Haematological features in Barth syndrome

This review highlights recent advances concerning pathogenesis, clinical presentation, diagnosis and treatment of Barth syndrome with particular regard to haematological abnormalities (e.g., neutropenia).

Directed motility and killing activity of neutrophils is normal in patients with Barth syndrome, but neutrophils and eospinophils show phosphatidylserine exposure without exhibiting other markers of apoptosis. Apparently, neutropenia does not result from apoptosis of myeloid precursors or end-stage neutrophils but from reactive oxygen species triggered exposure of phosphatidylserine, leading to increased clearance of neutrophils by tissue macrophages. Lymphoblasts of patients with Barth syndrome show increased variability of mitochondrial size and increased mitochondrial mass due to increased clustering of fragmented mitochondria inside nuclear invaginations. Lymphoblast mitochondria show reduced cristae density, reduced cristae alignment and heterogenous cristae distribution. Areas of adhesion of opposing inner membranes result in obliteration of the inter-cristae space. Short or extended adhesion zones result in sheets of collapsed cristae, which are packaged as multiple concentric layers. In single patients, neutropenia may favourably respond to biweekly injections of granulocyte colony stimulating factor.

Neutropenia in Barth syndrome is most likely due to reactive oxygen species induced exposure of phosphatidylserine, leading to increased clearance of neutrophils by tissue macrophages. In single patients, application of granulocyte colony stimulating factor may resolve neutropenia in Barth syndrome.