A case of congenital dyserythropoietic anemia type II, Gilbert's syndrome and malleolar trophic ulcers

Whole-exome sequencing indicates FLG2 variant associated with leg ulcers in Brazilian sickle cell anemia patients

Although sickle cell anemia results from homozygosity for a single mutation at position 7 of the β-globin chain, the clinical aspects of this condition are very heterogeneous. Complications include leg ulcers, which have a negative impact on patients’ quality of life and are related to the severity of the disease. Nevertheless, the complex pathogenesis of this complication has yet to be elucidated. To identify novel genes associated with leg ulcers in sickle cell anemia, we performed whole-exome sequencing of extreme phenotypes in a sample of Brazilian sickle cell anemia patients and validated our findings in another sample. Our discovery cohort consisted of 40 unrelated sickle cell anemia patients selected based on extreme phenotypes: 20 patients without leg ulcers, aged from 40 to 61 years, and 20 with chronic leg ulcers. DNA was extracted from peripheral blood leukocytes and used for whole-exome sequencing. After the bioinformatics analysis, eight variants were selected for validation by Sanger sequencing and TaqMan® genotyping in 293 sickle cell anemia patients (153 without leg ulcers) from two different locations in Brazil. After the validation, Fisher’s exact test revealed a statistically significant difference in a stop codon variant (rs12568784 G/T) in the FLG2 gene between the GT and GG genotypes ( P = 0.035). We highlight the importance of rs12568784 in leg ulcer development as this variant of the FLG2 gene results in impairment of the skin barrier, predisposing the individual to inflammation and infection. Additionally, we suggest that the remaining seven variants and the genes in which they occur could be strong candidates for leg ulcers in sickle cell anemia.

Impact statement

To our knowledge, the present study is the first to use whole-exome sequencing based on extreme phenotypes to identify new candidate genes associated with leg ulcers in sickle cell anemia patients. There are few studies about this complication; the pathogenesis remains complex and has yet to be fully elucidated. We identified interesting associations in genes never related with this complication to our knowledge, especially the variant in the FLG2 gene. The knowledge of variants related with leg ulcer in sickle cell anemia may lead to a better comprehension of the disease’s etiology, allowing prevention and early treatment options in risk genotypes while improving quality of life for these patients.

Clinical and genetic features of congenital dyserythropoietic anemia (CDA)

INTRODUCTION

Congenital dyserythropoietic anemias (CDA) are characterized by hyporegenerative anemia with inadequate reticulocyte values, ineffective erythropoiesis, and hemolysis. Distinctive morphology of bone marrow erythroblasts and identification of causative genes allow classification into 4 types caused by variants in CDAN1, c15orf41, SEC23B, KIF23, and KLF1 genes.

OBJECTIVE

Identify pathogenic variants in CDA patients.

METHODS

Massive parallel sequencing with a targeted gene panel, Sanger sequencing, Comparative Genome Hybridization (CGH), and in silico predictive analysis of pathogenicity.

RESULTS

Pathogenic variants were found in 21 of 53 patients studied from 44 unrelated families. Six variants were found in CDAN1: two reported, p.Arg714Trp and p.Arg725Trp and, four novel, p.Arg623Trp, p.Arg946Trp, p.Phe1125Ser and p.Ser1227Gly. Twelve variants were found in SEC23B: seven reported, p.Arg14Trp, p.Glu109Lys, p.Arg217Ter, c.835-2A>G, p.Arg535Ter, p.Arg550Ter and p.Arg718Ter and, five novel, p.Val164Leu, p.Arg190Gln, p.Gln521Ter, p.Arg546Trp, and p.Arg611Gln. The variant p.Glu325Lys in KLF1 was found in one patient and p.Tyr365Cys in ALAS2 in an other. Moreover, we identified genomic rearrangements by CGH in some SEC23B-monoallelic patients.

CONCLUSIONS

New technologies for genetic studies will help to find variants in other genes, in addition to those known, that contribute to or modulate the CDA phenotype or support the correct diagnosis.

