A rapid multifluorescent polymerase chain reaction for genetic counselling in Chinese haemophilia A families

Direct and indirect gene diagnosis of hemophilia A pedigrees in the Chinese population

Hemophilia A (HA) is an X‑linked recessive hereditary disorder caused by defects in the coagulation factor VIII (FVIII) gene. In order to diagnose patients with presymptomatic HA and carriers, the present study conducted direct gene diagnosis for the common abnormalities in FVIII and subsequently performed indirect gene diagnosis for the other abnormalities in FVIII for Chinese HA pedigrees. Direct gene diagnosis was performed in 10 HA pedigrees using inverse shifting‑polymerase chain reaction to detect intron 22 inversion (inv22), intron 22 deletion, intron 22 duplication and inv1 of FVIII. Pedigrees with no detected mutations were further analyzed using indirect genetic diagnosis (haplotype linkage analysis), where the genetic markers of FVIII included one variable number of tandem repeat, seven short tandem repeats and three restriction fragment length polymorphisms. The results of three pedigrees were taken as examples. Pedigree 1 underwent direct gene diagnosis, which demonstrated that the proband was inv22 distal pattern hemophiliac and the mother was an inv22 distal pattern carrier. The other two pedigrees were subjected to indirect gene diagnosis. In pedigree 2, the detection of DXS52, 13(CA) n, DXS9901(GT) n, intron (int)18, int19 and int22 confirmed the proband's baby brother was normal, the proband's maternal aunt was a carrier and her baby son was normal. Detection of DXS9901(GT)n, int18, int19 and int22 in pedigree 3 demonstrated that the proband's maternal grandmother was not a carrier. As the maternal grandfather was not affected by the disease, it was deduced that a mutation of FVIII occurred in the proband's mother. The combination of direct and indirect gene diagnoses provides reliable evidence for the use of genetic counseling in HA pedigrees, particularly for screening presymptomatic males and female carriers with normal offspring.

Single-tube tetradecaplex panel of highly polymorphic microsatellite markers < 1 Mb from F8 for simplified preimplantation genetic diagnosis of hemophilia A

Essentials Preimplantation genetic diagnosis (PGD) of severe hemophilia A relies on linkage analysis. Simultaneous multi-marker screening can simplify selection of informative markers in a couple. We developed a single-tube tetradecaplex panel of polymorphic markers for hemophilia A PGD use. Informative markers can be used for linkage analysis alone or combined with mutation detection.

SUMMARY

Background It is currently not possible to perform single-cell preimplantation genetic diagnosis (PGD) to directly detect the common inversion mutations of the factor VIII (F8) gene responsible for severe hemophilia A (HEMA). As such, PGD for such inversion carriers relies on indirect analysis of linked polymorphic markers. Objectives To simplify linkage-based PGD of HEMA, we aimed to develop a panel of highly polymorphic microsatellite markers located near the F8 gene that could be simultaneously genotyped in a multiplex-PCR reaction. Methods We assessed the polymorphism of various microsatellite markers located ≤ 1 Mb from F8 in 177 female subjects. Highly polymorphic markers were selected for co-amplification with the AMELX/Y indel dimorphism in a single-tube reaction. Results Thirteen microsatellite markers located within 0.6 Mb of F8 were successfully co-amplified with AMELX/Y in a single-tube reaction. Observed heterozygosities of component markers ranged from 0.43 to 0.84, and ∼70-80% of individuals were heterozygous for ≥ 5 markers. The tetradecaplex panel successfully identified fully informative markers in a couple interested in PGD for HEMA because of an intragenic F8 point mutation, with haplotype phasing established through a carrier daughter. In-vitro fertilization (IVF)-PGD involved single-tube co-amplification of fully informative markers with AMELX/Y and the mutation-containing F8 amplicon, followed by microsatellite analysis and amplicon mutation-site minisequencing analysis. Conclusions The single-tube multiplex-PCR format of this highly polymorphic microsatellite marker panel simplifies identification and selection of informative markers for linkage-based PGD of HEMA. Informative markers can also be easily co-amplified with mutation-containing F8 amplicons for combined mutation detection and linkage analysis.

Evaluation of factor VIII polymorphic short tandem repeat markers in linkage analysis for carrier diagnosis of hemophilia A

