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© Schattauer 2009
Case Report
Identification of a novel factor X
deletion in combination with a
missense mutation in the F10 gene
Genotype-phenotype correlation in a girl with severe
factor X deficiency
I. Hainmann1; J. Oldenburg2; A. Pavlova2; A. Superti-Furga1; B. Zieger1
1Department
2Institute
of Paediatrics and Adolescent Medicine, University Medical Center Freiburg;
of Experimental Hematology and Transfusion Medicine, University Hospital Bonn
Keywords
Schlüsselwörter
Factor X deficiency, compound heterozygous
mutation, deletion, missense mutation
Faktor-X-Mangel, compound heterozygote
Mutation, Deletion, Missense-Mutation
Summary
Zusammenfassung
The genotype-phenotype relationship of compound heterozygous factor X deficiency in a
young girl with severe factor X deficiency and
bleeding symptoms is characterized. We
identified a novel deletion of exon 6 and a
missense mutation (c.856G>A, Val286Met) in
exon 7 of the F10 gene leading to a compound
heterozygous state and causing severe factor
X deficiency. Therapeutic options for patients
with symptomatic factor X deficiency are
demonstrated.
Dieser Artikel charakterisiert das Verhältnis
von Genotyp zu Phänotyp bei compound
heterozygotem Faktor-X-Mangel anhand des
Falles eines Mädchens mit schwerem symptomatischen Faktor-X-Mangel. Wir konnten
erstmalig eine Deletion von Exon 6 und eine
Missense-Mutation (c.856G>A, Val286Met)
in Exon 7 des F10-Gens als ursächlich für einen schweren Faktor-X-Mangel identifizieren.
Des Weiteren werden therapeutische Optionen für symptomatische Patienten mit schwerem Faktor-X-Mangel dargestellt.
Correspondence to
Dr. Ina Hainmann
Department of Pediatrics and Adolescent Medicine
University Medical Center Freiburg
Mathildenstr. 1, 79106 Freiburg, Germany
Tel. +49/(0)761/270 43 00, Fax +49/(0)761/270 46 16
E-mail: [email protected]
Identifikation einer neuen Deletion in Kombination mit einer Missense-Mutation im F10-Gen –
Genotyp-Phänotyp-Korrelation bei einem
Mädchen mit schwerem Faktor X Mangel
Hämostaseologie 2009; 29: 184–186
Factor X is a vitamin K dependent plasma glycoprotein that plays a central role for both the
intrinsic and the extrinsic part of the coagulation cascade. Factor Xa is composed of a 17
kDa light chain and a 45 kDa heavy chain associated through a disulfide bond (6). The
heavy chain contains the catalytic serine protease domain that is structurally homologous
to that of other serine proteases (3). The
human F10 gene is located on chromosome
13q34. It is composed of eight exons spanning
a region of 25 kb.
Congenital factor X deficiency is one of
the rarest autosomal-recessive bleeding disorders. The incidence of homozygous factor
X deficiency is 1 : 1 000 000 in the general
population. There are only very few reports of
compound heterozygous inheritance of severe factor X deficiency. Factor X levels do not
correlate well with the clinical phenotype and
the severity of the haemorrhagic diathesis.
Sometimes symptoms do not emerge until
adolescence, and heterozygotes are often
asymptomatic.
Modern classification of factor X variants
is based on the molecular level, and multiple
mutations and deletions have been identified
(1). At present, no conclusive data on genotype-phenotype relation are available.
There is no purified factor X concentrate
available, so far, so that therapeutic options
are limited: Application of red blood cells,
fresh frozen plasma (FFP), and intermediatepurity factor IX concentrates (containing factor IX and factor X) has been described.
A girl with FX deficiency
We report on a young girl with severe factor X
deficiency who first presented to our hospital
at the age of 15 months. The blood tests which
had been performed because of a serious otitis
media had shown a severe microcytic anaemia
(haemoglobin 5.1 g/dl) and pathologic values
for the global coagulation tests (PT 9%, INR
9.67, aPTT 125 s). Factor X-activity (FX : C)
was analysed using a one-stage method: Factor X deficient plasma from Technoclone®
with a thromboplastin reagent (Thromborel®
S from Dade Behring). Analysis of the clotting
factors revealed that FX : C was less than 1%
corresponding to severe factor X deficiency.
At that time the patient had experienced
neither any major haematomas nor epistaxis
nor any other bleeding episode. The anaemia
turned out to be in part diet-related.
One year after the first admission she presented with a tooth bleeding after a trauma
when she had fallen on the face. The bleeding
could be stopped initially by intravenous injection of tranexamic acid and subsequent
application of a plasma-derived factorX-containing factor IX preparation. After 25
U/kg body weight of this intermediate-purity
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Hainmann et al.: A novel FX deletion
factor IX concentrate the plasmatic FX : C increased from <1% to 74%, PT from 7% to
86%, and the aPTT shortened from 147 s to
46 s. Four teeth were successfully removed
under this treatment.
Eight months later the girl was admitted
with haemarthros of the left ankle after a
minor trauma (씰Fig. 1). She recovered and
was free of pain after 29 U/kg body weight of
the factor-X-containing factor IX preparation and could be discharged the next day.
