With increasing attention on early manifestations of transthyretin amyloidosis as well as emerging treatments appropriate studies to confirm the types and variants of transthyretin amyloidosis are fundamental to improve prognosis. The main advantage of this protocol is that this test is feasible and easy to preform in the clinical laboratory. To begin the protocol obtain a DNA extraction kit, add 10 milliliters of solution one to the previous obtained 4.0 milliliter blood sample and incubate the sample on ice for 10 minutes.
After incubation centrifuge the sample at 2000 G for five minutes at four degrees Celsius. Carefully remove and discard the supernatant. Re suspend the pellet in three milliliters of solution one.
Centrifuge the sample at 2000 G for five minutes at four degrees Celsius again. Discard the supernatant. Re suspend the pellet in three milliliters of solution two.
Next, add 10 microliters of Pronase stock solution to get a final concentration of 100 micrograms per milliliter and mix the contents well. Incubate the DNA at 37 degrees Celsius overnight. The next day, chill the tube on ice for 10 minutes.
Add 0.8 milliliters of solution three to the sample and invert it three to five times. Then, place the sample on ice for five minutes. Centrifuge the sample at 3000 G for 15 minutes at four degrees Celsius.
Carefully transfer the supernatant to a 15 milliliter sterile conical centrifuge tube and add six microliters of RNase stock solution to obtain a final concentration of 20 micrograms per milliliter. Incubate the sample, add 2.5 milliliters of isopropyl alcohol to the tube and gently invert the tube several times to precipitate the DNA which appears as strands of white flocculant material. With a large bore pipette transfer the precipitate to a new 1.5 milliliter centrifuge tube.
Centrifuge the precipitate at 12, 000 G for three minutes at four degrees Celsius. Discard the supernatant carefully. Then wash the DNA pellet by adding 500 microliters of 70%ethanol.
Centrifuge the DNA at 12, 000 G for one minute and discard the supernatant. Air dry the DNA pellet at room temperature. Add 100 microliters of DDH2O and incubate the sample at 65 degrees Celsius for 15 minutes to re suspend the DNA.
Perform PCR in a 25 microliter reaction mixture using a DNA polymerase kit. Add the reagents to a 0.2 milliliter PCR tube. Mix the contents gently and briefly centrifuge them in a bench top centrifuge.
Place the tube in a thermal cycler. Perform the PCR for 30 cycles with a denaturation step for 30 seconds at 94 degrees Celsius, primer enabling for 30 seconds at 58 degrees Celsius and polymerase extension for 45 seconds at 72 degrees Celsius. Prepare a 1.2%agarose gel by mixing 1.2 grams of agarose powder with 100 milliliters of 0.5 XTBE in a microwaveable flask.
Microwave the solution for two minutes until the agarose is completely dissolved. Cool down the agarose mixture to 55 degrees Celsius. Add two microliters of ethidium bromide solution to the agarose mixture and mix gently.
Pour the mixture into a gel tray to about five to seven millimeters. Then, insert the comb. Allow the gel to solidify for at least 30 minutes.
After the gel has solidified carefully remove the comb. Place the gel and tray into the electrophoresis cell. Fill the electrophoresis cell with 0.5 XTBE until the gel is covered.
Carefully load two microliters of a 100 base pair DNA ladder into the one lane of the gel as a molecular size marker. Load the dye and sample mixture into the additional lanes. Turn on the power supply and run the gel for 25 minutes at 100 volts.
Remove the gel from the electrophoresis cell. Finally, visualize the DNA fragments under UV light in an imaging system. Agarose gel electrophoresis of two patients and one healthy individual reveal bands of the expected sizes including a 454 base pair PCR product for exon four of the TTR gene.
Sequence chromatograms disclosed a nucleotide T substitution for G in exon four of the TTR gene resulting in a missense mutation and an alanine to serine substitution at amino acid position 97 in two patients. After watching this video you should have a good understanding of how to confirm the presence of point mutations for the diagnosis of hereditary transthyretin amyloidosis.
