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What is Philadelphia chromosome is and explain in detail?
Ans. a (Chromosome 9 - 22 translocation). (Ref. Harrison's Medicine, 18th/ ch.83, Table 83-2)# Specific translocation seen in CML is the Philadelphia chromosome (Ph) which is derived from a reciprocal translocation between chromosomes 9 and 22 with the breakpoint joining the sequences of the ABL oncogene with the BCR gene.# The first reproducible chromosome abnormality detected in human malignancy was Philadelphia chromosome. Seen in CML. This occurs by reciprocal translocation involving ABL oncogene, a tyrosine kinase on chromosome 9 being replaced in proximal to BCR on chromosome 22 t (9, 22).# Consequences of expression of BCR ABL gene product is activation of signal transudation pathways, leading to cell growth independent of normal external growth factors.# Robertsonian translocation is translocation between two acrocentric chromosomes & it most often involves 14 & 21 Reciprocal transactions involve mutual exchanges between any 2 chromosomes.Also note:# Cytogenetic changes have been particularly well studied in (1) leukemias, e.g., Philadelphia chromosome translocation in CML ; and (2) lymphomas, e.g., translocations of MYC in Burkitt's .These and other translocations are useful for diagnosis, classification, and prognosis.Representative Oncogenes at Chromosomal TranslocationsGene (Chromosome)TranslocationMalignancyABL (9q34.1)-BCR (22q11)(9;22)(q34;q11)Chronic myeloid leukemiaATF1 (12q13 )-EWS (22q12)(12;22)(q13;q12)Malignant melanoma of soft partsBCL1 (11q13.3 )-1gH (14q32)(11;14)(q13;q32)Mantle cell lymphomaBCL2 (18q21.3 )-1gH (14q32)(14;18)(q32;q21)Follicular lymphomaFLI1 (11q24)-EWS (22q12)(11;22)(q24;q12)Ewing's sarcomaLCK (1p34 )-TCRB (7q35)(1;7)(p34;q35)T cell acute lymphocytic leukemiaMYC (8q24 )-IgH(14q32)(8;14)(q24;q32)Burkitt's lymphoma, B cell acute lymphocytic leukemiaPAX3(2q35)-FKHR/ALV (13q14)(2;13)(q35;q14)Alveolar rhabdomyosarcomaPAX7(lp36KHR/ALV(13q14)(1;13)tp36;q14)Alveolar rhabdomyosarcomaREL (2p13)-NRG (2p11.2-14)Inv(2(p13;pll.2-14)Non-Hodgkin's lymphomaRET (10q11.2)-PKAR1A(17q23)(10;17)(q11.2;q23)Thyroid carcinomaTAL1(1p32)-TCTA (3p21)(1;3)(p34;p21)Acute T cell leukemiaTRK (1q23-1q24 (1q31)Inv1(q23;q31)Colon carcinomaWT1 (11p13)-EWS (22q 12)(11;22)(p13;q12)Desmoplastic small round cell tumor