2008 Barcelona - European Society of Human Genetics

Molecular and biochemical basis of disease
Conclusion: The B haplogoup and the 9 bp small deletion indicate the
east-Asian origin of this family which could be explained by the Hungarian
history . The 9 bp deletion may serve as a susceptibility factor for
further mtDNA alterations . We assume that the clinical symptoms are
related to the pathogenic C8270T mutation and the coexistences of the
A8347C and A8332G mutations may modify the clinical symptoms .
P05.127
mitochondrial nonsyndromic hearing impairment: the spanish
exception?
D. Feldmann 1 , L. Jonard 1 , A. F. Roux 2 , C. Lemarechal 3 , K. Olszewski 1 , C. Francannet
4 , R. Couderc 1 , F. Denoyelle 1 , S. Marlin 1 ;
1 AP-HP, Paris cedex 12, France, 2 génétique moléculaire IURC, Montpellier,
France, 3 Génétique Inserm U613, Brest, France, 4 génétique médicale, Clermont-Ferrand,
France.
Nonsyndromic sensorineural hearing impairment (NSHI) can be
caused by few mitochondrial mutations . Among these mtDNA mutations,
A1555G mutation in the 12S rRNA gene has been worldly reported
and is associated with NSHI maternally transmitted or with aminoglycoside-induced
NSHI . A high frequency of A1555G was observed
in Spain .
From a large cohort of NSHI patients studied in the National Reference
Center for Genetic Deafness in Paris, France, we selected 156
unrelated patients with NSHI maternally inherited and 124 sporadic
NSHI exposed to aminoglycosides before hearing loss onset . A1555G
was studied by PCR-restriction enzyme analysis and confirmed by sequencing
. Absence of GJB2 mutations and GJB6 deletions was verified.
A1555G mutation was observed in 7 of the 156 NSHI familial cases
(4,5%) and in 0 of the 124 sporadic cases . The 7 families with A1555G
originated respectively from China, Martinique, Arab/Israel, Portugal,
Iran, Madagascar and Spain . Homoplasmic A1555G mutation was detected
in all the descendants of the oldest studied mother . The HI was
present in 51 of the 102 maternal relatives . The calculated penetrance
of A1555G in this study is 50% . The HI was very heterogeneous with
an onset ranging from 0 to 30 years and a severity varying from mild
to profound .
This study shows that the frequency of A1555G in NSHI maternally
inherited is lower in France than in Spain (4,5% versus 61%) and in
sporadic cases (0 versus 3%) . This reported variability could be due to
the different use of aminoglycoside antibiotics in the two countries or
to genetics factors .
P05.128
mitochondrial AtPase 6 gene as a hot spot for
Neurodegenerative disorders?
M. Banoei, M. Houshmand;
National Institute of Genetic Engineering and Biotechnology, Tehran, Islamic
Republic of Iran.
The mitochondrial DNA (mtDNA) may play an essential role in the
pathogenesis of the respiratory chain complex activities in neurodegenerative
disorders such as Huntington’s disease (HD), Spinocerebellar
Ataxias (SCA), and Multiple Sclerosis (MS), Ataxia-Telangiectasia
(AT), Friedreish’s Ataxia (FA) and Duchene Muscular Dystrophy
(DMD) as neuromuscular disease . Dysfunction of the mitochondrial
Respiratory Chain (RC) has been shown in patients with neurological
disorders . the tRNA genes mutations are one of hot spots that cause
mitochondrial disorders .
To determine mtDNA damage, we investigated deletions based in four
areas of mitochondrial DNA, in a group of 120 patients clinically diagnosed
with one of mentioned neurological disorders . We screened
for tRNA Leu , tRNA Lys , COII, ATPase6/8 and NDI genes of mtDNA of
patients with HD, SCA, MS, AT, FA and DMD .
Results showed that ATPase 6 gene is a hot spot region rather than
other regions . Several new nucleotide variations resulting in amino
acid changes were observed in patients that altered protein structure
regarding to essential changes in amino acids .
The secondary mitochondrial respiratory chain defects encountered in
these disorders can also be explained by mitochondrial that degenerate
either as part of a more widespread cellular insult, or as a consequence
of a different specific defect. Most mitochondrial proteins have
to be imported from the cytoplasm and directed to the mitochondria .
So this study suggests that the high rate of mutations in ATPase 6
could be result in interaction of nuclear protein with mtDNA genome .
