Many techniques are available to efficiently pick up (point) mutations, all with their own strong and weak points and limitations. The most powerful qualitative techniques include denaturing gradient gel electrophoresis (DGGE) (see Chapter 8), chemical cleavage of mismatches (CCM) (see Chapter 7), and denaturing high-performance liquid chromatography (DHPLC). Of the quantitative techniques, Southern blotting, quantitative polymerase chain reaction (qPCR) (see Chapter 25) and multiplex ligation-dependent probe amplification (MLPA) are most popular. The protein truncation test (PTT) (1 , also known as the in vitro synthesized protein assay (IVSP) (2 , is rather exceptional and has several unique features. The most prominent of these are that it uses an RNA template, scans for mutations at the protein level, has a high sensitivity, and hardly gives false positives. In addition, PTT detects truncating mutations only and the large majority of these are disease causing and thus directly clinically relevant. No PTT-detected alterations have been reported that could not be confirmed by sequence analysis; PTT analysis could thus be used directly for diagnostic purposes.