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Kuroda Y, Ritter A, Mullegama SV, Izumi K. Mosaic RAI1 variant in a Smith-Magenis syndrome patient with total anomalous pulmonary venous return. Am J Med Genet A 2022; 188:3130-3134. [PMID: 35833697 DOI: 10.1002/ajmg.a.62907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 04/23/2022] [Accepted: 06/30/2022] [Indexed: 01/31/2023]
Affiliation(s)
- Yukiko Kuroda
- Division of Human Genetics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Alyssa Ritter
- Division of Human Genetics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | | | - Kosuke Izumi
- Division of Human Genetics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
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2
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Neira-Fresneda J, Potocki L. Neurodevelopmental Disorders Associated with Abnormal Gene Dosage: Smith-Magenis and Potocki-Lupski Syndromes. J Pediatr Genet 2015; 4:159-67. [PMID: 27617127 DOI: 10.1055/s-0035-1564443] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Accepted: 06/23/2015] [Indexed: 12/22/2022]
Abstract
Smith-Magenis syndrome (SMS) and Potocki-Lupski syndrome (PTLS) are reciprocal contiguous gene syndromes within the well-characterized 17p11.2 region. Approximately 3.6 Mb microduplication of 17p11.2, known as PTLS, represents the mechanistically predicted homologous recombination reciprocal of the SMS microdeletion, both resulting in multiple congenital anomalies. Mouse model studies have revealed that the retinoic acid-inducible 1 gene (RAI1) within the SMS and PTLS critical genomic interval is the dosage-sensitive gene responsible for the major phenotypic features in these disorders. Even though PTLS and SMS share the same genomic region, clinical manifestations and behavioral issues are distinct and in fact some mirror traits may be on opposite ends of a given phenotypic spectrum. We describe the neurobehavioral phenotypes of SMS and PTLS patients during different life phases as well as clinical guidelines for diagnosis and a multidisciplinary approach once diagnosis is confirmed by array comparative genomic hybridization or RAI1 gene sequencing. The main goal is to increase awareness of these rare disorders because an earlier diagnosis will lead to more timely developmental intervention and medical management which will improve clinical outcome.
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Affiliation(s)
- Juanita Neira-Fresneda
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States
| | - Lorraine Potocki
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States; Texas Children's Hospital, Houston, Texas, United States
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3
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Poisson A, Nicolas A, Sanlaville D, Cochat P, De Leersnyder H, Rigard C, Franco P, des Portes V, Edery P, Demily C. [Smith-Magenis syndrome is an association of behavioral and sleep/wake circadian rhythm disorders]. Arch Pediatr 2015; 22:638-45. [PMID: 25934608 DOI: 10.1016/j.arcped.2015.03.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Revised: 12/21/2014] [Accepted: 03/21/2015] [Indexed: 12/12/2022]
Abstract
Smith-Magenis syndrome (SMS) is a genetic disorder characterized by the association of facial dysmorphism, oral speech delay, as well as behavioral and sleep/wake circadian rhythm disorders. Most SMS cases (90%) are due to a 17p11.2 deletion encompassing the RAI1 gene; other cases stem from mutations of the RAI1 gene. Behavioral issues may include frequent outbursts, attention deficit/hyperactivity disorders, self-injuries with onychotillomania and polyembolokoilamania (insertion of objects into bodily orifices), etc. It is noteworthy that the longer the speech delay and the more severe the sleep disorders, the more severe the behavioral issues are. Typical sleep/wake circadian rhythm disorders associate excessive daytime sleepiness with nocturnal agitation. They are related to an inversion of the physiological melatonin secretion cycle. Yet, with an adapted therapeutic strategy, circadian rhythm disorders can radically improve. Usually an association of beta-blockers in the morning (stops daily melatonin secretion) and melatonin in the evening (mimics the evening deficient peak) is used. Once the sleep disorders are controlled, effective treatment of the remaining psychiatric features is needed. Unfortunately, as for many orphan diseases, objective guidelines have not been drawn up. However, efforts should be focused on improving communication skills. In the same vein, attention deficit/hyperactivity disorders, aggressiveness, and anxiety should be identified and specifically treated. This whole appropriate medical management is underpinned by the diagnosis of SMS. Diagnostic strategies include fluorescent in situ hybridization (FISH) or array comparative genomic hybridization (array CGH) when a microdeletion is sought and Sanger sequencing when a point mutation is suspected. Thus, the diagnosis of SMS can be made from a simple blood sample and should be questioned in subjects of any age presenting with an association of facial dysmorphism, speech delay with behavioral and sleep/wake circadian rhythm disorders, and other anomalies including short stature and mild dysmorphic features.
