It is a disease caused by the presence in the same individual of two or more thalassaemic characters.

The severity of the pathology is tightly connected to the different mutations that determine it. The term " thalassemia intermedia " refers to the pathological picture that can be intermedia between a slightly clinical situation more marked than the heterozygote untill a condition similar to the Mediterranean anaemia one.

Thalassaemia intermedia caused by defects of the β genes

In the β thalassaemia intermedia the genotype can be constituted:

• from the homozygosis due to a β light thalassaemia defect (in Italy the most frequent are the IVS -6 T→C, -87 C→G, -101 C→T mutations and the δβ 'Sicilian' deletion),
• from a compound heterozygosis due to a severe defect and a mild one (this last is very often in Italy the -101 C→T mutation),
• from a double heterozygosis due to a β thalassaemic defect and the α genes' triplication of located on chromosome 16.

While the first condition is cause of a serious pathology, similar to the Mediterranean anaemia one, the last two genotypes give arise to a such mild thalassaemia intermedia that can simulate even the picture of a simple very marked β thalassemia heterozigosity.

The α thalassaemia, if present in a subject with β thalassaemia intermedia, represents an attenuating factor of the pathological picture.

Thalassaemia intermedia caused by α genes' defects

In the α thalassaemia intermedia, the genotype is characterized by the presence of a deletion that causes a α⁰ thalassaemia (in Italy the deletion - - MED or - α^20.5) and of a defect that causes a α⁺ thalassaemia (in Italy it is more often the deletion - α^3.7).

The presence in the haemoglobin picture of a small HbH level, characteristic of the α thalassaemia intermedia, gives to the disease the name of thalassaemia intermedia with Hb H.

Patients usually have normal physical development and very long or even normal survival. They are anaemic since the infancy but they are not transfusion-dependent. With the years they run into siderosis from iron alimentary hyperabsorbiment; the appearance of erythropoietic extramedullary masses; haepato-splenomegaly that can reach enormous dimensions; thrombus-embolic phenomenons; chronic ulcerations to the inferior limbs and an aggravation of the anaemia that can make a necessary systematic haemotransfusional therapy in the adult or pre-senile age.