Cytogenetic and molecular genetic findings in 91 patients with Turner syndrome are reported. In 87 patients, chromosome studies were carried out both in lymphocyte and fibroblast cultures. Mosaicism was demonstrated in 58 of these patients (66.7%), whereas only 18 (20.7%) were apparent non-mosaic 45,X, and 11 patients (12.6%) showed non-mosaic structural aberrations of the X chromosome. Among the mosaic cases 16 (18.4% of all patients) displayed a second cell line containing small marker chromosomes. The association of Y-specific chromosomal material with the presence of marker chromosomes was demonstrated in 6 out of 7 mixoploid fibroblast cell lines by polymerase chain reaction amplification and by Southern-blot analysis. The observation of ring formation and morphological variability in vivo and in vitro, and the continuous reduction in the percentage of cells containing marker chromosomes in longterm cultivation experiments indicated an increased instability of marker chromosomes. The findings suggest that in vivo selection of structurally altered sex chromosomes exists. Thus, the observation of apparent non-mosaic 45,X chromosomal complements in liveborn individuals with Turner syndrome does not contradict the hypothesis that some degree of mosaicism is necessary for survival in early pregnancy.

We have mapped the autosomal sex reversal locus, SRA1, associated with campomelic dysplasia (CMPD1) to 17q24.3-q25.1 by three independent apparently balanced de novo reciprocal translocations. Chromosome painting indicates that the translocated segment of 17q involves about 15% of chromosome 17 in all three translocations, corresponding to a breakpoint at the interphase between 17q24-q25. All three 17q breakpoints were localized distal to the growth hormone locus (GH), and proximal to thymidine kinase (TK1). Due to the distal location of the breakpoints, previously mentioned candidate genes, HOX2 and COL1A1, can be excluded as being involved in CMPD1/SRA1. The mouse mutant tail-short (Ts) which maps to the homologous syntenic region on mouse chromosome 11, displays some of the features of CMPD1.

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PITX1 is a bicoid-related homeodomain transcription factor implicated in vertebrate hindlimb development. Recently, mutations in PITX1 have been associated with autosomal-dominant clubfoot. In addition, one affected individual showed a polydactyly and right-sided tibial hemimelia. We now report on PITX1 deletions in two fetuses with a high-degree polydactyly, that is, mirror-image polydactyly. Analysis of DNA from additional individuals with isolated lower-limb malformations and higher-degree polydactyly identified a third individual with long-bone deficiency and preaxial polydactyly harboring a heterozygous 35 bp deletion in PITX1. The findings demonstrate that mutations in PITX1 can cause a broad spectrum of isolated lower-limb malformations including clubfoot, deficiency of long bones, and mirror-image polydactyly.

Stromal defects are part of the etiology of severe aplastic anemia (SAA), and hematopoietic engraftment is poor in unrelated and mismatched transplant. Therefore, we wanted to find out whether human mesenchymal stem cells (MSC) are partly of donor origin in patients with SAA years after successful bone marrow transplant (BMT). Three SAA patients 3, 5, and 8 years after BMT (cyclophosphamide, ATG) with bone marrow from an HLA-identical sibling donor of the opposite sex were investigated. MSC were grown from patients' bone marrow aspirates according to Caplan et al. The number of MSC that were isolated from SAA bone marrow post transplant was about 10 times lower than in normal controls. Primary cultures of adherent MSC and passage-one cells were analyzed by dual-color interphase fluorescence in situ hybridization (FISH) analysis using centromere-specific DNA probes for X and Y chromosome. FISH did not show any clear evidence of donor cells in the adherent MSC: In all cases, less than 0.5% of nuclei showed a donor-type signal pattern that is well within assay limits. In a female patient, the absence of male donor cells was confirmed by sensitive and quantitative, Y chromosome-specific TaqMan PCR (QYCS-PCR). In contrast, Ficoll-separated hematopoietic cells from the same aspirates were greater than 90% of donor origin, as expected. In SAA, as previously found in patients with lysosomal and peroxisomal storage disease, bone marrow MSC remain host-derived despite successful hematopoietic engraftment years after allogeneic BMT.