Savio Woo of the Mount Sinai School of Medicine in New York has retracted two more papers this week, the blog Retraction Watch reported today. That brings Woo’s total number of retractions this year to six, following an investigation that found evidence of scientific misconduct committed by two of his postdocs. (See ‘Researchers dismissed at gene therapy lab’ for more detail.)

Four of the six retracted papers, including the two most recently pulled, describe a technique that harnesses a viral enzyme called ‘phiBT1 integrase’ to shuttle genes into the mouse genome, particularly in the liver. The retractions for all of these papers merely cite “data irregularities”. Michele Calos, a geneticist at Stanford University, says her lab was unable to reproduce the phiBT1 work and found numerous factual errors in the published procedures. Also, Woo’s team claimed that phiBT1 only inserted into the genome at the regions between genes—a key advantage of the technique because it reduced the odds that an insertion would disrupt the function of a normal gene. But that didn’t hold up in her lab, Calos notes.

Calos says she informed Woo of these problems, “among many others”, in 2008.