Alpha-thalassemia (α-thalassemia, α-thalassaemia) is a form of thalassemia involving the genes HBA1 and HBA2. Thalassemias are a group of inherited blood conditions which result in the impaired production of hemoglobin, the molecule that carries oxygen in the blood. Normal hemoglobin consists of two alpha chains and two beta chains; in alpha-thalassemia, there is a quantitative decrease in the amount of alpha chains, resulting in fewer normal hemoglobin molecules. Furthermore, alpha-thalassemia leads to the production of unstable beta globin molecules which cause increased red blood cell destruction. The degree of impairment is based on which clinical phenotype is present (how many genes are affected). Signs and symptoms
The presentation of individuals with alpha-thalassemia consists of:

Cause
Alpha-thalassemias are most commonly inherited in a Mendelian recessive manner. They are also associated with deletions of chromosome 16p. Alpha thalassemia can also be acquired under rare circumstances. Pathophysiology
The mechanism sees that α thalassemias results in decreased alpha-globin production, therefore fewer alpha-globin chains are produced, resulting in an excess of β chains in adults and excess γ chains in newborns. The excess β chains form unstable tetramers called hemoglobin H or HbH of four beta chains. The excess γ chains form tetramers which are poor carriers of O2 since their affinity for O2 is too high, so it is not dissociated in the periphery. Homozygote α0 thalassaemias, where numerous γ4 but no α-globins occur at all (referred to as Hb Barts), often result in death soon after birth. Diagnosis
Diagnosis of alpha-thalassemia is primarily by laboratory evaluation and molecular diagnosis.
Monocephalus is a genus of dwarf spiders that was first described by F. P. Smith in 1906. Species
As of May 2019 it contains two species:
Monocephalus castaneipes (Simon, 1884) – Europe
Monocephalus fuscipes (Blackwall, 1836) (type) – Europe

See also
List of Linyphiidae species (I–P)


== References ==