Test Details: FISH helps in aneuploidy detection for chromosomes 13 and 21 which account for greater than 90% of chromosomal aberrations. Autosomal monosomies are usually not compatible with life. Autosomal trisomy of chromosomes 13 and 21 are most common trisomy detected in live-births. Trisomy 21 is associated with Down Syndrome and is the single most common known cause of mental retardation. Trisomy 13 is associated with Patau Syndrome.