Two Novel Somatic Mutations of the ATRX Gene in Female Patients with Acquired Alpha Thalassemia of Myelodysplastic Syndrome (ATMDS).
Authors: Haas Peter S. , Schwabe Michael , Fisher Chris , Gibbons Richard , Higgs Doug R. , Bissé Emanuel , Lübbert Michael 
Published: October 2019

Introduction: In contrast to the classical thalassemias, two distinct thalassemias were recently described in which the molecular defect does not reside in the globin genes but in a transcriptional activator of alpha-globin genes. This protein, ATRX, is mutated in the rare inherited disease of alpha-thalassemias (AT) with mental retardation (ATR-X syndrome) whose affected individuals show a mild form of AT. In addition, and independent of the ATR-X syndrome, there have been approximately 100 case reports worldwide of the association of an acquired form of AT with hematological neoplasms, the large majority of those cases being MDS (ATMDS). The clinical characteristics of such patients encompass the typical features of the underlying hematological disorder plus microcytic anemia. The latter is due to massively reduced alpha-globin gene transcription resulting in excess hemoglobin H (HbH), as revealed by supravital staining of peripheral blood erythrocytes and hemoglobin electrophoresis. The molecular defect of ATMDS lies in a mutation of the ATRX protein and, thus, represents a form of acquired alpha-thalassemia. ATMDS shows a striking male preponderance for reasons that are as yet unclear.

We systematically studied patients with MDS and low MCV and/or MCH but without iron deficiency for the possible presence of HbH cells (indicative of ATMDS). Supravital staining and sequence analysis of the ATRX gene were performed as described (Steensma et al. Blood.2004;103(6):2019–26).

Results: Two female pts with AT-MDS were identified by this strategy. Pat 1 was a 69 year old pt who diagnosed with MDS of the subtype refractory cytopenia with multilineage dysplasia (RCMD), ringed sideroblasts and thrombocytosis (MDS/MPS overlap syndrome, JAK2 negative). She presented with microcytic anemia (Hb 7,5 g/dl, MCV 76,5 fl, MCH 22.4 pg). Supravital staining of a peripheral blood smear revealed massive erythrocytic HbH inclusions. Sequencing of the ATRX coding sequence revealed a novel missense mutation with an A>G transition in codon 2234. This mutation (D2234G) results in an amino acid substitution in ATRX exon 32. It represents the 14th ATRX mutation described thus far and, moreover, the first mutation detected in a female. Pat 2 (61 years old) with initially RCMD and microcytic anemia (Hb 10.4 g/ld, MCV 69 fl, MCH 15.2 pg) had increasing erythrocytosis of 6.93 Mio/μl maximum (also JAK2 negative). Molecular analysis of the ATRX gene also showed a not previously reported ATRX point mutation in exon 8 (G521A) which results in an amino acid change from cysteine to tyrosine and consequently in loss of a zinc finger.

Conclusions: Though AT-MDS is mostly diagnosed in males we have identified two female patients, both showing novel ATRX somatic mutations. ATMDS might be more frequent in female than previously thought. Microcytic anemia in association with a hematological neoplasm, most commonly MDS, should alert to ATMDS which is easily diagnosed by supravital staining of peripheral blood smears. The remarkable thrombocytosis and erythrocytosis, respectively, in our 2 pts are at least suggestive of other phenotypic abnormalities possibly associated with the acquired ATRX genotypes on the MDS background.