2008 Barcelona - European Society of Human Genetics

Molecular and biochemical basis of disease
Golgi casein kinase occurs .
We demonstrated that dysfunction of (VK-dependent) calcification inhibitors
forms a common pathway in the PXE-like syndrome and PXE .
Our findings suggest that ABCC6 dysfunction does not merely lead to
decreased serum levels of its substrate but causes a chain of intracellular
events involving carboxylation and phosphorylation of calcification
inhibitors .
P05.165
Characterization of a novel mutation in the CTSK Gene in a
family with PYcD
J. Toral-Lopez 1 , L. M. Gonzalez-Huerta 2 , S. A. Cuevas 3 ;
1 Centro Medico ISSEMYM, Ecatepec, Mexico, 2 Hospital General de Mexico,
Mexico D.F., Mexico, 3 Hospital General de Mexico, Fac Medicina, UNAM,
Mexico D.F., Mexico.
Pycnodysostosis is an inborn error of metabolism due to the deficient
activity of cathepsin K, a lysosomal cysteine protease from the papain
family of proteases . The autosomal recessive disorder is consequence
of the diminished capacity of osteoclasts to degrade organic bone matrix
. Pycnodysostosis is clinically characterized by short stature, osteosclerosis,
delayed cranial suture closure, hypoplastic mandibule,
acro-osteolysis, hypoplastic clavicle and dental anomalies . The spine
may be affected with kyphosis, scoliosis or lumbar lordosis . Pathological
fractures, nonunion of fractures and spondylolisthesis are frequent
complications in pycnodysostosis . The gene of the pycnodysostosis
(CTSK) has been mapped on the human chromosome 1q21 . A few
CTSK gene mutations have been identified in several non-related
families with pycnodysostosis . In the present study, we analyzed the
CTSK gene in three members of a family with pycnodysostosis and
identified a novel missense mutation. The parents agreed to participate
. Whole blood was obtained from each patient as well as from the
parents and 100 normal controls . Genomic DNA was extracted from
whole blood samples . All exons of the CTSK gene were amplified and
sequenced from genomic DNA of the patients, parents and controls by
PCR and DNA sequencing analysis . We found a novel mutation in the
carboxyl extreme of the cathepsin K . This mutation, and previous data,
show that affection of carboxyl-terminus of the enzyme is important in
the genesis of pycnodysostosis phenotype .
P05.166
copy Number Variations and Long-Qt syndrome
J. Barc 1 , S. Schmitt 1,2 , F. Briec 1 , M. Le Cunff 1 , C. Vieyres 3 , C. Le Caignec 1,2 , F.
Kyndt 1,2 , H. Le Marec 1,4 , V. Probst 1,4 , J. Schott 1,2 ;
1 INSERM U915, l’institut du thorax, Nantes, France, 2 Laboratoire de génétique
CHU, Nantes, France, 3 Cabinet de cardiologie, Angoulême, France, 4 Clinique
cardiologique CHU, l’institut du thorax, Nantes, France.
Long-QT Syndrome (LQTS) is an inherited cardiac arrhythmia characterized
by a prolonged QT interval on the surface ECG associated with
syncope and sudden death caused by torsades de pointes polymorphic
ventricular tachycardia . It is estimated to affect 1 in 5000 individuals .
LQTS may be caused by mutations in 4 major genes encoding potassium
channel pore forming (KCNQ1, KCNH2) and auxiliary (KCNE1,
KCNE2) subunits and in the gene encoding the cardiac sodium channel
SCN5A. Approximately 25% of patients diagnosed with LQTS have
no mutation in one of five LQTS genes. Genetic testing detection failures
due to large genomic rearrangements are one explanation . The
purpose of this study was to determine the relative copy number in
the 5 major LQTS genes in 100 mutation-negative LQTS probands .
A MLPA approach was used and aberrant exon copy numbers were
confirmed using Agilent 244K CGH array.
This study identified 2 large deletions in KCNH2 gene in 2 probands
with QTc intervals of 478 ms and 554 ms. The first patient carries an
estimated 145 Kb deletion including KCNH2, and ABP1 genes. The
second deletion spanning 650 Kb includes KCNH2 exon 4 to 15, ABP1
and 18 additional genes. Familial investigations identified 3 additional
affected individuals carrying the KCNH2 deletion . Both deletions are
expected to be non functional, decreasing I Kr current in ventricular cardiomyocytes,
suggesting haploinsufficiency as the most likely mechanism
leading to LQTS .
