Recently, it has also been shown that HbS-β+ thalassemia due to the IVS-1 (-2) (A→C) mutation had significant levels of HbA, indicating that this mutation is a relatively milder β+ thalassemia allele,[15] whereas HbS-β thalassemia involving an AT transition at codon 132 of the β-globin gene had severe clinical manifestations.[16] The effects of β thalassemia mutations on the clinical severity of HbS-β thalassemia are well documented. This evidence concerns the gene PPIB and thalassemia.