2008 Barcelona - European Society of Human Genetics

Molecular and biochemical basis of disease
P06.057
clinical and immunohistochemical pre-screening and RNA
sequencing increase mutation detection rate for the collagen Vi
genes
T. P. Cullup 1 , C. Jimenez-Mallebrera 2 , L. Feng 2 , S. Robb 2 , F. Muntoni 2 , S. Yau 1 ,
S. Abbs 1 ;
1 DNA Laboratory, Guy’s & St. Thomas’ NHS Foundation Trust, London, United
Kingdom, 2 Neuromuscular Unit, Hammersmith Hospital, London, United Kingdom.
Ullrich Congenital Muscular Dystrophy (UCMD) and the milder Bethlem
Myopathy (BM) are caused by mutations in COL6A1, COL6A2
and COL6A3 which collectively are comprised of 106 coding exons .
Neither phenotypic nor immunohistochemical analyses are able to pinpoint
which of these genes to target for mutation screening .
We have established a diagnostic mutation screening service for these
three genes based on sequencing cDNA derived from fibroblast cultures
. This requires only 26 overlapping cDNA fragments, compared
with over 100 fragments needed to cover the genes using genomic
sequencing .
Mutations have been detected in 14 out of an initial cohort of 16 patients;
this 87 .5% detection rate compares favourably with the 62%
detection reported in Lampe et al . This higher rate of detection can
be partly attributed to the sequential use of clinical and immunohistochemical
screening prior to molecular analysis and partly to the RNAbased
approach . In particular a change ten bases from the start of
the exon in COL6A2 (c .1117-10A>G) is likely to be responsible for the
splicing out of exon 13 in one patient, and in a second patient an absence
of exon 10 at the cDNA level of the same gene has as yet no
confirmed mechanism at the DNA level.
Surprisingly eight patients with a UCMD phenotype, previously thought
of as a recessively-inherited form, have a single mutation; this reinforces
current thinking that the two disorders represent either end of a
phenotypic spectrum .
Lampe, A . K . et al; J Med Genet 2005;42:108-120
P06.058
A computational test for biological relatedness in genetic
association studies using probabilistically inferred haplotypes
L. Xumerle, G. Malerba, P. F. Pignatti;
Department Maternal Infantile and of Biology-Genetics. Section of Biology and
Genetics, University of Verona, Italy.
An association between gene and disease may be incorrectly estimated
if the allele frequencies differ among cases and controls depending
on inbreeding or unrecognized population stratification.
A program (http://medgen .univr .it/jenoware/) was developed to compute
the probability of genetic relatedness in pairs of individuals using
a likelihood ratio test .
Using loci that are in LD decreases the accuracy of parentage assignments
. Groups of SNPs in linkage disequilibrium (LD) were simulated
to verify the effects of linkage on relatedness assignment . The probability
of genetic relatedness was computed using the single SNPs
and treating the SNPs as composite markers with different r² threshold
values . Haplotypes were probabilistically inferred using the PHASE
and Gerbil programs . False positive rate and power were assessed by
simulation in unrelated individuals and in pedigrees .
As an example of results, in order to estimate the support for II degree
relatedness with power 80%, and false positive rate 5%, the following
was needed: 100 SNPs with no linkage; 275 SNPs having r²=0 .4;
20 probabilistically inferred haplotypes (100 SNPs having r²=0 .4); 40
probabilistically inferred haplotypes (200 SNPs having r²=0 .8) .
In conclusion, if LD blocks are examined, the biological relatedness
can be computed with a limited number of markers increasing test accuracy
with probabilistically inferred haplotypes .
P06.059
A new gene for X-linked congenital Ataxia maps to Xq25-q27.1
G. Zanni 1,2 , E. Bertini 2 , C. Bellcross 3 , B. Nedelec 1 , G. Froyen 4 , G. Neuhäuser 5 ,
J. M.Opitz 6 , J. Chelly 1 ;
1 Université Paris Descartes, Institut Cochin, Departement Génétique et Développement,
Paris, France, 2 Ospedale Pediatrico Bambin Gesù, Unit of Molecular
Medicine, Rome, Italy, 3 Dean Medical Center, Department of Perinatology,
Madison, WI, United States, 4 Human Genome Laboratory, Department of Human
Genetics, Catholic University Leuven, Leuven, Belgium, 5 Department of
Pediatrics, Justus Liebig Universität, Giessen, Germany, 6 Department of Pediatrics,
Medical Genetics, Human Genetics, Pathology, Obstetrics and Gynaecology,
University of Utah, Salt Lake City, UT, United States.
