Placental Pathology in Down Syndrome-Associated Transient Abnormal Myelopoiesis

The hematopoietic microenvironment of the fetal liver and transient abnormal myelopoiesis associated with Down syndrome: A review

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome is a distinct form of leukemia or preleukemia that mirrors the hematological features of acute megakaryoblastic leukemia. However, it typically resolves spontaneously in the early stages. TAM originates from fetal liver (FL) hematopoietic precursor cells and emerges due to somatic mutations in GATA1 in utero. In TAM, progenitor cells proliferate and differentiate into mature megakaryocytes and granulocytes. This process occurs both in vitro, aided by hematopoietic growth factors (HGFs) produced in the FL, and in vivo, particularly in specific anatomical sites like the FL and blood vessels. The FL's hematopoietic microenvironment plays a crucial role in TAM's pathogenesis and may contribute to its spontaneous regression. This review presents an overview of current knowledge regarding the unique features of TAM in relation to the FL hematopoietic microenvironment, focusing on the functions of HGFs and the pathological features of TAM.

The effect of leucocytosis on retinopathy of prematurity

Postnatal leukocytosis reflects the general condition of inflammatory. Infection and inflammatory reaction have been proven to affect the occurrence of ROP and other visual dysfunction. Infants with a gestational age of < 28 weeks who were less than three days of age and admitted to the hospital between September 2015 and March 2021 were included in the study. Infants with a white blood cell (WBC) count ≥ 30 × 109/L were assigned to the leucocytosis group (n = 82). Gestational age- and weight-matched infants without leucocytosis were included as a control group (n = 85). The incidence and prognosis of ROP in preterm infants were compared between the groups. Receiver operating characteristic (ROC) curves were used to analyse the correlation between the WBC count and severe ROP. Compared to the infants in the control group, those in the leucocytosis group had lower 1-min Apgar scores (p < 0.001); higher C-reactive protein (p < 0.001) and procalcitonin (p < 0.001); and higher incidences of intracranial haemorrhage (p = 0.007), leukomalacia (p = 0.045), sepsis (p = 0.006), bronchopulmonary dysplasia (p = 0.017). The maternal age was higher in the leucocytosis group (p < 0.001). After adjusting for gestational age at 45 weeks, the incidence of severe ROP (p = 0.001) and the requirement for ranibizumab injections (p = 0.004) were higher in the leucocytosis group. The cut-off WBC count was determined to be 19.1 × 109/L, with a sensitivity of 88.6%, a specificity of 77.3%, and an area under the curve of 0.941 (95% confidence interval: 0.904-0.978) for the detection of severe ROP. Leucocytosis may be associated with severe ROP in premature infants.

Myeloid cell thrombus and fetal vascular malperfusion in placentas with transient abnormal myelopoiesis

Transient abnormal myelopoiesis (TAM), also known as transient myeloproliferative disorder or transient leukemia, is a self-regressing neoplasia that afflicts infants with trisomy 21. A recent review article documented "myeloid cell thrombus (MCT)" and "fetal vascular malperfusion (FVM)" in placentas with TAM, although the characteristic TAM placental findings have not been clarified. Here, we compared the clinical and pathological placental findings between trisomy 21 patients with or without TAM. In 13 cases of trisomy 21, we identified six placentas with TAM and seven placentas without TAM. The six placentas with TAM included two stillborn cases. Microscopically, MCT was noted in all the cases, and a high incidence of FVM (50%) was observed in TAM cases. Immunohistochemically, MCT was found to be a platelet-rich thrombus. The placentas were grouped according to the presence or absence of TAM and subsequently compared. Clinically, the incidences of abnormal fetal heart rate pattern and fetal or neonatal death were significantly higher in TAM cases. Pathologically, placenta in TAM cases weighted more than those in cases without TAM, and the incidence of MCT was significantly higher in placentas with TAM. Moreover, the incidence of FVM was higher in placentas with TAM, but this difference was not statistically significant. We propose that MCT is a diagnostic feature of placentas with TAM and may be associated with poor fetal outcomes.