Diagnosis of chr 22 deletions in CML | Crack AIIMS NOV 2016 MCQs

True statement regarding diagnosis of chr 22 deletions in CML is

A. Increased incorporation of labelled acetate into histones of chromatin regions on 22
B. Altered DNA restriction patterns of chromosome 22 regions with methylationsensitive endonucleases
C. Altered pattern of small RNAs along leukemic chromatin
D. Altered DNA sequence for at least one chromosome 22 locus

Answer. D. Altered DNA sequence for at least one chromosome 22 locus

Chromosome deletion involves a breakage of DNA, with loss of the distal chromosome. The primary change in chronic myelogenous leukemia with chromosome 22 deletion would be a break in the chromosomal DNA that deletes certain sequences, joining DNA before the deletion point with telomeric sequences that do the chromosome replication (option d).

Other chromosomal alterations not there in Chr 22 deletions, but in other cancers include:

- altered primary transcription, altered “second” code of epigenesis through histone modification, altered Methylation

The Philadelphia chromosome (22 deletion) actually have a chromosome 9:22 translocation that joins the Abelson ABL oncogene on chromosome 9 to a BCR (breakpoint cluster region) on chromosome 22