Test Details: Fluorescence in situ hybridization (FISH) is a technique for detecting and locating a specific DNA sequence on a chromosome. Three distinct neurodevelopmental disorders arise primarily from deletions or duplications that occur at the 15q11-q13 locus: Prader-Willi syndrome (PWS), Angelman syndrome (AS) and 15q11-q13 duplication syndrome (Dup15q syndrome). SNRPN gene duplication is associated with neurodevelopmental disabilities. FISH is typically done in conjunction with a karyotype.