Another four months later she presented
with a mucosal bleeding due to a stomatitis
aphtosa. After injection of 40 U/kg body
weight of the intermediate-purity factor IX
concentrate the bleeding from the mucosal
lesions stopped. The child received another
40 U/kg body weight and the lesions healed
very fast.
During the following three years the patient was recurrently readmitted because of
haematomas of the right sole of foot, an assumed joint bleeding of the right knee, a large
haemorrhage at the left calf and several minor
mucosal bleeding episodes. The patient always responded clinically very well to substitution with human intermediate-purity factor IX concentrate (containing also factor X)
without any side effects. She never experienced life-threatening events such as intracranial haemorrhage.
DNA analysis of the F10 gene demonstrated a compound heterozygous state: The
patient was heterozygous for a large deletion
of exon 6 of the F10 gene which has not been
described in the literature or databases, so far.
She was also heterozygous for the missense
mutation c.856G>A, Val286Met in exon 7
that codes for the catalytic region of factor X
(nomenclature according to the Human Genome Variation Society: HGVS at www.
genomic.unimelb.edu.au/mdi/mutnomen/).
The mother turned out to be heterozygous
for the deletion and the father for the above
mentioned missense mutation.
Discussion
We identified a compound heterozygous state
of the F10 gene resulting in severe factor X
deficiency (FX:C <1%) in a young girl with severe bleeding symptoms. The clinical presentation of factor X deficiency is variable and is
mainly characterized by soft tissue and muco-
Fig. 1
Haemarthros of the left ankle
sal bleeding. In older children and teenagers
episodes of epistaxis and menorrhagia have
been described. A haemophilia-like bleeding
pattern with haemarthros and intramuscular
haemorrhage is very rare. Young children with
factor X deficiency are often less symptomatic
and usually do not show severe bleeding episodes. Our young patient showed severe clinical haemorrhagic symptoms which is most
probably caused by the very low FX : C.
Most affected individuals with severe factor X deficiency have low but measurable levels of FX : C (4). Factor X knockout mice die
in utero or shortly after birth suggesting that
complete absence of FX in plasma may be incompatible with life in mice (2). Interestingly,
in this patient FX : C was less than 1%.
Normally, mature FX is activated by the
cleavage of the activation peptide by factor
IXa (in the intrinsic pathway), or by factor
VIIa (in the extrinsic pathway). Factor Xa
then converts prothrombin to thrombin in
the presence of factor Va, Ca+2 and phospholipids. Interestingly, in our patient both
aPTT (the intrinsic) and PT (the extrinsic
pathway of the coagulation cascade) were severely affected.
This is the first characterization of a patient with severe factor X deficiency caused by
a deletion of the whole exon 6 and by a concomitant missense mutation of the F10 gene.
Deletions of single exons causing factor X
deficiency are very uncommon since most of
the reported genetic defects in the F10 gene
are missense mutations. A deletion of exon 6
of the F10 gene has not been described in the
literature, so far. The deletion that was identified in our patient is exceptionally large (at
least 245 bp). Exon 6 codes for the activation
peptide of factor X. Former analyses of mutations within the activation peptide showed
a markedly reduced FX:C. Additionally, defects within the activation peptide seem to
lead to an increased plasma clearance rate of
factor X (6).
The reported clinical phenotypes of patients with alterations in the activation peptide on the molecular level are heterogeneous
and range from mild to severe bleeding diatheses.
The patient’s mother is heterozygous for
this deletion and exhibits a slightly diminished FX : C of 56% without increased bleeding symptoms. The mother has normal values for PT but shows a prolonged aPTT (50 s).
Approximately 75% of patients with factor X deficiency have causative missense mutations (4). The heterozygous missense mutation c.856G>A, Val286Met found in our patient locates to the end of exon 7 in the catalytic domain of factor X. This mutation has
not been published in the international factor
X mutation register, so far. Extensive literature analysis revealed that the mutation
c.856G>A, Val286Met is identical with the
mutation found in the first index patient: Mr.
Stuart (6).
Mutations in the catalytic domain usually
go along with a low FX : C and a severe bleeding tendency in the homozygous state.
This mutation was inherited from the paternal side, and the asymptomatic heterozygous father shows reduced FX : C of 33%,
slightly prolonged aPTT and a borderline PT
of 70%.
The combination of these two genetic defects in our case offers interesting insights
into the genotype-phenotype correlation in
patients with the rare constellation of compound heterozygous factor X deficiency. In a
former study 7% of subjects with causative
mutations in the F10 gene were compound
heterozygous (2). All of them were symptomatic and showed a severe bleeding pattern
that was comparable to homozygous patients. The case highlights that in a patient
with a compound heterozygous state causing
severe factor X deficiency, a severe course of
disease can develop.
© Schattauer 2009
Hämostaseologie 2/2009
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185
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Hainmann et al.: A novel FX deletion
Conclusion
References
Molecular genetic analysis and further genotype-phenotype correlation of patients with
factor X deficiency is needed to comprehend
the bleeding tendency and to specify the optimal treatment. In our case, substitution with
a plasma-derived factor-X-containing factor
IX preparation was an effective therapy
option in the event of a severe bleeding.
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4. Peyvandi F, Menegatti M, Santagostino E et al. Gene
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Hämostaseologie 2/2009
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