2009 Vienna - European Society of Human Genetics
2009 Vienna - European Society of Human Genetics
2009 Vienna - European Society of Human Genetics
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Molecular basis <strong>of</strong> Mendelian disorders<br />
can be used as a sensitive and efficient alternative diagnostic method<br />
compared to conventional techniques for measuring fragment lengths<br />
in trinucleotide diseases.<br />
P12.159<br />
characterization <strong>of</strong> two novel mutations in tricho-rhinophalangeal<br />
syndrome<br />
S. Cuevas 1 , A. Flores 2 , R. Ortiz de Luna 3 , M. Rivera-Vega 4 , J. Morales 5 , O.<br />
Mutchinick 5 , L. Gonzalez 4 ;<br />
1 Hospital General de Mexico, Universidad Nacional Autonoma de Mexico,<br />
Mexico d.f., Mexico, 2 Hospital Infantil de Mexico, Mexico d.f., Mexico, 3 Hospital<br />
Infantil de Mexico, Mexico D.F., Mexico, 4 Hospital General de Mexico, Universidad<br />
Nacional Autonoma de Mexico, Mexico D.F., Mexico, 5 Instituto Nacional de<br />
Ciencias Medicas Salvador Zubiran, Mexico D.F., Mexico.<br />
Mutations <strong>of</strong> the TRPS1 gene lead to the tricho-rhinophalangeal syndromes<br />
(TRPS) types I or III. They are characterized by crani<strong>of</strong>acial<br />
and skeletal abnormalities. Cone-shape epiphyses are the characteristic<br />
radiographic findings. The patients have sparse scalp hair, a<br />
bulbous tip <strong>of</strong> the nose, a long flat philtrum, and a thin upper vermillion<br />
border. TRPS III is similar to TRPS I except by the presence <strong>of</strong> severe<br />
brachydactyly due to short metacarpals and severe short stature.<br />
TRPS II or Langer-Giedion syndrome is a microdeletion syndrome<br />
affecting both the TRPS1 and EXT1 genes and differs from TRPS I<br />
and TRPS III by the presence <strong>of</strong> mental retardation and multiple cartilaginous<br />
exostoses. TRPS I is inherited as an autosomal dominant<br />
trait and is due to molecular defects in the TRPS1 gene. In the present<br />
study we describe two novel mutations in 2 families affected with<br />
TRPS I. We screened all exons <strong>of</strong> the TRPS1 from the patients. The<br />
mutation analysis showed missense mutation in exon 3 and nonsense<br />
mutation in exon 4 <strong>of</strong> the TRPS1 gene. The TRPS I phenotypes <strong>of</strong><br />
most patients with a nonsense mutation and with a TRPS1 deletion or<br />
disruption are very similar. All nonsense mutations in a heterozygous<br />
state, reduce the doses <strong>of</strong> TRPS1 protein, supporting that haploinsufficiency<br />
is the cause <strong>of</strong> TRPS. Our data show a higher genotypic spectrum<br />
in the TRPS I and demonstrate that mutations within the initial<br />
region <strong>of</strong> the enzyme and in the GATA region <strong>of</strong> the TRPS1 gene result<br />
in TRPS I syndrome.<br />
P12.160<br />
Large genomic rearrangements in the Usher genes<br />
L. Larrieu 1 , V. Faugère 1 , S. Le Guédard-Méreuze 2 , C. Abadie 1 , B. Gilbert-Dussardier<br />
3 , C. Blanchet 4 , C. Hamel 4 , P. Castorina 5 , G. Lina 6 , M. Claustres 1,2 , A. F.<br />
Roux 1,2 ;<br />
1 CHU de Montpellier, Laboratoire de Génétique Moléculaire, Montpellier, France,<br />
2 Inserm, U827, Montpellier, France, 3 CHU de Poitiers, Service de génétique<br />
médicale, Poitiers, France, 4 CHU de Montpellier, Centre National de Référence<br />
des Affections Sensorielles Génétiques, Montpellier, France, 5 Ospedale Maggiore<br />
Policlinico, Mangiagalli e Regina Elena, Milano, Italy, 6 CHU de Lyon,<br />
service ORL, Lyon, France.<br />
Usher syndrome is an autosomal recessive hearing loss which combines<br />
sensorineural deafness and retinitis pigmentosa. It is both clinically<br />
and genetically heterogeneous. Three clinical subtypes are defined<br />
in respect to the vestibular dysfunction and the degree <strong>of</strong> hearing<br />
loss. Type I (USH1) patients have pr<strong>of</strong>ound hearing loss (HL) and<br />
vestibular dysfunction. Type II (USH2) is the most frequent form and<br />
patients have moderate to severe HL and normal vestibular function.<br />
Type III (USH3) is characterized by progressive HL. So far, 9 genes<br />
are known to be responsible for Usher syndrome (5 for USH1, 3 for<br />
USH2 and 1 for USH3). We have developed an exhaustive molecular<br />
analysis based on sequencing <strong>of</strong> the 9 genes (exons + flanking intronic<br />
regions). More than 180 USH families have been analysed so far. We<br />
identified the pathogenic mutations in most cases; however, 15% <strong>of</strong><br />
our cohort carries either one or no mutation in any <strong>of</strong> the genes. The<br />
