Abstract 11

We have previously localized a major locus for Diamond-Blackfan anemia (DBA) to chromosome 19q13.2. Samples from additional families have been collected in order to identify key recombinations, microdeletions and the possibility of heterogeneity for the disorder. In total, 29 multiplex DBA families and 50 families comprising sporadic DBA cases have been analyzed with polymorphic 19q13 markers. The results from DNA analysis of 29 multiplex families revealed that 26 of these were consistent with a DBA gene on 19q13. However, in three multiplex families the DBA candidate region on 19q13 was excluded from the segregation of marker alleles. Our results suggest genetic heterogeneity for DBA and we show that a gene region on chromosome 19q segregates with the disease in the majority of familial cases. Among the 50 families comprising speradic DBA cases we identified two novel and overlapping microdeletions on chromosome 19q13. In combination, the three known microdeletions associated with DBA restrict the critical gene region to approximately 1 Mb.