A rare 6q11+ heteromorphism: cytogenetic analysis and in situ hybridization

Acquired centromeric heteromorphism of chromosome 7 yields discordant results between fluorescent in situ hybridization and karyotype analysis in a child with severe congenital neutropenia

Monosomy 7 is an indicator of malignant transformation in patients with different subtypes of severe congenital neutropenias (SCNs). We present the case of a 5-year-old male diagnosed with SCN. Standard karyotype and fluorescent in situ hybridization (FISH) analyses for centromere of chromosome 7 (chromosome enumeration probe 7 [CEP7]) in bone marrow samples showed disomy for chromosome 7 and a single copy of CEP7. In all cells examined, karyotype analysis of peripheral PHA-stimulated blood samples revealed disomy for chromosome 7. Our results address the issue of centromeric heteromorphism in cytogenetic analysis. Herein, we report a case where FISH using CEP7 in the bone marrow sample showed the presence of only one signal suggesting monosomy seven due to an acquired heteromorphism, whereas extensive conventional karyotyping showed disomy of chromosome 7.

Prenatal diagnosis of a rare de novo centromeric chromosome 6 variant

Cytogenetic heteromorphisms are described as heritable variations at specific chromosomal regions without phenotypic effect. Polymorphisms of the size of heterochromatic centromeric regions of chromosomes 1, 9 and 16 have been well documented in humans but only four previous reports described centromeric polymorphism of chromosome 6. We present a prenatal diagnosis of a rare de novo centromeric chromosome 6 variant. Cytogenetic and molecular techniques were used to characterize this variant and confirm the de novo nature of this event. This case illustrates the importance of reporting unusual variant chromosomes for genetic counseling and for determination of the frequency of variant chromosomes in the general population.

A diminutive chromosome 21 centromere in acute lymphoblastic leukemia

A chance observation of a tiny constitutional variant for the centromere of chromosome 21 in two patients with acute lymphoblastic leukemia (ALL), suggested a possible correlation with the cytogenetic findings in their leukemic cells. Interphase FISH revealed three 13/21 centromeric signals and a single MLL signal in the blast cells of each patient. Metaphase FISH with dual-color application of whole-chromosome paint (wcp) and centromeric probes for chromosome 21 showed two copies of chromosome 21, one with a tiny centromeric signal which corresponded to the invisible centromere in the interphase cells. Patient 2700 had a normal karyotype in his bone marrow at diagnosis. All metaphases from his stimulated peripheral blood also had the tiny chromosome 21 centromere, proving it to be a constitutional variant. Patient 3314 showed the abnormal karyotype 46,XY,inv(1)(p?q?),del(11)(q?),del(12)(p?),inc in his bone marrow. Interphase FISH revealed only one copy each of the ABL and ETV6 genes, in addition to the loss of the MLL signal. The question arises, is there an association between the diminutive centromeric signals for chromosome 21 and the chromosomal instability demonstrated by the deletions of key genes from the leukemic blasts of these two patients?

Spurious monosomy 7 in leukemia due to centromeric heteromorphism

We report heteromorphism of the centrometric region of human chromosome 7, which was observed in the cytogenetic assessment of a complete remission of a pre-B acute lymphoblastic leukemia in the bone marrow cells of a 25-year-old woman. Classical cytogenetic study was performed, as well as metaphase and interphase fluorescence in situ hybridization (FISH) carried out with an alphoid DNA probe specific for the chromosome 7 centromere for detection of leukemic clones with monosomy 7 found at the initial diagnosis. We show an important centromeric heteromorphism of this chromosome detected by FISH and clearly visible on all metaphases and nuclei analyzed. This heteromorphism is observable as a fluorescent signal five- or sixfold larger than that on the homologue. To our knowledge, this heteromorphism of chromosome 7 has not been reported in the literature. However, with the use of FISH analysis, it could be easily mistaken for a mosaicism of monosomy 7, which can be misleading in the interpretation of the results.