Translocations and deletions with breakpoint on 21q are nonrandomly associated with treatment-related acute nonlymphocytic leukemia and preleukemia

mBAND analysis for high- and low-LET radiation-induced chromosome aberrations: a review

During long-term space travel or cancer therapy, humans are exposed to high linear energy transfer (LET) energetic heavy ions. High-LET radiation is much more effective than low-LET radiation in causing various biological effects, including cell inactivation, genetic mutations, cataracts and cancer induction. Most of these biological endpoints are closely related to chromosomal damage, and cytogenetic damage can be utilized as a biomarker for radiation insults. Epidemiological data, mainly from survivors of the atomic bomb detonations in Japan, have enabled risk estimation from low-LET radiation exposures. The identification of a cytogenetic signature that distinguishes high- from low-LET exposure remains a long-term goal in radiobiology. Recently developed fluorescence in situ hybridization (FISH)-painting methodologies have revealed unique endpoints related to radiation quality. Heavy-ions induce a high fraction of complex-type exchanges, and possibly unique chromosome rearrangements. This review will concentrate on recent data obtained with multicolor banding in situ hybridization (mBAND) methods in mammalian cells exposed to low- and high-LET radiations. Chromosome analysis with mBAND technique allows detection of both inter- and intrachromosomal exchanges, and also distribution of the breakpoints of aberrations.

Association of inter- and intrachromosomal exchanges with the distribution of low- and high-LET radiation-induced breaks in chromosomes

To study the effects of low- and high-linear energy transfer (LET) radiation on break locations within a chromosome, we exposed human epithelial cells in vitro to (137)Cs γ rays at both low and high dose rates, secondary neutrons at a low dose rate, and 600 MeV/u iron ions at a high dose rate. Breakpoints were identified using multicolor banding in situ hybridization (mBAND), which paints chromosome 3 in 23 different colored bands. For all four radiation scenarios, breakpoint distributions were found to be different from the predicted distribution based on band width. Detailed analysis of chromosome fragment ends involved in inter- or intrachromosomal exchanges revealed that the distributions of fragment ends participating in interchromosomal exchanges were similar between the two low-LET radiation dose rates and between the two high-LET radiation types, but the distributions were less similar between low- and high-LET radiations. For fragment ends participating in intrachromosomal exchanges, the distributions for all four radiation scenarios were similar, with clusters of breaks found in three regions. Analysis of the locations of the two fragment ends in chromosome 3 that joined to form an intrachromosomal exchange demonstrated that two breaks with a greater genomic separation can be more likely to rejoin than two closer breaks, indicating that chromatin folding can play an important role in the rejoining of chromosome breaks. Comparison of the breakpoint distributions to the distributions of genes indicated that the gene-rich regions do not necessarily contain more breaks. In general, breakpoint distributions depend on whether a chromosome fragment joins with another fragment in the same chromosome or with a fragment from a different chromosome.

Acquired monosomy 7 in donor cells in a patient treated for acute lymphoblastic leukemia with bone marrow transplantation

Two years after a bone marrow transplant (BMT) from his haploidentical mother, a 28-year-old male with a history of acute lymphoblastic leukemia (ALI.) developed myelodysplastic syndrome (MDS) with monosomy 7 in his female bone marrow cells. Follow-up cytogenetic studies, including fluorescence in situ hybridization (FISH) performed twenty-seven and thirty-one months post-BMT consistently showed a female chromosome pattern with monosomy 7. Thirty-six and thirty-nine months post-BMT, further clonal evolution occurred, with the appearance of a sideline of the female cells that first expressed a del(10)(p11.2) and then developed a translocation, t(10;21)(p11.2;q22), in addition to the monosomy 7. Cytogenetic monitoring of this male patient helped to reveal a rare case of early MDS in transplanted donor cells and evolution of the acquired abnormal clone by identifying chromosomal alterations in the donated female bone marrow cells.