2008 Barcelona - European Society of Human Genetics

Molecular and biochemical basis of disease
for Biomedical Research on Rare Diseases (CIBERER), Madrid, Spain, 3 School
of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United
Kingdom.
The TECTA gene encodes alpha-tectorin (TECTA), a major non-collagenous
component of the tectorial membrane (TM) . In humans,
mutations in TECTA lead to either dominant (DFNA8/A12) or recessive
(DFNB21) forms of non-syndromic hearing loss . All missense
mutations in TECTA that have been reported thus far are associated
with the dominant subtype, whereas those leading to recessive deafness
are all inactivating mutations . Here we characterize a spontaneous
missense mutation (c .1046C>A, p .A349D) arising in the mouse
Tecta gene that is, unlike all previously reported missense mutations
in TECTA, recessive . The morphological phenotype of the Tecta A349D/
A349D mouse resembles, but is not identical to, that previously described
for the Tecta ΔENT/ΔENT mouse . As in the Tecta ΔENT/ΔENT mouse, the TM is
completely detached from the surface of the organ of Corti and spiral
limbus, lacks striated-sheet matrix, and is deficient in both beta-tectorin
(Tectb) and otogelin. A significant amount of Tecta is, however,
detected in the TM of the Tecta A349D/A349D mouse and numerous, electron-dense
matrix granules are seen interspersed amongst the disorganised
collagen fibrils. Mutated Tecta A349D is therefore incorporated
into the TM but presumably unable to interact with either Tectb or
otogelin . The Tecta A349D/A349D mouse therefore reveals that missense
mutations in Tecta can be recessive and lead to TM detachment, and
suggest that should similar mutations arise in the human population,
they would likely cause deafness .
P05.196
molecular genetic analysis of the Wiskott-Aldrich syndrome in
four Russian families
V. V. Zabnenkova, I. G. Sermyagina, A. V. Polyakov;
Research Centre for Medical Genetics, Moscow, Russian Federation.
The Wiskott-Aldrich syndrome is a rare X-linked recessive immunodeficiency
disorder caused by mutations in the WASP gene .
WASP gene located at Xp11 .22-p11 .23, has 12 exons containing 1823
base pairs .
A search for WASP gene mutations was performed by direct DNA sequencing
analysis of all exons and exon-intron junctions .
Four different WASP gene mutations were found in the four unrelated
families with Wiskott-Aldrich syndrome .
In the first case only biological material of an affected proband’s mother
was available for searching for mutations . The frameshift mutation
(p .Phe36fs44) was found in the exon 1 of WASP gene in heterozygosity
. Also, the prenatal diagnosis of Wiskott-Aldrich syndrome was
carried out for this family . In the second case the missense mutation
(p .Asp224Gly) was found in the exon 7 . Proband’s mother was heterozygous
for the mutation . In the third and fourth families the splice site
mutations were found in the intron 8 of WASP gene - IVS 8 + 1nt G →
C and IVS 8 + 1nt G → A, respectively. Probands mothers were heterozygous
for found mutations . Also, in the last case proband’s brother
had the same mutation and maternal aunt and grandmother were non
carriers of this mutation .
One novel mutation p .Asp224Gly was found in this molecular investigation,
the others have been reported . We supposed the mutations
“hot spot” in intron 8 of WASP gene .
P05.197
Hereditary forms of thrombophilia in patients with fetal loss in
the Kazakh population
G. S. Svyatova, G. K. Rapilbekova;
The Scientific Centre of obstetric, gynecology and perinatology, Almaty, Kazakhstan.
The aim of this research is to detect hereditary forms of thrombophilia
in patients with syndrome of loss of fetus in the Kazakh population .
We investigated the genotype frequencies of the C677T mutation of
the MTHFR gene, the G20210A mutation of the prothrombin gene
and the Factor V Leiden mutation in 100 Kazakh patients with a history
of fetal loss and 200 healthy female as controls . The hereditary
thrombophilias were found in 53% of patients . The C677T mutation
was present in 41% of patients, 35% women were heterozygous and
6% patients were homozygous . This mutation was found in isolation
in 28% of patients, and in combination with other mutations in 13% .
