SSCP analysis and sequencing of exon 3 of the GPIIIa gene: identification of the mutation carried by the father (L.J.). (A) SSCP analysis of exon 3 of 4 family members. Two bands, a and b, were seen for L.J. and L.M., for whom C.M.'s serum was reactive against their platelets, while only band a was observed for C.M. and L.P., for whom C.M.'s serum was unreactive against their platelets. (B) Direct DNA sequencing of the corresponding amplification product for L.J. and C.M. The position of the mutation is indicated with a horizontal arrow, and the substituted base with a bold letter; the amino acid substitution is indicated together with its position in the GPIIIa protein.