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J Med Genet. 2011 Jan;48(1):1-9. doi: 10.1136/jmg.2010.080382. Epub 2010 Oct 23.

Molecular analysis of ring chromosome 20 syndrome reveals two distinct groups of patients.

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  • 1Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, The University of Pennsylvania School of Medicine, 19104, USA.

Abstract

BACKGROUND:

The ring chromosome 20 syndrome (R20) is a rare genetic disorder associated with a refractory electroclinical epilepsy syndrome and variably expressed comorbidities of intellectual disability and dysmorphism.

METHODS:

To understand the structure and composition of the ring chromosome 20 (r(20)) in this patient cohort, blood specimens from 28 affected individuals were analysed by cytogenetic, fluorescence in situ hybridisation, and/or high resolution whole genome single nucleotide polymorphism array analysis.

RESULTS:

These studies revealed two distinct groups of patients. Group 1 (N=21) was mosaic for the r(20) and a normal cell line with no detectable deletions or duplications of chromosome 20 in either cell line. The mosaic nature of these rings suggests a postzygotic origin with formation of the ring by fusion of the telomeric regions with no apparent loss of subtelomeric or telomeric DNA. Group 2 (N=7) had non-mosaic ring chromosomes with a deletion at one or both ends of the chromosome, near the ring fusion point. The non-mosaic nature of these rings is consistent with a meiotic origin. The age of onset of seizures was significantly lower in the non-mosaic patients (group 2, median age of onset 2.1 years) than in the mosaic patients (group 1, median age of onset 6.0 years). Patients from group 2 had more extensive comorbidities.

CONCLUSIONS:

These studies demonstrate that r(20) is molecularly heterogeneous and formed by two distinct mechanisms, which, in turn, produce different phenotypic spectrums.

PMID:
20972251
[PubMed - indexed for MEDLINE]
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