Qualitative analysis of TPO gene expression in fetal organs. Typical RT-PCR results from three patients are shown. The GAPDH signal did not differ between organs and between individuals, confirming constant efficiency of RNA preparation and cDNA synthesis. The intensity of the TPO signal varied between different organs and between the same organ of different individuals. Only liver and kidney samples were always positive for TPO mRNA. m, 100-bp DNA ladder; Ø, negative RT control, liver RNA plus all reagents except reverse transcriptase.