The presence of a supernumerary 18p isochromosome is a rare chromosomal abnormality that results in 18p tetrasomy. This is a report on the clinical, cytogenetic and molecular findings of 2 non-related patients with a supernumerary 18p isochromosome. Both patients present some features of the 18p tetrasomy syndrome (strabismus, low-set ears, long and narrow fingers and toes), but additional characteristics were also observed. Cytogenetic analysis, FISH, MLPA and SNP array techniques showed that one of the isochromosomes is symmetric and monocentric, while the other is asymmetric and dicentric, yet resulting in a similar tetrasomy of the 18pter-18p10 region, followed by a partial 18q11.2 trisomy, an unprecedented finding in the literature.
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Prenatal diagnosis and genetic analysis of small supernumerary marker chromosomes in the eastern chinese han population: A retrospective study of 36 cases.
Chromosome Res
July 2024
Medical Genetic Diagnosis and Therapy Center, Fujian Key Laboratory for Prenatal Diagnosis and Birth Defect, Fujian Maternity and Child Health Hospital, College of Clinical Medicine for Obstetrics & Gynecology and Pediatrics, Fujian Medical University, No. 18 Daoshan Road, Gulou District, Fuzhou City, 350001, Fujian Province, China.
Article Synopsis
- - Background research on small supernumerary marker chromosomes (sSMCs) indicates that their structure and origins are poorly understood, making it challenging to provide accurate genetic counseling for affected fetuses.
- - A study analyzing 36 sSMC cases revealed that 19 were mosaic, and 27 had pathogenic or likely pathogenic copy number variants (CNVs), with notable associations to Turner syndrome and other syndromes based on specific CNVs identified.
- - The findings highlight the importance of cytogenetic analysis in determining the pathogenic nature of sSMCs, which can significantly improve the accuracy of genetic counseling for affected families.
Molecular and cytogenetic analysis of small supernumerary marker chromosomes in prenatal diagnosis.
Mol Cytogenet
September 2023
Prenatal Diagnosis Center, Hangzhou Maternity and Child Care Hospital, #369 Kunpeng Road, Shangcheng District, Hangzhou, 310008, Zhejiang, China.
Background: Small supernumerary marker chromosome (sSMC) is a structurally abnormal chromosome of unknown origin by conventional cytogenetics. The understanding of clinical significance of sSMC is still limited in prenatal diagnosis. The presence of sSMC poses a challenge for genetic counselling.
View Article and Find Full Text PDFPartial tetrasomy 18 mosaicism: Pre and postnatal diagnosis of a unique pattern.
Taiwan J Obstet Gynecol
January 2022
Unidade de Genética Médica, Centro de Genética Médica Doutor Jacinto Magalhães - Centro Hospitalar Universitário do Porto, Porto, Portugal; Life and Health Sciences Research Institute (ICVS), School of Medicine, University of Minho, Braga, Portugal; ICVS/3B's - PT Government Associate Laboratory, Braga/Guimarães, Portugal.
Objective: To present prenatal diagnosis and cytogenetic characterization of a unique pattern of partial tetrasomy 18 mosaicism.
Case Report: A 34-year-old woman underwent amniocentesis at 25 weeks of gestation due to anomalies detected in obstetric ultrasound. It revealed a de novo supernumerary partial isochromosome 18 in 11 of 37 metaphases of cultured amniocytes.
Tetrasomy 18p Initially Misdiagnosed as Cerebral Palsy in an Adult Patient.
Cureus
November 2021
Neurology, University of Florida, Gainesville, USA.
Tetrasomy 18p is a rare genetic condition characterized by a supernumerary 18p isochromosome with two copies of the p arm of chromosome 18 causing patients to have an extra chromosome. Most cases are de novo; however, a few maternally inherited cases have been reported. The most commonly reported manifestations of this condition are developmental delay, cognitive impairments, muscle tone abnormalities, and dysmorphic facial features.
View Article and Find Full Text PDFMolecular characterization of a complex small supernumerary marker chromosome derived from chromosome 18p: an addition to the literature.
Mol Cytogenet
January 2021
Division of Biology and Genetics, Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy.
Background: Small supernumerary marker chromosomes (sSMC) are a heterogeneous group of structurally abnormal chromosomes, with an incidence of 0,044% in newborns that increases up to almost 7 times in developmentally retarded patients. sSMC from all 24 chromosome have been described, most of them originate from the group of the acrocentric, with around half deriving from the chromosome 15. Non-acrocentric sSMC are less common and, in the 30 percent of the cases, are associated with phenotypic effect.
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