Chromosome abnormalities

Unlike the Philadelphia chromosome in CML, there is no pathognomonic chromosomal abnormality associated with the MPDs. However, a number of recurrent chromosomal abnormalities have been documented in the MPDs. Chromosomal abnormalities are seen in approximately one-third of patients with PV and IMF. The most frequent chromosomal abnormalities in these disorders, as detected by G-banding, are shown in Table 9.3. Detection of cytogenetic abnormalities is infrequent in ET patients.

In PV, although the numbers of patients were small or not well matched, there is some evidence that the survival of patients with a chromosomal abnormality is less than that of patients with a normal karyotype. For IMF, studies with large numbers of patients have demonstrated that an abnormal karyotype at diagnosis tends to be associated with a poorer prognosis.

Some chromosomal changes, such as deletions or mono-somies of chromosomes 5 and 7, are almost invariably seen after exposure to myelosuppressive therapy and frequently as part of a complex karyotype. It is therefore unlikely that these chromosomes contain genes involved in the etiology of the MPDs. By contrast, deletions of part of the long arm of chromosomes 20 (del 20q) and 13 (del 13q), trisomies of chromosomes 8 and 9 and duplication of part of the long arm of chromosome 1 have all been seen in untreated patients and are frequently present as sole abnormalities. They are likely, therefore, to mark the sites of genes which play an early role in the pathogenesis of the MPDs.

Table 9.3 Summary of major karyotypic abnormalities identified by G-banding in PV and IMF.

Polycythemia vera

Idiopathic myelofibrosis

Number of occurrences

Number of occurrences

Abnormality

of abnormality % of all patients

of abnormality

% of all patients

Deletion of 20q

36 8.6

46

10.6

Deletion of 13q

15 3.6

39

9.0

Trisomy 8

27 6.4

23

5.3

Trisomy 9

25 6.0

13

3.0

Duplication of 1q

14 3.3

24

5.5

Deletion of 7q or monosomy 7

5 1.2

14

3.2

Deletion of 5q or monosomy 5

17 4.1

7

1.6

Total number of patients with one

145 34.6

1B5

42.5

or more abnormality

Total patients

419

435

Data taken from Berger et al, 1984; Demory et al., 1988; Rege-Cambrin et al., 1987; Swolin et al., 19

BB; Diez-Martin et al, 1991; Mertens et

al, 1991; Dupriez et al, 1996; Reilly et al, 1997; Tefferi et al, 2001.

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