We observed a large American family of Norwegian descent with Xlinked
nonprogressive congenital ataxia (XCA) and normal cognitive
development in six affected males over three generations . Neuroimaging
showed global cerebellar atrophy without evidence of supratentorial
anomalies . Linkage analysis resulted in a maximum LOD score
Z=3.44 for marker DXS1192 at θ =0.0 with flanking markers DXS1047
and DXS1227 defining a region of 12cM in Xq25-q27.1. The clinical
and neuroradiological findings in the present family are very similar to
those described in two other reported X-linked families however, the
newly identified locus does not overlap with the one defined previously
in Xp11 .21-Xq24, indicating that there are at least two genes responsible
for this rare form of X-linked congenital cerebellar ataxia with
normal intelligence .
P06.060
Autosomal dominant left atrial isomerism with suggestive
linkage to chromosome 9q
K. van Engelen, J. B. A. van de Meerakker, J. Lam, R. H. Lekanne dit Deprez,
I. B. Mathijssen, M. J. H. Baars, B. J. M. Mulder, A. F. Moorman, A. V. Postma;
Academic Medical Centre, Amsterdam, The Netherlands.
Background
Left isomerism is a laterality disorder, characterized by bilateral left sidedness
including cardiovascular malformations, bilateral bilobed lungs
and polysplenia . Autosomal dominant laterality disorders are infrequent
and have only been reported in a few families . In this study, we
analyzed a large three generation family with cardiac left isomerism .
Methods and results
We obtained phenotypic information, including physical examination,
electrocardiography, echocardiography and blood samples of 22 family
members . Thirteen individuals had a cardiac anomaly, with considerable
variation between patients . Cardiac anomalies considered to
be part of the left isomerism spectrum were, among others, bilateral
left atrial appendages, septal defects, persistent left superior caval
vein and specific electrocardiographic disturbances compatible with
absence of the sinoatrial node . Other heart defects were present as
well . The condition was inherited in an autosomal dominant pattern .
Subsequent genome wide linkage analysis demonstrated linkage to
a single locus on chromosome 9q shared by all affected individuals,
with a multipoint maximum LOD score of 2 .20 at marker D9S283 . The
shared locus was delineated by markers D9S167 and D9S1677, was
26 Mb in size and contained 218 genes . Sequence analysis of three
candidate genes in this region (Inversin, TGFBR1 and IPPK) revealed
no mutations .
Conclusions
The mapping of a suggestive locus for this autosomal dominant laterality
disorder on chromosome 9q represents an important step toward
the discovery of genes implied in laterality disorders . Further sequencing
and investigation of genomic duplications/deletions of candidate
genes will be the next steps in the identification of the susceptibility
gene .
P06.061
implication of HOXB9 and cOL1A1 genes in congenital hip
dislocation : a case-control association study in Brittany
(Western-France)
K. Rouault 1,2 , V. Scotet 1 , S. Autret 3 , F. Dubrana 4 , B. Fenoll 5 , F. Gaucher 6 , D.
Tanguy 7 , C. Yaacoub 8 , C. Ferec 1,2 ;
1 INSERM U613, BREST, France, 2 Laboratoire de Génétique moléculaire, CHU
Morvan, Brest, France, 3 Université de Bretagne Occidentale, BREST, France,
4 Department of orthopedic surgery, CHU La Cavale Blanche, BREST, France,
5 Department of pediatric surgery, CHU Morvan, BREST, France, 6 Department
of orthopedic surgery, Hotel Dieu, Pont l’abbe, France, 7 Department of physical
medicine, Centre de Perharidy, ROSCOFF, France, 8 Department of orthopedic
surgery, CH Cornouaille, QUIMPER, France.
Congenital dislocation of the hip (CDH) is a complex disease which
presents a mechanical component due to the pregnancy and delivery
conditions and a genetic component linked to the ethnical predispositions
and the familial aggregation . A case-control association study was
set up in the area of Finistère (western Brittany, France) where CDH
is frequent in order to study the implication of two candidate genes,
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