The germline p53 activation syndrome: A new patient further refines the clinical phenotype.

The tumor suppressor p53 has well known roles in cancer development and germline cancer predisposition disorders, but increasing evidence supports the role of activation of this transcription factor in the pathogenesis of inherited bone marrow failure and chromosomal instability disorders. Here we report a patient with red cell aplasia, which was steroid responsive, as well as intellectual disability, seizures, microcephaly, short stature, cellular radiosensitivity, and normal telomere lengths, who had a germline heterozygous C-terminal frameshift variant in TP53 similar to others that activate the transcription factor. This is the third reported individual with a germline p53 activation syndrome, with several unique features that refine the clinical disease associated with these variants.

Expansion of the clinical phenotype of GALE deficiency.

Congenital disorders of glycosylation are a group of rare monogenic inborn errors of metabolism caused by defective glycoprotein and glycolipid glycan synthesis and attachment. Here, we present a patient with galactose epimerase deficiency, also known as GALE deficiency, accompanied by pancytopenia and immune dysregulation. She was first identified by an abnormal newborn screen for galactosemia with subsequent genetic evaluation due to pancytopenia and immune dysregulation. The evaluation ultimately revealed that her known diagnosis of GALE deficiency was the cause of her hematologic and immune abnormalities. These findings further expand the clinical spectrum of disease of congenital disorders of glycosylation.

Effective hemostasis in children with Von Willebrand factor defects undergoing adenotonsillar procedures.

INTRODUCTION: Children with low von Willebrand factor (VWF) activity or type 1 von Willebrand disease (VWD) have increased risk of bleeding after adenotonsillar procedures and the optimal perioperative management to minimize bleeding is unknown. AIM: To report the effectiveness and safety of an institutional protocol in minimizing postoperative bleeding in children with type 1 VWD or low VWF activity. METHODS: We conducted a retrospective chart review in children with type 1 VWD or low VWF activity treated via an institutional protocol that utilizes repeated doses of Desmopressin acetate (DDAVP, 1-deamino 8-D arginine- vasopressin) or VWF concentrate, brief hospitalization for observation and extended use of oral epsilon aminocaproic acid (EACA). RESULTS: From 2010 to 2017, 13 children underwent an adenotonsillar procedure and were treated with this protocol. Although 7.6% had minor immediate bleeding and 23% had minor delayed bleeding, no patients experienced major bleeding or required transfusion, additional surgery or other measures not specified by the protocol. Mild hyponatremia was observed in 80% of patients who received DDAVP. CONCLUSION: Our institutional protocol specifying repeated dosing of DDAVP or VWF concentrate to sustain elevated VWF levels during periods of highest bleeding risk and extended use of EACA is effective at preventing major bleeding episodes after adenotonsillar procedures. However, this analysis raised safety concerns that prompted changes in the institutional protocol and highlight the need for further prospective studies to determine the optimal strategy for safely reducing bleeding complications in these patients.

Barriers to and Facilitators of Iron Therapy in Children with Iron Deficiency Anemia.

OBJECTIVE: To characterize barriers to and facilitators of successful iron therapy in young children with iron deficiency anemia (IDA) from an in-depth parental perspective. STUDY DESIGN: Prospective, mixed methods study of children age 9 months to 4 years with a diagnosis of nutritional IDA by clinical history and laboratory criteria and their parents. Clinical data were obtained from the electronic health record. Semistructured interviews focused on knowledge of IDA, clinical effects, experience with iron therapies, and motivation were conducted with the parent who identified as the child's primary caregiver. RESULTS: Twenty patient-parent dyads completed the study; 80% (n = 16) identified as Hispanic/Latino (white). Patients' median age was 23 months (50% male); median initial hemoglobin concentration was 8.2 g/dL and duration of oral iron therapy was 3 months. Parents' median age was 29 years (85% female); 8 interviews (40%) were conducted in Spanish. Barriers included difficulty in administering oral iron owing to side effects and poor taste. Facilitators included provision of specific instructions; support from healthcare providers and additional caregivers at home; motivation to benefit child's health, which was strengthened by strong emotional reactions (ie, stress, anxiety) to therapy and follow-up; and an appreciation of child's improvement with successful completion of therapy. CONCLUSIONS: Our findings support the need for interventions designed to promote oral iron adherence in children with IDA. Rather than focusing on knowledge content related to IDA, interventions should aim to increase parental motivation by emphasizing the health benefits of adhering to iron therapy and avoiding more invasive interventions.

