Ring chromosome

About: Ring chromosome is a research topic. Over the lifetime, 1546 publications have been published within this topic receiving 31061 citations. The topic is also known as: supernumerary circular chromosome.

Autosomal ring chromosomes in human genetic disorders

Abstract: Ring chromosomes arise following breakage and rejoining in both chromosome arms. They are heterogeneous with variable size and genetic content and can originate from any chromosome. Phenotypes associated with ring chromosomes are highly variable as apart from any deletion caused by ring formation, imbalances from ring instability can also occur. Of interest is ring chromosome 20 which has a significant association with epilepsy with seizure onset in early childhood. Severe growth deficiency without major malformations is a common finding in the ring chromosome carrier. This phenotype associated with ring behaviour and mitotic instability and independent of the chromosome involved has been termed the “ring syndrome”. Precise genotype-phenotype correlations for ring chromosomes may not be possible as influencing factors vary depending on the extent of deletion in ring formation, ring instability and the level of mosaicism. Although ring chromosomes usually arise as de novo events, familial transmission of rings from carrier to offspring has been described and prenatal diagnosis for any pregnancies should always be considered.

The genetics and clinical characteristics of constitutional ring chromosomes.

Abstract: Constitutional ring chromosomes are generally believed to be the result of de novo breakage of both end-segments of a chromosome during meiosis or early postzygotic mitosis, with the ends joining to give a continuous ring. This mechanism presumes the loss of some genetic material during ring formation. Ring chromosomes thus represent deletions of genetic material. But an accurate delineation of identifiable syndromes is not possible in the majority of cases even when the patients have apparently identical ring chromosomes and phenotypic charactristics. In many patients with a ring, independent of the chromosome involved, there is a similar clinical phenotype characterized by the presence of extreme growth failure without major malformation, with only a few or no minor anomalies and mild to moderate mental retardation. This phenotype is generally referred to as "ring syndrome." The description of the features of this chromosome anomaly has to-date been based on standard cytogenetic banding techniques. However, recent observations made with novel molecular techniques have brought new insights into the nature of ring chromosomes, contributing to the understanding of the genetic and clinical consequences. This review examines constitutional rings and is based on the generally accepted "classical" knowledge but also takes into consideration new molecular findings.

Ring chromosome 20 epilepsy syndrome in children Electroclinical features

Abstract: Article abstract— Ring chromosome 20 mosaicism is associated with dysmorphic features, mental retardation, and intractable seizures, including recurrent episodes of nonconvulsive status epilepticus. The authors’ findings in four children, all without dysmorphic features, indicate that mental deterioration and frequent subtle nocturnal frontal lobe seizures, associated with a characteristic EEG pattern, represent prominent additional clinical features not previously described in this syndrome. This emphasizes the importance of full-night video-EEG in children with frontal lobe seizures and cognitive deterioration.