Key Points: HLA-identical sibling transplantation for SCD offers excellent long-term survival. Mortality risk is higher for older patients; event-free survival has improved in patients transplanted after 2006.

Germline GATA2 mutations cause cellular deficiencies with high propensity for myeloid disease. We investigated 426 children and adolescents with primary myelodysplastic syndrome (MDS) and 82 cases with secondary MDS enrolled in 2 consecutive prospective studies of the European Working Group of MDS in Childhood (EWOG-MDS) conducted in Germany over a period of 15 years. Germline GATA2 mutations accounted for 15% of advanced and 7% of all primary MDS cases, but were absent in children with MDS secondary to therapy or acquired aplastic anemia. Mutation carriers were older at diagnosis and more likely to present with monosomy 7 and advanced disease compared with wild-type cases. For stratified analysis according to karyotype, 108 additional primary MDS patients registered with EWOG-MDS were studied. Overall, we identified 57 MDS patients with germline GATA2 mutations. GATA2 mutations were highly prevalent among patients with monosomy 7 (37%, all ages) reaching its peak in adolescence (72% of adolescents with monosomy 7). Unexpectedly, monocytosis was more frequent in GATA2-mutated patients. However, when adjusted for the selection bias from monosomy 7, mutational status had no effect on the hematologic phenotype. Finally, overall survival and outcome of hematopoietic stem cell transplantation (HSCT) were not influenced by mutational status. This study identifies GATA2 mutations as the most common germline defect predisposing to pediatric MDS with a very high prevalence in adolescents with monosomy 7. GATA2 mutations do not confer poor prognosis in childhood MDS. However, the high risk for progression to advanced disease must guide decision-making toward timely HSCT. Publisher9s Note: There is an Inside Blood Commentary on this article in this issue. Key Points Germline GATA2 mutations account for 15% of advanced and 7% of all primary pediatric MDS and do not influence overall survival. The majority (72%) of adolescents with MDS and monosomy 7 carry an underlying GATA2 deficiency.

Until recently, thrombocytopenia 2 (THC2) was considered an exceedingly rare form of autosomal dominant thrombocytopenia and only 2 families were known. However, we recently identified mutations in the 5′-untranslated region of the ANKRD26 gene in 9 THC2 families. Here we report on 12 additional pedigrees with ANKRD26 mutations, 6 of which are new. Because THC2 affected 21 of the 210 families in our database, it has to be considered one of the less rare forms of inherited thrombocytopenia. Analysis of all 21 families with ANKRD26 mutations identified to date revealed that thrombocytopenia and bleeding tendency were usually mild. Nearly all patients had no platelet macrocytosis, and this characteristic distinguishes THC2 from most other forms of inherited thrombocytopenia. In the majority of cases, platelets were deficient in glycoprotein Ia and α-granules, whereas in vitro platelet aggregation was normal. Bone marrow examination and serum thrombopoietin levels suggested that thrombocytopenia was derived from dysmegakaryopoiesis. Unexplained high values of hemoglobin and leukocytes were observed in a few cases. An unexpected finding that warrants further investigation was a high incidence of acute leukemia. Given the scarcity of distinctive characteristics, the ANKRD26-related thrombocytopenia has to be taken into consideration in the differential diagnosis of isolated thrombocytopenias.

Juvenile myelomonocytic leukemia is an aggressive myeloproliferative disorder characterized by malignant transformation in the hematopoietic stem cell compartment with proliferation of differentiated progeny. Seventy-five percent of patients harbor mutations in the NF1, NRAS, KRAS, or PTPN11 genes, which encode components of Ras signaling networks. Using single nucleotide polymorphism arrays, we identified a region of 11q isodisomy that contains the CBL gene in several JMML samples, and subsequently identified CBL mutations in 27 of 159 JMML samples. Thirteen of these mutations alter codon Y371. In this report, we also demonstrate that CBL and RAS/PTPN11 mutations were mutually exclusive in these patients. Moreover, the exclusivity of CBL mutations with respect to other Ras pathway-associated mutations indicates that CBL may have a role in deregulating this key pathway in JMML.

Autoimmune hemolytic anemia (AIHA) in children is sometimes characterized by a severe course, requiring prolonged administration of immunosuppressive therapy. Rituximab is able to cause selective in vivo destruction of B lymphocytes, with abrogation of antibody production. In a prospective study, we have evaluated the use of rituximab for the treatment of AIHA resistant to conventional treatment. Fifteen children with AIHA were given rituximab, 375 mg/m²/dose for a median of 3 weekly doses. All patients had previously received 2 or more courses of immunosuppressive therapy; 2 patients had undergone splenectomy. After completing treatment, all children received intravenous immunoglobulin for 6 months. Treatment was well tolerated. With a median follow-up of 13 months, 13 patients (87%) responded, whereas 2 patients did not show any improvement. Median hemoglobin levels increased from 7.7 g/dL to a 2-month posttreatment level of 11.8 g/dL (P < .001). Median absolute reticulocyte counts decreased from 236 to 109 × 10⁹/L (P < .01). An increase in platelet count was observed in patients with concomitant thrombocytopenia (Evans syndrome). Three responder patients had relapse, 7, 8, and 10 months after rituximab infusion, respectively. All 3 children received a second course of rituximab, again achieving disease remission. Our data indicate that rituximab is both safe and effective in reducing or even abolishing hemolysis in children with AIHA and that a sustained response can be achieved in the majority of cases. Disease may recur, but a second treatment course may be successful in controlling the disease.

Germ line PTPN11 mutations cause 50% of cases of Noonan syndrome (NS). Somatic mutations in PTPN11 occur in 35% of patients with de novo, nonsyndromic juvenile myelomonocytic leukemia (JMML). Myeloproliferative disorders (MPDs), either transient or more fulminant forms, can also occur in infants with NS (NS/MPD). We identified PTPN11 mutations in blood or bone marrow specimens from 77 newly reported patients with JMML (n = 69) or NS/MPD (n = 8). Together with previous reports, we compared the spectrum of PTPN11 mutations in 3 groups: (1) patients with JMML (n = 107); (2) patients with NS/MPD (n = 19); and (3) patients with NS (n = 243). Glu76 was the most commonly affected residue in JMML (n = 45), with the Glu76Lys alteration (n = 29) being most frequent. Eight of 19 patients with NS/MPD carried the Thr73Ile substitution. These data suggest that there is a genotype/phenotype correlation in the spectrum of PTPN11 mutations found in patients with JMML, NS/MPD, and NS. This supports the need to characterize the spectrum of hematologic abnormalities in individuals with NS and to better define the impact of the PTPN11 lesion on the disease course in patients with NS/MPD and JMML. (Blood. 2005;106:2183-2185)