Vivien A. Sheehan

Genetic modifiers of sickle cell anemia in the BABY HUG cohort: influence on laboratory and clinical phenotypes.

The recently completed BABY HUG trial investigated the safety and efficacy of hydroxyurea in infants with sickle cell anemia (SCA). To investigate the effects of known genetic modifiers, genomic DNA on 190 randomized subjects were analyzed for alpha thalassemia, beta‐globin haplotype, polymorphisms affecting endogenous fetal hemoglobin (HbF) levels (XmnI, BCL11A, and HBS1L‐MYB), UGT1A1 promoter polymorphisms, and the common G6PD A− mutation. At study entry, infants with alpha thalassemia trait had significantly lower mean corpuscular volume, total bilirubin, and absolute reticulocyte count. Beta‐globin haplotypes associated with milder disease had significantly higher hemoglobin and %HbF. BCL11A and XmnI polymorphisms had significant effects on baseline HbF, while UGT1A1 promoter polymorphisms significantly influenced baseline serum bilirubin. At study exit, subjects randomized to placebo still exhibited laboratory effects of alpha thalassemia and other modifiers, while those assigned hydroxyurea had treatment effects that exceeded most genetic influences. The pain phenotype was influenced by HbF modifiers in both treatment groups. These data document that genetic polymorphisms do modify laboratory and clinical phenotypes even in very young patients with SCA. The hydroxyurea effects are more potent, however, indicating that treatment criteria should not be limited to certain genetic subsets, and supporting the use of hydroxyurea for all young patients with SCA. Am. J. Hematol. 88:571–576, 2013.

Genetic mapping and exome sequencing identify 2 mutations associated with stroke protection in pediatric patients with sickle cell anemia

Stroke is a devastating complication of sickle cell anemia (SCA), occurring in 11% of patients before age 20 years. Previous studies of sibling pairs have demonstrated a genetic component to the development of cerebrovascular disease in SCA, but few candidate genetic modifiers have been validated as having a substantial effect on stroke risk. We performed an unbiased whole-genome search for genetic modifiers of stroke risk in SCA. Genome-wide association studies were performed using genotype data from single-nucleotide polymorphism arrays, whereas a pooled DNA approach was used to perform whole-exome sequencing. In combination, 22 nonsynonymous variants were identified and represent key candidates for further in-depth study. To validate the association of these mutations with the risk for stroke, the 22 candidate variants were genotyped in an independent cohort of control patients (n = 231) and patients with stroke (n = 57) with SCA. One mutation in GOLGB1 (Y1212C) and another mutation in ENPP1 (K173Q) were confirmed as having significant associations with a decreased risk for stroke. These mutations were discovered and validated by an unbiased whole-genome approach, and future studies will focus on how these functional mutations may lead to protection from stroke in the context of SCA.

Whole Exome Sequencing Identifies Novel Genes for Fetal Hemoglobin Response to Hydroxyurea in Children with Sickle Cell Anemia

Hydroxyurea has proven efficacy in children and adults with sickle cell anemia (SCA), but with considerable inter-individual variability in the amount of fetal hemoglobin (HbF) produced. Sibling and twin studies indicate that some of that drug response variation is heritable. To test the hypothesis that genetic modifiers influence pharmacological induction of HbF, we investigated phenotype-genotype associations using whole exome sequencing of children with SCA treated prospectively with hydroxyurea to maximum tolerated dose (MTD). We analyzed 171 unrelated patients enrolled in two prospective clinical trials, all treated with dose escalation to MTD. We examined two MTD drug response phenotypes: HbF (final %HbF minus baseline %HbF), and final %HbF. Analyzing individual genetic variants, we identified multiple low frequency and common variants associated with HbF induction by hydroxyurea. A validation cohort of 130 pediatric sickle cell patients treated to MTD with hydroxyurea was genotyped for 13 non-synonymous variants with the strongest association with HbF response to hydroxyurea in the discovery cohort. A coding variant in Spalt-like transcription factor, or SALL2, was associated with higher final HbF in this second independent replication sample and SALL2 represents an outstanding novel candidate gene for further investigation. These findings may help focus future functional studies and provide new insights into the pharmacological HbF upregulation by hydroxyurea in patients with SCA.

Severe Neutropenia in Patients with Chronic Hepatitis C: A Benign Condition

Background/Aims: Patients with chronic hepatitis C virus (HCV) infection may develop neutropenia, which can delay or prevent treatment. Severe neutropenia, absolute neutrophil counts (ANC) ≤0.500 × 109/l, is a rare finding, with only two isolated reports published in the literature. The aim of this study was to evaluate the incidence and natural history of severe neutropenia in hepatitis C patients. Methods: The records of 685 patients with active HCV were reviewed to identify those with severe neutropenia. The laboratory parameters and clinical history data of patients with severe neutropenia were then compared to a cohort of patients with HCV patients who had the more common minor neutropenia (ANC = 1.000–1.500 109/l). Results: There was no significant difference in race, MELD (Model for End Stage Liver Disease) scores, portal hypertension, splenomegaly, viral load, viral type, or hemoglobin or platelet levels. Neither group suffered serious systemic infections. Conclusions: Severe neutropenia in HCV patients is underreported and not associated with serious HCV complications such as elevated MELD score or cirrhosis. Serious infection is rare and patients respond well to granulocyte colony-stimulating factor. Severely neutropenic patients with HCV appear to have a benign course and may be candidates for antiviral therapy.

