Figure 1 Detection of amyloid precursor protein (APP) duplication by quantitative multiplex PCR of short fluorescent fragments (QMPSF). The electropherogram of the affected subject (in red) was superimposed on that of a normal individual (in blue) by adjusting the peaks obtained from the control amplicon PCBD2 located on chromosome 5 to the same level. The vertical axis shows fluorescence in arbitrary units and the horizontal axis indicates the size of the amplicons in base pairs. Arrows indicate heterozygous duplication of the amplicons, as detected by a 1.5 fold heightening of the corresponding peaks. This QMPSF covers four genes located at 21q21: MRPL39, GABPA, APP and CYYR1.