2008 Barcelona - European Society of Human Genetics

Molecular and biochemical basis of disease
cessive primary microcephaly). So far four genes have been identified:
MCPH1, encoding Microcephalin; MCPH3, encoding CDK5RAP2;
MCPH5, encoding ASPM, and MCPH6, encoding CENPJ . MCPH5
and MCPH1 are the most common loci based on MCPH heterogeneity
studies in Pakistani and Indian populations . The objective of this study
was to investigate prevalence of ARMR associated with microcephaly
in Iranian families from northeast & southeast of Iran . A total of 20 consanguineous
families with two or more affected individuals with ARMR
inheritance pattern have been collected after obtaining consent form .
Clinical examination and exclusion of chromosomal abnormalities of
the families were completed and followed by homozygosity mapping
using STRs (Short Tandem Repeats) markers for six mentioned MCPH
loci . Sequencing was performed for the linked families . Nine out of
twenty families were linked to four of these loci as follows: Five were
linked to MCPH5 (25%), and MCPH1, MCPH2 were linked to one family
each (5%), and two were linked to MCPH6 (10%) . We have been
able to identify four novel mutations in four families of the MCPH5 . According
to our findings MCPH5 seems to be the most prevalent loci in
Iranian families with mental retardation and microcephaly . Sequencing
for the other linked families is currently underway .
P05.123
microRNA expression and post-transcriptional target genes
analysis from one pair of monozygotic twins discordant for
trisomy 21: understanding phenotypic variability in Ds patients
C. Borel, S. Deutsch, C. Gehrig, M. Gagnebin, S. E. Antonarakis;
Department of Genetic Medicine and Development, University of Geneva Medical
School, CH, GENEVA, Switzerland.
The understanding of the molecular pathogenesis of trisomy 21 (T21)
is remarkably poor since it is not clear how the extra copy of HSA21
leads to a wide range of phenotypes . We investigated a new class
of functional sequences: microRNAs (miRNAs), that act primarily as
post-transcriptional repressors of target genes through 3’UTR interactions.
We studied microRNA gene variation on primary fibroblasts and
heart tissue from one pair of monozygotic twins discordant for T21 .
Expression was assayed using Taqman qRT-PCR on 365 mature miR-
NAs, 4 of which are encoded by HSA21 . Most of deregulated microR-
NAs are tissue specific. Around 12% (fibroblasts) and 25% (heart) of
microRNAs show a statistically significant difference between the T21
and normal twin, with an average up-regulation of 1 .6fold and downregulation
of 0 .6fold . Expression levels revealed that HSA21-miR-155
and HSA21-miR-99a are up-regulated about 2fold in fibroblasts and
heart tissue, respectively . We have also examined transcripts that are
post-transcriptionally deregulated in T21 and potential target genes
of those deregulated microRNAs . To do so, we separated RNA molecules
of primary fibroblasts from the same pair of twin in a sucrose
gradient according to their association with ribosomes . Pools of fractions
corresponding to the heavy ribosomal fraction (translated RNA)
and total RNA were hybridized to a gene expression microarray . We
identified 45 and 63 transcripts with a post-transcriptional up-regulation
and downregulation in the T21 twin, respectively . To complete this
study, we are currently looking for predicted miRNA target genes and
correlated miRNA expression with the expression of its target genes .
P05.124
Distinctive patterns of miRNA expression in human muscular
disorders
I. Eisenberg1,2 , A. Eran1 , H. G. Lidov1 , P. B. Kang1 , I. S. Kohane1 , L. M. Kunkel1,2
;
1 2 Children’s Hospital Boston, Boston, MA, United States, Howard Hughes Medical
Institute, Boston, MA, United States.
The muscular disorders are a heterogeneous group of inherited diseases
characterized by muscle wasting and progressive weakness,
resulting in significant morbidity and disability. Although considerable
progress has been made in the understanding of these disorders, the
underlying molecular pathways remain poorly understood . In light of
their involvement in modulating cellular phenotypes we hypothesized
that miRNAs might be involved in the regulation of the pathological
pathways leading to muscle dysfunction . We describe a comprehensive
miRNA expression profile aiming to identify new elements involved
in the regulatory networks of muscle and the signature pattern of 185
miRNAs associated with ten common myopathological conditions in
human. While five miRNAs were found to be consistently dysregulated
in all samples analyzed suggesting that these miRNAs are involved in
a common underlying regulatory pathway among all diseases, other
miRNAs were identified to be dysregulated only in one given disease
and not in any of the others thus pointing to their involvement in a
unique regulatory mechanism .
