Rsa I restriction analysis in two groups of Italian patients, 22 carriers of the Leiden mutation (FV 506RQ) with APC ratio < 0.57 (below the 15th percentile) and 10 functionally APC resistant patients. The APC ratio value is reported for each patient under the corresponding lane. Size of the restriction fragments that identify the R1 and R2 alleles are indicated. C, normal controls; B, amplification without template DNA; M, molecular weight marker.