In humans, congenital heart disease is a common birth defect that affects approximately 1 out of 125 live births. Using reverse transcription PCR (RT-PCR) Samir Zaidi and colleagues [(2013) Nature 498:220.223] determined that approximately 10 percent of the cases resulted from point mutations, often involving histone function. To capture products of gene expression in developing hearts, they used oligo(dT) in their reverse transcription protocol.

Compared with oligo(dT) primers, a pool of random sequence primers requires a trickier assessment of annealing temperature. Why?