ABSTRACT
Chromosomal aneuploidies especially trisomies 13, 18, 21, monosomy X and 47, XXY account for up to 95% of live born cytogenetic abnormalities. The diagnosis of aneuploidies usually done by conventional cytogenetic analysis (CCA) is associated with technical difficulties and requires about 1-3 weeks for providing a result, especially in prenatal diagnosis. In the present study, Fluorescence In Situ Hybridization (FISH) was used on interphase cells for rapid prenatal and postnatal detection of aneuploidies. The frequent indications of high pregnancies included for prenatal diagnosis were previous child with chromosomal abnormalities, abnormal ultrasound scan and advanced maternal age (> 35 years). Interphase FISH was done using probes specific for chromosomes 13, 18, 21, X and Y on uncultured chorionic villi and amniotic fluid samples. All samples were analyzed subsequently using conventional cytogenetics. The analysis of aneuploidies for chromosomes 13, 15, 16, 18, 21, 22, X and Y using FISH was extended to abortuses from spontaneous abortion cases. In cases where cytogenetics was not informative, a diagnosis could be made using interphase FISH. For postnatal diagnosis, interphase FISH was done to confirm low-level mosaicism in patients with primary amenorrhea, suspected cases of Klinefelter syndrome, and mental retardation using probes specific for various autosomes, X and Y chromosomes. FISH was also done using probe specific for the sex-determining region (SRY) on the Y chromosome in cases with ambiguous genitalia. The SRY region could be identified in cases that lacked the Y chromosome on conventional cytogenetic analysis thereby emphasizing on the high resolution of FISH technique in detecting sub-microscopic rearrangements. To conclude, interphase FISH decreases the time interval between sampling and diagnosis. This is of tremendous value in prenatal diagnosis of urgent high-risk pregnancies, management of ambiguous genitalia and low-level mosaicism where result can be obtained within 24 hours.