2008 Barcelona - European Society of Human Genetics

Clinical genetics
P01.210
the high frequency of new mutations in dystrophin gene in
the group of Polish patients affected with Duchenne?Becker
muscular dystrophy
J. G. Zimowski, M. Holding, W. Szirkowiec, E. Fidzianska, J. Kubalska, E.
Zdzienicka, J. Zaremba;
Institute of Psychiatry and Neurology, Warsaw, Poland.
The frequency of Duchenne/Becker muscular dystrophy (DMD/BMD)
among the newborn males is 1: 3500 . The constant of DMD/BMD incidence
in male population is the evidence of the stable frequency
of new mutations . Although men affected with DMD/BMD usually are
not abble to reproduce incidence of the disease remains the same . It
is assumed that 1/3 of single DMD/BMD male are the cases of new
mutations .
The study of carriership was carried out in a group of 249 mothers with
one son affected with DMD/BMD in whom deletions in dystrophin gene
were found . The studies of microsatellite sequences in the mothers
revealed the presence of two different alleles in 138 females, therefore
their carriership could be excluded . In 38 cases, in which mothers or
daughters (sisters of affected males) were tested, the presence of the
deletion was observed . The homozygozity was detected among 73 females
. Some of them may be instances of hemizygozity . The exclusion
of carriership in 55% of tested females is statistically different from the
expected incidence of 33% .
Support from State Committee Scientific Research (PBZ-KBN-122/
P05/2004)
P01.211
two novel mutations in a Russian family with X-linked Emery-
Dreifuss muscular dystrophy
A. L. Chuhrova, T. B. Tiburkova, O. A. Schagina, E. L. Dadaly, A. V. Polyakov;
Research centre for medical genetics, Moscow, Russian Federation.
Emery-Dreifuss muscular dystrophy (EDMD) is a neuromuscular
disease characterised by early contractures of Achilles-heel, elbows
and spine, slow progression and symmetric weakness prominent in
humero-peroneal muscle, cardiac conduction abnormality and/or cardiomyopathy
and myopathic features . Two main modes of inheritance
exist: X-linked and autosomal dominant . The frequency of the X-linked
form is at 1:100 000 . EMD gene mutations, which encodes a nuclear
membrane protein named emerin, are causes of the X-linked form of
EDMD . EMD gene has been mapped to the region Xq28 . Mutation
analysis in EMD gene was performed by direct automatic sequence
on Genetic Analyzer 3130 of all exons and exon-intron splices . We
describe two novel mutations in the EMD gene in two Russian families
. Mutations change nucleotide sequence of the sixth exon in the
EMD gene . Family 1 had a c .664C>T (p .Gln222Stop) which causes a
premature stop-codon at position 222 . In second family we found the
mutation c .449+1delG which causes a disappearance donor spicingsite
and subsequent - a premature stop-codone at position 221 .
P01.212
Genotype-phenotype correlates in autosomal recessive
myotonia congenita
I. Torrente 1 , A. Modoni 2 , E. Pisaneschi 1 , A. D’Amico 2 , L. Merlini 3 , G. Silvestri 2 ,
E. M. Valente 1,4 , B. Dallapiccola 1,5 , M. Lo Monaco 2 ;
1 CSS-Mendel Institute, Rome, Italy, 2 Department of Neuroscience, Catholic
University of Rome, Rome, Italy, 3 Department of Experimental and Diagnostic
Medicine, Division of Medical Genetics, University of Ferrara, Ferrara, Italy,
4 Dpt of Medical and Surgical Pediatric Science, University of Messina, Messina,
Italy, 5 Department of Experimental Medicine and Pathology, “La Sapienza”
University of Rome, Rome, Italy.
