甲型血友病国际指南2010版

Practice Guidelines for the Molecular Diagnosis of Haemophilia A.

Guidelines prepared by Steve Keeney, Mike Mitchell and Anne Goodeve on behalf of the Clinical Molecular Genetics Society, the UK Haemophilia Centre Doctors’ Organisation (UKHCDO) and the Haemophilia Genetics Laboratory Network following a workshop held on 9th October, 2003.

1.0 GENERAL RECOMMENDATIONS

It is recommended that genetic testing for haemophilia in the UK should preferably be performed in a member laboratory of the UKHCDO Haemophilia Genetics Laboratory Network. This is a consortium of laboratories, mostly within Comprehensive Care Haemophilia Centres, which work to agreed peer-reviewed standards of quality.

2.0 NOMENCLATURE AND GENE ID

Table 1.

Gene Name Factor VIII HUGO nomenclature ( F8) OMIM Number 306700 GeneCards ID F8 Ensembl Gene ID ENSG00000165769 Chromosomal location Xq28 Medline MESH Term Haemophilia A, factor-VIII NCBI LocusLink HsF8 (Locus ID 2157)

3.0 DESCRIPTION OF THE DISEASE

measurement of plasma FVIII:C level. Where there is a prior family history of haemophilia, male cord blood can be tested at birth to determine FVIII:C. Males with moderate to mild haemophilia may not present until adult life. It is recommended that all children with haemophilia are investigated to establish the causative FVIII gene mutation. For detailed discussion of genetic service provision in inherited bleeding disorders, reference should be made to the UKHCDO document "Clinical Genetics Services for Haemophilia" (ISBN 901787 07 9).

Genetic analysis is required to reliably determine female carrier status, as Lyonisation can markedly skew female FVIII:C levels. Female relatives may request carrier analysis when a male relative is first diagnosed as having haemophilia, when they wish to start a family, or frequently, when in early pregnancy.

Genetic counselling should be performed by suitably qualified health professionals with in-depth knowledge of haemophilia. Ideally a professional with experience of managing and treating patients with haemophilia and their families should be involved.

4. 0 THE GENE

Haemophilia A is a X-linked, recessively inherited bleeding disorder which results from deficiency of procoagulant factor VIII (FVIII). Affected males suffer from joint and muscle bleeds and easy bruising, the severity of which is closely correlated with the level of activity of coagulation factor VIII (FVIII:C) in their blood.

Haemophilia severity is defined by FVIII:C level in plasma, where severely affected individuals have <0.01 iu/dl (<1% of normal); moderate 0.01-0.05 iu/dl (1%-5% of normal); and mild >0.05 - <0.40 iu/dl (>5% - <40% of normal) (White et al, 2001). The disease affects approximately 1 in 5,000 males world-wide (reviewed in Forbes, 1997, Bolton-Maggs and Pasi, 2003).

3.0 COMMON REASONS FOR REFERRAL

The factor VIII gene spans 186kb and is comprised of 26 exons, which range from 69bp (exon 5) to 3.1kb (exon 14) in size. The FVIII message is nearly 9kb in size and encodes a mature protein of 2332 amino acids. Mild/moderate haemophilia A and approximately half of all severe haemophilia A results from heterogeneous mutations which occur throughout the FVIII gene. For a review of the molecular aspects of haemophilia A see Bowen (2002).

A regularly updated website http://europium.csc.mrc.ac.uk/WebPages/Main/main.htm is maintained by Dr. Kemball-Cook at the MRC Clinical Sciences Centre, London.

Further tips can be found here

Family history of the disease is an indicator for referral, however, approximately one third of cases have no prior history of haemophilia A (sporadic disease). In severe haemophilia A, diagnosis often follows the observation of unexplained severe bruising or bleeding in young males, who often present when they first become mobile around one year of age. Their haemophilia status can readily be assessed by

5.0 APPROACHES AND PROTOCOLS

5.1 Diagnostic strategy

The severity of haemophilia A in the pedigree should be determined first as this will influence the diagnostic strategy

employed. Severe haemophiliacs should be screened for the intron 22 inversion mutation followed by the intron 1 inversion mutation. This approach should identify the underlying

mutation in 45-50% of severe haemophilia A patients. The remaining severe haemophilia A pedigrees should then be analysed further either by full mutation or linkage analysis. Moderate and mild haemophilia A is not associated with a common mutational mechanism and patients require either full mutation or linkage analysis.

5.1.1 Intron 22 inversion screening

The factor VIII gene intron 22 inversion mutation (Lakich et al, 1993; Naylor et al, 1993) accounts for disease in 20% of all patients and always produces severe disease (causative

mutation in approximately 45% of severe haemophilia A). It results from homologous recombination between copies of a repeated DNA sequence, the intron 22 homologous region (int22h), one copy located in intron 22 of FVIII, the other two copies distal and telomeric to FVIII.

In families with severe haemophilia A, the affected male(s) should first be tested for the presence of the FVIII intron 22 gene inversion. The inversion is detectable by Southern blotting (Lakich et al, 1993) or more recently by Long PCR based protocols (Liu et al, 1999) (sections 5 and 12). The Long PCR method allows results to be obtained within 24 hours and uses a small amount of DNA, an important consideration when performing PND on a limited quantity of chorionic villus biopsy (CVB) material.

The second most common mutation in severe haemophilia A is the intron 1 inversion mutation. This was initially reported to be present in approximately 5% of patients (Bagnall et al, 2002) but in the UK s …… 此处隐藏：37333字，全部文档内容请下载后查看。喜欢就下载吧 ……