Roles of SLX1–SLX4, MUS81–EME1, and GEN1 in avoiding genome instability and mitotic catastrophe

The resolution of recombination intermediates containing Holliday junctions (HJs) is critical for genome maintenance and proper chromosome segregation. Three pathways for HJ processing exist in human cells and involve the following enzymes/complexes: BLM–TopoIIIα–RMI1–RMI2 (BTR complex), SLX1–SLX4–MUS81–EME1 (SLX–MUS complex), and GEN1. Cycling cells preferentially use the BTR complex for the removal of double HJs in S phase, with SLX–MUS and GEN1 acting at temporally distinct phases of the cell cycle. Cells lacking SLX–MUS and GEN1 exhibit chromosome missegregation, micronucleus formation, and elevated levels of 53BP1-positive G1 nuclear bodies, suggesting that defects in chromosome segregation lead to the transmission of extensive DNA damage to daughter cells. In addition, however, we found that the effects of SLX4, MUS81, and GEN1 depletion extend beyond mitosis, since genome instability is observed throughout all phases of the cell cycle. This is exemplified in the form of impaired replication fork movement and S-phase progression, endogenous checkpoint activation, chromosome segmentation, and multinucleation. In contrast to SLX4, SLX1, the nuclease subunit of the SLX1–SLX4 structure-selective nuclease, plays no role in the replication-related phenotypes associated with SLX4/MUS81 and GEN1 depletion. These observations demonstrate that the SLX1–SLX4 nuclease and the SLX4 scaffold play divergent roles in the maintenance of genome integrity in human cells.     

Critical function for the Ras-GTPase activating protein RASA3 in vertebrate erythropoiesis and megakaryopoiesis

Phenotype-driven approaches to gene discovery using inbred mice have been instrumental in identifying genetic determinants of inherited blood dyscrasias. The recessive mutant scat (severe combined anemia and thrombocytopenia) alternates between crisis and remission episodes, indicating an aberrant regulatory feedback mechanism common to erythrocyte and platelet formation. Here, we identify a missense mutation (G125V) in the scat Rasa3 gene, encoding a Ras GTPase activating protein (RasGAP), and elucidate the mechanism producing crisis episodes. The mutation causes mislocalization of RASA3 to the cytosol in scat red cells where it is inactive, leading to increased GTP-bound Ras. Erythropoiesis is severely blocked in scat crisis mice, and ~94% succumb during the second crisis (~30 d of age) from catastrophic hematopoietic failure in the spleen and bone marrow. Megakaryopoiesis is also defective during crisis. Notably, the scat phenotype is recapitulated in zebrafish when rasa3 is silenced. These results highlight a critical, conserved, and nonredundant role for RASA3 in vertebrate hematopoiesis.     

Anaemia during pregnancy: impact on birth outcome and infant haemoglobin level during the first 18 months of life

To determine the effect of maternal anaemia on pregnancy outcome and describe its impact on infant haemoglobin level in the first 18 months of life, we conducted a prospective study of 617 pregnant women and their children in Benin. Prevalence of maternal anaemia at delivery was 39.5%, and 61.1% of newborns were anaemic at birth. Maternal anaemia was not associated with low birth weight [OR = 1.2 (0.6-2.2)] or preterm birth [OR = 1.3 (0.7-2.4)], whereas the newborn's anaemia was related to maternal anaemia [OR = 1.8 (1.2-2.5)]. There was no association between an infant's haemoglobin level until 18 months and maternal anaemia. However, malaria attacks during follow-up, male gender and sickle cell trait were all associated with a lower infant haemoglobin level until 18 months, whereas good infant feeding practices and a polygamous family were positively associated with a higher haemoglobin level during the first 18 months of life.     

Delivery of Predialysis Care in an Academic Referral Nephrology Practice

The purpose of this study was to obtain a detailed picture of the delivery of all aspects of pre-end stage renal disease (ESRD) care in an academic nephrology practice. The study consisted of a cross-sectional review of the charts of 111 patients with chronic kidney disease (CKD) (Creatinine > 1.5 mg/dL for males, Creatinine > 1.3 mg/dL for females) followed either in a private practice or a public hospital clinic. Charts were reviewed for evidence of a number of quality of care items including the degree of blood pressure control, the use of angiotensin II blockade, treatment of anemia, bone disease, and cardiovascular risk factors, as well as evidence of dialysis orientation and vascular access placement. Compared with previous published studies, this study shows encouraging trends towards better outcomes in at least two areas with evidence of improvement in hemoglobin levels, use of angiotensin II blockade, and degree of blood pressure control. However it also reveals many areas where care could be improved. This was particularly true in the areas of access placement, bone and mineral metabolism, and cardiovascular disease. It will be interesting to see whether the recent introduction of CKD guidelines by the National Kidney Foundation (NKF) and the associated educational initiatives for primary care physicians and nephrologists that are planned will further serve to improve the management of CKD patients in the years to come.     

Fatal warm autoimmune hemolytic anemia in a child due to IgM‐type autoantibodies

Herein is described a case of immunoglobulin M (IgM) warm autoimmune hemolytic anemia (AIHA) in a child who consequently died within 3 days of clinical onset. A previously healthy 11‐year‐old boy presented with fever, anemia, jaundice, and deteriorating consciousness. On direct agglutination test against group O red blood cells, agglutination was seen even at 37°C in saline, which was abolished on dithiothreitol treatment of the serum, indicating that the responsible autoantibody was IgM and had a warm‐reactive capacity. A diagnosis of IgM warm AIHA was therefore made. Hemagglutination in the visceral capillaries was considered as the direct cause of organ dysfunction. The patient died due to respiratory failure. IgM warm AIHA is a very severe condition that is difficult to reverse in an advanced state. Both prompt, definite diagnosis and intervention are therefore vital to prevent severe multi‐organ dysfunction in cases of IgM warm AIHA.     

Transient neonatal hemolytic anemia due to the novel gamma globin gene mutation HBG2:C.290T>C,p.Leu97Pro (hemoglobin Wareham)

Unstable gamma globin variants can cause transient neonatal hemolytic anemia. We have identified a novel variant in a newborn who presented with jaundice and anemia requiring phototherapy and red blood cell transfusion. The patient was found to be heterozygous for the mutation HGB2:c.290T>C, p.Leu97Pro, which we have termed hemoglobin (Hb) Wareham. This substitution is expected to generate an unstable hemoglobin with increased oxygen affinity based on the homologous mutation previously described in the beta globin gene, which is termed as Hb Debrousse. The patient fully recovered by 9 months of age as expected with the transition from fetal to adult hemoglobin.