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Affiliation(s)
- A Poisson
- UDEIP, centre de dépistage et de prise en charge des troubles psychiatriques d'origine génétique, centre hospitalier le Vinatier, 95, boulevard Pinel, 69678 Bron cedex, France; Centre de neurosciences cognitives, UMR 5229 CNRS, 69500 Bron, France; Université Lyon 1, 69500 Lyon, France.
| | - A Nicolas
- UDEIP, centre de dépistage et de prise en charge des troubles psychiatriques d'origine génétique, centre hospitalier le Vinatier, 95, boulevard Pinel, 69678 Bron cedex, France; Université Lyon 1, 69500 Lyon, France
| | - D Sanlaville
- Université Lyon 1, 69500 Lyon, France; Service de génétique, centre des anomalies du développement, laboratoire de cytogénétique, hospices civils de Lyon, 69500 Bron, France
| | - P Cochat
- Université Lyon 1, 69500 Lyon, France; Service de néphrologie et rhumatologie pédiatrique, centre de référence des maladies rénales rares, Inserm U820, hospices civils de Lyon, 69500 Bron, France
| | - H De Leersnyder
- Centre de recherche en neurosciences de Lyon, Inserm U1028, CNRS UMR 5292, UCBL, équipe TIGER, 69500 Bron, France
| | - C Rigard
- UDEIP, centre de dépistage et de prise en charge des troubles psychiatriques d'origine génétique, centre hospitalier le Vinatier, 95, boulevard Pinel, 69678 Bron cedex, France; Centre de neurosciences cognitives, UMR 5229 CNRS, 69500 Bron, France
| | - P Franco
- Université Lyon 1, 69500 Lyon, France; Unité d'hypnologie, service de neuropédiatrie, Inserm U 628, hospices civils de Lyon, 69500 Bron, France
| | - V des Portes
- Université Lyon 1, 69500 Lyon, France; Centre de référence X fragile et autres déficiences intellectuelles de causes rares, hospices civils de Lyon, 69500 Bron, France
| | - P Edery
- Service de génétique, centre de référence des anomalies du développement et des syndromes malformatifs, hospices civils de Lyon, 69500 Bron, France; Université Lyon 1, 69500 Lyon, France; Centre de référence X fragile et autres déficiences intellectuelles de causes rares, hospices civils de Lyon, 69500 Bron, France
| | - C Demily
- UDEIP, centre de dépistage et de prise en charge des troubles psychiatriques d'origine génétique, centre hospitalier le Vinatier, 95, boulevard Pinel, 69678 Bron cedex, France; Centre de neurosciences cognitives, UMR 5229 CNRS, 69500 Bron, France; Université Lyon 1, 69500 Lyon, France
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4
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Watson CT, Marques-Bonet T, Sharp AJ, Mefford HC. The genetics of microdeletion and microduplication syndromes: an update. Annu Rev Genomics Hum Genet 2014; 15:215-244. [PMID: 24773319 DOI: 10.1146/annurev-genom-091212-153408] [Citation(s) in RCA: 115] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Chromosomal abnormalities, including microdeletions and microduplications, have long been associated with abnormal developmental outcomes. Early discoveries relied on a common clinical presentation and the ability to detect chromosomal abnormalities by standard karyotype analysis or specific assays such as fluorescence in situ hybridization. Over the past decade, the development of novel genomic technologies has allowed more comprehensive, unbiased discovery of microdeletions and microduplications throughout the human genome. The ability to quickly interrogate large cohorts using chromosome microarrays and, more recently, next-generation sequencing has led to the rapid discovery of novel microdeletions and microduplications associated with disease, including very rare but clinically significant rearrangements. In addition, the observation that some microdeletions are associated with risk for several neurodevelopmental disorders contributes to our understanding of shared genetic susceptibility for such disorders. Here, we review current knowledge of microdeletion/duplication syndromes, with a particular focus on recurrent rearrangement syndromes.
