Molecular genotyping of the Italian cohort of patients with hemophilia B.
OBJECTIVE
The aim of the study, funded by the Italian Ministry of Health, was to identify the causative mutation in all known patients with hemophilia B in Italy.


METHODS
Overall, 269 patients followed by 25 regional centers were considered in the study; after exclusion of the related individuals, 238 unrelated patients were analyzed (153 with severe, 59 with moderate and 26 with mild hemophilia B). Screening of the factor IX gene was performed using conformation sensitive gel electrophoresis (CSGE) followed by denaturing high performance liquid chromatography (dHPLC) or direct sequencing in negative cases, or by dHPLC/sequencing (36 cases).


RESULTS
A mutation was identified in 236 of the 238 patients: 6 had large gene deletions (4 total and 2 partial), 14 small deletions, 1 combined deletion/insertion and 215 single nucleotide substitutions. A correlation was observed between the type of mutation and severity of hemophilia; however, a number of patients with the same genotype had varying severities of the disease. Eight of the 169 patients with severe hemophilia B (4.7%) developed inhibitors: 2 of these had a complete gene deletion, 1 had a large partial deletion (from exon A to part of exon H) while 5 had 3 different nonsense mutations. One patient with a nonsense mutation developed anaphylaxis. We also studied 65 families with hemophilia B involving 144 females (14 obligatory carriers, 85 carriers and 45 non-carriers) and performed 12 antenatal diagnoses.


CONCLUSIONS
The data have been used to build the Italian mutation database to provide each family with knowledge of the disease-causing defect for genetic counseling. This Italian study confirms the marked heterogeneity of factor IX mutations in the population and the presence of a degree of genotype/phenotype discordance. The identification of the mutation can also be used to predict risk of inhibitor development.
Belvini
Donata
D
Dipartimento di Laboratorio, Servizio Trasfusionale, Centro Regionale per le Malattie del Sangue e Presidio Regionale Malattie Rare per le Coagulopatie Congenite, Castelfranco Veneto Hospital, 31033 Castelfranco Veneto TV, Italy.
Salviato
Roberta
R
Radossi
Paolo
P
Pierobon
Federica
F
Mori
Piergiorgio
P
Castaldo
Giuseppe
G
Tagariello
Giuseppe
G
D001323:Autoantibodies / Q000276:immunology; D002851:Chromatography, High Pressure Liquid; D041321:Chromosomes, Human, X / Q000235:genetics*; D018389:Codon, Nonsense; D015331:Cohort Studies; D004252:DNA Mutational Analysis; D016208:Databases, Factual; D004591:Electrophoresis, Polyacrylamide Gel; D005164:Factor IX / Q000235:genetics* / Q000276:immunology; D005260:Female; D017353:Gene Deletion; D006580:Genetic Carrier Screening; D005820:Genetic Testing; D005838:Genotype; D002836:Hemophilia B / Q000175:diagnosis / Q000196:embryology / Q000453:epidemiology / Q000235:genetics*; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D009154:Mutation; D020125:Mutation, Missense; D010641:Phenotype; D011296:Prenatal Diagnosis; D011401:Promoter Regions, Genetic / Q000235:genetics; D022821:RNA Splice Sites / Q000235:genetics; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion
D001323:Autoantibodies; D018389:Codon, Nonsense; D022821:RNA Splice Sites; D005164:Factor IX