Ring chromosome 18 in a patient with multiple anomalies

The past, present, and future for constitutional ring chromosomes: A report of the international consortium for human ring chromosomes

Human ring chromosomes (RCs) are rare diseases with an estimated newborn incidence of 1/50,000 and an annual occurrence of 2,800 patients globally. Over the past 60 years, banding cytogenetics, fluorescence in situ hybridization (FISH), chromosome microarray analysis (CMA), and whole-genome sequencing (WGS) has been used to detect an RC and further characterize its genomic alterations. Ring syndrome featuring sever growth retardation and variable intellectual disability has been considered as general clinical presentations for all RCs due to the cellular losses from the dynamic mosaicism of RC instability through mitosis. Cytogenomic heterogeneity ranging from simple complete RCs to complex rearranged RCs and variable RC intolerance with different relative frequencies have been observed. Clinical heterogeneity, including chromosome-specific deletion and duplication syndromes, gene-related organ and tissue defects, cancer predisposition to different types of tumors, and reproductive failure, has been reported in the literature. However, the patients with RCs reported in the literature accounted for less than 1% of its occurrence. Current diagnostic practice lacks laboratory standards for analyzing cellular behavior and genomic imbalances of RCs to evaluate the compound effects on patients. Under-representation of clinical cases and lack of comprehensive diagnostic analysis make it a challenge for evidence-based interpretation of clinico-cytogenomic correlations and recommendation of follow-up clinical management. Given recent advancements in genomic technologies and organized efforts by international collaborations and patient advocacy organizations, the prospective of standardized cytogenomic diagnosis and evidence-based clinical management for all patients with RCs could be achieved at an unprecedented global scale.

A Case of Ring Chromosome 18 with Single Umbilical Artery Detected During Prenatal Period

Fetuses with a single umbilical artery have a risk of increased chromosomal anomalies and congenital malformations. Ring chromosomes are rare and the phenotypic and clinical characteristics of affected individuals show great variability depending on the quantity of the lost critical genes or gains during the formation of the ring or due to mitotic instability. Ring chromosome 18 [r(18)] is characterized by short stature, craniofacial dysmorphism, mental and motor retardation, autoimmune disorders, extremity anomalies, dermal lesions, structural heart malformations, and kidney abnormalities. In this study, the clinical findings of a female patient who had a single umbilical artery in the prenatal period and was diagnosed as de novo r(18) by molecular karyotype analysis were compared with those in the literature. A detailed ultrasonographic examination of the fetus with a single umbilical artery may enable the detection of additional anomalies and thus the early diagnosis of chromosomal anomalies may be possible with prenatal genetic analysis.

Cromosoma 18 ad Anello

In a girl affected by mental deficiency and slight malformations, a 46,XX, 18r chromosome set was found. Metaphases with irregularly sized or absent rings amounted to 14% in peripheral blood cultures. Tritiated thymidine incorporation pattern in the ring chromosome was similar to that of the normal 18 chromosome.

Mammalian chromosomes contain cis-acting elements that control replication timing, mitotic condensation, and stability of entire chromosomes

Recent studies indicate that mammalian chromosomes contain discrete cis-acting loci that control replication timing, mitotic condensation, and stability of entire chromosomes. Disruption of the large non-coding RNA gene ASAR6 results in late replication, an under-condensed appearance during mitosis, and structural instability of human chromosome 6. Similarly, disruption of the mouse Xist gene in adult somatic cells results in a late replication and instability phenotype on the X chromosome. ASAR6 shares many characteristics with Xist, including random mono-allelic expression and asynchronous replication timing. Additional "chromosome engineering" studies indicate that certain chromosome rearrangements affecting many different chromosomes display this abnormal replication and instability phenotype. These observations suggest that all mammalian chromosomes contain "inactivation/stability centers" that control proper replication, condensation, and stability of individual chromosomes. Therefore, mammalian chromosomes contain four types of cis-acting elements, origins, telomeres, centromeres, and "inactivation/stability centers", all functioning to ensure proper replication, condensation, segregation, and stability of individual chromosomes.

Conenital hypothyroidism in association with a ring chromosome 18

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A ring-4 chromosome in a patient with normal intelligence and short stature

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Comparative behavior of ring chromosomes

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Absent IgA and deletions of chromosome 18

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Immunological profile in a chromosome 18 deletion syndrome with IgA deficiency

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E ring chromosome with persistent left superior vena cava and hypertrophic subaortic stenosis

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Congenital malformations associated with a ring 4 chromosome

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