2008 Barcelona - European Society of Human Genetics

Molecular and biochemical basis of disease
One particularly interesting case involves a patient with a clinical diagnosis
of autosomal recessive multi-minicore disease in whom we
found three RYR1 mutations - two missense mutations previously reported
as pathogenic and one previously unreported three base pair
deletion .
In addition to causing congenital myopathy, mutations in certain regions
of the RYR1 gene are also associated with malignant hyperthermia
susceptibility (MHS) and it is important that the implications of this
are clearly explained to other family members .
P05.174
Role of Attct repeat interruptions in spinocerebellar ataxia
type 10
I. Alonso 1 , T. Almeida 1 , L. B. Jardim 2 , O. Artigalas 2 , M. L. Saraiva-Pereira 2 , T.
Matsuura 3 , J. Sequeiros 1,4 , I. Silveira 1 ;
1 UnIGENe - IBMC, Univ. Porto, Porto, Portugal, 2 Hosp. Clinicas de Porto
Alegre, Porto Alegre, Brazil, 3 Center for Neurological Diseases and Cancer,
Nagoya University Graduate School of Medicine, Nagoya, Japan, 4 ICBAS, Univ.
Porto, Porto, Portugal.
Spinocerebellar ataxia type 10 (SCA10) is a dominant neurological
disease, caused by the expansion of an (ATTCT)n in intron 9 of
ATXN10, of still unknown function. SCA10 was first described in Mexican
families with ataxia and seizures . We have previously described
an expansion of the ATTCT repeat in two Brazilian families presenting
ataxia without seizures . We found reduced penetrance alleles of 360-
370 repeats, in elderly asymptomatic subjects .
To investigate a previous hypothesis of interruptions in the (ATTCT)n
tract, functioning as a disease modifier, we assessed the interruption
in another family with ataxia and seizures, and more than 2000 ATTCT
units .
By a modified PCR technique, an abnormal discontinuous ladder, exceeding
the range observed for normal alleles, was detected in this
Brazilian family, presenting progressive cerebellar ataxia with associated
seizures and onset during or after the 3 rd decade . This suggested
the presence of interruptions within the ATTCT expansion. Modified
PCR products of patients showing an interrupted pattern were agarose-gel
purified and cloned with TOPO TA cloning kit for sequencing
analysis and determination of the interrupted motif .
In this family, the ATTCT repeat seems to be interrupted by a large
stretch, unrelated to the repeat sequence, and patients show progressive
cerebellar ataxia with associated seizures . In contrast, the previous
SCA10 families identified by us, showed cerebellar ataxia without
seizures, caused by the expansion of uninterrupted ATTCT tracts . This
newly identified family reinforces the hypothesis that interruptions in
the (ATTCT)n tract function as a disease modifier.
P05.175
Ribosomal frameshifting on expanded ATXN transcripts: a
Drosophila model
C. Gaspar 1 , S. Stochmanski 1 , J. Laganière 1 , M. Therrien 1 , D. Rochefort 1 , D.
Van Meyel 2 , G. A. Rouleau 1 ;
1 Centre of Excellence in Neuromics, Université de Montréal, Montreal, QC,
Canada, 2 Centre for Research in Neuroscience, McGill University, Montreal,
QC, Canada.
Background: Spinocerebellar ataxia type 3 (SCA3) is caused by the
expansion of a coding CAG repeat in the ATXN3 gene . We have previously
shown that the expanded CAG repeat in SCA3 is prone to -1
ribosomal frameshifting, leading to the production and aggregation of
proteins containing polyalanine stretches . These frameshifted molecules
confer increased toxicity to cells when compared to constructs
containing expanded CAA repeats, which code for polyglutamine in the
main frame but lack the ability to frameshift into an alanine frame . Anisomycin
(a ribosome interacting antibiotic that reduces -1 frameshifting)
decreases frameshifting in expanded CAG tracts and ameliorates
the cellular toxic phenotype .
Aims: To model expCAG repeat -1 frameshifting in vivo; to assess the
contribution of -1 frameshifting to expCAG toxicity in the fly.
Methods: Full-length ATXN3 Drosophila transgenic lines carrying either
wtCAG, expCAG or expCAA constructs containing epitope tags in
the three possible reading frames were generated and comparatively
analysed .
Results: We show that: (1) transgenic expression of expCAG ATXN3
constructs is deleterious in the fly; (2) transgenic expression of exp-
CAA ATXN3 constructs, despite adequate levels of protein expression,
is not toxic; (3) -1 frameshifting occurs in Drosophila and is restricted to
the expanded CAG transgenic lines .
