ACTN1-related thrombocytopenia: identification of novel families for phenotypic characterization.

Inherited thrombocytopenias (ITs) are a heterogeneous group of syndromic and nonsyndromic diseases caused by mutations affecting different genes. Alterations of ACTN1, the gene encoding for α-actinin 1, have recently been identified in a few families as being responsible for a mild form of IT (ACTN1-related thrombocytopenia; ACTN1-RT). To better characterize this disease, we screened ACTN1 in 128 probands and found 10 (8 novel) missense heterozygous variants in 11 families. Combining bioinformatics, segregation, and functional studies, we demonstrated that all but 1 amino acid substitution had deleterious effects. The clinical and laboratory findings of 31 affected individuals confirmed that ACTN1-RT is a mild macrothrombocytopenia with low risk for bleeding. Low reticulated platelet counts and only slightly increased serum thrombopoietin levels indicated that the latest phases of megakaryopoiesis were affected. Given its relatively high frequency in our cohort (4.2%), ACTN1-RT has to be taken into consideration in the differential diagnosis of ITs.

Platelet diameters in inherited thrombocytopenias: analysis of 376 patients with all known disorders.

Abnormalities of platelet size are one of the distinguishing features of inherited thrombocytopenias (ITs), and evaluation of blood films is recommended as an essential step for differential diagnosis of these disorders. Nevertheless, what we presently know about this subject is derived mainly from anecdotal evidence. To improve knowledge in this field, we evaluated platelet size on blood films obtained from 376 patients with all 19 forms of IT identified so far and found that these conditions differ not only in mean platelet diameter, but also in platelet diameter distribution width and the percentage of platelets with increased or reduced diameters. On the basis of these findings, we propose a new classification of ITs according to platelet size. It distinguishes forms with giant platelets, with large platelets, with normal or slightly increased platelet size, and with normal or slightly decreased platelet size. We also measured platelet diameters in 87 patients with immune thrombocytopenia and identified cutoff values for mean platelet diameter and the percentage of platelets with increased or reduced size that have good diagnostic accuracy in differentiating ITs with giant platelets and with normal or slightly decreased platelet size from immune thrombocytopenia and all other forms of IT.

The strange case of the lost NRAS mutation in a child with juvenile myelomonocytic leukemia.

Juvenile myelomonocytic leukemia (JMML) is a rare myelodysplastic/myeloproliferative disorder of early childhood characterized by mutations of the RAS-RAF-MAP kinase signaling pathway. We report the case of a child with a diagnosis of JMML carrying two mutations of NRAS gene (c.37G>C and c.38G>A) independently occurring in long-term culture initiating cells. However, only the former was consistently found in more mature hematopoietic cells, suggesting that cancer transformation may lead to the loss of a mutation. This case also indicates that molecular analysis on cell types other than peripheral blood leukocytes may be useful to obtain relevant biological information on JMML pathogenesis.

Germ-line mutation of the NRAS gene may be responsible for the development of juvenile myelomonocytic leukaemia.

We report the case of a child with clinical and haematological features indicative of juvenile myelomonocytic leukaemia (JMML). The patient showed dysmorphic features: high forehead, bilateral epicanthal folds, long eyebrows, low nasal bridge and slightly low-set ears. A 38G>A (G13D) mutation in exon 1 of the NRAS gene was first demonstrated on peripheral blood cells, and then confirmed on granulocyte-macrophage colony-forming units. The same mutation was also found in buccal swab, hair bulbs, endothelial cells, skin fibroblasts. This case suggests for the first time that constitutional mutations of NRAS may be responsible for development of a myeloproliferative/myelodysplastic disorder in children.

Different outcomes of allogeneic hematopoietic stem cell transplant in a pair of twins affected by juvenile myelomonocytic leukemia.

A twin pair affected by juvenile myelomonocytic leukemia (JMML) with the same somatic PTPN11 mutation and abnormal chromosome 7 in bone marrow samples but distinct prognostic gene expression signatures, received a matched-unrelated donor and matched-unrelated cord blood transplant, respectively. Both twins fully engrafted, but after 6 months, the twin with an acute-myeloid-like (AML-like) signature at diagnosis rejected the graft and had an autologous reconstitution. A second transplant with an unrelated 5/6-HLA-matched-loci cord blood performed after 4 months from rejection was unsuccessful. After 25 months from diagnosis, the twin with the AML-like gene expression signature died of liver failure while on progression of his JMML. The other twin, who had a non-acute-myeloid-like (non-AML-like) gene expression signature at diagnosis is in complete hematological remission with full donor chimera. This observation suggests a biological diversity of JMML also in patients with a common genetic background.