microdeletion syndrome microdeletion syndrome a microdeletion syndrome is a syndrome caused by a chromosomal deletion smaller than 5 million base pairs (5 mb) spanning several genes that is too small to be detected by conventional cytogenetic methods or high resolution karyotyping (2–5 mb). detection is done by fluorescence in situ hybridization (fish). larger chromosomal deletion syndromes are detectable using karyotyping techniques. examples digeorge syndrome or velocardiofacial syndrome – most common microdeletion syndrome prader–willi syndrome angelman syndrome neurofibromatosis type i neurofibromatosis type ii williams syndrome miller–dieker syndrome smith–magenis syndrome rubinstein–taybi syndrome wolf–hirschhorn syndrome