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Affiliation(s)
- Corey T Watson
- Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, NY 10029.,Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029
| | - Tomas Marques-Bonet
- Institut de Biologia Evolutiva, Universitat Pompeu Fabra/CSIC, 08003 Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain.,Centro Nacional de Análisis Genómico, 08023 Barcelona, Spain
| | - Andrew J Sharp
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029
| | - Heather C Mefford
- Department of Pediatrics, University of Washington, Seattle, Washington 98195
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5
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Goh ESY, Banwell B, Stavropoulos DJ, Shago M, Yoon G. Mosaic microdeletion of 17p11.2-p12 and duplication of 17q22-q24 in a girl with Smith-Magenis phenotype and peripheral neuropathy. Am J Med Genet A 2013; 164A:748-52. [PMID: 24357149 DOI: 10.1002/ajmg.a.36322] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Accepted: 10/11/2013] [Indexed: 11/08/2022]
Abstract
We report on a girl with a de novo mosaic derivative chromosome 17 involving a 7.4 Mb deletion of chromosome region 17p11.2 to 17p12 and a duplication of a 12.35 Mb region at 17q22 to 17q24. She was ascertained because of developmental delay, peripheral neuropathy, brachydactyly and minor anomalies. The derivative chromosome was present in approximately 12% of lymphocytes based on FISH studies, and was detected by array comparative genomic hybridization. To our knowledge, this is the third case of mosaicism involving deletion of the 17p11.2 region and the lowest level of mosaicism reported in a patient with Smith-Magenis syndrome (SMS).
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Affiliation(s)
- Elaine Suk-Ying Goh
- Department of Pediatrics, Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, University of Toronto, Toronto, Canada
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6
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Williams S, Zies D, Mullegama S, Grotewiel M, Elsea S. Smith-Magenis syndrome results in disruption of CLOCK gene transcription and reveals an integral role for RAI1 in the maintenance of circadian rhythmicity. Am J Hum Genet 2012; 90:941-9. [PMID: 22578325 DOI: 10.1016/j.ajhg.2012.04.013] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Revised: 03/27/2012] [Accepted: 04/06/2012] [Indexed: 12/11/2022] Open
Abstract
Haploinsufficiency of RAI1 results in Smith-Magenis syndrome (SMS), a disorder characterized by intellectual disability, multiple congenital anomalies, obesity, neurobehavioral abnormalities, and a disrupted circadian sleep-wake pattern. An inverted melatonin rhythm (i.e., melatonin peaks during the day instead of at night) and associated sleep-phase disturbances in individuals with SMS, as well as a short-period circadian rhythm in mice with a chromosomal deletion of Rai1, support SMS as a circadian-rhythm-dysfunction disorder. However, the molecular cause of the circadian defect in SMS has not been described. The circadian oscillator temporally orchestrates metabolism, physiology, and behavior largely through transcriptional modulation. Data support RAI1 as a transcriptional regulator, but the genes it might regulate are largely unknown. Investigation into the role that RAI1 plays in the regulation of gene transcription and circadian maintenance revealed that RAI1 regulates the transcription of circadian locomotor output cycles kaput (CLOCK), a key component of the mammalian circadian oscillator that transcriptionally regulates many critical circadian genes. Data further show that haploinsufficiency of RAI1 and Rai1 in SMS fibroblasts and the mouse hypothalamus, respectively, results in the transcriptional dysregulation of the circadian clock and causes altered expression and regulation of multiple circadian genes, including PER2, PER3, CRY1, BMAL1, and others. These data suggest that heterozygous mutation of RAI1 and Rai1 leads to a disrupted circadian rhythm and thus results in an abnormal sleep-wake cycle, which can contribute to an abnormal feeding pattern and dependent cognitive performance. Finally, we conclude that RAI1 is a positive transcriptional regulator of CLOCK, pinpointing a novel and important role for this gene in the circadian oscillator.
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Edelman EA, Girirajan S, Finucane B, Patel PI, Lupski JR, Smith ACM, Elsea SH. Gender, genotype, and phenotype differences in Smith-Magenis syndrome: a meta-analysis of 105 cases. Clin Genet 2007; 71:540-50. [PMID: 17539903 DOI: 10.1111/j.1399-0004.2007.00815.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Smith-Magenis syndrome (SMS) is a multisystem disorder characterized by developmental delay and mental retardation, a distinctive behavioral phenotype, and sleep disturbance. We undertook a comprehensive meta-analysis to identify genotype-phenotype relationships to further understand the clinical variability and genetic factors involved in SMS. Clinical and molecular information on 105 patients with SMS was obtained through research protocols and a review of the literature and analyzed using Fisher's exact test with two-tailed p values. Several differences in these groups of patients were identified based on genotype and gender. Patients with RAI1 mutation were more likely to exhibit overeating, obesity, polyembolokoilamania, self-hugging, muscle cramping, and dry skin and less likely to have short stature, hearing loss, frequent ear infections, and heart defects when compared with patients with deletion, while a subset of small deletion cases with deletions spanning from TNFRSF13B to MFAP4 was less likely to exhibit brachycephaly, dental anomalies, iris abnormalities, head-banging, and hyperactivity. Significant differences between genders were also identified, with females more likely to have myopia, eating/appetite problems, cold hands and feet, and frustration with communication when compared with males. These results confirm previous findings and identify new genotype-phenotype associations including differences in the frequency of short stature, hearing loss, ear infections, obesity, overeating, heart defects, self-injury, self-hugging, dry skin, seizures, and hyperactivity among others based on genotype. Additional studies are required to further explore the relationships between genotype and phenotype and any potential discrepancies in health care and parental attitudes toward males and females with SMS.