Conclusions: We propose that -1 ribosomal frameshifting is a major
contributor to the toxicity observed in expanded CAG repeat diseases .
This novel pathological mechanism may open new therapeutic opportunities
for these diseases .
P05.176
mutation analysis of the scN1A gene and genotype-phenotype
correlations in Bulgarian epilepsy patients
I. Yordanova 1,2 , L. Claes 3 , I. Ivanov 4 , A. Suls 3 , I. Litvinenko 5 , P. Dimova 6 , D.
Hristova 5 , V. Bozinova 6 , I. Kremensky 1,2 , P. De Jonghe 3 , A. Jordanova 2,3 ;
1 National Genetics Laboratory, Sofia, Bulgaria, 2 Molecular Medicine Center,
Medical University, Sofia, Bulgaria, 3 VIB Department of Molecular Genetics,
University of Antwerp, Antwerpen, Belgium, 4 Department of Pediatrics, Medical
University, Plovdiv, Bulgaria, 5 Department of Pediatrics, Medical University,
Sofia, Bulgaria, 6 Department of Neurology, Medical University, Sofia, Bulgaria.
Epilepsy is a common neurological disease, affecting more than 1%
of people from any age, gender and ethnical origin . Mutations in the
alpha1-subunit (α1) of the neuronal voltage gated sodium channel
Na v 1 .1, are associated with generalized epilepsy with febrile seizures
plus (GEFS+) and severe myoclonic epilepsy in infancy (SMEI) . It is
encoded by 26 exons of the SCN1A gene on chromosome 2q24 .
We performed a mutation analysis of SCN1A in 28 patients with
GEFS+, 20 with SMEI and 62 with other types of infantile epilepsy .
Genomic DNA was extracted from peripheral blood lymphocytes using
a standard sodium chloride precipitation method . The SCN1A point
mutation screening included PCR analysis followed by direct sequencing
of all exons and exon-intron boundaries of the gene . In addition, all
patients were analyzed for exonic deletions and duplications by MAQ
assay .
We identified 11 disease-causing mutations, including 6 missense,
2 nonsense, 1 splice-site mutation and 2 single base deletions . Two
missense and all truncating mutations were found in SMEI patients,
consistent with the severity of the epilepsy phenotype . Four GEFS+
patients carried a missense mutation. All mutations we identified had
not been reported in the literature. This is the first large scale study of
SCN1A gene analysis in Bulgarian epilepsy patients .
In our sample, a mutation was identified in 23% of patients with GEFS+
or SMEI, and none in the other epilepsy patients . This nicely illustrates
that GEFS+ and SMEI are part of a continuous spectrum of fever associated
epilepsy phenotypes caused by mutations in SCN1A .
P05.177
KPQ del in SCN5a gene in two different types of SCD in one
family
S. Saber 1 , K. Banihashemi 1 , M. Eftekharzadeh 2 , M. KhosroHeidari1 1 , m. a.
SadrAmeli 3 , A. F. Fazelifar 3 , M. Haghjoo 3 , m. Houshmand 4 , E. V. Zaklyazminskaya
5 ;
1 Special medical center genetic lab ward , Russian Academy of Science DNA
lab, Tehran, Islamic Republic of Iran, 2 Tehran clinic arrhythmia center, Tehran,
Islamic Republic of Iran, 3 Heart center shahid Rajaee hospital electrophysiology
ward, Tehran, Islamic Republic of Iran, 4 Special medical center genetic lab
ward, Tehran, Islamic Republic of Iran, 5 Russian Academy of Science DNA lab,
Moscow, Russian Federation.
Cardiac action potentials are generated and propagated through the
coordinated activity of multiple ion channels, including voltage-gated
sodium channels, calcium channels and potassium channels . Mutations
in genes encoding these channels cause familial arrhythmias .
Heart rhythm disturbances constituent some inherited syndromes any
kind of genetic nature
Many kinds of arrhythmia caused SCD (sudden cardiac death) and
the prevalence of SCD is 1: 1000 individuals . Some of SCDs were
caused by Na channelopathy such as LQT3 and Brugada Syn these
are two of main caused of sudden cardiac death in young people with
out any detectable cardiac abnormality with routine tests and we know
that Brugada syndrome was caused by loss of function of Na channel
and LQT3 was caused by gain of function Na channel in heart . . We
can check SCN5a gene for ruling out of this gene as a main gene
of Na channelopathy in heart arrhythmias . We check by SSCP and
Sequencing this gene . We checked SCN5A in a family with 11 affected
person that approved by ECG and EPS study and some persons