Paternal isodisomy 7q secondary to monosomy 7 at recurrence in a Down syndrome child with acute myelogenous leukemia

We report a boy with Down syndrome and leukemia who acquired uniparental isodisomy of chromosome 7q as a secondary chromosomal change during recurrence of the disease. His karyotype before therapy was 46,XY,der(1)t(1;1)(p36;q32),−7,+21c[17]/46,idem,del(9)(p22)[10], whereas at recurrence it was 46,XY,der(1)t(1;1)(p36;q32,−7,der(7)(qter→p22∼pter::q10→qter),del(9)(p22),+21c[13]/47,XY,+21c[2]. By using polymerase chain reaction amplification of D7S493 and D7S527 markers, we identified the loss of the maternal chromosome 7 with a consequent paternal isodisomy in the clone with dup7q. This rearrangement could be implicated in the progression of the disease by causing (1) nullisomy for a gene or genes located on 7p22→pter, (2) functional double doses of exclusively paternal expressed genes, and (3) restoration of the effects produced by haploinsufficiency of biparental expressed genes.