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Affiliation(s)
- E A Edelman
- Department of Human Genetics, Virginia Commonwealth University, Richmond, VA 23298, USA
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8
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Sharp AJ, Hansen S, Selzer RR, Cheng Z, Regan R, Hurst JA, Stewart H, Price SM, Blair E, Hennekam RC, Fitzpatrick CA, Segraves R, Richmond TA, Guiver C, Albertson DG, Pinkel D, Eis PS, Schwartz S, Knight SJL, Eichler EE. Discovery of previously unidentified genomic disorders from the duplication architecture of the human genome. Nat Genet 2006; 38:1038-42. [PMID: 16906162 DOI: 10.1038/ng1862] [Citation(s) in RCA: 441] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Accepted: 07/20/2006] [Indexed: 01/29/2023]
Abstract
Genomic disorders are characterized by the presence of flanking segmental duplications that predispose these regions to recurrent rearrangement. Based on the duplication architecture of the genome, we investigated 130 regions that we hypothesized as candidates for previously undescribed genomic disorders. We tested 290 individuals with mental retardation by BAC array comparative genomic hybridization and identified 16 pathogenic rearrangements, including de novo microdeletions of 17q21.31 found in four individuals. Using oligonucleotide arrays, we refined the breakpoints of this microdeletion, defining a 478-kb critical region containing six genes that were deleted in all four individuals. We mapped the breakpoints of this deletion and of four other pathogenic rearrangements in 1q21.1, 15q13, 15q24 and 17q12 to flanking segmental duplications, suggesting that these are also sites of recurrent rearrangement. In common with the 17q21.31 deletion, these breakpoint regions are sites of copy number polymorphism in controls, indicating that these may be inherently unstable genomic regions.
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Affiliation(s)
- Andrew J Sharp
- Department of Genome Sciences and The Howard Hughes Medical Institute, University of Washington School of Medicine, 1705 NE Pacific St., Seattle, Washington 98195, USA
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9
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Bi W, Park SS, Shaw CJ, Withers MA, Patel PI, Lupski JR. Reciprocal crossovers and a positional preference for strand exchange in recombination events resulting in deletion or duplication of chromosome 17p11.2. Am J Hum Genet 2003; 73:1302-15. [PMID: 14639526 PMCID: PMC1180396 DOI: 10.1086/379979] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2003] [Accepted: 09/16/2003] [Indexed: 01/15/2023] Open
Abstract
Smith-Magenis syndrome (SMS) is caused by an approximately 4-Mb heterozygous interstitial deletion on chromosome 17p11.2 in approximately 80%-90% of affected patients. Three large ( approximately 200 kb), complex, and highly homologous ( approximately 98%) low-copy repeats (LCRs) are located inside or flanking the SMS common deletion. These repeats, also known as "SMS-REPs," are termed "distal," "middle," and "proximal." The directly oriented distal and proximal copies act as substrates for nonallelic homologous recombination resulting in both the deletion associated with SMS and the reciprocal duplication: dup(17)(p11.2p11.2). Using restriction enzyme cis-morphism analyses and direct sequencing, we mapped the regions of strand exchange in 16 somatic-cell hybrids that harbor only the recombinant SMS-REP. Our studies showed that the sites of crossovers were distributed throughout the region of homology between the distal and proximal SMS-REPs. However, despite approximately 170 kb of high homology, 50% of the recombinant junctions occurred in a 12.0-kb region within the KER gene clusters. DNA sequencing of this hotspot (positional preference for strand exchange) in seven recombinant SMS-REPs narrowed the crossovers to an approximately 8-kb interval. Four of them occurred in a 1,655-bp region rich in polymorphic nucleotides that could potentially reflect frequent gene conversion. For further evaluation of the strand exchange frequency in patients with SMS, novel junction fragments from the recombinant SMS-REPs were identified. As predicted by the reciprocal-recombination model, junction fragments were also identified from this hotspot region in patients with dup(17)(p11.2p11.2), documenting reciprocity of the positional preference for strand exchange. Several potential cis-acting recombination-promoting sequences were identified within the hotspot. It is interesting that we found 2.1-kb AT-rich inverted repeats flanking the proximal and middle KER gene clusters but not the distal one. The role of any or all of these in stimulating double-strand breaks around this positional recombination hotspot remains to be explored.
