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An X isochromosome for the long arm was studied in 3 patients with Turner's syndrome using the BrdUrd-Hoechst 33258-Giemsa method and C-staining. In all 3 patients studied, the long arms of the i(Xq) were asymmetrical with respect to chronology of DNA synthesis. The most striking asynchrony of DNA replication was observed in large early replicating segments adjacent to the centromeric region. Two C bands of similar appearance were observed localized symmetrically in both arms. The data are interpreted in accordance with two possible origins of an abnormal X which is known as i(Xq).

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Human rRNA genes contain variable regions, one of which is located in nontranscribed spacers (NTSs) closely downstream from the 3'-end of the transcribed region. This polymorphism may be detected by means of blot hybridization analysis as a set of distinct restriction fragments corresponding to this part of the rRNA genes. We have analyzed DNA of 51 individuals and found eight structural NTS variants of this region; two of these were common to all individuals analyzed, and six others were found in different combinations and with different frequencies. The copy number of each variant also differed but was not less than 10-20 copies per cell. The analysis of DNA isolated from leukocytes of the members of 11 families indicated that some of the structural variants (of the NTS region) are inherited as a single Mendelian locus. We propose that rRNA genes that belong to one particular structural variant form clusters on separate chromosomes. To test this proposition, we developed a combined method, including AgNO3-staining of chromosomes, in situ hybridization, and DNA analysis with methylation-sensitive restrictases, and used it for study of persons who had methylated rRNA genes located on AgNO3-negative nucleolar organizers. It was found that in three of four cases methylated genes really belonged to one structural variant. This approach may be used for detailed localization of separate classes of NTS structural variants of human rRNA genes.

Transplant-associated thrombotic microangiopathy (TA-TMA) is a rare complication of hematopoietic stem cell transplantation with an endothelial damage being the major cause of clinical signs. Currently, four major set of diagnostic criteria exist which capture different populations of patients with variable severity of endothelial dysfunction and target organ involvement. Absence of widely excepted criteria for TA-TMA severity, outcome and response measures complicate the comparison of different treatment approaches. Withdrawal or tapering of calcineurin inhibitors is a widely excepted intervention; however, there are studies that indicate no benefit of this intervention in improving overall survival. Different strategies of substituting calcineurin inhibitors with other immunosuppressive may also have impact on survival in TA-TMA patients.Novel approaches in treatment include oligonucleotides and complement inhibitors. Indications for these treatments according to different diagnostic criteria are still to be defined. Currently published evidence highlight the need for cooperative effort to gather empirical data and harmonize definitions required for comparative clinical studies of novel agents.

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