High gene frequency of factor XI (PTA) deficiency in Ashkenazi Jews.

Factor Xi deficiency has previously been observed mainly in Jews. For 34 of 36 probands with factor XI deficiency in Israel, reliable information on ethnic background was obtained. Of 34 probands 33 were of definite Ashkenazi Jewish origin; 1 was of probable Ashkenazi origin. From a survey of factor Xi levels among 428 unrelated healthy Ashkenazi Jews, 35 had partial factor XI deficiency (factor Xl levels 0.15-0.49 U/mI), 1 had severe deficiency (0.02 U/mI) and 392 had normal levels (0.5-2.1 U/mI). The calculated frequency of the mutant gene was 0.043; the 95% confidence limits for the frequency of homozygotes in the total population was 0.1 %-O.3% and for heterozygotes 5.5%-i 1 %. In 20 of 41 obligatory carriers of the mutant gene factor Xl levels were in the normal range. Since in the survey only subjects with deficient factor Xi levels were considered as carriers, the true frequency of the mutant gene may be even higher. Factor Xl deficiency can therefore be added to the list of genetic disorders common to Ashkenazi Jews. Since patients with factor Xl deficiency may bleed excessively following trauma, it is advisable to carry out the appropriate tests in any Ashkenazi Jewish patient undergoing surgery.