Fluorescence in situ hybridization (FISH) using non-commercial probes in the diagnosis of clinically suspected microdeletion syndromes

BACKGROUND & OBJECTIVES: Microdeletion syndromes are characterized by small (<5 Mb) chromosomal deletions in which one or more genes are involved. These are frequently associated with multiple congenital anomalies. The phenotype is the result of haploinsufficiency of genes in the critical interval. Fluorescence in situ hybridization (FISH) technique is commonly used for precise genetic diagnosis of microdeletion syndromes. This study was conducted to assess the role of FISH in the diagnosis of suspected microdeletion syndrome. METHODS: FISH was carried out on 301 clinically suspected microdeletion syndrome cases for the confirmation of clinical diagnosis using non-commercial probes. Of these, 177 cases were referred for 22q11.2 microdeletion, 42 cases were referred for William syndrome, 38 cases were referred for Prader Willi/Angelman and 44 cases were referred for other suspected microdeletion syndromes. RESULTS: FISH was confirmatory in 23 cases only (7.6%). There were 17 cases of 22q11.2 microdeletion, four cases of Prader Willi syndrome and two cases of William syndrome. INTERPRETATION & CONCLUSION: We conclude that FISH should not be the method of choice for clinically suspected microdeletion syndromes. We propose to follow strict clinical criteria for FISH testing or preferably to follow better methods (genotype first approach). Whole genome screening may be used as first line of test and FISH may be used for confirmation of screening result, screening of family members and prenatal diagnosis.