GATA-1 mutation R216Q: increased bone marrow angiogenesis and reticulin fibrosis in X-linked thrombocytopenia with thalassaemia trait (XLTT)

Background

GATA-1, a transcription factor, is known to regulate megakaryo- and erythropoiesis. Rarely found missense mutations (V205M, G208S, R216Q, R216W, D218G and D218Y) in the N-terminal zinc-finger coding region of the GATA-1 gene on the X-chromosome lead to defect DNA binding of GATA-1 and variable degrees of macro- thrombocytopenia with or without abnormalities in the erythrocyte lineage.

The GATA-1 mutation R216Q causes “X-linked thrombocytopenia with thalassaemia trait” (XLTT). Four families with this mutation have been described until now. Clinical characteristics include thrombocytopenia, dysfunctional platelets, imbalanced globin chain synthesis, haemolysis and splenomegaly in males, whereas women heterozygous for the mutation have a milder phenotype usually without thrombocytopenia.
Reticulin fibrosis in the bone marrow (BM) has previously been described in other GATA-1 defects and in the “gray platelet syndrome”  but not in XLTT.

Methods and Results

We describe a 4-generation family with XLTT followed since 1993. The diagnosis was suspected on clinical grounds and verified in the affected males by DNA sequencing of exon 4 of GATA-1.
Moderate apparently non-progressive splenomegaly is present in III. BM scintigraphy in III revealed pathological BM distribution with abnormal uptake in distal femur and proximal tibia, consistent with myeloid metaplasia.

A capillary from the BM of a MF patient. Green cells are pericytes (stained for SMA-α), red cells are endothelial cells (stained for CD34). Part of the vessel appears to consist only of pericytes.

BM biopsy from I. Immunofluore-scent staining for CD34 (expressed by endothelial cells, red color) and SMA-α (expressed by pericytes, green color). High microvessel density, MVD (27/HPF) was found, but only a minor
portion of vessels were pericyte coated (6%).

Platelets are of varying size in our XLTT patients. BM findings in both males include normal / increased numbers of megakaryocytes of varying and sometimes small size and a small portion of erythroblasts with nuclear abnormalities. (Haematoxylin-Eosin x 50, patient I).

CD34 staining of endothelial cells (brown color) by IHC in a BM biopsy from patient I with XLTT (x10) . Only the number but not the size of the microvessels is increased.

Pericytes from III had apparently a normal morphology but were
scarce. 4.1-15.7% of vessels were pericyte coated compared to 51%
in healthy controls and 92% in MF patients.

Future directions:

Comparison of platelet characteristics and functions as well as of cytokines and cell types involved in bone marrow angiogenesis and fibrosis in XLTT and MF.

 

Conclusions

In a novel 4-generation family with XLTT, males show increased bone marrow angiogenesis (defined as higher microvessel density) and reticulin fibrosis. Contrary to the malignant disease myelofibrosis (MF), the fibrosis in XLTT appears non-progressive. The numerically increased microvessels are smaller and have lower pericyte coverage in XLTT than in MF.