focus is on the areas of fibrous tissue replacement, which are either operatively released or gradually stretched with physiotherapy to reduce contractures. Operative procedures and techniques that do not account for the unique problems of the muscle and fibrous tissue replacement have poor clinical and functional outcomes. Important implications exist to facilitate patients' legitimate opportunity to meaningfully overcome functional limitations and become well.
Topics: Abnormalities, Multiple; Contracture; Craniofacial Dysostosis; Humans; Limb Deformities, Congenital
PubMed: 30630514
DOI: 10.1186/s13023-018-0984-2 -
American Journal of Human Genetics May 2023Heterozygous pathogenic variants in POLR1A, which encodes the largest subunit of RNA Polymerase I, were previously identified as the cause of acrofacial dysostosis,...
Heterozygous pathogenic variants in POLR1A, which encodes the largest subunit of RNA Polymerase I, were previously identified as the cause of acrofacial dysostosis, Cincinnati-type. The predominant phenotypes observed in the cohort of 3 individuals were craniofacial anomalies reminiscent of Treacher Collins syndrome. We subsequently identified 17 additional individuals with 12 unique heterozygous variants in POLR1A and observed numerous additional phenotypes including neurodevelopmental abnormalities and structural cardiac defects, in combination with highly prevalent craniofacial anomalies and variable limb defects. To understand the pathogenesis of this pleiotropy, we modeled an allelic series of POLR1A variants in vitro and in vivo. In vitro assessments demonstrate variable effects of individual pathogenic variants on ribosomal RNA synthesis and nucleolar morphology, which supports the possibility of variant-specific phenotypic effects in affected individuals. To further explore variant-specific effects in vivo, we used CRISPR-Cas9 gene editing to recapitulate two human variants in mice. Additionally, spatiotemporal requirements for Polr1a in developmental lineages contributing to congenital anomalies in affected individuals were examined via conditional mutagenesis in neural crest cells (face and heart), the second heart field (cardiac outflow tract and right ventricle), and forebrain precursors in mice. Consistent with its ubiquitous role in the essential function of ribosome biogenesis, we observed that loss of Polr1a in any of these lineages causes cell-autonomous apoptosis resulting in embryonic malformations. Altogether, our work greatly expands the phenotype of human POLR1A-related disorders and demonstrates variant-specific effects that provide insights into the underlying pathogenesis of ribosomopathies.
Topics: Humans; Mice; Animals; Mandibulofacial Dysostosis; Apoptosis; Mutagenesis; Ribosomes; Phenotype; Neural Crest; Craniofacial Abnormalities
PubMed: 37075751
DOI: 10.1016/j.ajhg.2023.03.014 -
Nature Communications Apr 2023Craniofacial microsomia (CFM; also known as Goldenhar syndrome), is a craniofacial developmental disorder of variable expressivity and severity with a recognizable set...
Craniofacial microsomia (CFM; also known as Goldenhar syndrome), is a craniofacial developmental disorder of variable expressivity and severity with a recognizable set of abnormalities. These birth defects are associated with structures derived from the first and second pharyngeal arches, can occur unilaterally and include ear dysplasia, microtia, preauricular tags and pits, facial asymmetry and other malformations. The inheritance pattern is controversial, and the molecular etiology of this syndrome is largely unknown. A total of 670 patients belonging to unrelated pedigrees with European and Chinese ancestry with CFM, are investigated. We identify 18 likely pathogenic variants in 21 probands (3.1%) in FOXI3. Biochemical experiments on transcriptional activity and subcellular localization of the likely pathogenic FOXI3 variants, and knock-in mouse studies strongly support the involvement of FOXI3 in CFM. Our findings indicate autosomal dominant inheritance with reduced penetrance, and/or autosomal recessive inheritance. The phenotypic expression of the FOXI3 variants is variable. The penetrance of the likely pathogenic variants in the seemingly dominant form is reduced, since a considerable number of such variants in affected individuals were inherited from non-affected parents. Here we provide suggestive evidence that common variation in the FOXI3 allele in trans with the pathogenic variant could modify the phenotypic severity and accounts for the incomplete penetrance.
Topics: Animals; Mice; Goldenhar Syndrome; Facial Asymmetry; Pedigree; Forkhead Transcription Factors
PubMed: 37041148
DOI: 10.1038/s41467-023-37703-6 -
Developmental Dynamics : An Official... Sep 2020The spliceosome is a complex of RNA and proteins that function together to identify intron-exon junctions in precursor messenger-RNAs, splice out the introns, and join... (Review)
Review
The spliceosome is a complex of RNA and proteins that function together to identify intron-exon junctions in precursor messenger-RNAs, splice out the introns, and join the flanking exons. Mutations in any one of the genes encoding the proteins that make up the spliceosome may result in diseases known as spliceosomopathies. While the spliceosome is active in all cell types, with the majority of the proteins presumably expressed ubiquitously, spliceosomopathies tend to be tissue-specific as a result of germ line or somatic mutations, with phenotypes affecting primarily the retina in retinitis pigmentosa, hematopoietic lineages in myelodysplastic syndromes, or the craniofacial skeleton in mandibulofacial dysostosis. Here we describe the major spliceosomopathies, review the proposed mechanisms underlying retinitis pigmentosa and myelodysplastic syndromes, and discuss how this knowledge may inform our understanding of craniofacial spliceosomopathies.
