X-autosome and X-Y Translocations in Female Carriers: X-chromosome Inactivation Easily Detectable by 5-ethynyl-2-deoxyuridine (EdU).

Here we report one new case each of an X-autosome translocation (maternally derived), and an X-Y-chromosome translocation. Besides characterizing the involved breakpoints and/or imbalances in detail by molecular cyto-genetics, also skewed X-chromosome inactivation was determined on single cell level using 5-ethynyl-2-deoxyuridine (EdU). Thus, we confirmed that the recently suggested EdU approach can be simply adapted for routine diagnostic use. The latter is important, as only by knowing the real pattern of the skewed X-chromosome inactivation, correct interpretation of obtained results and subsequent reliable genetic counseling, can be done.

Molecular Cytogenetic Study of the NF2 Gene Deletion in Meningioma in Sudanese Patients.

Meningioma is the second most common adult central nervous system tumor. Mutations and/or deletions within the tumor suppressor gene neurofibromatosis type 2 (NF2) are associated with meningioma development and progression. We studied 29 meningioma samples by cytogenetic analysis and interphase fluorescence in situ hybridization (I-FISH) using a locus-specific probe for the NF2 gene region. We detected loss of the NF2 gene in all samples except for one. In 10 of the 29 samples, karyotypic analyses confirmed the I-FISH results and revealed additional numerical and/or structural rearrangements in nine of them. Our study confirmed: i) the limited role of banding cytogenetics in assessing chromosomal rearrangements in meningioma, as this tumor is hard to be grown in cell culture; ii) we could show that two-color I-FISH is well-suited for NF2-deletion screening. Our results were in accordance with those of comparable studies, even though the frequency of 97.0% of meningiomas with NF2 deletions is exceptionally high in the studied Sudanese patients.

Evidence for correlation of fragile sites and chromosomal breakpoints in carriers of constitutional balanced chromosomal rearrangements.

A molecular cytogenetic study of 251 cases with balanced chromosomal rearrangements detected due to infertility of unclear origin or in prenatal diagnostics with a later normal outcome was done. Balanced translocations (127 cases), inversions (105 cases), insertions (three cases), balanced complex rearrangements (four cases), or derivative chromosomes leading to no imbalance (12 cases), were studied by multicolor banding (MCB) and/or subcentromeric multicolor fluorescence in situ hybridization (subcenM-FISH). Five-hundred and twenty-nine break-events were characterized by molecular cytogenetics. Only 150 of these were unique breakpoints, the remainder were observed between two and 10 times. According to the results obtained, there was cytogenetic co-localization of fragile site (FS) in ~71% of the studied 529 break-events. Nine selected cases with evidence for breakpoints within FS were further analyzed by FS-specific bacterial artificial chromosome (BAC) probes; only one did not show a co-localization. Further detailed molecular analysis will be necessary to characterize the mechanisms and genetic basis for this phenomenon.