Small supernumerary marker chromosomes (sSMC) : why do they break, where they break and how to distinguish harmful from harmless sSMC? / Ahmed Basheer Hamid
Small supernumerary marker chromosomes (sSMC) are defined as additional centric chromosome fragments too small to be identified or characterized unambiguously by banding cytogenetics alone. Even though certain sSMC were associated with specific clinical pictures and syndromes, for most of the sSMC only first steps towards genotype-phenotype correlations were achieved. Therefore sSMC are still a problem in clinical cytogenetics and can be harmful due to different mechanisms like induction of genomic imbalances and/or uniparental disomy of the sSMCs sister chromosomes. This study had the aim to provide new insights into the questions (i) if and why sSMC include specific breakpoints and (ii) how to distinguish harmful from harmless sSMC. Thus, several approaches for better sSMC characterization (HCM-FISH) and/or, characterization of sSMC breakpoints were developed (PCL-FISH; 1MB sets spanning the transitions of dosage-sensitive and dosage-insensitive pericentric regions) and established. sSMC breakpoints were characterized in detail using these new approaches, but also by microdissection based array-comparative genomic hybridization. First hints were obtained that breakpoints involved in sSMC formation are situated preferentially in gene- poor regions of the pericentric regions. Concerning genotype-phenotype correlation of sSMC the present study further identified one new complex sSMC associated syndrome: the der(13 or 21)t(13 or 21;18) syndrome, which is associated with a mild clinical phenotype irrespective of partial trisomy 18p. Finally, influence of mosaicism on sSMC-related phenotypes was studied in detail. In conclusion, the present study provided important new data for genotype-phenotype correlation and biological understanding of sSMC.
|Dissertation Note:||Jena, Univ., Diss., 2015|
|Type of content:||Hochschulschrift|
|Related resources:||Erscheint auch als Online-Ausgabe: Small supernumerary marker chromosomes (sSMC)|
|Physical description:||V, 112 Bl. : Ill., graph. Darst. ; 30 cm|
|Basic Classification:||44.48 Medizinische Genetik|