The identification of 2% large deletions in LQTS genes strongly suggests
screening for copy number variants in mutation negative LQTS
probands .
P05.167
mitochondrial DNA mutations and recurrent miscarriage
M. Kaare 1 , V. Ulander 2 , R. Kaaja 2 , K. Aittomäki 1,3 ;
1 Folkhälsan Institute of Genetics, Helsinki, Finland, 2 Department of Obstetrics
and Gynecology, Helsinki University Central Hospital, Helsinki, Finland, 3 Department
of Clinical Genetics, Helsinki University Central Hospital, Helsinki,
Finland.
The mitochondrias are involved in ATP production and apoptosis .
These processes are important in early development and may be disturbed
by mutations in mtDNA, thereby leading to spontaneous miscarriage
. Phenotype causing mutations are usually heteroplasmic and
cause a phenotype when the proportion of mutant mtDNA increases
beyond a threshold . This proportion can shift at cell division/when inherited
and therefore the phenotype often shows remarkable variation
within a family . Accordingly, such a shift can occur from a mother with
mild or no phenotype to an embryo with significant enrichment of mutated
mtDNA causing fetal demise and possibly recurrent miscarriage
(RM) .
To study the role of mtDNA mutations in RM we screened 48 women
with RM for mitochondrial mutations using dHPLC, a sensitive method
which can detect ~5% heteroplasmy . So far, 10 different heteroplasmic
variations have been detected . By screening placental samples available
from 3 women with different variations we have been able to show
that the variations have been inherited by the fetus, and are in some
cases present in a higher proportion of mtDNAs in the fetus compared
to the mother . So far, we have been able to determine the exact sequence
change of three variations . Two changes are previously reported
in the Mitomap database as normal variations . One variation
is not reported in the database and is predicted to be a synonymous
change in the mtND6 gene. Futher studies are ongoing to define the
remaining variations to determine if the variations may be the actual
cause of miscarriages .
P05.168
Validating the role of REt in the cNs: discovery of novel
interactors
D. Fusco1 , M. Vargiolu1 , E. Bonora1 , L. F. Pennisi1 , R. Baumeister2 , G. Romeo1 ;
1 2 U.O. Genetica Medica, Bologna, Italy, Bio3/Bioinformatics and Molecular
Genetics, Albert-Ludwigs University of Freiburg, Freiburg, Germany.
RET encodes a tyrosine kinase receptor mainly expressed in neural
crest derived and urogenital cells . Two major isoforms of RET are produced
by alternative splicing: RET51 and RET9 .
Mutations of RET protooncogene have been associated with both neoplasia
(MEN2A, MEN2B and FMTC) and Hirschsprung disease .
The precise role of RET in the maturation of the periferic nervous system,
in kidney morphogenesis and in spermatogenesis has been estabilished
. RET is responsive to signals induced by neurotrophic factors
of the GDNF-family ligands .
Recent studies have shown that RET binds the neurotrophin NGF .
This suggests a functional role of RET in the Central Nervous System
(CNS) . Nonetheless, no signaling pathway involving RET is known in
the CNS . Hence we developed a strategy aimed at identifying novel interactors
that may help us to reconstruct the pathway connecting RET
and NGF . To accomplish this task, we applied to RET51 the technique
of the yeast two hybrid split ubiquitin system, that allows detection of
interacting molecules belonging to the cytoplasm and the membrane .
A first screening for RET 51 interactors has revealed 10 candidates.
Among these we focused on a neurotrophic factor . Validation of the
interaction was carried out through a co-immunoprecipitation assay in
HEK293 cells . We either ascertained that this interaction occurs via a
specific amino acid residue activated after binding of NGF.
On the basis of these preliminary results, we are currently testing the
hypothesis that RET 51 might have a central role in the growth and the
trophism of CNS cells .
P05.169
A high-resolution RNA expression atlas of Retinitis Pigmentosa
genes in the human and mouse retinas
D. Trifunovic 1 , M. Karali 1 , D. Camposampiero 2 , D. Ponzin 2 , V. Marigo 3 , S.
Banfi 1 ;
1 TIGEM, Naples, Italy, 2 Fondazione Banca degli Occhi del Veneto, Venice, Italy,
3 Department of Biomedical Sciences, University of Modena and Reggio Emilia,