The role of BCL11A and HMIP-2 polymorphisms on endogenous and hydroxyurea induced levels of fetal hemoglobin in sickle cell anemia patients from southern Brazil.

High levels of fetal hemoglobin (HbF) reduce sickle cell anemia (SCA) morbidity and mortality. HbF levels vary considerably and there is a strong genetic component that influences HbF production. Genetic polymorphisms at three quantitative trait loci (QTL): Xmn1-HBG2, HMIP-2 and BCL11A, have been shown to influence HbF levels and disease severity in SCA. Hydroxyurea (HU) is a drug that increases HbF. We investigated the influence of single nucleotide polymorphisms (SNPs) at the Xmn1-HBG2 (rs7482144); BCL11A (rs1427407, rs4671393 and rs11886868); and HMIP-2 (rs9399137 and rs9402686) loci on baseline and HU-induced HbF levels in 111 HbSS patients. We found that both BCL11A and HMIP-2 were associated with increased endogenous levels of HbF. Interestingly, we also found that BCL11A was associated with higher induction of HbF with HU. This effect was independent of the effect of BCL11A on baseline HbF levels. Additional studies will be needed to validate these findings and explain the ample inter-individual variations in HbF levels at baseline and HU-induced in patients with SCA.

Hepatitis C and neutropenia.

Purpose of reviewThis review describes the pathogenesis and therapeutic implications of neutropenia in patients with hepatitis C. Recent findingsMild-to-moderate neutropenia is increasingly recognized as the hepatitis C population has caused increased cirrhosis. Multiple mechanisms for the neutropenia have been postulated, with recent evidence pointing toward a combination of hypersplenism, autoimmunity, and direct viral infection of bone marrow cells. Advances in antiviral therapy are associated with worsened neutropenia and dose modification. Severe neutropenia is underreported and is generally not associated with increased rates of infection. SummaryAlthough neutropenia is common in hepatitis C patients it generally has a benign course and may not prohibit antiviral therapy.

Transcranial doppler velocity and brain MRI/MRA changes in children with sickle cell anemia on chronic transfusions to prevent primary stroke

Chronic transfusions help prevent primary stroke in children with sickle cell anemia (SCA) and abnormal transcranial Doppler (TCD) velocities. However, the effects of transfusions on TCD velocities and brain MRI/MRA findings are incompletely described.

Whole-exome sequencing of sickle cell disease patients with hyperhemolysis syndrome suggests a role for rare variation in disease predisposition: WES IN SCD PATIENTS WITH HHS

Hyperhemolysis syndrome (HHS) is an uncommon, but life‐threatening, transfusion‐related complication of red blood cell transfusion. HHS has predominantly been described in patients with sickle cell disease (SCD) and is difficult to diagnose and treat. The pathogenesis of HHS, including its occurrence in only a subset of apparently susceptible individuals, is poorly understood. We undertook whole‐exome sequencing (WES) of 12 SCD‐HHS patients to identify shared genetic variants that might be relevant to the development of HHS.

Fetal haemoglobin induction in sickle cell disease

Fetal haemoglobin (HbF, α2γ2) induction has long been an area of investigation, as it is known to ameliorate the clinical complications of sickle cell disease (SCD). Progress in identifying novel HbF‐inducing strategies has been stymied by limited understanding of gamma (γ)–globin regulation. Genome‐wide association studies (GWAS) have identified variants in BCL11A and HBS1L‐MYB that are associated with HbF levels. Functional studies have established the roles of BCL11A, MYB, and KLF1 in γ–globin regulation, but this information has not yielded new pharmacological agents. Several drugs are under investigation in clinical trials as HbF‐inducing agents, but hydroxycarbamide remains the only widely used pharmacologic therapy for SCD. Autologous transplant of edited haematopoietic stem cells holds promise as a cure for SCD, either through HbF induction or correction of the causative mutation, but several technical and safety hurdles must be overcome before this therapy can be offered widely, and pharmacological therapies are still needed.

Metformin induces FOXO3-dependent fetal hemoglobin production in human primary erythroid cells

Induction of red blood cell (RBC) fetal hemoglobin (HbF; α2γ2) ameliorates the pathophysiology of sickle cell disease (SCD) by reducing the concentration of sickle hemoglobin (HbS; α2βS2) to inhibit its polymerization. Hydroxyurea (HU), the only US Food and Drug Administration (FDA)-approved drug for SCD, acts in part by inducing HbF; however, it is not fully effective, reflecting the need for new therapies. Whole-exome sequence analysis of rare genetic variants in SCD patients identified FOXO3 as a candidate regulator of RBC HbF. We validated these genomic findings through loss- and gain-of-function studies in normal human CD34+ hematopoietic stem and progenitor cells induced to undergo erythroid differentiation. FOXO3 gene silencing reduced γ-globin RNA levels and HbF levels in erythroblasts, whereas overexpression of FOXO3 produced the opposite effect. Moreover, treatment of primary CD34+ cell-derived erythroid cultures with metformin, an FDA-approved drug known to enhance FOXO3 activity in nonerythroid cells, caused dose-related FOXO3-dependent increases in the percentage of HbF protein and the fraction of HbF-immunostaining cells (F cells). Combined HU and metformin treatment induced HbF additively and reversed the arrest in erythroid maturation caused by HU treatment alone. HbF induction by metformin in erythroid precursors was dependent on FOXO3 expression and did not alter expression of BCL11A, MYB, or KLF1. Collectively, our data implicate FOXO3 as a positive regulator of γ-globin expression and identify metformin as a potential therapeutic agent for SCD.