DELETED CHROMOSOME-20 FROM A PATIENT WITH ALAGILLE-SYNDROME ISOLATED IN A CELL HYBRID THROUGH LEUCINE TRANSPORT SELECTION - STUDY OF 3 CANDIDATE GENES

Alagille syndrome (AGS) is a well-defined genetic entity assigned to t he short arm of Chromosome (Chr) 20 by a series of observations of AGS patients associated with microdeletions in this region. By fusing lym phoblastoid cells of an AGS patient that exhibited a microdeletion in the short arm of Chr 20 encompassing bands p11.23 to p12.3 with rodent thermosensitive mutant cells (CHOtsH1-1) deficient in-leucyl-tRNA syn thetase, we isolated a somatic cell hybrid segregating the deleted hum an Chr 20. This hybrid clone, designated NR2, was characterized by sev eral methods, including PCR, with eight pairs of oligonucleotides mapp ed to Chr 20: D20S5, D20S41, D20S42, D20S56, D20S57, D20S58, adenosine deaminase (ADA), and Prion protein (PRIP); Restriction Fragment Lengt h Polymorphism (RFLP) analyses with four genomic anonymous probes (D20 S5, cD3H12, D20S17, D20S18); and fluorescent in situ hybridization (FI SH) with total human DNA and D20Z1, a sequence specific to the human C hr 20 centromere, as probes. The NR2 hybrid allowed us to exclude thre e candidate genes for AGS: hepatic nuclear factor 3 beta (HNF3 beta), paired box 1 (PAX1), and cystatin C (CST3) as shown by their localizat ion outside of the deletion. The NR2 hybrid is a powerful tool for the mapping of new probes of this region, as well as for obtaining new in formative probes specific for the deletion by subtractive cloning of t he region. Such markers will be useful for linkage analysis and screen ing of cDNA libraries.