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Affiliation(s)
- Weimin Bi
- Departments of Molecular and Human Genetics, Neurology, and Pediatrics, Baylor College of Medicine, and Texas Children’s Hospital, Houston
| | - Sung-Sup Park
- Departments of Molecular and Human Genetics, Neurology, and Pediatrics, Baylor College of Medicine, and Texas Children’s Hospital, Houston
| | - Christine J. Shaw
- Departments of Molecular and Human Genetics, Neurology, and Pediatrics, Baylor College of Medicine, and Texas Children’s Hospital, Houston
| | - Marjorie A. Withers
- Departments of Molecular and Human Genetics, Neurology, and Pediatrics, Baylor College of Medicine, and Texas Children’s Hospital, Houston
| | - Pragna I. Patel
- Departments of Molecular and Human Genetics, Neurology, and Pediatrics, Baylor College of Medicine, and Texas Children’s Hospital, Houston
| | - James R. Lupski
- Departments of Molecular and Human Genetics, Neurology, and Pediatrics, Baylor College of Medicine, and Texas Children’s Hospital, Houston
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Park SS, Stankiewicz P, Bi W, Shaw C, Lehoczky J, Dewar K, Birren B, Lupski JR. Structure and evolution of the Smith-Magenis syndrome repeat gene clusters, SMS-REPs. Genome Res 2002; 12:729-38. [PMID: 11997339 PMCID: PMC186597 DOI: 10.1101/gr.82802] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
An approximately 4-Mb genomic segment on chromosome 17p11.2, commonly deleted in patients with the Smith-Magenis syndrome (SMS) and duplicated in patients with dup(17)(p11.2p11.2) syndrome, is flanked by large, complex low-copy repeats (LCRs), termed proximal and distal SMS-REP. A third copy, the middle SMS-REP, is located between them. SMS-REPs are believed to mediate nonallelic homologous recombination, resulting in both SMS deletions and reciprocal duplications. To delineate the genomic structure and evolutionary origin of SMS-REPs, we constructed a bacterial artificial chromosome/P1 artificial chromosome contig spanning the entire SMS region, including the SMS-REPs, determined its genomic sequence, and used fluorescence in situ hybridization to study the evolution of SMS-REP in several primate species. Our analysis shows that both the proximal SMS-REP (approximately 256 kb) and the distal copy (approximately 176 kb) are located in the same orientation and derived from a progenitor copy, whereas the middle SMS-REP (approximately 241 kb) is inverted and appears to have been derived from the proximal copy. The SMS-REP LCRs are highly homologous (>98%) and contain at least 14 genes/pseudogenes each. SMS-REPs are not present in mice and were duplicated after the divergence of New World monkeys from pre-monkeys approximately 40-65 million years ago. Our findings potentially explain why the vast majority of SMS deletions and dup(17)(p11.2p11.2) occur at proximal and distal SMS-REPs and further support previous observations that higher-order genomic architecture involving LCRs arose recently during primate speciation and may predispose the human genome to both meiotic and mitotic rearrangements.
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MESH Headings
- Abnormalities, Multiple/genetics
- Base Composition/genetics
- Cell Line
- Cell Line, Transformed
- Chromosomes, Human, Pair 17/genetics
- Cloning, Molecular/methods
- Contig Mapping/methods
- DNA Fingerprinting/methods
- Evolution, Molecular
- Gene Dosage
- Gene Duplication
- Genome, Human
- Humans
- Intellectual Disability/genetics
- Multigene Family/genetics
- Repetitive Sequences, Nucleic Acid/genetics
- Sequence Alignment/methods
- Sequence Analysis, DNA/methods
- Sequence Homology, Nucleic Acid
- Syndrome
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Affiliation(s)
- Sung-Sup Park
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030, USA
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11
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Abstract
An increasing number of human diseases are recognized to result from recurrent DNA rearrangements involving unstable genomic regions. These are termed genomic disorders, in which the clinical phenotype is a consequence of abnormal dosage of gene(s) located within the rearranged genomic fragments. Both inter- and intrachromosomal rearrangements are facilitated by the presence of region-specific low-copy repeats (LCRs) and result from nonallelic homologous recombination (NAHR) between paralogous genomic segments. LCRs usually span approximately 10-400 kb of genomic DNA, share >or= 97% sequence identity, and provide the substrates for homologous recombination, thus predisposing the region to rearrangements. Moreover, it has been suggested that higher order genomic architecture involving LCRs plays a significant role in karyotypic evolution accompanying primate speciation.
