Abstract
Fluorescent in situ Hybridisation (FISH) is a valuable option for follow-up or confirmatory testing especially when the chromosome region of interest is known. FISH is primarily used to detect known structural chromosomal abnormalities and mosaic patterns. Aberrations may be missed or require further testing for interpretation after array comparative genomic hybridisation (aCGH) has been performed.
The aim of this study was to validate a new probe hybridisation protocol and evaluate the utility of FISH as a follow-up test for patients referred for aCGH testing. Patient records at the Division of Human Genetics were reviewed and a total of 14 cases were selected for FISH analysis based on probes available within the laboratory. The laboratory protocol was modified, according to the manufacturer’s recommendations, to make use of the Vysis IntelliFISH Hybridisation Buffer (Abbott Molecular Inc., Des Plaines, IL). Slides for peripheral blood cultures were made according to the in-house slide-making protocol. Buccal swabs were applied directly to slides to create a smear. Both sets of slides were processed and visualised under a fluorescent microscope. A total of 100 interphase nuclei were screened from peripheral blood cultures. For buccal smears, 300 interphase cells were screened per slide. For 11 cases, single colour and dual colour probes were used. The final four cases made use of whole chromosome paint, but unfortunately all were unsuccessful in hybridising.
The results for nine of the 11 successful cases correlated with the aCGH findings. Of these, six were for 22q11.2 deletion syndrome, two for Wolf-Hirschhorn syndrome and one for Prader-Willi/Angelman syndrome. Two cases were negative on aCGH but were positive for Pallister-Killian syndrome on FISH, confirming the clinical diagnosis.
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The Vysis IntelliFISH Hybridisation (Abbott Molecular Inc., Des Plaines, IL) was successfully validated with improved turn-around-time for FISH testing in the laboratory. We have therefore established that offering FISH as a follow-up test to aCGH is beneficial in specific circumstances for example in tissue-specific mosaicism as illustrated by the PKS cases, or for family cascade testing of a confirmed microdeletion or microduplication. Genetics laboratories should consider implementing FISH studies as a follow-up test for post-natal microarray results.