Topics: Animals; Humans; Mandibulofacial Dysostosis; Mutation; Myelodysplastic Syndromes; Retinitis Pigmentosa; Spliceosomes
PubMed: 32506634
DOI: 10.1002/dvdy.214 -
Annals of Cardiac Anaesthesia Jan 2017Goldenhar syndrome or oculo-auriculo-vertebral dysplasia was defined by Goldenhar in 1952 and redefined by Grolin et al. later. As the name denotes, children with this... (Review)
Review
Goldenhar syndrome or oculo-auriculo-vertebral dysplasia was defined by Goldenhar in 1952 and redefined by Grolin et al. later. As the name denotes, children with this syndrome present with craniofacial and vertebral anomalies which increase the risk of airway compromise. Neonates and infants with this syndrome often have premature internal organs, low birth weight, and airway disorders. For this reason, safe anesthesia in such infants requires a complete knowledge regarding metabolism and side effects of the drugs. The association of cardiovascular abnormalities is not uncommon and possesses additional challenge for anesthetic management. The aim of this review is to draw attention to the various perioperative problems that can be faced in these infants when they undergo surgery or the correction of the underlying cardiac problem.
Topics: Adult; Anesthesia; Anesthesiologists; Cardiac Surgical Procedures; Child; Goldenhar Syndrome; Humans; Infant; Infant, Newborn
PubMed: 28074825
DOI: 10.4103/0971-9784.197802 -
Proceedings of the National Academy of... Aug 2022Ribosomal RNA (rRNA) transcription by RNA polymerase I (Pol I) is a critical rate-limiting step in ribosome biogenesis, which is essential for cell survival. Despite its...
Ribosomal RNA (rRNA) transcription by RNA polymerase I (Pol I) is a critical rate-limiting step in ribosome biogenesis, which is essential for cell survival. Despite its global function, disruptions in ribosome biogenesis cause tissue-specific birth defects called ribosomopathies, which frequently affect craniofacial development. Here, we describe a cellular and molecular mechanism underlying the susceptibility of craniofacial development to disruptions in Pol I transcription. We show that Pol I subunits are highly expressed in the neuroepithelium and neural crest cells (NCCs), which generate most of the craniofacial skeleton. High expression of Pol I subunits sustains elevated rRNA transcription in NCC progenitors, which supports their high tissue-specific levels of protein translation, but also makes NCCs particularly sensitive to rRNA synthesis defects. Consistent with this model, NCC-specific deletion of Pol I subunits , , and associated factor in mice cell-autonomously diminishes rRNA synthesis, which leads to p53 protein accumulation, resulting in NCC apoptosis and craniofacial anomalies. Furthermore, compound mutations in Pol I subunits and associated factors specifically exacerbate the craniofacial anomalies characteristic of the ribosomopathies Treacher Collins syndrome and Acrofacial Dysostosis-Cincinnati type. Mechanistically, we demonstrate that diminished rRNA synthesis causes an imbalance between rRNA and ribosomal proteins. This leads to increased binding of ribosomal proteins Rpl5 and Rpl11 to Mdm2 and concomitantly diminished binding between Mdm2 and p53. Altogether, our results demonstrate a dynamic spatiotemporal requirement for rRNA transcription during mammalian cranial NCC development and corresponding tissue-specific threshold sensitivities to disruptions in rRNA transcription in the pathogenesis of congenital craniofacial disorders.
Topics: Animals; Craniofacial Abnormalities; Mandibulofacial Dysostosis; Mice; Neural Crest; Proto-Oncogene Proteins c-mdm2; RNA Polymerase I; RNA, Ribosomal; Ribosomal Proteins; Skull; Transcription, Genetic; Tumor Suppressor Protein p53
PubMed: 35881792
DOI: 10.1073/pnas.2116974119 -
Journal of Postgraduate Medicine 1994A 2 1/2 month old male child was admitted with loose motions and mild dehydration. He was full term normal delivery, born of a non-consanguinous marriage. On...
A 2 1/2 month old male child was admitted with loose motions and mild dehydration. He was full term normal delivery, born of a non-consanguinous marriage. On examination, he had trigonocephaly; anteverted nostrils, long philtrum and hypoplastic supraorbital ridges. X-ray showed sutural separation. Karyotyping confirmed deletion of short arm of chromosome 9 distal to band p22.