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Affiliation(s)
- Paweł Stankiewicz
- Dept Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030-3498, USA
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12
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Abstract
Cytogenetic imbalance in the newborn is a frequent cause of mental retardation and birth defects. Although aneuploidy accounts for the majority of imbalance, structural aberrations contribute to a significant fraction of recognized chromosomal anomalies. This review describes the major classes of constitutional, structural cytogenetic abnormalities and recent studies that explore the molecular mechanisms that bring about their de novo occurrence. Genomic features flanking the sites of recombination may result in susceptibility to chromosomal rearrangement. One such substrate for recombination is low-copy region-specific repeats. The identification of genome architectural features conferring susceptibility to rearrangements has been accomplished using methods that enable investigation of regions of the genome that are too small to be visualized by traditional cytogenetics and too large to be resolved by conventional gel electrophoresis. These investigations resulted in the identification of previously unrecognized structural cytogenetic anomalies, which are associated with genetic syndromes and allowed for the molecular basis of some chromosomal rearrangements to be delineated.
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Affiliation(s)
- L G Shaffer
- Department of Molecular and Human Genetics, Department of Pediatrics, Baylor College of Medicine, and Texas Children's Hospital, Houston, Texas 77030, USA.
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13
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Babovic-Vuksanovic D, Jalal SM, Garrity JA, Robertson DM, Lindor NM. Visual impairment due to macular disciform scars in a 20-year-old man with Smith-Magenis syndrome: another ophthalmologic complication. AMERICAN JOURNAL OF MEDICAL GENETICS 1998; 80:373-6. [PMID: 9856566 DOI: 10.1002/(sici)1096-8628(19981204)80:4<373::aid-ajmg13>3.0.co;2-m] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We describe a 20-year-old man with Smith-Magenis syndrome and a 46,XY,del(17)(p11.2p11.2) karyotype. The interstitial deletion was confirmed by metaphase analysis using the fluorescent in situ hybridization probe (D17S29) for the Smith-Magenis region. The patient had hypertelorism, exotropia, and high myopia. Examination under anesthesia showed a lacquer crack near the right macula and a disciform scar of the left macula. Six months later, the patient presented with subacute visual loss. Examination demonstrated end-stage macula degeneration with bilateral disciform scars. There was no evidence of retinal detachment. Prior reports of Smith-Magenis syndrome mention telecanthus, ptosis, strabismus, iris anomalies, cataract, microcornea, optic nerve hypoplasia, myopia, retinal detachment, and lattice retinal degeneration. Bilateral macular degeneration has not been reported previously, and it may be an additional ophthalmologic manifestation of Smith-Magenis syndrome, either as a primary manifestation or as a direct consequence of high myopia.
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Llerena Jr. JC, Almeida JCCD. Cytogenetic and molecular contributions to the study of mental retardation. Genet Mol Biol 1998. [DOI: 10.1590/s1415-47571998000200018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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15
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Abstract
Smith-Magenis syndrome is caused by a 17p11.2 deletion. It associates mental retardation, facial dysmorphism and brachydactyly; aberrant behavior and major sleep problems are present in 70% of the cases. It is probably under-diagnosed because the facial abnormalities are mild and the behavioral problems with hyperactivity and self-injuries are dominant, leading to the diagnosis of psychiatric pathology. However these behavioral problems are sufficiently characterized to allow the diagnosis of the syndrome and look for a 17p11.2 microdeletion. Otorhinolaryngologic, ophthalmologic, cardiac and renal abnormalities can be associated and their evaluation is necessary. Smith-Magenis syndrome is considered as a contiguous gene syndrome. Genes have been mapped and isolated to the critical region, but their participation in the pathogenesis of the syndrome remains unclear.
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Affiliation(s)
- M O Livet
- Service de neurologie pédiatrique, hôpital d'enfant de la Timone, Marseille, France
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