Mitotic stability of small supernumerary marker chromosomes: a study based on 93 immortalized cell lines.

Small supernumerary marker chromosomes (sSMC) are known for being present in mosaic form as 47,+mar/46 in >50% of the cases with this kind of extra chromosomes. However, no detailed studies have been done for the mitotic stability of sSMC so far, mainly due to the lack of a corresponding in vitro model system. Recently, we established an sSMC-cell bank (Else Kröner-Fresenius-sSMC-cellbank) with >150 cell lines. Therefore, 93 selected sSMC cases were studied here for the presence of the corresponding marker chromosomes before and after Epstein-Barr virus-induced immortalization. The obtained results showed that dicentric inverted duplicated-shaped sSMC are by far more stable in vitro than monocentric centric minute- or ring-shaped sSMC. Simultaneously, a review of the literature revealed that a comparable shape-dependent mitotic stability can be found in vivo in sSMC carriers. Additionally, a possible impact of the age of the sSMC carrier on mitotic stability was found: sSMC cell lines established from patients between 10-20 years of age were predominantly mitotically unstable. The latter finding was independent of the sSMC shape. The present study shows that in vitro models can lead to new and exciting insights into the biology of this genetically and clinically heterogeneous patient group.

A method to identify new molecular markers for assessing minimal residual disease in acute leukemia patients.

Acute leukemias (AL) comprise a heterogeneous group of hematologic malignancies, and individual patient responses to treatment can be difficult to predict. Monitoring of minimal residual disease (MRD) is thus very important and holds great potential for improving treatment strategies. Common MRD targets include recurrent cytogenetic abnormalities and mutations in important hematological genes; unfortunately well-characterized targets are lacking in many AL patients. Here we demonstrate a technical approach for the identification and mapping of novel clone-specific chromosomal abnormalities down to the nucleotide level. We used molecular cytogenetics, chromosome microdissection, amplification of the microdissected material, and next-generation sequencing to develop PCR-based MRD assays based on unique breakpoint sequences.

Analysis of SYCP3 encoding synaptonemal complex protein 3 in human aneuploidies.

OBJECTIVES: To test the hypothesis that mutations of SYCP3 encoding synaptonemal complex protein 3, result in increased frequency of aneuploidies in humans. METHODS: Mutation analysis of the PCR-amplified 8 coding exons and exon-intron boundaries of the SYCP3 gene was done by direct sequencing of DNA isolated from 35 aneuploid fetuses of women having a potentially increased likelihood for an underlying genetic predisposition for chromosomal non-disjunction. RESULTS: Based on the results of conventional karyotyping, the 35 aneuploid fetuses of 33 women were divided into separate groups: 9 aneuploid conceptuses of couples with recurrent aneuploid conceptions (4 of the women 35 years or younger), 12 conceptuses with double/multiple aneuploidies (5 of the women 35 years or younger), and 14 conceptuses with single aneuploidies of women younger than 35 years (8 trisomies and 6 monosomies). No pathogenic mutations in the SYCP3 coding exons and the immediately flanking intronic sequences were found. CONCLUSIONS: Under the assumption that genetic predisposition for chromosomal non-disjunction leading to aneuploidy is most likely polygenic in nature, our data suggest that SYCP3 mutations are not one of the common causes in humans.

Mild phenotype in two unrelated patients with a partial deletion of 21q22.2-q22.3 defined by FISH and molecular studies.

We describe two unrelated patients with cytogenetically visible deletions of 21q22.2-q22.3 and mild phenotypes. Both patients presented minor dysmorphic features including thin marfanoid build, facial asymmetry, downward-slanting palpebral fissures, depressed nasal bridge, small nose with bulbous tip, and mild mental retardation (MR). FISH and molecular studies indicated common deleted areas but different breakpoints. In patient 1, the breakpoint was fine mapped to a 5.2 kb interval between exon 5 and exon 8 of the ETS2 gene. The subtelomeric FISH probe was absent on one homologue 21 indicating a terminal deletion spanning approximately 7.9 Mb in size. In patient 2, the proximal breakpoint was determined to be 300-700 kb distal to ETS2, and the distal breakpoint 2.5-0.3 Mb from the 21q telomere, indicating an interstitial deletion sized approximately 4.7-7.3 Mb. The 21q- syndrome is rare and typically associated with a severe phenotype, but different outcomes depending on the size and location of the deleted area have been reported. Our data show that monosomy 21q of the area distal to the ETS2 gene, representing the terminal 7.9 Mb of 21q, may result in mild phenotypes comprising facial anomalies, thin marfanoid build, and mild MR, with or without signs of holoprosencephaly.