Southern blot analysis of HindIII-digested genomic DNA probed with GPIIIa cDNA encompassing exons 10 through 14. The expected HindIII fragments in normal genomic DNA are graphically illustrated in the upper panel. In the autoradiogram, an extra band (4.4 kb) is seen in DNA samples of the proband (lane 4) and her father (lane 3). This band is absent in the sample of the mother (lane 2) and in the sample of a normal control (lane 1).