Partial Chromosome Deletion: A New Trisomy Rescue Mechanism?

Abstract

Objective: We described a first case of a fetus with multiple congenital malformations associated with full trisomy 5 on direct CVS analysis and a partial trisomy 5 after cell culture. Methods: CVS karyotype (direct examination and culture) was performed after ultrasound examination and genetic counseling. Results: Direct CVS preparation showed a female karyotype with a homogeneous entire chromosome 5 trisomy, and karyotype of cultured CVS showed partial chromosome 5 trisomy, with an extra chromosome resulting from a deleted chromosome 5: 47,XX,del(5q31),+5. Only macroscopic examination could be performed because parents decided against postmortem examination and further analysis. Conclusion: After a brief literature review, we argue that all de novolargechromosome deletions need to be considered as potentially associated with a trisomy rescue and uniparental disomy.

Cytogenetic contribution to uniparental disomy (UPD)

“…As UPD and sSMC formation can go together, chromosome demolition would be a process of deliberate fragmentation and/or removal of one of the sets of three chromosomes during ana- or metaphase. Such chromosome fragmentation is seen in Howel Joly bodies [37] and a case with a del(5)(q31) recently reported could be interpreted as incomplete chromosome fragmentation [38]. Also the recently recognized phenomenon that "developmental chromosome instability" is significantly increased during embryonic stage and affects different tissues is to be mentioned in this context [39].…”

Full trisomy 5 in a sample of spontaneous abortion and arias stella reaction

“…By using conventional and trypsin G-staining and by DNA typing using highly polymorphic microsatellite markers, trisomy 5 in spontaneous abortion material was recorded in a total of 6 cases [5–8]. Comparative genomic hybridization, a powerful new molecular cytogenetic technique, has been used for chromosome analysis in spontaneous abortions in only a limited number of studies [10–12]; however, trisomy 5 was recorded in only 1 first trimester missed abortion [9].…”

“…However, despite of the molecular cytogenetic techniques used for aneuploidy detection, trisomy 5 in aborted material has been observed only in sporadic cases [5–8]. …”

Small supernumerary marker chromosomes: A legacy of trisomy rescue?

“…A probably less frequent phenomenon is a partial trisomy rescue in which only a part of the original trisomic chromosome is eliminated while a part remains, more often in the form of a supernumerary marker, in mosaic with a normal cell line. Cases in which the initial full trisomy could be documented by direct villus analysis with the subsequent partial correction leading to the presence of a sSMC are few (Srebniak et al., ; Vialard et al., ). More numerous are the cases in which the presence of the de novo sSMC is accompanied by maternal hetero/isodisomy of the homologous chromosomes (Ahram et al., ; Liehr et al., ; Melo et al., ), a situation that can only be explained by a partial trisomic rescue of the supernumerary chromosome of paternal origin, after a nondisjunction event at the maternal MI.…”