Identification of Two Point Mutations in Japanese Patients with Congenital Coagulation Factor XIII A Subunit Deficiencies

Congenital factor XIII (FXIII) deficiency is a rare autosomal recessive bleeding disorder. To date 33 patients with FXIII deficiency have been reported in Japan. we examined the genetic defects in two unrelated Japanese families in which three patients had been diagnosed as congenital FXIII A subunit deficiency. Exons I-XV of the gene encoding the FXIII A subunit were individually amplified by polymerase chain reaction (PCR) and the PCR products were directly sequenced by the dideoxy termination method. The sequence analysis revealed a substitution from G to A at position 1468 in exon XI resulting in Gly461Arg in Family A, and a substitution from C to T at position 2068 in exon XIV resulting in Arg661stop in Family B. One patient of Family A was homozygote of the Gly461Arg mutation and his daughter and grandchild were heterozygote. Since this mutation did not generate or lose any restriction endonuclease recognition sites, we designed a mutagenic primer (F13E11Mut) that serves to generate a new EcoN restriction site in the amplified DNA from affected individuals, when 100 normal alleles were amplified by PCR using the F13E11Mut primer and digested by EcoN, the G to A mutation was not found in any of the normal alleles, and no other mutation was found in the remaining region of the gene encoding the FXIII A subunit. This suggests that Gly461Arg would cause a FXIII A subunit deficiency in Family A. Two patients in Family B were homozygote of the mutation Arg661stop and three other members of this family were heterozygote. This mutation has previously been reported by Mikkola et al. They observed this mutation in six of eight Finnish families and one Swedish family with congenital FXIII deficiency. Since the mutation is due to CpG dinucleotide change to TpG, a hot spot mutation site, the Arg661stop is considered to be a common cause of FXIII A subunit deficiency.