2009 Vienna - European Society of Human Genetics

Molecular basis of Mendelian disorders
bands diagnosed with FXIII deficiency. The identification of this founder
mutation and polymorphisms allowed a genetic counselling in relatives
of these families and the antenatal diagnosis is now available.
P12.063
A survey of PORcN mutations in focal dermal hypoplasia -
strategies to survive lethal mutations
F. Oeffner1 , D. Bornholdt1 , R. Happle2 , A. König2 , K. Grzeschik1 ;
1 2 Centre of Human Genetics, Marburg, Germany, Department of Dermatology,
Marburg, Germany.
Focal dermal hypoplasia (FDH, Goltz syndrome, MIM #305600) is a
pleiotropic birth defect characterized by widespread lesions of dermal
hypoplasia or even aplasia. The resulting skin changes follow the lines
of Blaschko, indicating mosaicism. Another major diagnostic sign is
longitudinal striation of the long bones, likewise hinting to functional
mosaicism. Associated variable features include areas of hairlessness,
hypoplasia or aplasia of bones, malformations of the autopod,
and microphthalmia or unilateral anophthalmia. In addition, hypodontia,
hearing loss, horseshoe kidney, and papillomatosis of the larynx
may be found.
Recently, we had shown that the disease is caused by mutations of
PORCN in Xp11.23 (Nature Genetics 2007, 39: 833-835). The attachment
of palmitoleic acid by the O-acyltransferase PORCN prepares
Wnt signaling molecules for the transport through the Golgi apparatus
for secretion, signal gradient formation, and receptor binding.
We have replenished the scope of known mutations considerably by
analyzing PORCN in 24 novel patients:
i) In sporadic cases PORCN is affected primarily by nonsense mutations
whereas large deletions encompassing various neighboring
genes are mostly familial.
ii) The missense mutations known so far almost exclusively exchange
highly conserved amino acids in transmembrane domains or in the
lumenal loops.
iii) To override the consequences of lethal PORCN mutations, male
patients are somatic mosaics or show more than one X-chromosome.
Females, survive either due to extreme skewing of X-chromosome
inactivation, which is particularly evident in familial deletions, or they
appear to be likewise somatic mosaics.
P12.064
Evaluation of the Qiaxcel system for the analysis of products
generated with the Abbott Fragile-X PcR kit
D. Heine-Suñer, J. Martínez-Falcó, M. Rosado, B. Sierra, C. Vidal, J. Rosell;
Hospital Universitari Son Dureta, Palma de Mallorca, Spain.
Fragile X syndrome is the single most common inherited cause of
mental impairment and shows an approximate prevalence 1/4000. The
gene responsible for fragile X syndrome, FMR1, contains an unstable
repeat sequence of (CGG) n that when expanded causes the syndrome.
PCR is a fast and effective method for the diagnosis of (CGG) n
repeat number. However, PCR methods traditionally were only useful
for repeat sizes in the lower premutation ranges (up to 70-100 repeats)
because amplification becomes increasingly difficult as repeat number
increases. Recently, a commercial kit by Abbott has become available
that has overcome such problem, as it amplifies products in all the premutation
ranges (up to 200 repeats) and full mutation ranges (over 250
repeats). The analysis and sizing of the fluorescence labelled products
generated using the Abbott fragile-X kit require a genetic analyser
(sequencer). This equipment is expensive and not all laboratories
have access to one. As an alternative, we have successfully tested the
Qiaxcel system of Qiagen. We have found such a system adequate for
routine screening purposes with the Abbott Fragile-X PCR kit. However,
samples that are in the higher resolution limit (full mutations) or
lower resolution limit (females with 1 repeat differences), need to be
analysed under special conditions. The removal of the gender primers
increases the PCR efficiency for large repeat sizes and may be more
adequate for the detection of full mutations.
P12.065
Friedreich Ataxia and mitochondria
E. Vafaei1 , M. Houshmand2 ;
1 2 Special Medical Center, Tehran, Islamic Republic of Iran, National Institute of
Genetic Engineering and Biotechnology, Tehran, Islamic Republic of Iran.
Friedreich’s Ataxia (FA) is the commonest genetic cause of ataxia and
is associated with the expansion of a GAA repeat in intron 1 of the
frataxin gene. Frataxin deficiency leads to excessive free radical production,
dysfunction of respiratory chain complexes and progressive
iron accumulation in mitochondria.Common deletion were identified
and confirmed by southern blotting in FA patients.Homozygous GAA
expansion was found in 21 (84%) of all cases. In four cases (16%),
no expansion was observed, ruling out the diagnosis of Friedreich’s
ataxia. In cases with GAA expansions, ataxia, scoliosis and pes cavus,
cardiac abnormalities and some neurological findings occurred
more frequently than in our patients without GAA expansion. Molecular
analysis was imperative for diagnosis of Friedreich’s ataxia, not only
for typical cases, but also for atypical ones. mtDNA deletions were
present in 76% of our patients representing mtDNA damage, which
may be due to iron accumulation in mitochondria. Our findings showed
that complex I activities and intracellular ATP were significantly reduced
(P=0.001) in patients compared with control. 8.6 kb deletion in
mtDNA was detected in all of patients by multiplex PCR but Southern
blot analysis confirmed the presence of deletion in 9 of 12 patients.
Decreased Frataxin expression in FA cells result in accumulation of
mitochondrial iron and increased free iron levels leads to free radical
generation, increasing mtDNA mutation and decreasing complex I activity
and intracellular ATP content.
P12.066
Identification of novel mutations of the mitochondrial DNA
associated with iranian Friedreich’s ataxia
M. M. Heidari 1 , M. Houshmand 2 , M. Khatami 1 , S. Nafissi 3 , B. Scheiber-Mojdehkar
4 ;
1 Department of Biology, Science School, Yazd University, Yazd, Iran, Yazd,
Islamic Republic of Iran, 2 Department of Medical Genetic, National Institute for
Genetic Engineering and Biotechnology (NIGEB), Tehran, Iran, Tehran, Islamic
Republic of Iran, 3 Department of Neurology, Medical Science, Tehran University,
Tehran, Iran, Tehran, Islamic Republic of Iran, 4 Department of Medical
Chemistry, Medical University of Vienna, Austria, Vienna, Austria.
Friedreich’s ataxia (FRDA) is an autosomal recessive neurodegenerative
disorder caused by decreased expression of the protein Frataxin.
Frataxin deficiency leads to excessive free radical production. Mitochondrial
DNA (mtDNA) could be considered a candidate modifier factor
for FRDA disease. It prompted us to focus on the mtDNA and monitor
the nucleotide changes of genome which are probably the cause of
respiratory chain defects and reduced ATP generation. We searched
about 46% of the entire mitochondrial genome by Temporal Temperature
Gradient Gel Electrophoresis (TTGE) and DNA fragments showing
abnormal banding patterns were sequenced for identification of the
exact mutations.
In 20 patients, for the first time we detected 26 Mitochondrial DNA
mutations which 11 (42.5%) was novel and 15 (57%) have been reported
in other diseases. Our results showed that NADH dehydrogenase
(ND) genes mutations in FRDA samples was higher than normal
controls (P