*3.2.2 Hypodiploidy*

Hypodiploidy, characterized by less than 44 chromosomes is less frequent than hyperdiploid ALL. Three cytogenetic subgroups of hypodiploidy were defined: near haploidy, with 24–31 chromosomes; low hypodiploid, with 32–39 chromosomes; and high hypodiploid, with 40–43 chromosomes [55]. Near-haploidy patients showed common chromosomal gains, rare structural abnormalities and a

co-incident doubled hyperdiploid population [56–58]. Low hypodiploidy karyotypes are usually monosomic for chromosomes 3, 7, 15, 16, 17, and disomic for chromosomes 1, 6, 11, and 18. In this subgroup, the phenomenon of doubling-up occurs, and sub-clones with near-triploid karyotypes are common. Furthermore, evidence indicates that in near-haploid situations, cytogenetic research is more likely to show only the doubled-up clone. Overall Hypodiploid acute lymphoblastic leukemia (ALL) has been associated with a dismal prognosis [59, 60].