Topics: Child, Preschool; Chromosome Deletion; Chromosomes, Human, Pair 9; Craniofacial Dysostosis; Humans; Male; Skull; Syndrome
PubMed: 8568717
DOI: No ID Found -
Indian Journal of Ophthalmology Jul 2022The current literature review aims to evaluate the ocular findings and associated ophthalmic features in Crouzon syndrome. Craniosynostoses are syndromes characterized... (Review)
Review
The current literature review aims to evaluate the ocular findings and associated ophthalmic features in Crouzon syndrome. Craniosynostoses are syndromes characterized by premature fusion of sutures of the skull and Crouzon syndrome is the most common of the craniosynostosis syndromes. Early fusion of sutures results in craniofacial anomalies, including abnormalities of the orbits. To prepare this review of the ophthalmic findings in this disorder, an organized search on online databases such as PubMed, Scopus, Cochrane Library, and Ovid was carried out. The key terms searched were "Crouzon", "craniosynostosis", "eye" and "ophthalmic", and 51 research items were found. A total of 17 articles were included after scrutiny of the databases and a further 25 articles were added after augmented search. A detailed review was performed from the final 42 articles. A comprehensive description of associated anomalies is given along with the author's own technique of surgical management in cases with Crouzon syndrome having bilateral luxation bulbi with exposure keratopathy. However, for optimum management of cranial and oculo-facial dysmorphisms, a multidisciplinary team of specialists is required.
Topics: Craniofacial Dysostosis; Craniosynostoses; Eye; Face; Humans; Syndrome
PubMed: 35791116
DOI: 10.4103/ijo.IJO_3207_21 -
Nature Feb 2018Many craniofacial disorders are caused by heterozygous mutations in general regulators of housekeeping cellular functions such as transcription or ribosome biogenesis....
Many craniofacial disorders are caused by heterozygous mutations in general regulators of housekeeping cellular functions such as transcription or ribosome biogenesis. Although it is understood that many of these malformations are a consequence of defects in cranial neural crest cells, a cell type that gives rise to most of the facial structures during embryogenesis, the mechanism underlying cell-type selectivity of these defects remains largely unknown. By exploring molecular functions of DDX21, a DEAD-box RNA helicase involved in control of both RNA polymerase (Pol) I- and II-dependent transcriptional arms of ribosome biogenesis, we uncovered a previously unappreciated mechanism linking nucleolar dysfunction, ribosomal DNA (rDNA) damage, and craniofacial malformations. Here we demonstrate that genetic perturbations associated with Treacher Collins syndrome, a craniofacial disorder caused by heterozygous mutations in components of the Pol I transcriptional machinery or its cofactor TCOF1 (ref. 1), lead to relocalization of DDX21 from the nucleolus to the nucleoplasm, its loss from the chromatin targets, as well as inhibition of rRNA processing and downregulation of ribosomal protein gene transcription. These effects are cell-type-selective, cell-autonomous, and involve activation of p53 tumour-suppressor protein. We further show that cranial neural crest cells are sensitized to p53-mediated apoptosis, but blocking DDX21 loss from the nucleolus and chromatin rescues both the susceptibility to apoptosis and the craniofacial phenotypes associated with Treacher Collins syndrome. This mechanism is not restricted to cranial neural crest cells, as blood formation is also hypersensitive to loss of DDX21 functions. Accordingly, ribosomal gene perturbations associated with Diamond-Blackfan anaemia disrupt DDX21 localization. At the molecular level, we demonstrate that impaired rRNA synthesis elicits a DNA damage response, and that rDNA damage results in tissue-selective and dosage-dependent effects on craniofacial development. Taken together, our findings illustrate how disruption in general regulators that compromise nucleolar homeostasis can result in tissue-selective malformations.
Topics: Animals; Apoptosis; Benzothiazoles; Cell Nucleolus; Cell Nucleus; Chromatin; DEAD-box RNA Helicases; DNA Damage; DNA, Ribosomal; DNA-Directed RNA Polymerases; Embryonic Stem Cells; HeLa Cells; Humans; Intracellular Signaling Peptides and Proteins; Mandibulofacial Dysostosis; Mice; Naphthyridines; Neural Crest; Nuclear Proteins; Organ Specificity; Phenotype; Phosphoproteins; Protein Transport; RNA Helicases; RNA Polymerase I; RNA, Ribosomal; Ribosomal Proteins; Ribosomes; Skull; Stress, Physiological; Tumor Suppressor Protein p53; Xenopus; Zebrafish; Zebrafish Proteins
PubMed: 29364875
DOI: 10.1038/nature25449