Novel mechanisms of PIEZO1 dysfunction in hereditary xerocytosis.

Mutations in PIEZO1 are the primary cause of hereditary xerocytosis, a clinically heterogeneous, dominantly inherited disorder of erythrocyte dehydration. We used next-generation sequencing-based techniques to identify PIEZO1 mutations in individuals from 9 kindreds referred with suspected hereditary xerocytosis (HX) and/or undiagnosed congenital hemolytic anemia. Mutations were primarily found in the highly conserved, COOH-terminal pore-region domain. Several mutations were novel and demonstrated ethnic specificity. We characterized these mutations using genomic-, bioinformatic-, cell biology-, and physiology-based functional assays. For these studies, we created a novel, cell-based in vivo system for study of wild-type and variant PIEZO1 membrane protein expression, trafficking, and electrophysiology in a rigorous manner. Previous reports have indicated HX-associated PIEZO1 variants exhibit a partial gain-of-function phenotype with generation of mechanically activated currents that inactivate more slowly than wild type, indicating that increased cation permeability may lead to dehydration of PIEZO1-mutant HX erythrocytes. In addition to delayed channel inactivation, we found additional alterations in mutant PIEZO1 channel kinetics, differences in response to osmotic stress, and altered membrane protein trafficking, predicting variant alleles that worsen or ameliorate erythrocyte hydration. These results extend the genetic heterogeneity observed in HX and indicate that various pathophysiologic mechanisms contribute to the HX phenotype.

Population Pharmacokinetics of Enoxaparin in Pediatric Patients.

BACKGROUND: There are no studies evaluating the pharmacokinetics of enoxaparin in the hospitalized pediatric patient population. OBJECTIVE: To characterize the pharmacokinetics of enoxaparin in pediatric patients. METHODS: A retrospective review of inpatients 1 to 18 years of age admitted to our institution who received enoxaparin with anti-factor Xa activity level monitoring was performed. Demographic variables, enoxaparin dosing, and anti-factor Xa activity levels were collected. Population pharmacokinetic analysis was performed with bootstrap analysis. Simulation (n = 10 000) was performed to determine the percentage who achieved targeted anti-Xa levels at various doses. RESULTS: A total of 853 patients (male 52.1%, median age = 12.2 years; interquartile range [IQR] = 4.6-15.8 years) received a mean enoxaparin dose of 0.86 ± 0.31 mg/kg/dose. A median of 3 (IQR = 1-5) anti-factor Xa levels were sampled at 4.4 ± 1.3 hours after a dose, with a mean anti-factor Xa level of 0.52 ± 0.23 U/mL. A 1-compartment model best fit the data, and significant covariates included allometrically scaled weight, serum creatinine, and hematocrit on clearance, and platelets on volume of distribution. Simulations were run for patients both without and with reduced kidney function (creatinine clearance of ≤30 mL/min/1.73 m2). A dose of 1 mg/kg/dose every 12 hours had the highest probability (72.3%) of achieving an anti-Xa level within the target range (0.5-1 U/mL), whereas a dose reduction of ~30% achieved the same result in patients with reduced kidney function. CONCLUSIONS: Pediatric patients should initially be dosed at 1-mg/kg/dose subcutaneously every 12 hours for treatment of thromboembolism followed by anti-Xa activity monitoring. Dose reductions of ~30% for creatinine clearance ≤30 mL/min/1.73 m2 are required.

Population pharmacokinetics of human antithrombin concentrate in paediatric patients.

AIMS: Antithrombin is increasingly used in paediatric patients, yet there are few age-specific pharmacokinetic data to guide dosing. We aimed to describe the pharmacokinetic profile of human (plasma-derived) antithrombin concentrate in paediatric patients. METHODS: A 5-year retrospective review was performed of patients <19 years of age admitted to our institution who received antithrombin concentrate, were not on mechanical circulatory support and had baseline (predose) and postdose plasma antithrombin activity levels available for analysis. Demographic and laboratory variables, antithrombin dosing information and data on the use of continuous infusion unfractionated heparin were collected. Population pharmacokinetic analysis was performed with bootstrap analysis. The model developed was tested against a validation dataset from a cohort of similar patients, and a predictive value was calculated. RESULTS: A total 184 patients met the study criteria {46.7% male, median age [years] 0.35 [interquartile range (IQR) 0.07-3.9]}. A median of two antithrombin doses (IQR 1-4) were given to patients (at a dose of 46.3 ± 13.6 units kg-1 ), with median of three (IQR 2-7) postdose levels per patient. Continuous infusion unfractionated heparin was administered in 87.5% of patients, at a mean dose of 34.1 ± 22.7 units kg-1 h-1 . A one-compartment exponential error model best fit the data, and significant covariates included allometrically scaled weight on clearance and volume of distribution, unfractionated heparin dose on clearance, and baseline antithrombin activity level on volume of distribution. The model resulted in a median -1.75% prediction error (IQR -11.75% to 6.5%) when applied to the validation dataset (n = 30). CONCLUSIONS: Antithrombin pharmacokinetics are significantly influenced by the concurrent use of unfractionated heparin and baseline antithrombin activity.

