For all these reasons, in an ideally diagnostic algorithm for the investigation of patients with ptosis and/or limitations of eye movements, FTIR spectroscopy could precede Southern blot or long-range PCR for its high ability to differentiate single mtDNA deletion from mutations in nuclear genes, such as POLG or PABPN1. A further advantage of FTIR compared with traditional techniques is the smaller amount of muscle needed. The gene discussed is POLG; the disease is ptosis.