Fluorescent In Situ Hybridisation (FISH) as a Followup Test for Postnatal Microarray Results

Background: Fluorescent in situ Hybridisation (FISH) is a valuable option for follow-up or confirmatory testing especially if aberrations have been missed or require further testing for interpretation after array comparative genomic hybridisation (aCGH). In this study, the Vysis IntelliFISH Hybridization Buffer (Abbott Molecular Inc.) hybridisation protocol was successfully validated with improved turn-around-time and the utility of FISH as a follow-up test for patients referred for aCGH testing was evaluated. Results: The results for nine of 11 selected 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. In addition, two cases were negative on aCGH but were positive for Pallister-Killian syndrome on FISH, confirming the clinical diagnosis. Conclusion: Offering FISH as a follow-up test to aCGH is beneficial in specific circumstances i.e., 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.