Unusual expression of mRNA typical of Philadelphia positive acute lymphoblastic leukemia detected in chronic myeloid leukemia

✍ Scribed by Kirk, Judy A.; Radich, Jerald; Edmands, Scott; Lee, Arthur; VanDevanter, Donald R.; Reems, Jo Anna; Bryant, Eileen M.

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 647 KB
• Volume: 52
• Category: Article
• ISSN: 0361-8609
• DOI: 10.1002/(sici)1096-8652(199607)52:3<129::aid-ajh1>3.0.co;2-v

✦ Synopsis

The Philadelphia chromosome (Ph) is found in both chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL). The Ph translocation, t(9;22)(q34;qll), can disrupt the BCR gene on chromosome 22 in one to two areas called the major (Mbcrl) and minor (mbcrl) breakpoint cluster regions. In CML the breakpoint has been mapped almost exclusively to Mbcrl, whereas in Ph positive ALL both Mbcrl and the upstream mbcrl breakpoints have been described. In this communication we describe an unusual patient with typical chronic phase Ph positive CML and evidence of the uncharacteristic mbcrl breakpoint, predicting expression of the ALL-type pl90 fusion protein. Fluorescence in situ hybridization demonstrated BCR gene rearrangement, the reverse transcription polymerase chain reaction detected the BCR-ABL fusion mRNA characteristic of the mbcrl breakpoint, and failed to detect BCR-ABL mRNA characteristic of the Mbcrl breakpoint. Southern blot analysis revealed no rearrangement in Mbcrl , and direct sequencing of the PCR product confirmed it to be the ALL-type mbcrl fusion mRNA with the first exon of the BCR gene fused to ABL exon a2. This case differs from the previously reported cases of "pl90" CML in that the patient presented without abnormal hematopoietic features other than those found in typical CML and provides further evidence that the p190 mRNA is not sufficient to cause an acute rather than chronic leukemia.