Described in infants and young children; 4 cases of acute myeloid leukemia (AML) (Pui et al., 1987; Raimondi et al., 1989; Pui et al., 1989; Harrison et al., 1998) and one case of acute lymphoblastic leukemia (ALL) (Smith et al., 1973). With one exception, the FAB types in cases of AML were M4. Peripheral leucocytes at diagnosis of this ALL case were cultured and are presently known as the KARPAS-45 cell line (Karpas et al., 1977). In addition, MLL/AFX1 fusion was confirmed in an AML case with highly complex change originally published involving the Xq22 locus (Nacheva et al., 1982; Parry et al., 1994; Borkhardtet al., 1997).

This translocation has also been found in 2 cases of CLL (Bentz et al., 1995; Kalla et al., 2005). In one case a t(X;11)(q13;q23) was cloned revealing the involvement of BRWD3 gene recently located on Xq21.1 (Kalla et al., 2005).

Suggested involvement of a pluripotent stem cell or a myeloid progenitor cell; very rarely in lymphoid lineage.

No known prior exposure; case of AML M2 developed in a 6 years old male previously treated by chemotherapy and radiotherapy for acute lymphoblastic leukemia (Harrison et al., 1998).

6 cases to date, children aged 6 months to 5 years, male predominance; sex ratio 4M/2F.

From the known data: WBC: 21.6 to 91x10⁹/L, case with a complex t(X;11) associated with fever, enlargement of the liver, spleen and parotid glands, blood in the stool (Karpas et al., 1977); mediastinal mass, dyspnoea, no hepatosplenomegaly, WBC: 5x10⁹/L in T-ALL (Smith et al., 1973).

Survival: poor prognosis; 3 patients died within a year after diagnosis, and one patient died after 24.5 months.

Breakpoints difficult to ascertain in suboptimal preparations.

KMT2A/FOXO4 KMT2A (11q23.3) FOXO4 (Xq13.1) COF 1976