Materials and methods
The formalin-fixed tissue was embedded in paraffin and 5-µm sec-tions
(n = 5) were placed onto a specifically designed 1- to 3-µm-thick
stretched polyethylene membrane which was mounted onto a
glass slide and fixed with nail polish (Fig. 4). After heating the
slide for 1 h at 40 °C and deparaffinising in xylol for only 1 min in
order to avoid detachment of the section, routine hematoxylin and
eosin (HE) staining was performed. The membrane-tissue unit was
then placed upside-down on a 0.17-mm-thick glass slide. The
chorionic villi and control areas from the decidua were dissected
with a 337-nm-pulsed laser microbeam coupled with a micro-scope.
The dissected pieces of the support membrane with the at-tached
chorionic villi were pierced with a 30-gauge needle and
transferred into a PCR tube using a computer-controlled microma-nipulator
(Fig. 5)
The tissue was digested for 3 h at 56 °C using a standard lysis
buffer and proteinase K (2 mg/ml). After digestion the enzyme was
heat-inactivated for 10 min at 95 °C and the extract was directly
used for PCR.
In a second assay five sections were mounted on glass slides
and stained with HE. The villi-containing region (2 ×2 mm) was
manually cut out, placed in Tris buffer and boiled in the mi-crowave
for 1 min. After removing the paraffin and centrifugation,
the supernatent was digested with proteinase K.
DNA from a blood sample obtained during autopsy of the vic-tim
and from a blood sample taken from a suspect was isolated us-ing
standardised chelex extraction.
PCR was performed using the PCR amplification kits
AmpFlSTR Profiler and Profiler Plus (Perkin Elmer) on a Ge-neAmp
PCR System 2400 (Perkin Elmer). PCR conditions were as
recommended by the manufacturer except that the cycle number
was increased to 35 instead of 28, to enhance sensitivity. Of the
DNA extracted from the chorionic villi and the decidual tissue,
10 µl was used, corresponding to about 50–100 cells, in a reaction
volume of 25 µl.
Electrophoresis and analysis of the amplification products were
carried out on an ABI Prism 310 Genetic analyzer using GeneScan
Analysis 2.1. software.