Enoxaparin Population Pharmacokinetics in the First Year of Life.

AIMS: Enoxaparin dosing requirements in the first year of life can be highly variable. Characterization of pharmacokinetics in this patient population can assist in dosing. METHODS: Patients less than 1 year postnatal age who received enoxaparin and had an anti-factor Xa activity level drawn as inpatients were identified through the pharmacy database over a 5-year period. Patients on renal replacement therapy or with hyperbilirubinemia were excluded. Data collection included demographic variables, indication for enoxaparin, enoxaparin doses, anti-factor Xa activity levels, serum creatinine, hemoglobin, hematocrit, platelet count, and urine output over the previous 24 hours. Population pharmacokinetic analysis was performed with NONMEM. RESULTS: A total of 182 patients [male 50%, median 100 days postnatal age (range: 4-353 days)] met the study criteria. Patients received median 22 doses (range: 1-526) at a mean starting dose of 1.38 ± 0.43 mg/kg with median 5 (range: 1-56) anti-factor Xa activity levels measured. A 1-compartment proportional and additive error model best fits the data. Allometrically scaled weight significantly decreased the objective function value, as did serum creatinine on clearance, and postmenstrual age (PMA) on volume of distribution. When evaluated graphically, dosing based on PMA appeared to have less variability as compared to postnatal age-based dosing. CONCLUSIONS: Dosing of enoxaparin in infants younger than 1 year should incorporate PMA.

Pediatric Acquired von Willebrand Syndrome in Cardiopulmonary Disorders: Do Laboratory Abnormalities Predict Bleeding Risk?

There are conflicting reports on whether or not laboratory abnormalities in pediatric acquired von Willebrand syndrome (AVWS) predict bleeding manifestations in patients with cardiopulmonary disorders (CPD). We retrospectively reviewed charts of patients with AVWS and CPD (n=16) seen at Texas Children's Hospital from 2003 to 2012. The most common CPD were valve stenoses, ventricular septal defects, and pulmonary hypertension. All patients had loss of high molecular weight multimers. Fifteen (94%) patients presented with bleeding symptoms, with menorrhagia and epistaxis being the most common. Von Willebrand ristocetin cofactor activity (VWF:RCo), as well as the use of anticoagulant or antiplatelet medication, did not predict bleeding manifestations (P=0.70 and 0.84, respectively). VWF:RCo/VWF antigen (Ag) ratio of <0.7 was significantly associated with presence of bleeding symptoms. All patients who had complete repair of their cardiac defect experienced normalization of VWF multimers and VWF:RCo/Ag ratio, as well as bleeding symptom resolution. We conclude that increased bleeding risk is associated with low VWF:RCo/Ag ratio in pediatric AVWS due to CPD. However, other laboratory abnormalities such as VWF:RCo level and qualitative multimer analysis, do not appear to predict bleeding. Future studies exploring quantification of multimer loss may be helpful in further assessing bleeding risk associations.

Thrombopoietin Measurement as a Key Component in the Evaluation of Pediatric Thrombocytosis.

JAK2, MPL, and CALR mutations, which underlie essential thrombocythemia (ET) in most adults, are infrequent in children. Consequently, additional tests are needed to confirm pediatric ET diagnoses. We report a child with suspected ET and normal JAK2, MPL, and CALR analyses. Serum thrombopoietin (TPO) was markedly elevated, leading to analysis of the TPO gene, TPHO, which contains an upstream open reading frame (uORF) known to repress THPO translation. Sequencing revealed a de novo, germline stopgain mutation in the uORF, explaining the elevated TPO and thrombocytosis. This finding suggests that screening TPO levels and, if elevated, THPO 5' UTR sequencing could be diagnostic.

