detection of microdeletions by fish fluorescent in situ hybridization: report of 245 cases

microdeletion syndromes are contiguous gene deletion syndromes of less than 5 megabases.  most often, many of these syndromes are not detectable by  routine chromosomal analysis and require more specific testing techniques such as fish or more accurate general coverage like array comparative genomic hybridization.  as many of these syndromes are phenotypically recognizable and allow for easy clinical diagnosis, fish technique is still a common method for consolidation of clinical diagnosis.  in our laboratory we perform fish for common microdeletion syndromes including di george i, di george ii, prader-willi, angelman, williams, miller dieker, wolf hirschhorn, cri du chat, smith magenis, 22q13.3 microdeletion, 1p36 microdeletion, and shox.  in the past ten years we have performed 245 fish tests for microdeletion syndromes. 205 tests were performed on peripheral blood and 40 tests were performed prenatally on amniotic fluid cells or chorionic villi samples.  the frequency of requests were as follows: 62 for di george i, 5 for di george ii, 37 for angelman, 80 for prader willi, 46 for williams, 6 for miller dieker, 1 for smith magenis, 2 for cri du chat, 5 for wolf-hirschhorn.  results were positive in 7 di george cases, 10 angelman, 13 prader willi, 34 williams, 1 cri du chat syndromes.  the highest rate of clinical estimation of phenotype is for williams syndrome, which is probably the most recognizable phenotype.   considering that di george is the most frequent microdeletion syndrome 1/4000 in humans, it can be argued that there is not sufficient referral and recognition of symptoms in our clinical setting.   the second most frequent microdeletion/deletion syndrome is 1p36 which occurs in 1/5000.  again, a lack of clinical recognition is probably accountable for a lack of referral for this microdeletion syndrome.  on the other hand, we get a significant number of  referrals for pws/as and a good rate of confirmation 23/126.  we would recommend a familiarization with the phenotype of microdeletion syndromes in the clinical setting which could optimize diagnosis.