The subsequent identification of potential target genes and the unraveling
of biological signaling pathways involved in this regulatory
level in these disorders, point to an additional dimension of regulation
of muscle function mediated by miRNAs . Together with the tight post
transcriptional regulation at the mRNA level identified in Duchenne and
Miyoshi myopathy and specific mRNA:miRNA predicted interactions,
some of which are directly involved in compensatory secondary response
functions and others in muscle regeneration, these findings
suggest an important role of miRNAs in the pathology of muscular
dystrophy .
P05.125
multiple sclerosis Disease and mitochondria
M. Houshmand;
NIGEB, Tehran, Islamic Republic of Iran.
Multiple Sclerosis (MS) is a multifocal demyelinating central nervous
system disorder . To assess relationship between mtDNA haplogroups
and MS, we have sequenced the mtDNA HVS-I in 54 MS patients and
100 control subjects . In this study, kinetic analysis of mitochondrial
respiratory chain complex I enzyme was performed on intact mitochondria
isolated from fresh skeletal muscle in MS patients (n =10)
and control subjects (n =11) . The frequencies of the Asian (M, BM)
and European (N, J, K) mtDNA haplogroups in five major regions of
Iran was investigated . Unexpectedly, the frequencies of the Asian haplogroups
M and BM were low in Iran (2 .34% for haplogroup M; 17 .6%
for haplogroup BM and 80 .06% for haplogroup N) .
We have found that haplogroups A and K are significantly more abundant
in MS patients (P=0 .042 for haplogroup A and P=0 .0005 for haplogroup
K). Our findings showed that complex I activities were significantly
reduced ( P=0 .007) in patients compared with control . However,
we could not find deletion in mtDNA of patients with MS. Our results
revealed that 15 (75%) out of 20 MS patients had point mutations .
This study suggested that point mutation occurred in mtDNA might be
involved in pathogenesis of MS . Our data suggest that Iranian tribes
probably played a remarkable role in the formation of these ethnic
groups . It gives the indication that the haplogroup J may be older than
6000-10000 years, and probably developed in Iran, and then expanded
to different regions in Europe and Northwest Asia .
P05.126
the coexistence of an East-Asian mitochondrial anthropological
marker and the c8270t, A8332c, and A8347c mtDNA mutations
in a Hungarian family with dystonia and juvenile stroke
syndrome
A. Gal 1 , K. Pentelenyi 1 , V. Remenyi 1 , B. Csanyi 2 , G. Tomory 2 , I. Rasko 2 , M. J.
Molnar 1,3 ;
1 Department of Neurology, Semmelweis University, Center of Molecular Neurology,
Budapest, Hungary, 2 Biological Research Center, Szeged, Hungary, 3 Montreal
Neurological Institute, McGill University, Montreal, QC, Canada.
The high variability of the mitochondrial genome contributes to the
phenotype of the mtDNA-related disorders . MtDNA mutations have
been associated with a variety of clinical manifestations . The 9-bp
deletion between mtDNA 8271-8280 was originally thought to be an
anthropological marker for peoples of East-Asian origin .
The proband was investigated for marked dystonic features . The clinical
symptoms started after a long lasting episode of fever and elevated
serum ammonia and lactate level . His brother had transient hyperkinesis,
right hemiparesis . Their mother had in her childhood a stroke with
aphasia and right hemiparesis . Presently she has moderate truncal
ataxia, hypoacusis and cognitive dysfunction .
The mtDNA analysis of the proband found a 9bp deletion “CCCCCTCA”
in the mtDNA at the position nt8271-8280, and one C8270T substitution
between COII and tRNA Lys genes in the non-coding hypervariable
segment, and two SNPs (A8332G and A8347C) in the tRNA Lys gene .
The C8270T SNP is a pathogenic mutation, the A8332G and A8347C
SNPs are not described in the literature . None of the three SNP was
found in our 100 control cases . The affected Hungarian family belongs
to an ancient B mitochondrial haplogroup .