Available Assays

FISH is the most commonly used testing method for diagnosis of WS. The analysis is performed with a DNA probe containing a full-length copy of the ELN gene. Metaphase chromosome preparations from cultured peripheral blood lymphocytes are hybridized with the probe, and the 7q11.23 region of both chromosomes 7 are analyzed for the presence or absence of a hybridization signal. The assay generally includes a second probe, either for the centromere or a more distal locus on chromosome 7, to serve as an internal hybridization control.

Quantitative PCR can be used to assay the ELN copy number; however, there is no significant clinical or cost benefit to PCR over FISH. Whenever available, FISH is the preferred method for assessing genomic copy number because of the value gained by assessing individual cells. FISH testing for WS is usually ordered in conjunction with karyotyping, as other chromosome abnormalities may be part of the differential diagnosis. Addition of FISH testing requires no additional specimen and can be performed on fixed cell pellets after karyotyping is completed. In addition, although it is extremely rare, there have been reports of visible chromosome rearrangements that may result in disruption of the WS region, that would not be detected by PCR.

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