Sharon Singh

Chronic transfusion practices for prevention of primary stroke in children with sickle cell anemia and abnormal TCD velocities

Chronic transfusions are recommended for children with sickle cell anemia (SCA) and abnormal transcranial Doppler (TCD) velocities ( 200 cm/sec) to help prevent the occurrence of a primary stroke [1]. The goal is usually to maintain the sickle hemoglobin concentration (HbS) <30%; however, this goal is often difficult to achieve in clinical practice. The NHLBI-sponsored trial ‘‘TCD With Transfusions Changing to Hydroxyurea (TWiTCH)’’ will compare standard therapy (transfusions) to alternative therapy (hydroxyurea) for the reduction of primary stroke risk in this patient population. Transfusions will be given according to current transfusion practices at participating sites. To determine current academic community standards for primary stroke prophylaxis in children with SCA, 32 clinical sites collected data on 340 children with abnormal TCD velocities receiving chronic transfusions to help prevent primary stroke. The average (mean ± 1 SD) pretransfusion HbS was 34 ± 11% (institutional average 23–48%); the 75th and 90th percentiles were 41 and 50%, respectively. Lower %HbS was associated with higher pretransfusion Hb values and receiving transfusions on time. These data indicate variable current transfusion practices among academic pediatric institutions and in practice, 30% HbS may not be an easily attainable goal in this cohort of children with SCA and abnormal TCD. Children with sickle cell anemia (SCA) compose a high risk group for the development of stroke. If untreated, 11% will experience a clinical stroke by 20 years of age [2]. Adams et al. have shown that children with SCA who are at risk for primary stroke can be identified by measuring time-averaged mean blood flow velocities in the internal carotid or middle cerebral arteries by TCD [3]. Abnormal TCD velocities ( 200 cm/sec) are associated with high risk for stroke and warrant transfusion therapy to reduce the risk of primary stroke. First stroke can be successfully prevented in 90% of children with SCA and abnormal TCD velocities by the use of chronic transfusion therapy, with a goal of keeping HbS concentrations less than 30% [1]. TCD with Transfusions Changing to Hydroxyurea (TWiTCH) is an NHLBIsponsored, Phase III, multicenter trial comparing standard therapy (monthly transfusions) to alternative therapy (daily hydroxyurea) to reduce the risk of primary stroke in children with SCA and documented abnormal TCD velocities. Since transfusions compose the standard treatment arm, accurate %HbS values achieved in actual clinical practice were needed for protocol development. The majority of our information about transfusing patients with SCA to prevent stroke comes from secondary stroke prevention, i.e., the use of chronic red blood cell transfusions to prevent a second stroke after a first clinical stroke has occurred. Classically, transfusions are administered at 4-week intervals to maintain HbS at less than 30%. After several years of transfusion therapy, a few centers increase transfusion interval to 5–6 weeks and allow HbS to increase toward 50% in selected patients [4,5]. Our previous study in 295 children with SCA who received transfusions for secondary stroke prevention revealed an average pretransfusion HbS of 35 ± 11% with highly variable institutional %HbS levels ranging from 22 to 51% [6] In order to determine the current clinical standard of transfusion therapy for primary stroke prevention for elevated TCD velocities, we performed a larger survey of potential TWiTCH sites. We hypothesized that average pretransfusion HbS values achieved at pediatric academic centers would be higher than 30%. This study defines the current practice at academic medical centers in provision of chronic transfusion therapy to help reduce the risk of primary stroke in children with SCA. A total of 340 children with SCA and history of abnormal TCD velocities receiving chronic PRBC transfusions for primary stroke prophylaxis were identified at 32 institutions (Table I). The number of patients per site ranged from 3 to 33 (median 9 per site). A total of 3,970 transfusions were administered over the 12-month period, with a mean of 11.7 ± 2.8 transfusions per patient. Results were similar when analyzed by each patient contributing equally or each transfusion contributing equally (Table II). The predominant transfusion type by patient was defined as the technique used 6 times over the 12-month period. Most children (79%) received primarily simple transfusions, while 19% had primarily exchange transfusions (11% partial / manual exchange, 8% erythrocytapheresis), and 2% multiple transfusion types. The transfusion goal was <30% at almost all sites (84%), while at five sites, the %HbS was allowed in selected patients to increase to 50% after a period of clinical stability. The majority (95%) of the transfusions were administered within the defined 7-day window. On average, late transfusions were given 1.3 ± 5.5 days after the defined 7-day window. Thirty percent of the patients had at least one late transfusion and 14% had 2 or more late transfusions in the 1-year period. For the 3,653 transfusions with reported %HbS values (representing 92% of the 3,970 transfusions), the mean pretransfusion HbS percentage was 33.2 ± 14.0% (median 32%). The 75th percentile for HbS values was 41%, while the 90th percentile was 51%. There were substantial differences among institutional pretransfusion %HbS values, ranging from 23 ± 14% HbS at one institution where HbS was reported for 103 transfusions given to nine patients during the 12-month period, to 48 ± 15% at another institution where HbS was reported for 95 transfusions administered to nine patients during the same time frame (Table III). The five sites with increased HbS goals to 50% in selected patients did not have higher values than others. For each transfusion, subjects were less likely to have pretransfusion HbS <30% if they were older [OR 0.92 for each year increase in age, 95% CI (0.89, 0.96)] and on transfusions for a longer period of time [OR 0.90 for each year increase in duration, 95% CI (0.86, 0.94)]. Patients with higher pretransfusion Hb levels were more likely to have pretransfusion HbS <30% [OR 1.63 for each g/dL increase in Hb, 95% CI (1.46, 1.83)] and late transfusions were less likely to be associated with a pretransfusion HbS <30% [OR 0.27, 95% CI (0.18, 0.41)]. The Hb result does not appear to be a function of late transfusions since both covariates remained significant when modeled jointly. History of alloor autoantibodies, TCD velocity, and erythrocytapheresis use were not significant predictors of a pretransfusion HbS <30%. During the initial STOP study, transfusions were given to maintain pretransfusion HbS values at less than 30% [3]. However, there were frequent transient rises of HbS above this level [7]. Furthermore, extended follow-up results from the STOP study showed that pretransfusion %HbS values during the post-trial follow-up were higher than those during the STOP study [8]. The average %HbS per patient was 27.5 ± 12.4, still within the desired goal of 30%. However, pretransfusion HbS levels were 30–34.9% in 12%, 35–39.9% in 7%, and greater than 40% in 12% of the transfusions. In the STOP2 study, where children with abnormal TCD velocities whose Doppler readings became normal were randomly assigned to continue or stop transfusions, 24% of the patients had pretransfusion HbS levels greater than 30% [9]. These findings indicate that even in the context of a prospective clinical trial, maintaining HbS <30% was difficult to achieve. With the subsequent recommendation to treat all children with SCA who are at risk for primary stroke with transfusions to maintain HbS <30%, the feasibility of this approach in actual clinical practice is not known. Possible Letters

