A cluster of factor XI-deficient patients due to a new mutation (Ile 436 Lys) in northeastern Italy*

A family with factor-XI deficiency due to a compound heterozygosis between Gln 47 Pro (new mutation) in exon 3 and Leu 619 Pro in exon 15

A new factor XI mutation (Gln 47 Pro) has been found in combination with another known mutation (Leu 619 Pro) in a female patient with FXI deficiency and a moderate bleeding tendency. FXI activity and antigen in the proposita were 2% activity and less than 5% of normal, respectively. The parents are not consanguineous and are asymptomatic. The father is heterozygote for the new mutation whereas the mother is heterozygote for the known mutation. Other family members are heterozygotes for either one of the two mutations. The new mutation is not a polymorphism as it was not found in the population of the area. The geographical area, north-east of Italy, of the present family is the same area where a cluster of another new mutation (Ile 436 Lys) was recently reported. No relation was found between the present family and those with the previous mutation.

The spectrum of factor XI deficiency in Italy

Factor XI (FXI) deficiency is a rare inherited bleeding disorder invariably caused by mutations in the FXI gene. The disorder is rather frequent in Ashkenazi Jews, in whom around 98% of the abnormal alleles is represented by Glu117X and Phe283Leu mutations. A wide heterogeneity of causative mutations has been previously reported in a few FXI deficient patients from Italy. In this article, we enlarge the knowledge on the genetic background of FXI deficiency in Italy. Over 4 years, 22 index cases, eight with severe deficiency and 14 with partial deficiency, have been evaluated. A total of 21 different mutations in 30 disease-associated alleles were identified, 10 of which were novel. Among them, a novel Asp556Gly dysfunctional mutation was also identified. Glu117X was also detected, as previously reported from other patients in Italy, while again Phe283Leu was not identified. A total of 34 heterozygous relatives were also identified. Bleeding tendency was present in very few cases, being inconsistently related to the severity of FXI deficiency in plasma. In conclusion, at variance with other populations, no single major founder effect is present in Italian patients with FXI deficiency.

Type I mutation in the F11 gene is a third ancestral mutation which causes factor XI deficiency in Ashkenazi Jews

BACKGROUND

Factor XI (FXI) deficiency is one of the most frequent inherited disorders in Ashkenazi Jews (AJ). Two predominant founder mutations termed type II (p.Glu117Stop) and type III (p.Phe283Leu) account for most cases.

OBJECTIVES

To present clinical aspects of a third FXI mutation, type I (c.1716 + 1G>A), which is also prevalent in AJ and to discern a possible founder effect.

METHODS

Bleeding manifestations, FXI levels and origin of members of 13 unrelated families harboring the type I mutation were determined. In addition, eight intragenic and five extragenic polymorphisms were analyzed in patients with a type I mutation, in 16 unrelated type II homozygotes, in 23 unrelated type III homozygotes and in Ashkenazi Jewish controls. Analysis of these polymorphisms enabled haplotype analysis and estimation of the age of the type I mutation.

RESULTS

Four of 16 type I heterozygotes (25%) and 6 of 12 (50%) compound heterozygotes for type I mutation (I/II and I/III), or a type I homozygote had bleeding manifestations. Haplotype analysis disclosed that like type II and type III mutations, the type I is also an ancestral mutation. An age estimate revealed that the type I mutation occurred approximately 600 years ago. The geographic distribution of affected families suggested that there was a distinct origin of the type I mutation in Eastern Europe.

CONCLUSIONS

The rather rare type I mutation in the FXI gene is a third founder mutation in AJ.