الفهرس 
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Abstract
Hemophilia A is an X-linked recessive bleeding disorder characterized by qualitative and quantative deficiency of factor VIII resulting from heterogeneous mutations in the factor VIII gene located in the Xq28 region (Bolton-Maggs et al;2003). Factor VIII is a complex plasma glycoprotein of 2351 amino acids that is synthesized primarily by hepatocytes (Mei et al; 2006).The organization of the gene is very complex with large introns (Bowen; 2002). There is a 50% chance that a carrier mother will transmit the defective X-linked gene to the male or female child. All female offspring born to a hemophilic father are obligatory carriers. Sporadic cases result from de novo mutations (Peyvandi et al; 2006). There are two different approaches to the genetic evaluation of hemophilia. First is analysis of single nucleotide polymorphism or microsatellite variable number tandem repeat markers in the FVIII gene to track the defective X-chromosome in the family (linkage analysis).Second is Identification of the mutation in the FVIII gene (direct mutation detection) (Bowen ;2002). Linkage analysis can be reliable in up to 99% when applied to those with more than one affected member (familial hemophilia) but can only exclude the carrier status in a female when applied to a family with no prior history of hemophilia (sporadic hemophilia). The key requirement for linkage analysis is the heterozygosity of the polymorphic marker in the mother of the index case (Peyvandi et al; 2006). This requires a strategy for sequential analysis of different polymorphisms in FVIII gene depending on heterozygosity rates in the population. In view of considerable ethnic and geographical variation in the allele frequencies of these polymorphisms, it is necessary to establish the informativeness of these polymorphisms in different populations (Peyvandi et al; 2006). Linkage analysis is simple, fast and inexpensive to perform; therefore, many families request genetic diagnosis for hemophilia A. The most useful markers are Intron 13 and 22, both consisting of multiple repeats of dinucleotide CA .Dinucleotide CA-repeat markers in Intron 13 and 22 are highly informative. However, the analysis of these markers generally requires radioactive PCR and is relatively difficult. Small tandem repeat markers using fluorescent PCR have been successfully employed for prenatal diagnosis. Fluorescent PCR has improved both PCR accuracy (1–2 base pairs) and sensitivity (Kim et al; 2005). Direct mutation detection is being increasingly used for genetic diagnosis of hemophilia. This approach has a near 100% accuracy and is informative in over 95% of families with hemophilia A. It is equally efficient and sensitive in detecting mutations in both familial and sporadic hemophilia. The strategy employed includes amplification of the FVIII gene (exonic and their flanking intronic regions, 5’UTR and 3’UTR) by polymerase chain reaction (PCR) followed by detection of mutations by various screening methods or/and DNA sequencing (Peyvandi et al; 2006). Amongst the current techniques available, direct sequencing is the most accurate way of prenatally diagnosing hemophilia A. However, in countries with limited resources where direct sequencing is a costly option other alternative methods are used. Linkage analysis using restriction fragment length polymorphism (RFLP) and variable number tandem repeats (VNTR) markers such as CA repeats provides one such alternative method (Ranjan et al ;2007). Direct mutation detection of intron 22, 1 inversion mutation by polymerase chain reaction (PCR) or cordocentesis followed by measurement of FVIII levels in fetal blood are also suitable economical options (Ranjan et al ;2007). For reasons of cost and wide applicability, a simple mutation screening method prior to sequencing provides a powerful and accurate tool for genetic diagnosis. Various mutation screening techniques can be used to screen PCR products of FVIII genes. Abnormal PCR product profiles are sequenced to identify the nucleotide change. Moreover, there are high technologies such as the real time PCR or fluorescence-based capillary electrophoresis (Peyvandi et al; 2006). Finally, genetic diagnosis of hemophilia should be carried out in the context of appropriate cultural and legal requirements. Advances in molecular genetics and sequencing of the human genome led to isolation and characterization of the respective genes. This not only allowed advances in development of recombinant clotting factor concentrates but also facilitated the availability of genetic tests (Ludlam et al;2005).