The C677T mutation was found in 22% of controls, from them 21%
are heterozygotes and 1,5% were homozygous . The Leiden mutation
was found in 9% of patients and all were heterozygotes . In 4% of patients
the Leiden mutation was the only abnormality . It was present
in combination with other mutations in 5% . In contrast, the factor V
Leiden mutation was found in only 1,3% of controls . The G20210A
mutation of the prothrombin gene was found in 4% of patients, and
all are heterozygotes . The mutatnt was the only abnormility in 2% of
patients and it was present in combination with other mutations in a
further 2% . In controls this mutation was not found . The combination
of two and even of three defects of thrombophilia were found in 18%
of patients whereas in the control group we found only isolated defects
of thrombostasis .
P05.198
screening for the c46t polymorphism in the F gene by
melting point analysis with the Light cycler system: atypical
results, detection of the variant G47A
I. Tirado, I. Coll, E. Martínez-Sánchez, A. Santamaria, J. Soria, J. Fontcuberta;
Hospital Sant Pau Lab. Hematologia Unitat Hemostàsia i Trombosi, Barcelona,
Spain.
The C46T in the F12 gene is a novel genetic risk factors for thromboembolic
disease . Thus we designed a method, based on melting peak
analysis using fluorescence hybridization probes (Real Time PCR-
Lightcylcer, Roche), to genotype the C46T as a routine analysis . We
report the results of one case that showed atypical melting curves in
the LightCycler analysis .
The patient was a 53-year-old man with cerebral ischemia diagnosed
by computed tomography . A genetic analysis showed that he was heterozygote
for the prothrombin G20210A mutation and showed atypical
melting curves when the C46T polymorphism was analyzed . The
family study revealed that his father, his sisters and one son were also
carriers of the G20210A and they showed the same atypical melting
curves for C46T . Subsequent sequencing revealed a G47A heterozygous
variant . This variant was not detected in 250 healthy controls
indicating that this variant is extremely rare .
Although the G47A variant is rare, its position adjacent to the C46T
polymorphism imposes some diagnostic limitations in that C46T might
be undetectable . In addition individuals with C46T exhibit low levels of
FXII because this variant generates an alternative initial methionine
and as consequence a stop codon resulting in the synthesis of a premature
protein . The presence of both, G47A and C46T in such close
positions prevents the generation of an alternative methionine and
consequently cancels the effect of C46T .
This study was supported by the Ministerio Sanidad y Consumo, Instituto
de Salud Carlos III, RECAVA (03/01) and by PETRI (PET-2006-
0361) .
P05.199
A transporter of the thyroid hormone t3 (mct8) is implicated in
X-linked dysmyelination (Pelizaeus-Merzbacher Like Disease /
spastic Paraplegia type 2)
C. Vaurs-Barrière 1,2 , M. Deville 3 , C. Sarret 1,2 , G. Giraud 1,2 , V. Des Portes 4 , O.
Boespflug-Tanguy 1,5 , R. Touraine 3 ;
1 GReD INSERM U931, Clermont-Ferrand, France, 2 Université de Clermont,
UFR Médecine, Génétique Médicale, Clermont-Ferrand, France, 3 Service de
génétique clinique chromosomique et moléculaire, CHU, St Etienne, France,
4 Centre de référence des déficiences intellectuelles de causes rares, Service
de neurologie pédiatrique, Lyon, France, 5 Centre de référence des leucodystrophies,
Service de Génétique Médicale, CHU, Clermont-Ferrand, France.
Among the numerous genes implicated in X-linked mental retardation,
the one coding for the specific thyroid hormone T3 transporter, i.e.
monocarboxylate transporter 8 (MCT8, SLC16A2, MIM 300095), has
been initially implicated in boys presenting a severe delay of psychomotor
development and secondly in a syndromic mental retardation
affection characterized by a progressive spasticity, the Allan-Herndon-
Dudley syndrome (MIM 300523) . In those clinical pictures, abnormal
relative concentrations of thyroid hormones (total T4 decreased, TSH
borderline and total T3 increased) suggest the implication of this gene .
The identification of a MCT8 missense mutation in one of our patients
presenting a diffuse hypomyelination on MRI imaging until the age of
3 years old has inclined us to test the implication of this gene in Xlinked
early dysmyelination suggestive of Pelizaeus-Merzbacher Like
disease or spastic paraplegia type 2 . MCT8 coding sequences have