Discrepancies between forensic identification kits explained by a laser power supply shutdown

The occurrence of two null alleles for the same individual was suspected because of the discrepancy at two loci (vWA and THO1) between genotypes characterized by the mean of two different commercial kits. Reanalysis of the samples indicated there was no null allele, and that this abnormality was indeed related to an automatic laser power shutdown. The laser power supply was set to a value (6.4V) too close to the automatic shutdown threshold (6.0V). The alleles were undetected because of the absence of emission at the time of migration of the two alleles through the detection device. However, since no alarm is triggered in such an event, the users should monitor their laser power supply values.