Beta Thalassemia Modifier StripAssay (β-Thal Modifier)

The Viennalab Beta Thalassemia Modifier StripAssay identifies genotypes associated with the severity of beta thalassemia. The intended use in the IFU is the identification of genotypes associated with severity of beta-thalassemia based on PCR and reverse hybridisation.

What the assay does and does not do

The assay determines five polymorphisms that modify the course of the disease. It does not determine the HBB mutations that cause beta thalassemia, and it is therefore used alongside a mutation panel rather than instead of one. The Beta Thalassemia StripAssay covers the causal mutations in three regional versions.

The five loci

HBG2 g.-158C>T, the XmnI polymorphism in the promoter of the gamma-globin gene; BCL11A rs1427407 [G to T] and rs10189857 [A to G]; and HBS1L-MYB rs28384513 [A to C] and rs9399137 [T to C]. All five affect the level of fetal haemoglobin.

Why fetal haemoglobin matters

Fetal haemoglobin contains gamma-globin instead of beta-globin, so it compensates for the shortage of beta chains in beta thalassemia and reduces sickling in sickle cell disease. Patients who continue to produce HbF into adult life have a milder course, and these five loci account for a substantial part of that variation. That makes the modifier genotype relevant to prognosis and to the assessment of treatments that raise HbF.

Method and sample

The assay amplifies with biotinylated primers and hybridises the products to allele-specific probes immobilised as parallel lines on a test strip. Bound product is detected with streptavidin-alkaline phosphatase and a colour substrate, and the pattern is read by eye against the supplied Collector sheet. Fresh or frozen blood with EDTA or citrate as anticoagulant is used, and the kit contains the lysis solution and GENxTRACT resin. Taq DNA Polymerase is not supplied and is ordered separately as ViennaLab TAQ-500 or TAQ-2500. DNA isolated with the kit protocol goes straight into the PCR; for DNA prepared another way, 2 to 10 ng/µl is specified, which is 10 to 50 ng per reaction.

• Lysis Solution (50 ml)
• GENxTRACT Resin (5 ml)
• Amplification Mix (500 µl)
• Taq Dilution Buffer (500 µl)
• DNAT (1.5 ml)
• Typing Trays (3)
• Teststrips (20)
• Hybridization Buffer (25 ml)
• Wash Solution A (80 ml)
• Conjugate Solution (25 ml)
• Wash Solution B (80 ml)
• Color Developer (25 ml)

20 tests per kit, REF 4-170. Taq DNA Polymerase is not supplied and is ordered separately as ViennaLab TAQ-500 or TAQ-2500. Fresh or frozen blood with EDTA or citrate anticoagulant is used; for DNA prepared with another method, 2 to 10 ng/µl is specified.