Complex approach to the study of the Derivative Chromosome 8

Background. Derivative chromosome (der) is a structurally abnormal chromosome, the formation of which can occur as a result of rearrangements with the participation of two or more non-homologous chromosomes, or be the result of aberrations within one chromosome. Differential diagnosis of derivative chromosomes is very important for clarifying the origin of the chromosomal abnormality and for determining the tactics of medical genetic counseling in order to assess the repeated risk of chromosomal imbalance. This work presents seven cases of a derivative chromosome with different origins and mechanisms of formation, as well as a protocol for examining patients with derivative chromosome 8 in the karyotype. Aim: to study the structure and mechanisms of formation of the derivative chromosome 8. Methods. GTG-banded chromosomal analysis, M-FISH, MCB8, FISH with subtelomeric DNA probes, FISH with home-made DNA probes for 8p23.1. Results. As a result of a conventional cytogenetic study of seven unrelated probands a derivative chromosome 8 was found. In all cases, the mechanism of the formation of chromosomal rearrangements was determined. Derivative chromosomes of translocation origin were formed de novo in two cases- der(8)t(8;12) and der(8)t(7;8), and in one case -der(8)t(8;17) - as a result of malsegregation of the paternal reciprocal translocation. In the remaining four cases, the derivative chromosomes were identified as an inverted duplication/deletion 8p due to ectopic recombination. Conclusion. The presented results demonstrate the feasibility of an integrated laboratory approach in the diagnosis of derivative chromosome 8. Characterization of the origin of chromosomal imbalance is an integral part of the examination of patients with structurally abnormal chromosome 8 in the karyotype.

derivative chromosome 8, translocation, inv dup del(8p), FISH

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