Myotonia Congenita (MC) is a chloride channel disorder due to mutations
in the CLCN1 gene, inherited in autosomal dominant or recessive
fashion . Beside myotonia of variable severity, transitory weakness
(TW) can be detected, especially in recessive cases . Neurophysiologically,
TW corresponds to a transitory depression (TD) of the compound
muscle action potential during repetitive nerve stimulation (RNS) . We
sought to correlate specific CLCN1 mutations with both TW and RNSinduced
TD in 28 patients with recessive MC, by adopting a low frequency
RNS protocol (3Hz for 500 stimuli) . The 3Hz RNS induced a
significant TD in 19 patients, all of whom experienced variable episodes
of TW. Several mutations appeared to correlate with specific
TD patterns . In particular, the homozygous exon 9 deletion, C481X
and IVS1+3A>T mutations (5 cases), as well as the compound heterozygous
mutations G482R and T550R (1 case), always resulted in
marked TD . Conversely, F167L seems to associate with mild or no TD,
since 8 of 10 patients carrying this mutation (in compound heterozygosity
with other mutations) had clinical absence of TW and a negative
RNS test . Finally, the 3 patients heterozygous for the A531V change
(compound with either R377X or R894X) presented a peculiar pattern
of fluctuating TD. This study shows that the 3Hz RNS protocol, well
tolerated by patients, is able to identify distinct neurophysiological TD
patterns correlating with specific CLCN1 mutations. In turn, this may
help understand the molecular basis underlying the phenotypic variability
of MC, and may represent a step towards rational therapeutic
strategies .
P01.213
DNA-diagnostics of myotonic dystrophy type 1 in Belarus
T. Asadchuk, K. Mosse, N. Rumyantseva;
Scientific-Practical Center “Mother and Child”, Minsk, Belarus.
Myotonic dystrophy type 1 (DM1) is an autosomal dominant, multisystemic
disease, with an estimated incidence of 1 in 8000 . DM is caused
by expansion of CTG trinucleotide repeats located in the 3´ untranslated
region of the myotonin protein kinase (DMPK) gene . The range of
expansion varies widely from 50 to several thousand repeats . First, we
analysed the distribution of CTG-repeats in a cohort of normal individuals
from the Belarusian population, and assessed the heterozygosity
and number of alleles . PCR-products were analysed by the automated
capillary electrophoresis on the ABI Prism 310 . We found 15 different
allelic variants from 5 up to 28 CTG-repeats . The most common alleles
had 5 repeats (38%) . The heterozygosity of the CTG polymorphism of
the Belarusian population was established as 78% . DNA-diagnostics
of DM1 was done in 75 patients from 32 families showing different
symptoms related to the disease . We found small expansions with 70
and 86 CTG repeats in two affected men from two different families .
PCR analysis also shows the high risk of mutation of the DMPK gene
in 10 patients from 3 families, further confirmed by the Southern blot.
So our PCR-based protocol allows amplification of normal-sized alleles
and small expansions . For the large expansion Southern blot
analysis is still the method of choice .
P01.214
molecular studies on two myotonic dystrophies (Dm1 and Dm2)
in Polish patients group
W. Krysa1 , A. Sulek-Piatkowska1 , M. Rajkiewicz1 , E. Szmidt-Salkowska2 , A.
Kamińska2 , J. Zaremba1 ;
1 2 Institute of Psychiatry and Neurology, Warsaw, Poland, Medical University,
Warsaw, Poland.
Myotonic dystrophies type 1 and type 2 (DM1 and DM2) are autosomal
dominant disorders and share similar symptoms comprising myotonia,
muscular dystrophy, and multisystem involvement (cataracts, diabetes
and hypogonadism), but overall clinical picture of these two conditions
is not identical .
Molecular defect causing DM1 and DM2 is known as dynamic mutation
in DMPK and ZNF7 genes respectively . Expansions up to 4000
CTG repeats result in DM1 whereas a CCTG tetramers up to 11000 in
patients with DM2 are observed .
Molecular testing is the only reliable diagnostic definition in DM1 and
DM2 . Prior to its introduction we have performed the analysis of normal
alleles distribution in Polish control group . For DM1 locus the range is
5-31 repeats and for DM2 the range of repeat motif varied from 123
to 159 bp .
For 5 years 372 individuals were tested for DM1 and/or DM2 by routine
PCR, then all homozygous cases were analyzed by TP-PCR . Among
them we have identified 76 pedigrees with 144 DM1 and 34 pedigrees
with 35 DM2 mutation carriers . Within the group of DM1 patients we
identified one family with a case of premutation which resulted in full
mutation in the following generation. Moreover, we identified a patient
with a coexistence of full mutation and premutation in DMPK gene .
Among DM2 group we came across a family with two patients having
extended alleles - 189 bp and 197 bp i .e . clearly above the normal
range but below the considered as pathogenic range in DM2 (normal
range 104-176 bp) .