Analysis of 207 case reports on patients with ring autosome showed that: (1) Forty patients, a fifth of the total, had extreme growth failure together with an otherwise almost-normal appearance, viz. no major malformation, no specific deletion syndrome, no or only a few unspecific minor anomalies. This phenotype may be regarded as the “ring syndrome”, a term proposed by Cote et al. (1981) since it is independent of what chromosome is involved. (2) Severe growth failure, the sole major physical abnormality in the “ring syndrome”, was seen significantly more often among patients with ring of larger chromosomes than among patients with a smaller ring, indicating that the greater the chromosome involved in ring formation, the higher is the probability of severe growth failure. (3) Larger ring chromosomes showed significantly more often instability than smaller rings, suggesting that there may be a correlation between ring instability and the size of the chromosome involved. (4) Growth failure was present in significantly more patients with a “labile” ring than with a “stable” ring, indicating that a correlation may exist between ring instability and growth failure. It is suggested that the “ring syndrome” observed in many cases with ring autosome may result from end-to-end fusion of chromosome ends, an event not involving deletion in the genetic sense. It is also suggested that the “ring syndrome” is caused by a continuous generation of secondary aneuploid cells with increased mortality, i.e. structural ring instability which seems to be a function of the size of the chromosome involved. Thus, formation of a ring chromosome in certain cases might be regarded as a “structural mutation”, i.e. an alteration in the structure of the genetic material per se, rather than a loss or gain of genetic dosages.

Does "ring syndrome" exist? An analysis of 207 case reports on patients with a ring autosome

Summary: Purpose: The chromosome 20 ring [r(20)] is a rare chromosomal disorder without clear phenotypical markers. We describe the electroclinical pattern in a group of patients with r(20).



Methods: We observed 3 patients (a boy, patient 1; his mother, patient 2; and an unrelated man, patient 3), performing prolonged video-EEG and cytogenetic studies and fluorescent in situ hybridization (FISH) with chromosome-specific telomeric probes.



Results: All 3 patients had a very similar abnormal electroclinical pattern characterized by long bursts or trains of rhythmic theta waves, which were sharply contoured or had a notched appearance (with no detectable clinical correlate), and generalized spike waves (SW) associated with seizures of probable frontotemporal origin (SFT). In all 3 patients, the cytogenetic analysis of T lymphocytes showed mosaicism with a normal cell line and a second cell line with a chromosome 20, although the latter was little represented in patients 2 and 3. A few cells with a single chromosome 20 were also found. The same cytogenetic findings were confirmed in the lymphoblastoid cell line of patient 1 and in the fibroblasts of patient 3. FISH with chromosome-specific telomeric probes and TTAGGG sequences demonstrated the integrity of the ring chromosomes.



Conclusions: The clinical picture of these patients appears to be related to the instability of the r(20)-generating cells monosomic for chromosome 20 and is thus haploinsufficient for a gene. In these patients, the electroclinical pattern of theta waves (probably unrelated to epilepsy) and the SW and SFT, even with mild mental retardation (MR) or no MR and without dysmorphic features, suggest that the r(20) syndrome may be present.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1528-1157.1998.tb01443.x

Chromosome 20 ring: a chromosomal disorder associated with a particular electroclinical pattern

In situ hybridization of a telomeric (TTA-GGG)n sequence to metaphases from three cases of ring chromosome, involving respectively chromosomes 4, 16, and 20, showed the presence of the cognate sequences in all three rings. To investigate whether these ring chromosomes originated by telomere-telomere fusion, we determined, by in situ hybridization, whether telomere-associated sequences and/or specific distal sequences were still present in the ring chromosomes. The finding that these sequences were preserved in all the ring chromosomes strongly indicates that they originated by telomere-telomere fusion. All three subjects carrying the ring chromosomes are affected by the so-called ring syndrome, with failure to thrive, minor dysmorphic signs and no major anomalies. The r(4) patient has the ring in mosaic form with a normal cell line and has normal intelligence. The r(16) and the r(20) patients have moderate mental retardation and suffer from seizures. We conclude that the ring syndrome, even in its more severe manifestation, is caused by ring chromosome instability.

Presence of telomeric and subtelomeric sequences at the fusion points of ring chromosomes indicates that the ring syndrome is caused by ring instability

The term "ring syndrome" was proposed to describe a phenotype of growth failure without major malformations due to a ring autosome. The growth failure is thought to be caused by instability of the ring chromosome leading to aneusomy and cell death. Most previous studies of ring chromosomes were based on standard cytogenetic banding techniques and were limited to microscopically detectable deletions in the ring chromosomes. We report on two patients with complete ring (4) and ring (9) chromosomes, respectively. The first was a 15-month-old girl and the second was a 16-month-old boy. They both presented with severe, symmetrical growth failure and normal psychomotor development in the absence of malformations. Their parents had a normal phenotype. The first case had a whorled pattern of hyperpigmentation and hypopigmentation on part of the face and chest, and the second case had a patchy hyperpigmented rash on the trunk. Peripheral blood karyotype of the first patient was 46,XX, r(4)(p16.3q35.2) and of the second 45,XY,-9/46,XY,r(9)(p24q34.3). G-band analysis suggested no loss of material in the ring chromosomes. These findings were confirmed by fluorescence in situ hybridization (FISH) analysis using chromosome-specific subtelomeric probes. The common human telomeric sequences were intact in the first patient but absent in the second patient. The cytogenetic and FISH data in our two cases provide further evidence for the existence of a "complete ring" phenotype independent of the autosome involved. Pigmentary skin changes are a useful clinical sign of mosaicism caused by the ring instability.

Clinical, cytogenetic, and fluorescence in situ hybridization findings in two cases of "complete ring" syndrome.

Ring chromosomes are often associated with abnormal phenotypes due to loss of genomic material and also because of ring instability at mitosis after sister chromatid exchange events. We investigated ring chromosome instability in six patients with ring chromosomes 4, 14, 15, and 18 by examining 48- and 72-h lymphocyte cultures at the first, second and subsequent cell divisions after bromodeoxyuridine incorporation. Although most cells from all patients showed only one monocentric ring chromosome, ring chromosome loss and secondary aberrations were observed both in 48- and 72-h lymphocyte cultures and in metaphase cells of the different cell generations. We found no clear-cut correlation between ring size and ring instability; we also did not find differences between apparently complete rings and rings with genetic material loss. The cytogenetic findings revealed secondary aberrations in all ring chromosome patients. We concluded that cells with ring chromosome instability can multiply and survive in vivo, and that they can influence the patient's phenotype.

/pdf/ring-chromosome-instability-evaluation-in-six-patients-with-1nelf7c0f5.pdf

Ring chromosome instability evaluation in six patients with autosomal rings.

A ring 12 chromosome was found in a male child with minor phenotypic alterations. No obvious loss of chromosome material was detected. Since there is no other case of a ring 12 in the literature, it w

Ring chromosome 12 and latent centromeres

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Ring chromosome 12 and latent centromeres