Del(20q) Deletion Probe

Deletions of the long arm of chromosome 20 are found in 4.1% and 1.5% of MDS and AML cases respectively. Del(20q) also occurs in 10% of polycythemia vera patients and other subgroups of MPD. The deletions are predominantly interstitial and the breakpoints usually occur in the region q11.2-q13.1. Often other cytogenetic abnormalities are present such as del(5q), -7/del(7q), +8, del(18q), +21 and rearrangements of 13q. Due to the relatively small size of the deletion and the lack of banding features on chromosome 20, FISH is particularly useful in detecting this abnormality.

Prognosis for MDS cases, where del(20q) is the sole abnormality, is good, however if secondary abnormalities are present a poor outcome is indicated. The AML patients respond poorly to treatment and have reduced survival rates. The clinical outcome for MPD patients remains unchanged in the presence of the abnormality.

The mechanism of leukaemogenesis associated with del(20q) is unknown, however deletion of a TSG is thought to cause the increased proliferation of the cancer cells. Using RT-PCR analysis, Bench et al identified potential target genes in the region of overlap between the AML/MDS and MPD CDR’s at band 20q12. Five genes were expressed in both bone marrow and CD34 positive cells. Of the three previously identified genes h-lmbt regulates chromatin structure during mitosis, SFRS6 encodes an serine rich protein important to regulation of alternative splicing of mRNA and MYBL2, a member of the myb transcription factor family, is involved in cell cycle control.

The proximal 20q probe, labelled in red, covers a 301kb region of 20q12, extending from 12.4kb inside PTPRT. For the MYBL2 gene in band 20q13.12 the probe contig covers 321kb from 60kb 5’ of MYBL2 to 211kb 3’ of the gene.