Genetic instability of a dinucleotide repeat-rich region in three hematologic malignancies

Microsatellite instability is a newly identified mechanism of mutation that occurs in some heritable neurological and muscular disorders, as well as in an increasing number of human cancers. To extend previous data, we examined the genetic instability of a human genomic region, termed S3/1, which we isolated from a human DNA library. The S3/1 sequence contains a stretch with exceptionally high numbers of (GA)n and (CA)n dinucleotide repeats. An interesting rearranged pattern emerged from Southern blot analysis of genomic DNA from three patients with different hematopoietic proliferative diseases out of 69 analyzed (one case of essential thrombocytosis (ET), one of chronic myelogenous leukemia (CML) and one of acute myelogenous leukemia (AML)). The CML and ET patients showed a deletion of 300 to 400 base pairs (bp), and the AML an insertion of about 600 bp, involving the S3/1 locus. Amplification of the rearranged fragments confirmed these observations, and enabled a precise analysis of the region involved. In normal individuals, no gross rearrangements involving this region could be detected. Analysis of DNA from three consecutive bone marrow biopsies of the CML patient disclosed that the genetic alteration affecting S3/1 was no longer detectable following alpha 2-interferon therapy, neither by Southern blot nor by polymerase chain reaction (PCR), thus confirming the tumor-specificity of the alteration; in the same patient, moreover, two out of five other analyzed microsatellites showed tumor-specific alleles, suggesting a more generalized genetic instability in the leukemic cells. These results demonstrate genetic instability of a region containing high numbers of short dinucleotide repeats in a small percentage (4%) of human hematopoietic proliferative disorders.