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A letter to the editor is presented regarding the determination of two novel missense mutations which cause coagulation factor XIII (FXIII) deficiency.

Deficiency of coagulation factor XIII (FXIII) belongs to the rare bleeding disorders and its incidence is higher in populations with consanguineous marriages. The aims of this study were to characterize patients and relatives from seven families with suspected FXIII deficiency from Pakistan and to identify the underlying mutations. As a first indicator of FXIII deficiency, a 5M urea clot solubility test was used. Plasma FXIII A- and B-subunit antigen levels were determined by ELISA. FXIII activity was measured with an incorporation assay. Sequencing of all exons and intron/exon boundaries of F13A was performed, and a novel splice site defect was confirmed by RT-PCR analysis. Genetic analysis revealed six different mutations in the F13A gene. Two splice site mutations were detected, a novel c.1460+1G>A mutation in the first nucleotide of intron 11 and a previously reported c.2045G>A mutation in the last nucleotide of exon 14. Neither of them was expressed at protein level. A novel nonsense mutation in exon 4, c.567T>A, p.Cys188X, was identified, leading in homozygous form to severe FXIII deficiency. Two novel missense mutations were found in exons 8 and 9, c.1040C>A, p.Ala346Asp and c.1126T>C, p.Trp375Arg, and a previously reported missense mutation in exon 10, c.1241C>T, p.Ser413Leu. All patients homozygous for these missense mutations presented with severe FXIII deficiency. We have analysed a cohort of 27 individuals and reported four novel mutations leading to congenital FXIII deficiency. [ABSTRACT FROM AUTHOR]

Severe factor XIII (FXIII) deficiency is a rare autosomal recessive coagulation disorder affecting one in two million individuals. The aim of the present study was to screen for and analyse F13B gene defects in the German population. A total of 150 patients presenting with suspected FXIII deficiency and one patient with severe (homozygous) FXIII deficiency were screened for mutations in F13A and F13B genes. Twenty-five individuals presented with detectable heterozygous mutations, 12 of them in the F13A gene and 13 of them in the F13B gene. We report on the genotype–phenotype correlations of the individuals showing defects in the F13B gene. Direct sequencing revealed 12 unique mutations including seven missense mutations (Cys5Arg, Ile81Asn, Leu116Phe, Val217Ile, Cys316Phe, Val401Glu, Pro428Ser), two splice site mutations (IVS2-1G>C, IVS3-1G>C), two insertions (c.1155_1158dupACTT, c.1959insT) and one in-frame deletion (c.471–473delATT). Two of the missense mutations (Cys5Arg, Cys316Phe) eliminated disulphide bonds (Cys5-Cys56, Cys316-Cys358). Another three missense mutations, (Leu116Phe, Val401Glu, Pro428Ser) were located proximal to other cysteine disulphide bonds, therefore indicating that the region in and around these disulphide bonds is prone to functionally relevant mutations in the FXIII-B subunit. The present study reports on a fairly common prevalence of F13B gene defects in the German population. The regions in and around the cysteine disulphide bonds in the FXIII-B protein may be regions prone to frequent mutations. [ABSTRACT FROM AUTHOR]

Factor XIII (FXIII) deficiency is a very rare (1:2 000 000) severe autosomal recessive bleeding disorder, mostly due to mutations in the coagulation FXIII A-subunit gene. We have studied the molecular basis of FXIII deficiency in five unrelated Italian families. The coding region, intron–exon boundaries and 5′- and 3′-untranslated regions of the FXIII gene encoding the A subunit were amplified and directly sequenced. Candidate mutations were identified in all the patients. Three novel mutations occurred in three patients. These include a novel homozygous deletion of two base pairs (bp) in exon 14 (c.2002–2003 DelCT). This deletion causes a frameshift from Leu667 and the formation of a stop codon at amino acid position 681. The second patient presents a novel homozygous (c.2126 G>A) transition in exon 15, predicting a Ser708Asn in Barrel 2 domain. The third patient is compound heterozygote for two missense mutations, a previously reported Arg260His substitution, and a novel transition in exon 4 (c.560 C>T) predicting a Pro186Leu in the core domain. The remaining two patients have two previously reported mutations: a 4-bp homozygous deletion in exon 11 (c.1392–1395 Del AATT), previously reported to occur in the Vicenza Area, and a homozygous nonsense mutation in exon 8 (c.979 C>T) predicting an Arg326X in the core domain. The novel mutations occurred at amino acid residues highly conserved among different species (pig, monkey, mouse and dog) and were not detected in 110 normal alleles. Structural analysis shows that Pro186Leu mutation leads to the replacement of the rigid proline pyrrolidine ring by the larger and more flexible leucine side chain and Ser708Asn may probably disrupt the hydrogen bond with Ala291. [ABSTRACT FROM AUTHOR]

Inherited factor XIII (FXIII) deficiency is known as one of the most rare blood coagulation disorder in humans. In the present study, phenotype and genotype of eight FXIII deficient Polish patients from five unrelated families were compared. The patients presented with a severe phenotype demonstrated by a high incidence of intracerebral haemorrhages (seven of eight patients), haemarthrosis (six patients) and bleeding due to trauma (five patients). Introduction of regular substitution with FXIII concentrate prevented spontaneous bleeding in seven patients. In all patients, mutations within the F13A gene have been identified revealing four missense mutations (Arg77Cys, Arg260Cys, Ala378Pro, Gly420Ser), one nonsense mutation (Arg661X), one splice site mutation (IVS5-1 G>A) and one small deletion (c.499–512del). One homozygous large deletion involving exon 15 was detected by failure of PCR product. The corresponding mutations resulted in severely reduced FXIII activity and FXIII A-subunit antigen concentration, while FXIII B-subunit antigen remained normal or mildly decreased. Structural analysis demonstrated that the novel Ala378Pro mutation may cause a disruption of the FXIII catalytic triad leading to a non-functional protein which presumably undergoes premature degradation. In conclusion, the severe phenotype with high incidence of intracranial bleeding and haemarthrosis was in accordance with laboratory findings on FXIII and with severe molecular defects of the F13A gene. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented on heterogeneity ofin Italian families with factor XIII deficiency.