Variations in bone density at dental implant sites in different regions of the jawbone.

The survival rate of dental implants is markedly influenced by the quality of the bone into which they are placed. The purpose of this study was to determine the trabecular bone density at potential dental implant sites in different regions of the Chinese jawbone using computed tomography (CT) images. One hundred and fifty-four potential implant sites (15 in the anterior mandible, 47 in the anterior maxilla, 55 in the posterior mandible, and 37 in the posterior maxilla) were selected from the jawbones of 62 humans. The data were subjected to statistical analysis to determine any correlation between bone density (in Hounsfield units, HU) and jawbone region using the Kruskal-Wallis test. The bone densities in the four regions decreased in the following order: anterior mandible (530 +/- 161 HU, mean +/- s.d.) approximately equal anterior maxilla (516 +/- 132 HU) > posterior mandible (359 +/- 150 HU) approximately equal posterior maxilla (332 +/- 136 HU). The CT data demonstrate that trabecular bone density varies markedly with potential implant site in the anterior and posterior regions of the maxilla and mandible. These findings may provide the clinician with guidelines for dental implant surgical procedures (i.e., to determine whether a one-stage or a two-stage protocol is required).

Phenotypic correction of Fanconi anemia group C knockout mice.

Fanconi anemia (FA) is a genetic disorder characterized by bone marrow failure, congenital anomalies, and a predisposition to malignancy. FA cells demonstrate hypersensitivity to DNA cross-linking agents, such as mitomycin C (MMC). Mice with a targeted disruption of the FANCC gene (fancc -/- nullizygous mice) exhibit many of the characteristic features of FA and provide a valuable tool for testing novel therapeutic strategies. We have exploited the inherent hypersensitivity of fancc -/- hematopoietic cells to assay for phenotypic correction following transfer of the FANCC complementary DNA (cDNA) into bone marrow cells. Murine fancc -/- bone marrow cells were transduced with the use of retrovirus carrying the human fancc cDNA and injected into lethally irradiated recipients. Mitomycin C (MMC) dosing, known to induce pancytopenia, was used to challenge the transplanted animals. Phenotypic correction was determined by assessment of peripheral blood counts. Mice that received cells transduced with virus carrying the wild-type gene maintained normal blood counts following MMC administration. All nullizygous control animals receiving MMC exhibited pancytopenia shortly before death. Clonogenic assay and polymerase chain reaction analysis confirmed gene transfer of progenitor cells. These results indicate that selective pressure promotes in vivo enrichment of fancc-transduced hematopoietic stem/progenitor cells. In addition, MMC resistance coupled with detection of the transgene in secondary recipients suggests transduction and phenotypic correction of long-term repopulating stem cells. (Blood. 2000;95:700-704)

Retroviral gene transfer for the assignment of Fanconi anemia (FA) patients to a FA complementation group.

Fanconi anemia (FA) is an autosomal recessive disorder characterized by bone marrow failure, cancer susceptibility, and a variety of developmental defects. The disease is clinically heterogeneous; eight different complementation groups (FA A-H) and, thus, genetic loci have been discovered. Two genes, FAA and FAC, have been cloned. Disease-associated mutations have been detected and rapid mutation screening makes possible the assignment of patients without resorting to time-consuming cell fusion and complementation analysis. Amplification of specific cDNAs from RNA followed by direct or indirect sequence analysis is a standard method for mutation detection. During the course of such examinations of the FAC gene, we have noted that frequently only one of the expressed alleles is successfully amplified. This can lead to false assignment of patients to a complementation group. As we report here, such cases can be rapidly clarified by retroviral gene transfer and complementation analysis.

Functional correction of Fanconi anemia group A hematopoietic cells by retroviral gene transfer.

Fanconi anemia (FA) is an autosomal recessive genetic disorder characterized by a variety of physical anomalies, bone marrow failure, and an increased risk for malignancy. FA cells exhibit chromosomal instability and are hypersensitive to DNA cross-linking agents such as mitomycin C (MMC). FA is a clinically heterogeneous disorder and can be functionally divided into at least five different complementation groups (A-E). We previously described the use of a retroviral vector expressing the FAC cDNA in the complementation of mutant hematopoietic cells from FA-C patients. This vector is currently being tested in a clinical trial of ex vivo hematopoietic progenitor cell transduction. The FA-A group accounts for over 65% of all FA cases, and the FAA cDNA was recently identified by both expression and positional cloning techniques. We report here the transduction and phenotypic correction of lymphoblastoid cell lines from four unrelated FA-A patients, using two amphotropic FAA retroviral vectors. Expression of the FAA transgene was adequate to normalize cell growth, cell-cycle kinetics, and chromosomal breakage in the presence of MMC. We then analyzed the effect of retroviral vector transduction on hematopoietic progenitor cell growth. After FAA transduction of mutant progenitor cells, either colony number or colony size increased in the presence of MMC. In addition, FAA but not FAC retroviral transduction markedly improved colony growth of progenitor cells derived from an unclassified FA patient. FAA retroviral vectors should be useful for both complementation studies and clinical trials of gene transduction.