Thalassaemia is the most common monogenetic disease worldwide. Antenatal screening is effective and simple, and accurate genetic prenatal diagnosis can be achieved in early gestation. Less invasive methods are feasible with ultrasound fetal assessment for alpha-thalassaemia, analysis of circulating fetal nucleic acid in maternal plasma, and pre-implantation genetic diagnosis. Women with thalassaemia major and intermedia are at risk of various maternal complications, such as cardiac failure, alloimmunisation, viral infection, thrombosis, endocrine and bone disturbances. Therefore, it is prudent to adhere to a standard management plan in this group of pregnant women. Close monitoring of the maternal and fetal condition during pregnancy is essential, and various treatments, such as blood transfusion or postpartum prophylaxis for thromboembolism, may be indicated. After birth, resumption of iron chelation and bisphosphonates treatment is needed, and counselling on breast feeding and contraception should be given.
Introduction
Thalassaemia refers to a group of autosomal recessive disorders of haemoglobin synthesis, and consists of two main types: alpha and beta. Both are different from each other epidemiologically, and have different genetic defects, disease manifestation, and, consequently, prenatal diagnosis and management ( Table 1 ). Although its name (in Greek áλασσα: the sea, αĨμα: blood) implies its geographic prevalence in the Mediterranean region, the diseases are not restricted to southern Europe or northern Africa, and can spread through certain ethnic groups in the Middle East and Southern Asia. The estimated prevalence for different types of thalassaemia trait is up to 16% in southern European populations, 10% in Thai populations, and 3–8% in Indian, Pakistani, Bangladeshi and Chinese populations, making it the most common monogenetic disease worldwide.
| Alpha-thalassaemia | Beta-thalassaemia | |
|---|---|---|
| Genetics | ||
| Number of alleles | 4 | 2 |
| Gene allocation | chromosome 16. | chromosome 11. |
| Type of genetic defects | Commonly deletion. | Commonly point mutation. |
| Mode of inheritance | Autosomal–recessive. | Autosomal–recessive. |
| Epidemiology | More common in south China and Asia. | More prevalent in Mediterranean region. |
| Screening of carrier status | MCH less than 27 pg and MCV less than 81 fl. | MCH less than 27 pg and MCV less than 81 fl. |
| Diagnosis of carrier status | Haemoglobin inclusion bodies. | Elevated haemoglobin A2 3.5% or greater and haemoglobin F. |
| Prenatal diagnosis | ||
| Genetic diagnosis with chorionic villus sampling or amniocentesis | Yes | Yes |
| Haemoglobin pattern with cordocentesis | Yes | No |
| Ultrasound surveillance | Yes | No |
| Non-invasive prenatal diagnosis | No | Possible |
| Pre-implantation genetic diagnosis | Yes | Yes |
| Disease manifestation | ||
| Onset | In utero since first trimester. | Few months after birth. |
| Presentation | Cardiomegaly, thick placenta and hydropic changes in utero. | Anaemic symptoms during infancy. |
| Prognosis and treatment | Lethal. | Continuous transfusions or treat with bone marrow transplantation. |
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