Diagnostic Microarray Characterizes Supernumary Chromosomes

The information obtained from using this cytogenetic tool should lead to improved diagnosis and management of patients with marker chromosomes. In addition, high-resolution characterization of marker chromosomes will expand scientific knowledge of pericentromeric regions.

A diagnostic microarray for characterizing supernumerary marker chromosomes was constructed with over 900 bacterial artificial chromosome (BAC) clones, and represents, on average, more than 5.3 MB of each of the 43 unique pericentromeric regions of the human genome. Thus, the chromosomal origin of a marker can be determined together with the amount of euchromatin present.

The Signature MarkerChip, a diagnostic microarray for marker chromosomes, was developed by Signature Genomic Laboratories, LLC (Spokane, WA, USA). The chip is designed to analyze only the pericentromeric regions of the chromosomes to characterize marker chromosomes previously identified by chromosome analysis. The SignatureChip evaluates multiple areas of the genome for unbalanced microscopic and submicroscopic deletions and duplications.

A supernumary chromosome is a small chromosome containing a centromere occasionally seen in tissue culture, often in a mosaic state (present in some cells but not in others). A marker chromosome may be of little clinical significance or, if it contains material from one or both arms of another chromosome, may create an imbalance for whatever genes are present; assessment to establish the clinical significance, particularly if found in a fetal karyotype, is often difficult.

Clinicians are often required to use labor-intensive approaches to determine the origin and euchromatic content of a marker because traditional cytogenetic analysis is not always sufficient. Signature Genomic Laboratories recognized the need for a cytogenetic tool that could rapidly characterize marker chromosomes. Clinicians and cytogenetic laboratories can order the Signature MarkerChip whenever karyotype, fluorescent in situ hybridization (FISH), or general microarray analysis identifies a marker chromosome in an individual or a pregnancy.

If a marker chromosome does not contain euchromatin, the Signature MarkerChip will not detect the marker. In addition, low levels of mosaicism may not be detected by array comparative genomic hybridization (CGH).



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