Abstract
In order to understand the mechanism of chromosomal breakage at the DNA level, we recently studied a patient with a de novo ring 21 chromosome. His karyotype was described as 45, XY, -21/46, XY, r(21) (p13q22). Thus, he is monosomic for the sub band 21q22.3 in every cell and trisomic for the remainder of chromosome 21 in at least 70% of his cells.
Using five single copy DNA fragments randomly isolated from chromosome 21 as probes, we have found the following: (i) Four of DNA fragments mapped to the trisomic portion of chromosome 21. (ii) Using DNA polymorphisms associated with these fragments, we determined that the ring chromosome had originated from the mother. (iii) One DNA fragment (pPW231C) mapped at the break-points of the r(21). This latter conclusion was based on the fact that abnormal fragments were present in Southern blots of DNA derived from the proband's leukocytes and fibroblasts and absent from parental DNA. Using several restriction digests we were able to localize the breakpoints to within a 2.1 Kb EcoRI DNA genomic fragment. Nucleotide sequencing of both the normal and the rearranged DNA will provide important information concerning the DNA sequences involved in the rearrangement leading to formation of the ring 21 chromosome.
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Antonarakis, S., Gusella, J., Stetten, G. et al. RING 21 CHROMOSOME: LOCALIZATION OF THE BREAKPOINTS WITHIN A 2 KB DNA FRAGMENT. Pediatr Res 18 (Suppl 4), 219 (1984). https://doi.org/10.1203/00006450-198404001-00755
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DOI: https://doi.org/10.1203/00006450-198404001-00755