A novel factor V null mutation at Arg 506 causes a false positive Factor V Leiden result.

restriction endonuclease (3). The HFE Cys282Tyr and His63Asp mutations were detected by PCR-RFLP using the restriction endonucleases RsaI and BclI, respectively (4). Among the 100 patients with FV Leiden allele, 5 were heterozygous for the C282Y mutation, 26 were heterozygous for the H63D mutation, 2 were homozygous for the H63D mutation, and 1 was a double heterozygote for both mutations (Table 1). The frequency of the C282Y mutation among controls was 0.045 resulting in a carrier frequency of 9%. The frequency of the C282Y mutation among carriers of FV Leiden was 0.03 resulting in a carrier frequency of 6%. We found the frequency of C282Y and H63D heterozygotes among the FV Leiden patients not to be significantly different from that in our controls which is identical to the frequencies of hemochromatic mutation among the central European normal population (5, 6). All thrombotic patients with the allele C282Y were women, the sex ratio for the mutation H63D was 1.1 : 1.0 (male : female). There was no correlation of the clinical status of thrombosis with the presence or the absence of the hemochromatosis mutations in the FV Leiden mutation carriers. In contrast to the published preliminary report (1), we have found no association between the hemochromatosis mutations C282Y and/or H63D and factor V Leiden mutation among thrombotic patients in the Czech Republic. However, we have found female thrombotic patients with the FV Leiden allele to be carriers of the hemochromatic C282Y allele with the significantly higher frequency (x, p < 0.05) than the male patients. In normal population, the sex ratio for C282Y mutation is 1:1. This finding may be related to the higher depletion of the total body iron in women. In the previous study, the gender of the patients was not reported (1). The connection between hemochromatosis and thrombophilia should be resolved in future studies of larger number of individuals and a detailed assessment of iron status among the patient and control groups should be included.