Molecular pathology of haemophilia A in Turkish patients: identification of 36 independent mutations

Haemophilia A is an X-linked recessive bleeding disorder caused by heterogeneous mutations in the factor VIII gene. In an attempt to reveal the molecular pathology of Turkish haemophilia A patients, the coding sequence of the gene, excluding a large portion of exon 14, was amplified from genomic DNA and subjected to denaturing gradient gel electrophoresis prior to DNA sequencing. Fifty-nine haemophilia A patients were included in the study with severe, moderate and mild phenotypes observed in 24, 15 and 16 patients, respectively. Factor VIII activity and clinical phenotypes were not available for four patients. A total of 36 independent mutations were found, with a mutation detection efficacy of 61%. The mutations that were reported for the first time include 20 point mutations, one 8-bp insertion (TCAAGATA) in exon 4 and one large deletion greater than 2.8 kb involving exon 14. The novel point mutations were composed of three nonsense (Ser681Ter, Cys2021Ter and Gln2113Ter), one splicing error (IVS-1G-->A), 15 missense mutations (Lys48Asn; Leu-98Phe; Thr118Ala; Cys248Tyr; Glu456Lys; Asp560Ala; Tyr664Cys; Phe679Leu; Gly691Trp; Asp1769His; Val1857Leu; Gly2026Gln; Arg2163Pro; Asp2288Ala; and Arg2304Leu) and a T deletion in exon 25 that caused a frameshift followed by a stop codon. All missense mutations except Val1857Leu, which maintained a conserved nonpolar R group, occurred at amino acids conserved among four species and were most probably pathogenic. In addition, two sequence changes (IVS3-9C-->T) and (Leu2230Leu) were also detected in patients carrying Val1857Leu and Phe679Leu missense mutations, respectively. Identification of mutation origins in eight sporadic cases revealed an equal sex ratio of mutations.

Intron 22 inversions in the Turkish haemophilia A patients: prevalence and haplotype analysis

In about half of the severe haemophilia A cases, the disease is caused by an inversion that split the F.VIII gene into two parts separated by approximately 300-400 kb. Herein, we show that in the Turkish population this inversion mutation accounts for 29% of 141 haemophilia A cases and 42% of severe cases. Most of the inversions are of the distal type (72%) whereas nine were of the proximal type (28%). Haplotype analysis using 4 markers in the F.VIII gene did not reveal a single haplotype associated with the inversion. However, the pre- valence of one haplotype: HindIII (-) - Int13 (CA)20 - Int22 (CA + CT)26 - XbaI (-) is higher in the inversion patients. Since founder effect is excluded for the inversion patients, our results suggest that some as yet unknown factor(s) may make these alleles more prone for the inversion. However, a bias due to the low number of studied cases cannot be excluded.

Methylation levels at selected CpG sites in the factor VIII and FGFR3 genes, in mature female and male germ cells: implications for male-driven evolution

Transitional mutations at CpG dinucleotides account for approximately a third of all point mutations. These mutations probably arise through spontaneous deamination of 5-methylcytosine. Studies of CpG mutation rates in disease-linked genes, such as factor VIII and FGFR3, have indicated that they more frequently originate in male than in female germ cells. It has been speculated that these sex-biased mutation rates might be a consequence of sex-specific methylation differences between the female and the male germ lines. Using the bisulfite-based genomic-sequencing method, we investigated the methylation status of the human factor VIII and FGFR3 genes in mature male and female germ cells. With the exception of a single CpG, both genes were found to be equally and highly methylated in oocytes and spermatocytes. Whereas these observations strongly support the notion that DNA methylation is the major determining factor for recurrent CpG germ-line mutations in patients with hemophilia and achondroplasia, the higher mutation rate in the male germ line is apparently not a simple reflection of sex-specific methylation differences.

Application of HUMF13A01 (AAAG)n STR polymorphism to the genetic diagnosis of coagulation factor XIII deficiency

Deficiency of the A subunit of coagulation factor XIII causes a severe bleeding disorder requiring life long replacement therapy. The mutations causing A subunit deficiency appear to be very heterogeneous, and it is impractical to identify each mutation before genetic counselling or prenatal diagnosis can be attempted. In this study we have shown that a highly polymorphic short tandem repeat element, HUMF13A01 (AAAG)n that occurs in the 5' flanking sequence of the factor XIII A subunit gene, can be used to follow the segregation of deficiency causing mutations. We studied 6 families with factor XIII A subunit deficiency from 5 different ethnic groups. All parents were heterozygous for the repetitive element and therefore all the families were informative. The linked polymorphism was used to carry out the first prenatal diagnosis of factor XIII A subunit deficiency. The analysis of this polymorphism by the polymerase chain reaction is rapid, reliable, requires little DNA and is ideal for the genetic analysis of factor XIII A subunit deficiency.

New mutations causing the premature termination of translation in the A subunit gene of coagulation factor XIII

The amplification of factor XIII A subunit gene exons and heteroduplex analysis has been used to identify two new mutations that cause severe factor XIII deficiency. One mutation in a family of French origin results from a 4 bp deletion and leads to a premature termination of translation. The other mutation occurred in a Turkish family and results from a C-->T transition that inserts a premature translation stop signal at codon 400. Both mutations alter restriction enzyme sites and can be readily detected in amplified exon DNA for genetic counselling or prenatal diagnosis. The new mutations reflect the extensive molecular heterogeneity of factor XIII deficiency.

In vitro synthesis, release and uptake of storage proteins by the fat body of Manduca sexta: putative hormonal control

1. Two major proteins (P1 and P2) are synthesized by the fifth instar larval fat body of Manduca sexta and then released into the hemolymph. 2. These proteins are later sequestered by the pre-pupal fat body. 20-Hydroxyecdysone does not appear to affect the synthesis of either protein. 3. When day 2 fifth instar larvae are neck-ligated there is an excessive synthesis (supersynthesis) of P2 (arylphorin). 4. Juvenile hormone I (JH I) applications to ligated animals had no effect, but brain homogenate injections resulted in the inhibition of P2 synthesis. 5. Neck ligations of larvae between days 5 and 6 revealed a head critical period between day 5 + 12 hr and day 5 + 18 hr, after which the head is unnecessary for the sequestration of either protein by the fat body. 6. JH I and JH III applications to ligated larvae before the head critical period do not restore the ability of the fat body to sequester the storage proteins. 7. P1 and P2 appear to be synthesized differentially and P2 is sequestered by the fat body to a much lesser extent than P1. 8. P2 is the hemolymph storage protein of both larval and pupal stages, whereas P1 appears to be the storage protein of the pupal fat body. 9. The data indicate that the synthesis of arylphorin and the resorption of both proteins are controlled by a putative head factor(s).