Profound Vitamin B12 Deficiency in a 1-Year-Old Child in Botswana: A Call to Initiate Early Empiric Therapy.

Vitamin B12 deficiency is a rare diagnosis in young children. We present the case of a 1-year-old Zimbabwean child with profound anemia. Further testing revealed undetectable levels of vitamin B12 and positive intrinsic factor antibodies that were drawn after the initiation of empiric treatment with parenteral vitamin B12. We report the evaluation and management of vitamin B12 deficiency in a resource-limited setting. Vitamin B12 deficiency should be considered in children presenting with unexplained cytopenias with consideration of empiric treatment with parenteral vitamin B12, as developmental and neurological complications of vitamin B12 deficiency can be devastating and permanent.

Antithrombin Concentrate Use in Children Receiving Unfractionated Heparin for Acute Thrombosis.

OBJECTIVE: To characterize features of antithrombin concentrate (ATC) use in children receiving unfractionated heparin (UFH) therapy for acute thrombosis. STUDY DESIGN: All pediatric patients at Texas Children's Hospital who received ATC in the context of UFH therapy for acute thrombosis during February 2011 to May 2013 were analyzed. RESULTS: Fifty-one children received ATC during UFH therapy for acute thrombosis. Median age was 3 months (IQR 1 to 18 months). Clinical indications included venous (53%), arterial (37%), venous and arterial (6%), and intracardiac (4%) thrombosis. Median baseline antithrombin (AT) level was 61% and UFH dose was 26 U/kg/h. The median dose of ATC was 49.9 IU/kg (IQR 32.6 to 50.0 IU/kg). Although most patients (86%) did not undergo a change in UFH dose, there was a significant increase in both AT and anti-factor Xa level after the first dose of ATC (P < .001 for both). There was no correlation between ATC dose or increment in AT level above baseline and the achievement of targeted anticoagulation by anti-factor X activity level. Adverse bleeding events occurred in 10% of patients. CONCLUSIONS: There was a significant change in AT and anti-factor Xa activity level after a single dose of ATC despite little to no change in dose of UFH. ATC appears to facilitate anticoagulation with UFH in some children with acute thrombosis but the degree of response is variable and dependent on factors identified in this study. Bleeding and other theoretical risks must be carefully considered.

Unrecognized hepatitis B in pre-screened children with hematologic and oncologic conditions.

BACKGROUND: This study evaluates the effectiveness and interpretation of hepatitis B (HBV) screening in an at-risk cohort of children with cancer or blood disorders. PROCEDURE: We conducted a retrospective epidemiologic analysis of children who screened positive for HBV (HBsAg, HbcAb) from 1999 to 2009 at a quaternary children's hospital, focusing on patients with hematologic and oncologic conditions. Descriptive statistics were generated for demographics and serologies. Follow-up of positive serologies and clinical outcomes were analyzed. RESULTS: A total of 12,754 children were screened for HBV. Of 391 that screened positive, 118 had a hematologic or oncologic diagnosis. Leukemia, anemia, and thrombocytopenia comprised 84% of diagnoses. The majority (98%) tested HBcAb positive but only 20% received confirmatory HBV DNA testing. Three patients (13% of those HBV DNA tested) were identified to have chronic disease. HBV was not a known pre-existing condition, and chemotherapy preceded HBV diagnosis in all cases. CONCLUSIONS: The majority of children with cancer or blood disorders who screened HBV positive did not receive follow-up DNA testing, exposing them to reactivation risk and delaying definitive therapy. HBcAb may be the only indicator of chronic HBV infection and DNA confirmation should be routine. Our findings suggest a significant number of additional patients eligible for HBV treatment may have been identified with reflexive DNA testing.

Comparison of anti-Xa levels in obese and non-obese pediatric patients receiving treatment doses of enoxaparin.

