Search

Inherited factor (F)XI deficiency is a rare disorder in the general population, though it is commonly found in individuals of Ashkenazi Jewish ancestry. In particular, two mutations--a stop mutation (type II) and a missense mutation (type III)--which are responsible for FXI deficiency, predominate. The bleeding tendency associated with plasma FXI deficiency in patients is variable, with approximately 50% of patients exhibiting excessive post-traumatic or postsurgical bleeding. In this study, we identified the molecular basis of FXI deficiency in 10 patients belonging to six unrelated families of the Nantes area in France and one family of Lebanese origin. As in Ashkenazi Jewish or in French Basque patients, we have identified a new ancient mutation in exon 4 resulting in Q88X, specific to patients from Nantes, that can result in a severely truncated polypeptide. Homozygous Q88X was found in a severely affected patient with an inhibitor to FXI and in three other unrelated families, either as homozygous, heterozygous or compound heterozygous states. Other identified mutations are two nonsense mutations in the FXI gene, in exon 7 and 15, resulting in R210X and C581X, respectively, which were identified in three families. A novel insertion in exon 3 (nucleotide 137 + G), which causes a stop codon, was characterized. Finally, sequence analysis of all 15 exons of the FXI gene revealed three missense mutations resulting in G336R and G350A (exon 10) and T575M (exon 15). Two mutations (T575M and G350A) with discrepant antigen and functional values are particularly interesting because most of the described mutations are associated with the absence of secreted protein.

Aims/hypothesis: Glucokinase regulatory protein (GKRP) controls the activity of glucokinase in liver but possibly also in some areas of the central nervous system, suggesting that it could play a role in body mass control. Its gene is located in a region (2p21-23) linked to serum leptin levels. Our goal was to investigate whether mutations in the GKRP gene were associated with obesity., Methods: Mutations were sought in the GKRP gene of 57 patients from the families of the French genome-wide scan for obesity that contributed most to the positive LOD score with 2p21-23. The identified mutations were further sought in 720 unrelated obese individuals and 384 individuals of normal weight and their effect on the properties of recombinant GKRP were investigated., Results: The most frequent mutation (Pro446Leu) had a similar allele frequency in the obese (0.63) and normal weight (0.64) subjects and did not affect the properties of GKRP. Similarly, no effect on the properties of GKRP was observed with Arg590Tyr, found in 10 out of 720 obese subjects and in 2 out of 384 control subjects (p=0.18). Mutation Arg227Stop was found in one obese family and in 1 out of 384 control subjects and led to an insoluble protein. Mutation Arg518Gln, replacing a conserved residue, led to a marked decrease in the affinity of GKRP for both fructose 6-phosphate and fructose 1-phosphate and to a destabilization of GKRP. However, this mutation did not co-segregate with obesity in the single family in which it was found., Conclusions/interpretation: Mutations that affect the properties of GKRP are found in the French population, but they do not seem to account for the linkage between the 2p23 locus and quantitative markers of obesity.

Protein 4.1 pre-mRNA splicing is regulated in tissue- and development-specific manners. Exon 16, which encodes the N-terminal region of the spectrin/actin-binding domain, is one of the alternatively spliced sequence motifs. It is present in late differentiated erythroid cells but absent from early erythroblasts and from lymphoid cells. We describe a single nucleotide deletion of the erythroid protein 4.1 gene associated with hereditary elliptocytosis. The deletion located in exon 16 leads to a frameshift and a premature termination codon within the same exon. In an effort to examine the premature stop codon effect in relationship with exon 16 alternative splicing, we analyzed erythroid and lymphoid protein 4.1 mRNAs using the mutation and a linked downstream polymorphism as markers. We found that the premature stop codon does not affect the tissue-specific alternative splicing among the two cell types analyzed and that the resulting alteration of mRNA metabolism correlates with the retention of exon 16 in reticulocytes. Conversely, skipping of exon 16 in lymphoid cells converts the mutant mRNA to a normal lymphoid-specific mRNA isoform, hence bypassing the nonsense codon. Consistent with data obtained on constitutive nonsense exons, our observations argue in favor of a stop codon recognition mechanism that occurs after the regulated splicing status of the nonsense exon has been achieved., (Copyright 1999 Wiley-Liss, Inc.)

A novel complex mutation consisting of a small deletion/insertion (3958del5ins4) was found in the breast cancer-1 gene (BRCA-1) in three unrelated French breast and/or ovarian cancer families. These mutations occurred at the same nucleotide position of the 3' end of exon 11. The wild-type sequence, CTCAG, was deleted and replaced by AGGC in the three families. The consequence is the generation of a stop codon, TAG, resulting in a truncated protein. We propose two different mechanisms to explain the generation of this complex mutation: (i) the simultaneous occurrence of a deletion and an insertion in a stem-loop structure and (ii) the abortive integration of a human transposable element (Tigger 1) that deleted 5 nucleotides and inserted a 4-nucleotide "scar", corresponding to the 5' extremity of the transposon.