Critical Reviews: How we treat sickle cell patients with leg ulcers

The past five decades have seen an improvement in the mortality and morbidity of sickle cell disease (SCD) because of prophylaxis against infectious complications, improved and expanded red cell transfusions, implementation of hydroxyurea therapy, and advances in supportive care. Now that the majority of patients in the western hemisphere reaches adulthood, end organ diseases are frequent, which include vasculopathic complications such as chronic leg ulcers. The management of patients with leg ulcers requires the hematologist to lead a team of health care professionals, and investigates the presence of associated, but potentially still occult signs of vasculopathy, such as pulmonary hypertension, renal disease, priapism and retinopathy. These complications may be asynchronous, and long term careful screening is indicated, in order to ensure early diagnosis and intervention. It is crucial to address both the immediate consequences of pain, infection and disability, and long term effects on quality of life, employment and stigma associated with chronic ulceration. Recent insights into their pathophysiology may have practical implications. We propose a holistic approach to the management of patients' physical and emotional problems and mechanisms of ulcers formation and delayed healing. An overview of topical and systemic therapies for chronic ulcers is given, with the understanding that wound care therapy is best left to the wound specialists, medical and surgical, with whom the hematologist must keep an open line of communication. In the absence of evidence-based guidelines, our opinion is based on both a critical review of the literature and our personal clinical and research experience.

Pleiotropic effects of intravascular haemolysis on vascular homeostasis

The breakdown of senescent or defective red blood cells releases red cell contents, especially haemoglobin, which scavenges nitric oxide (NO) and decomposes to haem and free iron. These are potent oxidants, all of which have promoted the evolution of inducible and vasculoprotective compensatory pathways to rapidly clear and detoxify haemoglobin, haem and iron. Chronic haemolytic red cell disorders as diverse as sickle cell disease, thalassaemia, unstable haemoglobinopathy, cytoskeletal defects and enzymopathies have been linked to a clinical constellation of pulmonary hypertension, priapism, leg ulceration and possibly cerebrovascular disease and thrombosis. Besides free haemoglobin, haemolysis has been associated with extracellular arginase that limits substrate availability to NO synthase, endogenous inhibitors of NO synthase activity, and inappropriate activation of haemostatic pathways. This article reviews the haemolytic disorders that have been reported to manifest vascular complications, and explores the speculative possibility that haemolysis mediates some of the vascular complications of inflammation and diabetes.

Deconstructing sickle cell disease: reappraisal of the role of hemolysis in the development of clinical subphenotypes

Hemolysis, long discounted as a critical measure of sickle cell disease severity when compared with sickle vaso-occlusion, may be the proximate cause of some disease complications. New mechanistic information about hemolysis and its effects on nitric oxide (NO) biology and further examination of the subphenotypes of disease requires a reappraisal and deconstruction of the clinical features of sickle cell disease. The biology underlying clinical phenotypes linked to hemolysis may increase our understanding of the pathogenesis of other chronic hemolytic diseases while providing new insights into treating sickle cell disease. The pathophysiological roles of dysregulated NO homeostasis and sickle reticulocyte adherence have linked hemolysis and hemolytic rate to sickle vasculopathy. Nitric oxide binds soluble guanylate cyclase which converts GTP to cGMP, relaxing vascular smooth muscle and causing vasodilatation. When plasma hemoglobin liberated from intravascularly hemolyzed sickle erythrocytes consumes NO, the normal balance of vasoconstriction:vasodilation is skewed toward vasoconstriction. Pulmonary hypertension, priapism, leg ulceration and stroke, all subphenotypes of sickle cell disease, can be linked to the intensity of hemolysis. Hemolysis plays less of a role in the vaso-occlusive-viscosity complications of disease like the acute painful episode, osteonecrosis of bone and the acute chest syndrome. Agents that decrease hemolysis or restore NO bioavailability or responsiveness may have potential to reduce the incidence and severity of the hemolytic subphenotypes of sickle cell disease. Some of these drugs are now being studied in clinical trials.