Somatic mosaicism in Fanconi anemia: molecular basis and clinical significance.

Approximately 25% of patients with Fanconi anemia (FA) have evidence of spontaneously occurring mosaicism as manifest by the presence of two subpopulations of lymphocytes, one of which is hypersensitive to cross-linking agents (e.g. mitomycin C) while the other behaves normally in response to these agents. The molecular basis of this phenotypic reversion has not yet been determined. We have investigated 8 FA patients with evidence of mosaicism. Epstein-Barr virus-immortalized lymphoblastoid cell lines established from these patients exhibited an IC50 for mitomycin C of 25 to > 100 nM compared to a mean of 2 +/- 2 nM for 20 nonmosaic FA patients and 49 +/- 11 nM for 8 healthy controls. In 3 patients who were compound heterozygotes for pathogenic FAC gene mutations the molecular mechanism of the mosaicism was investigated by haplotype analysis. The results indicated that an intragenic mitotic recombination must have occurred leading to a segregation of a wild-type allele in the reverted cells and suggested two patterns of recombination. In 1 patient a single intragenic crossover between the maternally and paternally inherited mutations occurred associated with markers located distally to the FAC gene; in the other 2 patients (sibs) the mechanism appears to have been gene conversion resulting in segregants which have lost one pathogenic mutation. In 6 of the 8 patients the hematological symptoms were relatively mild despite an age range of 9-30 years.

Heterogeneous spectrum of mutations in the Fanconi anaemia group A gene.

Fanconi anaemia (FA) is a genetically heterogeneous autosomal recessive disorder associated with chromosomal fragility, bone-marrow failure, congenital abnormalities and cancer. The gene for complementation group A (FAA), which accounts for 60-65% of all cases, has been cloned, and is composed of an open reading frame of 4.3 kb, which is distributed among 43 exons. We have investigated the molecular pathology of FA by screening the FAA gene for mutations in a panel of 90 patients identified by the European FA research group, EUFAR. A highly heterogeneous spectrum of mutations was identified, with 31 different mutations being detected in 34 patients. The mutations were scattered throughout the gene, and most are likely to result in the absence of the FAA protein. A surprisingly high frequency of intragenic deletions was detected, which removed between 1 and 30 exons from the gene. Most microdeletions and insertions occurred at homopolymeric tracts or direct repeats within the coding sequence. These features have not been observed in the other FA gene which has been cloned to date (FAC) and may be indicative of a higher mutation rate in FAA. This would explain why FA group A is much more common than the other complementation groups. The heterogeneity of the mutation spectrum and the frequency of intragenic deletions present a considerable challenge for the molecular diagnosis of FA. A scan of the entire coding sequence of the FAA gene may be required to detect the causative mutations, and scanning protocols will have to include methods which will detect the deletions in compound heterozygotes.

Bone marrow transplantation in children: consequences for renal function shortly after and 1 year post-BMT.

The aim of this study was to investigate the effect of a bone marrow transplantation (BMT) on renal function in children. In a 5-year period, 142 children received a BMT at the Department of Pediatrics of the University Hospital Leiden. The study was performed retrospectively using the estimated glomerular filtration rate before and 1 year after BMT, and weekly measurements of serum creatinine during the first 3 months after BMT for assessment of renal function. Patient characteristics (sex, age, diagnosis), conditioning regimen, type of BMT, major complications (sepsis, veno-occlusive disease and graft-versus-host disease (GVHD)) and the use of nephrotoxic medication were listed. In the first 3 months after BMT 17 (12%) patients died, 13 from transplant-related complications other than renal failure and four from relapse of the disease. Forty-eight children (34%) had a period with acute renal insufficiency. A high pre-BMT serum creatinine, transplantation with either a non-HLA-identical related or a matched unrelated donor were risk factors for acute renal insufficiency after BMT. Sepsis and the use of intravenous vancomycin were risk factors for acute renal insufficiency only for patients with a high pre-BMT serum creatinine. GVHD seemed to have a beneficial effect on renal function of BMT recipients. One year after BMT a total of 35 (25%) patients had died, 16 from transplant-related complications and 19 from relapse of the disease; another 17 patients could not be evaluated. Twenty-five of 90 evaluable children (28%) had chronic renal insufficiency. Chronic renal insufficiency 1 year after BMT was correlated with a high serum creatinine in the first 3 months after BMT. None of the children of this retrospective study on renal function after BMT needed dialysis.

Paediatric allogeneic bone marrow transplantation for homozygous beta-thalassaemia, the Dutch experience.

We reviewed the results of the Dutch paediatric bone marrow transplant (BMT) program for children receiving HLA-identical BMT for beta-thalassaemia major over an 18-year period. In all, 19 patients underwent a total of 21 transplants in our treatment centre between July 1984 and February 2002. Eight females (age 0.3-12 years; median 5 years) and 11 males (age 0.8-18 years; median 6 years) were included. Information, prospectively collected, included molecular defects, donor genotype, beta/alpha-globin expression rates, serum ferritin levels, hepato-splenomegaly, chelation history, virology screening, liver pathology together with post-transplant outcome inclusive of leucocyte chimerism. In total, 11 patients received standard busulphan/cyclophosphamide (Bu/Cy) conditioning, with or without ATG. Stable engraftment was seen in 5/11 with late rejection occurring in six patients. Of these, two children underwent a second successful SCT. For this group, overall event-free survival (EFS) and disease-free survival (DFS) were 90 (10/11) and 64% (7/11), respectively. The probability of rejection was 55%. Subsequent addition of melphalan to the conditioning regimen resulted in long-term stable engraftment in all patients with an EFS/DFS for this group of 90% (9/10). Treatment-related mortality, irrespective of conditioning, was low at 5% (1/19 patients). Veno-occlusive disease (VOD) occurred in 19% (4/21 transplants) and acute GvHD in 19% (4/21 transplants). Post-BMT beta/alpha synthetic ratio measurement monitored donor erythroid engraftment and predicted rejection with a return to transfusion dependency. Maintained full donor chimerism is indicative of stable engraftment both for leucocyte and erythroid lineages, whereas mixed donor chimerism is not. Our results emphasise the importance of the conditioning regimen and post-transplant chimerism surveillance predictive of rejection or long-term stable engraftment.

