Philadelphia chromosome
An abnormal chromosome 22 resulting from t(9;22) translocation, creating the BCR-ABL fusion gene. Found in some pediatric leukemias.
Full Definition
The Philadelphia chromosome is an abnormally shortened chromosome 22 that results from a reciprocal translocation between chromosomes 9 and 22, written as t(9;22)(q34;q11). This translocation creates the BCR-ABL fusion gene, which produces an abnormal tyrosine kinase protein that drives malignant transformation. In pediatric hematology, Philadelphia chromosome-positive acute lymphoblastic leukemia represents a high-risk subset requiring intensive treatment and often targeted therapy with tyrosine kinase inhibitors like imatinib. The presence of this cytogenetic abnormality significantly impacts prognosis and treatment decisions, making rapid detection crucial for optimal patient management.
Usage
Usage note: Named after the city where it was discovered; always capitalize 'Philadelphia'.
In Context
- "Cytogenetic analysis revealed the Philadelphia chromosome in 95% of metaphases." — cytogenetics report
- "The patient was enrolled in a Philadelphia chromosome-positive ALL protocol." — treatment plan