P05.129
screening for mELAs mutations in italian patients having strokelike
episodes
V. Andreoli 1 , F. Trecroci 1 , A. Nucera 2 , A. La Russa 1 , M. Liguori 1 , I. Manna 1 , P.
Spadafora 1 , M. Caracciolo 1 , G. Di Palma 1 , R. Cittadella 1 ;
1 Institute of Neurological Sciences-National Research Council, Pianolago di
Mangone (CS), Italy, 2 Stroke Unit- Neurology, Santa Maria Nuova Hospital,
Reggio Emilia, Italy.
Mitochondrial encephalomyopathies are a multisystemic group of disorders
that are characterised by a wide range of clinical, biochemical,
and genetic mitochondrial defects . Among this group of disorders, the
Mitochondrial myopathy, Encephalopathy, Lactic Acidosis with Strokelike
episodes (MELAS) syndrome is one of the most frequently occurring
maternally inherited mitochondrial disorders . The age of onset is
highly variable and it is very rare in patients over the age of 40 . Mutations
in tRNA, especially A3243G in the MTTL1 (tRNA Leu ) gene, are
accounted for more than 80% of the cases and other mtDNA mutations
such as T3271C have also been described . We analyzed 55 Italian
patients clinically exhibiting stroke-like episodes, migraine, ataxia and
dementia for the two primary mutations mentioned above in the MT-
TL1 gene. This molecular investigation was carried out using PCR-
RFLP with the restriction endonuclease Apa I and Afl II respectively .
None of the patients or the 25 controls subjects, matched for ethnic
background, gender and age, were found to carry these mutations
(A3243G and T3271C) in homoplasmic/heteroplasmic form . However,
after direct sequencing of the MT-TL1 gene and a part of the MT-ND1
gene, we no detected mt-mutations in the tested patients and controls
and we confirmed that MELAS is an extremely rare disease . Moreover,
we also found a A3480G synonymous variation in the MT-ND1 in a
51- year-old man, whose medical history was significant for ischemic
stroke of undetermined origin and increase in lactate level in blood .
P05.130
two novel mitochondrial DNA mutations in muscle tissue of a
patient with limb-girdle myopathy
S. Seneca 1 , A. Meulemans 2 , B. De Paepe 3 , J. De Bleecker 4 , J. Smet 3 , L. De
Meirleir 5 , W. Lissens 1 , R. Van Coster 3 , I. Liebaers 1 ;
1 Center for Medical Genetics, UZ Brussel, Brussels, Belgium, 2 Department of
Pediatrics, ULB, Brussels, Belgium, 3 Department of Neurology & Pediatric Neurology
and Metabolism, Ghent University Hospital, Gent, Belgium, 4 Department
of Neurology, Ghent University Hospital, Gent, Belgium, 5 Department of Pediatrics
& Center for Medical Genetics, UZ Brussel, Brussels, Belgium.
Patients with an oxidative phosphorylation (OXPHOS) disorder often
present with complex clinical features, including neurological and
muscular dysfunction . Mutations underlying these diseases are located
in the mitochondrial or nuclear genome . Here, we report on a
forty-eight-year-old woman suffering from mild limb girdle myopathy .
The enzymatic activities of the OXPHOS enzymes in skeletal muscle
tissue of the patient were within the control ranges . However, activity
staining following BN-PAGE showed a decreased complex III activity
and the presence of complex V subcomplexes . Immunocytochemistry
demonstrated a mosaic staining pattern in a minority (about 20%) of
the muscle fibers for complex I (subunit 20kd) and complex IV (subunit
I). Molecular analyses identified two novel heteroplasmic mitochondrial
DNA nucleotide aberrations in muscle tissue : an insertion,
m .5888insA in the mt-tRNA Tyr gene and an alteration, m .14639A>G,
changing a leucine into a serine residue in the ND6 gene . Less than
1% of both mutant alterations were present in the patient‘s fibroblasts,
while they were undetectable in her blood and in blood and fibroblasts
from her mother .
Single muscle fiber analyses clearly demonstrated that COX-deficient
fibers, as compared to COX-positive fibers, harbored a significantly
higher level of both mtDNA mutations . These results, together with
previously defined canonical criteria determining the pathogenic character
of mtDNA analyses, suggest that both nucleotide changes are
pathogenic mutations .