Tube feeding and bone marrow transplantation.

BACKGROUND: Children undergoing bone marrow transplantation (BMT) have poor oral intake during the transplant period, caused mainly by the intensive therapy used for their conditioning. Nutritional support (NS) is almost always needed. Whenever possible, tube feeding (TF) is preferred to parenteral nutrition (PN) because its more physiologic and causes fewer complications. However, children undergoing BMT are usually parenterally fed. We, therefore, studied whether TF was tolerated in children undergoing BMT and whether the nutritional intake was adequate in comparison to PN. PROCEDURE: Two groups were compared: TF (n = 12) and PN (n = 22). If intolerance for TF occurred, additional or total PN was given. Nutritional status, intake, complications, and costs were assessed. RESULTS: Both groups had an adequate nutritional status and reached 85% of their nutritional requirements. TF was possible in 62% of the NS days and three children could be exclusively fed with TF. A longer pre-transplant duration of TF seemed to increase the enteral tolerance. Gastrointestinal symptoms were equally frequent in TF as in PN, but cholestasis was less frequent in TF. The mean nutritional cost per child in the TF group was 440 US dollars less than in the PN group. CONCLUSIONS: TF is possible and equal in efficacy to PN in children undergoing BMT, and may have budgetary benefits.

Evidence for at least eight Fanconi anemia genes.

Fanconi anemia (FA) is an autosomal recessive chromosomal breakage disorder with diverse clinical symptoms including progressive bone marrow failure and increased cancer risk. FA cells are hypersensitive to crosslinking agents, which has been exploited to assess genetic heterogeneity through complementation analysis. Five complementation groups (FA-A through FA-E) have so far been distinguished among the first 20 FA patients analyzed. Complementation groups in FA are likely to represent distinct disease genes, two of which (FAC and FAA) have been cloned. Following the identification of the first FA-E patient, additional patients were identified whose cell lines complemented groups A-D. To assess their possible assignment to the E group, we introduced selection markers into the original FA-E cell line and analyzed fusion hybrids with three cell lines classified as non-ABCD. All hybrids were complemented for cross-linker sensitivity, indicating nonidentity with group E. We then marked the three non-ABCDE cell lines and examined all possible hybrid combinations for complementation, which indicated that each individual cell line represented a separate complementation group. These results thus define three new groups, FA-F, FA-G, and FA-H, providing evidence for a minimum of eight distinct FA genes.

Malignant neoplasms in long-term survivors of bone marrow transplantation. Late Effects Working Party of the European Cooperative Group for Blood and Marrow Transplantation and the European Late Effect Project Group.

BACKGROUND: Patients who receive bone marrow transplants have increased risk for new malignant conditions because of several risk factors, including conditioning with radiation and chemotherapy, immune stimulation, and malignant primary disease. The occurrence of and risk factors for malignant neoplasm in long-term survivors must be assessed. OBJECTIVE: To determine the risk and define potential risk factors for new malignant conditions in long-term survivors after marrow transplantation. DESIGN: Retrospective multicenter study. SETTING: Study of the Late Effects Working Party with 45 transplantation centers cooperating in the European Cooperative Group for Blood and Marrow Transplantation. PATIENTS: 1036 consecutive patients who underwent transplantation for leukemia, lymphoma, inborn diseases of the hematopoietic and immune systems, or severe aplastic anemia. Transplantation was done before December 1985, and patients had survived more than 5 years. MEASUREMENTS: Reports on malignant neoplasms were evaluated, and the incidence was compared to that in the general population. Patient age and sex, primary disease and status at transplantation, histocompatibility of the donor, conditioning regimen, type of prophylaxis of graft-versus-host disease, development of acute and chronic graft-versus-host disease, and treatment of chronic graft-versus-host disease were evaluated as variables. RESULTS: Median follow-up since transplantation was 10.7 years (range, 5 to 22.1 years). Malignant neoplasms were seen in 53 patients; the actuarial incidence (+/- SE) was 3.5% +/- 0.6% at 10 years and 12.8% +/- 2.6% at 15 years. The rate of new malignant disease was 3.8-fold higher than that in an age-matched control population (P < 0.001). The most frequent malignant diseases were neoplasms of the skin (14 patients), oral cavity (7 patients), uterus (including cervix) (5 patients), thyroid gland (5 patients), breast (4 patients), and glial tissue (3 patients). Median age of patients and their donors was 21 years. Malignant neoplasms were more frequent in older patients and in patients with chronic graft-versus-host disease. Older patient age and treatment of chronic graft-versus-host disease with cyclosporine were significant risk factors for new malignant neoplasms after bone marrow transplantation. CONCLUSIONS: The spectrum of neoplasms and immunosuppressive treatment with cyclosporine for chronic graft-versus-host disease as dominant risk factors indicate that immunosuppression is the major cause of malignant neoplasms in patients receiving marrow transplants.