THE DETECTION OF CONTIGUOUS GENE DELETIONS AT THE NEUROFIBROMATOSIS-1LOCUS WITH FLUORESCENCE IN-SITU HYBRIDIZATION

Neurofibromatosis type 1 (NF1) is a common genetic disorder characteri zed primarily by the development of multiple neurofibromas and pigment ary changes. The recent identification of contiguous gene deletions in NF1, a previously unrecognized molecular basis for this disorder, rai ses important questions regarding deletion frequency in the patient po pulation and the role that contiguous genes may play in the physical m anifestations of NF1 patients. To facilitate the identification of pat ients with large NF1 deletions, we have isolated clones carrying large genomic segments from the NF1 locus and tested their efficacy as prob es for fluorescence in situ hybridization (FISH). Clone P 1-9 spans ap proximately 65 kb of the NF 1 gene, including exons 2-11, and clone P1 -12 carries similar to 55 kb of NF1 intron 27B. FISH studies performed with P1-9, P1-12, and a set of overlapping 1F10 cosmid clones mapping telomeric to the NF1 locus identified large deletions in two new neur ofibromatosis type 1 patients who, like previously characterized delet ion patients, had mildly dysmorphic facial features and large numbers of cutaneous neurofibromas.