ISOLATION OF COSMIDS CORRESPONDING TO THE CHROMOSOME BREAKPOINTS OF ADE-NOVO AUTOSOMAL TRANSLOCATION, T(6-19)(P21-Q13.1), IN A PATIENT WITH MULTICYSTIC RENAL DYSPLASIA

Hydronephrosis caused by pelvi-ureteric junction obstruction (PUJO) is a frequent urological malformation assumed to result from a deficient development of the ureteric bud. The exact etiology of pelvi-ureteric junction stenosis is unknown, but there is convincing evidence for a genetic cause: with linkage analysis predicting a hereditary hydroneph rosis locus on chromosome 6p. We encountered a patient with a de novo autosomal t(6;19)(p21;q13.1) and attendant bilateral multicystic renal dysplasia (MRD), bilateral PUJO resulting in massive hydronephrosis, and an associated von Mayer-Rokitansky-Kuster disorder. On the basis o f the presumption that in this patient the putative hydronephrosis gen e might be disrupted by the translocation, we sought to isolate DNA fr om the breakpoint regions as the initial step in a strategy to identif y genes affected by the t(6;19). Using sequential rounds of fluorescen ce in situ hybridization (FISH) with cosmids selected from a detailed integrated map of the long arm of chromosome 19, we have identified a cosmid clone that spans the breakpoint. The position of the breakpoint was further localized by Southern blot analysis. Using a vectorette P CR approach, rearranged DNA fragments were isolated and: by comparativ e nucleotide sequence analysis, these were shown to contain ectopic se quences. A cosmid clone containing these ectopic sequences was isolate d and shown by CASH (chromosome assignment using somatic cell hybrids) and FISH (fluorescence in situ hybridization) analysis to map to the short arm of chromosome 6 and to span the breakpoint found in the MRD patient. The isolated cosmid clones are useful reagents for analysis o f other MRD patients and for the search for genes at or flanking the b reakpoints.