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Β-Thalassemia is hematological condition that is caused by defective synthesis hemoglobin either due to decreased or absent synthesis of β-globin chains ( α-globin chain synthesis is normal).There are many mutations that can cause this condition (commonly point mutations in splice sites and promoters). Cooley and Lee described bone abnormalities and severe anemia with associated splenomegaly in 1921. Named for the Greek word for "sea" (θάλασσα - thálassa), as the condition is more prevalent in those living around the Mediterranean Sea e.g. extremities: widening/expansion of the metacarpal and metatarsal shafts.

ribs: rib-within-a-rib appearance, noted particularly in the middle and anterior portions of the ribs.

the ethmoid sinuses are spared due to lack of red bone marrow.

hypopneumatisation of the frontal, maxillary, and sphenoid sinuses, filled with marrow containing bone.

skull: the occipital bone is spared, due to lack of hemopoietic bone marrow.

Marrow proliferation consists of an expansion of the medulla, thinning of cortical bone, and resorption of cancellous bone resulting in a generalized loss of bone density and yellow-to-red bone marrow reconversion. The thalassemia trait may confer a degree of protection against malaria, which confers a selective survival advantage on carriers. β thalassemias are common in Africans, but also in Greeks and Italians. Deletion of one of the α loci has a high prevalence in people of African or Asian descent, making them more likely to develop α thalassemias. Thus, in a normal person with two copies of each chromosome, there are two loci encoding the β chain, and four loci encoding the α chain. The β globin chains are encoded by a single gene on chromosome 11 α globin chains are encoded by two closely linked genes on chromosome 16. In α thalassemias, production of the α globin chain is reduced, while in β thalassemia production of the β globin chain is reduced. The thalassemias are classified according to which chain of the hemoglobin molecule is affected. Thalassemia patients produce a deficiency of either α or β globin, unlike sickle cell disease, which produces a specific mutant form of β globin.

HbA contains two α globin chains and two β globin chains, and HbA2 contains two α globin chains and two δ globin chains. Normal adult hemoglobin is composed of HbA (98%) and HbA2 (2%). Thalassemia is a quantitative problem of globin synthesis, whereas sickle cell disease is a qualitative problem of synthesis of an incorrectly functioning globin. The resultant microcytic anemia is the characteristic presenting symptom of the thalassemias. The genetic defect causes a reduction in the rate of globin chain synthesis which causes the formation of abnormal hemoglobin molecules. Thalassemia is an autosomal recessive hemoglobinopathy that originated in the Mediterranean region. Osteitis CT (m, n): Bone focal lysis and erosions of osteitis (arrows) contiguous to a frontal sinusitis complicated with intracranial laminar abscess (dashed arrow) Bone sarcoidosis (k, l) CT (k) and T2WI (l): Mixed predominantly lytic multiple lesions with lace-like internal pattern of calcification and T2 hypointensity (dashed arrows). Thalassemia CT (j): Diffuse diploic widening and “hair-on-end” appearance (arrow) with characteristic occipital bone preservation (arrowhead). Renal osteodystrophy CT (g): shows characteristic “salt-and-pepper pattern.” Brown tumor (h, i): unspecific well-defined, cystic appearance (arrows). Amyloidoma (e, f) CT (e) and T2WI (f): Giant heterogeneous mass with marked T2 hypointensity and calcifications. Osteoporosis circumscripta cranii CT (c, d): large geographic radiolucent areas involving medullar and cortical bone in frontal and occipital regions (arrows). Paget disease (a, b) CT (a) and X-ray (b): Characteristic mixed bone lysis and sclerosis, cortical bone thickening, and expansion.