2. Classification

The RA are classified into two main groups: Hereditary and acquired, and in these groups, the mechanism of the anaemia can be sub classified into five different defects: (1) bone marrow (erythropoietic), (2) peripheral blood (red blood cell), (3) iron metabolism (sideroblastic and non-sideroblastic), (4) blood plasma (autoimmune haemolytic anaemia and related syndromes) and (5) microcirculation (haemolytic uremic syndrome and other microangiopathic disorders). This means that all RA are the consequence of haematopoietic system defects leading to a low RBC production (erythropoietic defects), or of RBC defects, either intrinsic or associated to plasma or microcirculation disorders, leading to low RBC survival or haemolysis (Table 1).

ENERCA is actively contributing to the WHO Update Platform ICD-10 of blood and blood forming organs. In this platform, anaemias, are classified into three main groups: D50-D53 (nutritional anaemias), D54-D59 (haemolytic anaemias), and D60-D64 (aplastic and other anaemias). This ICD classification includes all kind of anaemias, hereditary, acquired, common and rare, and ENERCA has extracted the RA group that has been individually listed in the ENERCA Web page (www.enerca.org).

For practical purposes, according to their mechanism, prevalence and/or relevant clinical and/or social impact in the European population, ENERCA has classified the Rare Anaemias into 10 different groups [6]:

Group 1. Haemoglobin disorders: Haemoglobinopathies and Thalassaemias.

Group 2. Hereditary Haemolytic Anaemias (HHA): Red blood cell enzymopathies and membrane defects.

Group 3. Hereditary erythropoietic failure or aplasia: Diamond-Blackfan anaemia (DBA) and Fanconi anaemia (FA),

Group 4. Congenital dyserythropoietic anaemias (CDA),

Group 5. Hereditary sideroblastic anaemias,

Group 6. Hereditary non-sideroblastic anaemias due to iron metabolism defects,

Group 7: Hereditary disorders of folic acid and cobalamin defects.

Group 8: Paroxysmal nocturnal haemoglobinuria (PNH),

Group 9: Anaemias due to rare complex mechanisms and.

Group 10: Anaemias of unknown origin (AUO).

The underlying cause of rare anaemias remains still unexplained in about 20% of patients, almost one third of which might be accounted for myelodysplastic syndromes. AUO can be also due to complex clinical situations and multifactorial mechanisms, in general associated with systemic, non-haematological, hereditary or acquired diseases. Their existence is a very important tackling exercise for clinical and biological research.