p53-Independent cell cycle and erythroid differentiation defects in murine embryonic stem cells haploinsufficient for Diamond Blackfan anemia-proteins: RPS19 versus RPL5.

Diamond Blackfan anemia (DBA) is a rare inherited bone marrow failure syndrome caused by ribosomal protein haploinsufficiency. DBA exhibits marked phenotypic variability, commonly presenting with erythroid hypoplasia, less consistently with non-erythroid features. The p53 pathway, activated by abortive ribosome assembly, is hypothesized to contribute to the erythroid failure of DBA. We studied murine embryonic stem (ES) cell lines harboring a gene trap mutation in a ribosomal protein gene, either Rps19 or Rpl5. Both mutants exhibited ribosomal protein haploinsufficiency and polysome defects. Rps19 mutant ES cells showed significant increase in p53 protein expression; however, there was no similar increase in the Rpl5 mutant cells. Embryoid body formation was diminished in both mutants but nonspecifically rescued by knockdown of p53. When embryoid bodies were further differentiated to primitive erythroid colonies, both mutants exhibited a marked reduction in colony formation, which was again nonspecifically rescued by p53 inhibition. Cell cycle analyses were normal in Rps19 mutant ES cells, but there was a significant delay in the G2/M phase in the Rpl5 mutant cells, which was unaffected by p53 knockdown. Concordantly, Rpl5 mutant ES cells had a more pronounced growth defect in liquid culture compared to the Rps19 mutant cells. We conclude that the defects in our RPS19 and RPL5 haploinsufficient mouse ES cells are not adequately explained by p53 stabilization, as p53 knockdown appears to increase the growth and differentiation potential of both parental and mutant cells. Our studies demonstrate that gene trap mouse ES cells are useful tools to study the pathogenesis of DBA.

