High Incidence of Fanconi Anemia in Patients with a Morphological Picture Consistent with Refractory Cytopenia of Childhood

Abstract 2780 Introduction: Refractory cytopenia in childhood (RCC) is the most common subtype of myelodysplastic syndrome (MDS) in children. Differential diagnosis from inherited bone marrow failure (IBMF) such as Fanconi anemia (FA) remains an intriguing challenge, because most patients with RCC have a hypocellular bone marrow (BM) and dysplastic features in haematopoiesis are observed in both RCC and IBMF. Moreover the spectrum of phenotypic findings in FA is extremely wide. Some FA patients have a mild phenotype without malformation. The purpose of this study is to estimate the incidence of FA in an RCC cohort without a full clinical feature of FA, but subsequently diagnosed by chromosome breaking test. Patients and Methods: Between 01/2007 and 12/2010 reference pathologists of the European Working Group of MDS in Childhood (EWOG-MDS) provided a morphological report consistent with RCC in 137 children studied in Germany. Seventeen patients with hypercellular BM or abnormal karyotype, 2 patients, in whom dyskeratosis congenital was diagnosed after initial inclusion and one patient, in whom chromosome breaking test was not performed, were excluded. Results: Seven of remaining 117 patients had facial and/or skeletal anomalies typically noted in FA and one patient had a brother with FA. In these 8 patients, FA had been suspected by their local physicians (group FA-1). Nine patients (8.3%) without these typical anomalies were subsequently diagnosed of FA by chromosome breakage test (group FA-2). The diagnosis of RCC was finally made in the remaining 100 patients with negative chromosomal breakage test (group RCC). The clinical features of patients in each group are summarized in the Table. The mean corpuscular volume of red cells (MCV) was elevated (> +2SD) for ages in all patients with FA, but only 42 % in patient with RCC. In some children of group FA-2 additional non-haematological abnormalities were also observed. However, they were not evident and or typical to prompt the treating physicians to suspect FA. A few patients in the group RCC also had some physical anomalies, not specific for any of the known IBMF disorders. Possibly that other known or not yet described IBMF disorders remain uncovered in children with “de novo” RCC. Conclusion: Our results illustrate that the same haematological features and congenital anomalies can be noted in FA and RCC. More importantly, they indicate that the exclusion of FA by a chromosomal breakage test or other methods is mandatory in all patients prior to diagnosis RCC. Chromosomal breakage analysis may identify patients with FA in 8% of patients with a morphological description of RCC without a full clinical picture of FA. Disclosures: No relevant conflicts of interest to declare.

The heterochronic Teopod1 and Teopod2 mutations of maize are expressed non-cell-autonomously.

Teopod1 and Teopod2 are dominant, unlinked mutations in maize that cause dramatic morphological abnormalities, including inappropriate expression of juvenile traits in adult vegetative phytomers and the transformation of reproductive structures into vegetative ones. These phenotypes are consistent with the constitutive expression of a juvenile phase of development throughout shoot growth. To investigate the basis of the Tp1 and Tp2 phenotypes we have analyzed their cell-autonomy in mosaic Teopod:wild-type plants. Mosaic plants were generated by three different mechanisms. Tp1 has previously been shown to be non-cell-autonomous; to verify and extend these results, large wild-type sectors were generated on Tp1 plants by the spontaneous loss of a B-A translocation chromosome containing the Tp1 gene. Analysis of Tp2 cell-autonomy was complicated by a lack of useful markers on chromosome 10L proximal to Tp2. To circumvent this problem two strategies were used. A reciprocal translocation was used to link Tp2 the wild-type allele of lw2. Sectors were induced in plants of this type by irradiation of imbibed seeds. Also, a chromosome-breaking Ds element located proximal to Tp2 was used to generate somatic sectors that uncovered w2, an albino mutation distal to Tp2. Our results demonstrate conclusively that both Tp1 and Tp2 are non-cell-autonomous. The general use of these techniques for clonal analysis in plants and the potential role of a diffusible factor in regulating the juvenile phase of development in maize are discussed.

Chromosome breakage by pairs of closely linked transposable elements of the Ac-Ds family in maize.

Chromosome breaks and hence chromosomal rearrangements often occur in maize stocks harboring transposable elements (TEs), yet it is not clear what types of TE structures promote breakage. We have shown previously that chromosomes containing a complex transposon structure consisting of an Ac (Activator) element closely linked in direct orientation to a terminally deleted or fractured Ac (fAc) element have a strong tendency to break during endosperm development. Here we show that pairs of closely linked transposons with intact ends, either two Ac elements--a common product of Ac transposition--or an Ac and a Ds (Dissociation) element, can constitute chromosome-breaking structures, and that the frequency of breakage is inversely related to intertransposon distance. Similar structures may also be implicated in chromosome breaks in other eukaryotic TE systems known to produce chromosomal rearrangements. The present findings are discussed in light of a model of chromosome breakage that is based on the transposition of a partially replicated macrotransposon delimited by the outside ends of the two linked TEs.