OBJECTIVE: To determine if using actual body weight to dose enoxaparin in obese pediatric patients results in higher anti-Xa levels compared with non-obese pediatric patients. STUDY DESIGN: This was a retrospective case-matched study of obese and non-obese pediatric patients receiving treatment doses of enoxaparin in a tertiary care children's hospital. Patients were included if they were initiated on treatment doses of enoxaparin, had appropriate anti-Xa levels drawn, and were between 2 and 18 years of age. Patients with renal insufficiency, hyperbilirubinemia, goal anti-Xa level <0.5 or >1 unit/mL, or receiving mechanical circulatory support were excluded. Obese patients who met study criteria were matched on a 1:1 basis with non-obese patients. RESULTS: All baseline characteristics were similar except for body mass index percentile (98.2 ± 2 vs 48.7 ± 15, P < .01). Obese patients had higher initial anti-Xa levels (0.67 ± 0.27 vs 0.53 ± 0.24 unit/mL, P = .028). Over time, obese patients required a lower mean dose to achieve therapeutic anti-Xa levels than non-obese patients (0.81 ± 0.19 vs 1.1 ± 0.4 mg/kg, P = .005). CONCLUSIONS: The mean initial anti-Xa level was higher in obese pediatric patients compared with non-obese pediatric patients, but a dosage adjustment was not required. Obese patients may need closer monitoring over time to avoid supratherapeutic levels and possible bleeding events.

Successful treatment of congenital TTP with a novel approach using plasma-derived factor VIII.

We describe a 19-year-old boy who was diagnosed with congenital thrombotic thrombocytopenic purpura (cTTP) at 7 months of age. He was subsequently treated with fresh frozen plasma infusions every 3 to 4 weeks for the next 15 years at which point he developed significant hypersensitivity reactions to fresh frozen plasma. He required immunosuppressive therapy with systemic desensitization in the intensive care unit but did not tolerate this regimen and suffered debilitating adverse effects. On the basis of the observations from United Kingdom, he was started on a trial with Koate, a plasma-derived factor VIII concentrate with ADAMTS-13 activity that is commercially available in the United States. He tolerated Koate without any complications and attained a target platelet count of>100,000/µL. He has now been in remission for 36 months and responds to exacerbations of cTTP with additional doses of Koate. For patients with cTTP who are intolerant to plasma infusions, therapy with select plasma-derived factor concentrates with ADAMTS-13 activity may represent a reasonable alternative therapy.

Plasma methotrexate, red blood cell methotrexate, and red blood cell folate values and outcome in children with precursor B-acute lymphoblastic leukemia: a report from the Children's Oncology Group.

Plasma steady state methotrexate (MTX) level and red blood cell (RBC) MTX and folate concentrations were evaluated in 1124 children with newly diagnosed acute lymphoblastic leukemia enrolled in the Pediatric Oncology Group studies 9005 (lower risk; Regimens A and C) and 9006 (higher risk; Regimen A). These regimens included intermediate-dose MTX (1 g/m) given as a 24 hours infusion every other week for 12 doses during intensification. Plasma MTX level was evaluated at the end of MTX infusions. RBC MTX and folate concentrations were measured at the end of intensification. The 5 year continuous complete remission was 76±1.4% versus 85±3.0% for those patients with steady state MTX levels less than or equal to and greater than 14 µM, respectively (P=0.0125). Hispanic children had significantly reduced median steady state MTX levels, 8.7 µM, compared with non-Hispanic children, 9.95 µM (P=0.0015), but this did not correlate with a difference in outcome. Neither RBC MTX, RBC folate, nor the RBC MTX:folate ratio identified children at increased risk of failure.

Red cell exchange does not appear to increase the rate of allo- and auto-immunization in chronically transfused children with sickle cell disease.

BACKGROUND: Allo- and auto-antibody development is a well recognized complication of chronic red cell transfusion (RCT) in sickle cell disease (SCD). Limited matching of Rh (C, c, D, E, e) and K red cell antigens reduces the incidence of immunization. PROCEDURE: We reviewed our experience with red cell allo- and auto-immunization in pediatric SCD patients receiving chronic and/or exchange transfusions, to evaluate the rate of immunization after limited red cell antigen matching and specifically during red cell exchange (RCE) transfusion. A retrospective chart review of the patients with SCD followed at our center between 2002 and 2006, who were started on chronic RCT before or during that time period, was conducted. RESULTS: Of the 93 patients who met study criteria, 23 (24%) developed antibodies during chronic red cell transfusions. Thirty-four antibodies (15 auto-antibodies, 18 allo-antibodies) developed after the institution of limited red cell antigen matching. The rate of allo- and auto-immunization per unit of red cell exposure after limited phenotyping was 1.5%, comparable to other published data. Fifteen patients underwent RCE, utilizing a total of 2,289 packed red cell units. None developed antibodies during RCE. CONCLUSION: We conclude that limited red cell antigen matching is an effective strategy for reducing the incidence of allo- and auto-immunization in chronically transfused children with SCD. RCE does not appear to increase the risk of allo- or auto-immunization, despite exposure to more red cell units.