Pearson Marrow Pancreas Syndrome In a Cohort Of Diamond Blackfan Anemia Patients

Pearson marrow pancreas syndrome (PS) is a congenital multisystem disorder characterized by sideroblastic anemia, pancreatic insufficiency, metabolic acidosis, and other defects, and is caused by mitochondrial DNA (mtDNA) deletions. Diamond Blackfan anemia (DBA) is a congenital hypoproliferative anemia with associated physical malformations, and in which mutations in ribosomal protein (RP) genes and GATA1 have been implicated. The clinical presentation of both of these bone marrow failure (BMF) syndromes shares several features including early onset of severe anemia, sporadic genetic inheritance, variable penetrance and manifestations, and episodes of spontaneous hematologic improvement. PS is less frequently occurring than DBA, with estimated incidences of < 1/1,000,000 versus 1/100,000 respectively, and therefore less often encountered by hematologists.

We hypothesized that some patients in whom the leading clinical diagnosis is DBA actually have PS. To test this hypothesis, we retrospectively evaluated DNA samples from a cohort of patients that were submitted to a research study for DBA genetic testing. The study cohort consists of clinical samples and/or data from 362 patients, with a primary inclusion criterion of known or suspected congenital anemia. Prior genetic studies from this cohort have yielded the novel identification or confirmation of mutations and deletions in several genes implicated in DBA (e.g. RP genes, GATA1), which are to date identifiable in 175/362 samples (48%), a proportion consistent with that found in independent DBA registries.

We screened peripheral blood DNA samples available from 173 genetically uncharacterized patients using a long PCR strategy, and found that 8 samples (4.6%) contained large mtDNA deletions. Deletion mapping and Southern blot analysis on DNA from these 8 patients confirmed the presence of a single deletion event within each patient, ranging in size from 2.3 - 7.0 kb of the 16.6 kb mitochondrial genome, existing as monomer or multimer mtDNA species, and in a proportion ranging from 55-80% of total mtDNA, all of which are consistent with the molecular diagnosis of PS.

Follow-up with referring providers in the 1 month to 8 year time span since sample submission revealed that 2 of the 8 patients (25%) were subsequently diagnosed with PS. Of the remaining 6 undiagnosed patients, 2 had died from complications of bone marrow transplantation, performed for worsening cytopenias and concern for myelodysplasia; one patient died from bacterial sepsis; and 3 were alive with the provisional diagnosis of DBA. One of the 3 patients had become transfusion-independent. Review of bone marrow examinations revealed that the pathological hallmarks of ringed sideroblasts and/or vacuolization of precursors described in PS were inconsistently present or reported in the diagnostic evaluation.

We conclude that PS is frequently overlooked in the diagnostic evaluation of children with congenital anemia. Establishing the diagnosis of PS, as distinct from DBA and other BMF disorders, holds important implications for patient management and family counseling. mtDNA deletion testing should be performed in the initial genetic evaluation of all patients with congenital anemia.