Hemophilia A (HA) is the most common inherited X-linked recessive bleeding disorder caused by heterogeneous mutations in the factor VIII gene (FVIII). Diagnosis of the carrier is critical for preventing the birth of children affected by this coagulation disorder, which ultimately facilitates its management. Due to the heterogeneous nature of mutations, the large inversions and the complexity of the FVIII gene, direct recognition of the disease-associated mutation in HA is complex. Indirect linkage analysis using highly informative heterozygous polymorphic markers is an alternative method for determining the co-segregation of the mutant gene within a family for carrier detection of HA. The aim of the present study was to perform carrier diagnosis in a family with HA. Rapid multifluorescent polymerase chain reaction (PCR) was performed with six extragenic short tandem repeats (STRs), DXS1073, DXS15, DXS8091, DXS1227, DXS991, DXS993 and one intragenic marker, STR22 for linkage analysis in the HA family. All the STR markers employed in the present study were informative for linkages of pathogenic and healthy haplotypes among family members, particularly STR22, DXS1073 and DXS15. The STR marker, STR22, is within the FVIII gene while the DXS1073 and DXS15 markers are very close to the FVIII gene, where the chances of recombination are comparatively low, and provided the most accurate interpretation analysis, indicating that the proband's sister may have been the HA carrier. Rapid multifluorescent PCR using STR markers and linkage analysis was identified to be a simple method for performing HA carrier diagnosis.

Analysis of five polymorphic DNA markers for indirect genetic diagnosis of haemophilia A in the Brazilian population

Hemophilia A is an X-linked, inherited, bleeding disorder caused by the partial or total inactivity of the coagulation factor VIII (FVIII). Due to difficulties in the direct recognition of the disease-associated mutation in the F8 gene, indirect diagnosis using polymorphic markers located inside or close to the gene is used as an alternative for determining the segregation of the mutant gene within families and thus for detecting carrier individuals and/or assisting in prenatal diagnosis. This study characterizes the allelic and haplotype frequencies, genetic diversity, population differentiation and linkage disequilibrium of five microsatellites (F8Int1, F8Int13, F8Int22, F8Int25.3 and IKBKG) in samples of healthy individuals from São Paulo, Rio Grande do Sul and Pernambuco and of patients from São Paulo with haemophilia A to determine the degree of informativeness of these microsatellites for diagnostic purposes. The interpopulational diversity parameters highlight the differences among the analyzed population samples. Regional differences in allelic frequencies must be taken into account when conducting indirect diagnosis of haemophilia A. With the exception of IKBKG, all of the microsatellites presented high heterozygosity levels. Using the markers described, diagnosis was possible in 10 of 11 families. The F8Int22, F8Int1, F8Int13, F8Int25.3 and IKBKG microsatellites were informative in seven, six, five and two of the cases, respectively, demonstrating the effectiveness of using these microsatellites in prenatal diagnosis and in carrier identification in the Brazilian population.

Improved criterion-referenced assessment in indirect tracking of haemophilia A using a 0.23 cM-resolution dense polymorphic marker set

In haemophilia A, linkage analysis with coagulation factor VIII (F8) intragenic and/or neighbouring extragenic short tandem repeats (STRs) enables indirect tracking F8 pathogenic allelic variant-carriers. Even where DNA sequencing is available, linkage analysis still has a role if no causative or candidate mutation is unveiled. The cumulative heterozygosity rate of the available multiplexed STRs haplotyping assays rarely reaches 100%. This means that in a proportion of women these loci are uninformative. The norm-referenced assessment is based on at least one informative marker criterion. We reasoned that by typing a dense market set, spanning a small fraction of recombination, we should be able to improve assessment. The aim of this study was to improve criterion-referenced assessment in polymorphism segregation analyses using a low-recombination fraction and dense informative STRs set. The multiplex quantitative fluorescence PCR assay comprises four novel tetranucleotide and pentanucleotide STRs distant < or = 0.15 cM from the F8 gene, and three F8 intragenic dinucleotide STRs, mapped to a 0.23 cM interval spanning the F8 on human chromosome band Xq28. We determined heterozygosity rates and allele frequencies from 100 unrelated healthy females. To investigate about segregation stability, we typed 50 true trios (mother, daughter and father) and 50 true mother-and-son duos from the general population. The heterozygosity rates for the extragenic markers ranged 0.49-0.76. The 0.23 cM-resolution heptaplex rendered a cumulative heterozygosity of 0.89 for a minimum of two informative markers, with at least one F8 intragenic. The heptaplex assay enabled improving the criterion-referenced assessment in indirect carrier-detection.

Analysis of Factor VIII polymorphic markers as a means for carrier detection in Brazilian families with haemophilia A

Haemophilia A is an X-linked, recessively inherited bleeding disorder of varying severity, which results from the deficiency of procoagulant factor VIII f(8). Linkage diagnosis using polymorphic markers in the f8 gene is widely used to detect carriers. The objective of this study was to verify the informativeness of three polymorphic markers in the Brazilian population, to evaluate the usefulness of such markers in carrier detection procedures. Sixty-three unrelated healthy volunteers and 10 haemophilic families were studied. Two microsatellite repeats and one HindIII RFLP markers were used. Carrier and non-carrier status could be determined in 80% of females investigated. Intron 13 markers presented the highest heterozygosity rate (79%) followed by intron 22 (68%) and intron 19 (57%). When all three markers were used together, linkage analysis informativeness increased significantly. We conclude that these markers are suitable for carrier detection in the Brazilian population and we recommend their use in combination to maximize diagnostic efficiency.