Organ iron accumulation in chronically transfused children with sickle cell anaemia: baseline results from the TWiTCH trial

Transcranial Doppler (TCD) With Transfusions Changing to Hydroxyurea (TWiTCH) trial is a randomized, open‐label comparison of hydroxycarbamide (also termed hydroxyurea) versus continued chronic transfusion therapy for primary stroke prevention in patients with sickle cell anaemia (SCA) and abnormal TCD. Severity and location of iron overload is an important secondary outcome measure. We report the baseline findings of abdominal organ iron burden in 121 participants. At enrollment, patients were young (9·8 ± 2·9 years), predominantly female (60:40), and previously treated with transfusions (4·1 ± 2·4 years) and iron chelation (3·1 ± 2·1 years). Liver iron concentration (LIC; 9·0 ± 6·6 mg/g dry weight) and serum ferritin were moderately elevated (2696 ± 1678 μg/l), but transferrin was incompletely saturated (47·2 ± 23·6%). Spleen R2* was 509 ± 399 Hz (splenic iron ~13·9 mg/g) and correlated with LIC (r2 = 0·14, P = 0·0008). Pancreas R2* was increased in 38·3% of patients but not to levels associated with endocrine toxicity. Kidney R2* was increased in 80·7% of patients; renal iron correlated with markers of intravascular haemolysis and was elevated in patients with increased urine albumin‐creatinine ratios. Extra‐hepatic iron deposition is common among children with SCA who receive chronic transfusions, and could potentiate oxidative stress caused by reperfusion injury and decellularized haemoglobin.

Breast cancer in a case of Shwachman Diamond syndrome

Shwachman Diamond syndrome (SDS) is a rare inherited bone marrow failure syndrome (IBMFS) characterized by neutropenia, exocrine pancreatic dysfunction, and cancer predisposition. Patients are at risk for myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML) but, unlike other IBMFS, there have been no reported cases of solid tumors. We report a novel case of a solid tumor in a patient with SDS and biallelic mutations in the Shwachman Bodian Diamond Syndrome gene (SBDS). Whether the development of breast cancer in this patient is due to SDS or an isolated case due to unknown factors requires further study. Pediatr Blood Cancer 2012; 59: 945–946.

Impaired growth, hematopoietic colony formation, and ribosome maturation in human cells depleted of Shwachman-Diamond syndrome protein SBDS.

Shwachman–Diamond syndrome (SDS), associated with SBDS mutations, is characterized by pancreatic exocrine dysfunction and marrow failure. Sdo1, the yeast ortholog of SBDS, is implicated in maturation of the 60S ribosomal subunit, with delayed export of 60S‐like particles from the nucleoplasm when depleted. Sdo1 is needed for release of the anti‐subunit association factor Tif6 from 60S subunits, and Tif6 may not be recycled to the nucleus when Sdo1 is absent.

Diminutive somatic deletions in the 5q region lead to a phenotype atypical of classical 5q− syndrome

Classical 5q- syndrome is an acquired macrocytic anemia of the elderly. Similar to Diamond Blackfan anemia (DBA), an inherited red cell aplasia, the bone marrow is characterized by a paucity of erythroid precursors. RPS14 deletions in combination with other deletions in the region have been implicated as causative of the 5q- syndrome phenotype. We asked whether smaller, less easily detectable deletions could account for a syndrome with a modified phenotype. We employed single-nucleotide polymorphism array genotyping to identify small deletions in patients diagnosed with DBA and other anemias lacking molecular diagnoses. Diminutive mosaic deletions involving RPS14 were identified in a 5-year-old patient with nonclassical DBA and in a 17-year-old patient with myelodysplastic syndrome. Patients with nonclassical DBA and other hypoproliferative anemias may have somatically acquired 5q deletions with RPS14 haploinsufficiency not identified by fluorescence in situ hybridization or cytogenetic testing, thus refining the spectrum of disorders with 5q- deletions.