Page 22 - Educacional Ponenecias Congreso SEHH-STH 2020

Red blood cell disorders
Celeste Bento
Hematology Department. Centro Hospitalar e Universitario de Coimbra. Portugal. CIAS – Research Centre for Anthropology and Health. University of Coimbra. Portugal
Red blood cells (RBC) are biconcave disks without nucle- us, mitochondria and other organelles. They are formed by the membrane skeleton, some metabolic enzymes and are rich in hemoglobin (Hb), which comprises of globin subunits and iron-containing heme groups. In a normal healthy individual the number of circulating RBC and their precursors remain more or less constant, with a balance between the continuous loss of mature cells by senescence and new RBC production in the bone marrow. There are precise homeostatic mechanisms to ensure sufficient, but not excess, RBCs production. Con- genital disorders affecting the constituents of the RBC (namely hemoglobinopathies, membranopathies or en- zymopathies) or affecting the erythropoiesis, can lead to anemia or to excess of RBC production (erythrocytosis).
The most common inherited RBC disorders are con- genital hemolytic anemias (CHA), caused by α- and β-hemoglobinopathies, red cell pyruvate kinase (PKLR) or glucose-6-phosphate dehydrogenase (G6PD) defi- ciency, and hereditary spherocytosis (HS), which affect millions of people worldwide. CHA can also be caused by other RBC enzymes deficiency, other forms of mem- branopathies and, more rarely, by ineffective erythro- poiesis as in congenital sideroblastic anemia (CSA) or congenital dyserythropoietic anemia (CDA).
RBC disorders can also be caused by congenital iron deficiency, leading to severe microcytic hypochro- mic anemia, as in Iron-refractory iron deficiency ane- mia (IRIDA) and DMT1-deficiency anemia.
❯ Red blood cells disorders diagnosis
Traditional diagnosis of CHA has been done via a step- by-step process starting to evaluate the disorder in the proper clinical context, the family history and transmis- sion pattern, the hematological parameters and the morphological analysis of peripheral blood. In the great number of cases this is enough to lead to the suspicious
of a hemoglobinopathy, membranopathy or enzymop- athy. Biochemical tests as Hb capillary electrophoresis or high performance liquid chromatography (HPLC), combination of an eosin-5’-maleimide test (EMA) with ektacytometry, and measurement of the RBC enzyme levels, can confirm the diagnosis of thalassemia, sickle cell disorders or other Hb variants, RBC membrane dis- orders or RBC enzymes deficiency, respectively. Com- plementary analysis of bone marrow smears are neces- sary for the diagnosis of CDA and CSA.
❯ Molecular studies
Although in the most of cases it’s possible to do the diagnosis without molecular studies, they are usually necessary to confirm the diagnosis, in order to establish suitable prognostic and treatment, and propose genet- ic counselling to the couples at risk. Molecular test are also used to find the disease-causing mutations in cas- es where traditional testing has failed, or when a patient has been transfused, leading to confounding biochem- ical testing findings due to mixed RBC populations.
For β-hemoglobinopathies, membrane and enzyme defects, CDA, CSA, IRIDA and DMT1-anemia, Sanger se- quencing of the affected gene(s) is usually sufficient to find the pathogenic variant(s) causing the disorder.
For α-thalassemia, δβ-thalassemia and γδβ-tha- lassemia, caused by large deletions of the correspond- ing genes, a GAP-PCR or MLPA study must be done.
Examples of situations when molecular diagnosis is crucial to establish prognostic and treatment or per- form genetic counselling are:
• Hemoglobinopathies:
– Differentiation between moderate β-thalassemia intermedia (homozygous or compound heterozygous β+ mutations; association of β0 mutations with α-genes triplication), severe β-thalassemia intermedia (β0/β+) and dominant β-thalassemia intermedia.
LXII Congreso Nacional de la Sociedad Española de Hematología y Hemoterapia / Ponencias
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