absence <strong>of</strong> mutation can sign the presence <strong>of</strong> large rearrangements<br />
that remain undetected by sequencing. Therefore we have developed<br />
a semi-quantitative non-fluorescent multiplex assay to identify large<br />
deletions or duplications. In addition, a MLPA kit has been recently<br />
designed for PCDH15.<br />
We have detected so far 12 large genomic rearrangements in 11<br />
families. The breakpoints could be identified for 6 families. This study<br />
shows that large genomic rearrangements are implicated in at least 6<br />
% <strong>of</strong> the Usher cases and their screening should be included for efficient<br />
molecular diagnosis.<br />
P12.161<br />
Functional analysis <strong>of</strong> splicing mutations in Usher syndrome<br />
genes<br />
T. Jaijo 1,2 , E. Aller 1,2 , I. Hernán 3 , M. J. Gamundi 3 , M. Carballo 3 , J. M. Millán 1,2 ;<br />
1 Hospital Universitario La Fe, Valencia, Spain, 2 CIBER de Enfermedades Raras<br />
CIBERER, Valencia, Spain, 3 Servicio de Laboratorio. Departamento de Genética<br />
y Biología Molecular. Hospital de Terrassa, Terrassa, Spain.<br />
Usher syndrome (USH) is an autosomal recessive disorder characterized<br />
by sensorineural hearing loss, Retinitis Pigmentosa and variable<br />
vestibular areflexia. Clinically three subtypes are distinguished (USH1-<br />
USH3) and to date, nine genes have been associated to the disease.<br />
The most prevalent USH genes are MYO7A for USH1 and USH2A for<br />
USH2, with prevalences that range 29-55% and 75% respectively.<br />
Five sequence variants, suspected to affect the splicing process,<br />
had been identified in our cohort <strong>of</strong> USH patients: c.2283-1G>T and<br />
c.5856G>A in the MYO7A gene, and c.1841-2A>G, c.2167+5G>A and<br />
c.5298+1G>C in the USH2A gene.<br />
In the present study, minigenes based on pCI-Neo Mammalian Expression<br />
vector were used to investigate the implication <strong>of</strong> these variants in<br />
the mRNA processing. Exons and flanquing intronic sequences, both<br />
wild type as mutated, were cloned. After transfection <strong>of</strong> COS-7 cells,<br />
RNA was extracted, retrotranscripted to cDNA and analyzed.<br />
All changes were observed to affect the splicing process, being responsible<br />
for the skipping <strong>of</strong> implicated exons. Furthermore, the mutation<br />
c.2167+5G>A generated too an alternative splicing, where the<br />
final <strong>of</strong> the affected exon is lost.<br />
It is important to analyze the role <strong>of</strong> putative splicing variants in USH<br />
genes in order to determine their pathologic effect. Most USH genes<br />
show an expression pr<strong>of</strong>ile restricted to hardly accessible tissues so,<br />
strategies as minigenes are needed to determine the implication <strong>of</strong><br />
identified variants in the mRNA processing.<br />
P12.162<br />
Unclassified variants in Usher syndrome and related disorders<br />
D. Baux1 , M. Claustres1,2 , A. F. Roux1,2 ;<br />
1CHU Montpellier, Laboratoire de génétique moléculaire, Montpellier, France,<br />
2Inserm, U827, Montpellier, France.<br />
Genes involved in Usher syndrome, the major cause <strong>of</strong> hereditary<br />
deaf-blindness, are particularly prone to alterations <strong>of</strong> unknown clinical<br />
significance (Unclassified Variants, UVs). In the MYO7A and USH2A<br />
genes, such alterations can account for up to 50% <strong>of</strong> the newly identified<br />
variants in molecular diagnosis. The most encountered type <strong>of</strong><br />
UV is missense variants, which can affect the protein structure and<br />
therefore its function. In vitro assessment is there difficult and expensive,<br />
and in silico studies represent an attractive way to classify these<br />
variants. We present here a multiple step analysis which combines<br />
biological observations and in silico studies. Six items are taken into<br />
account (4 <strong>of</strong> which are discussed in Greenblatt et al., 2008), and are<br />
presented below:<br />
Review <strong>of</strong><br />
published<br />
literature<br />
Biological observations In silico studies<br />
Position in cis or<br />
trans <strong>of</strong> a second<br />
alteration<br />
Presence or absence<br />
in relevant<br />
control DNAs<br />
Ortholog<br />
conservation<br />
Conservation in<br />
similar protein<br />
domains<br />
3D analysis<br />
Each item is then rated following precise rules, and the sum allows the classification<br />
<strong>of</strong> missense variants on a four-grade scale, UV1-4, as recommended in the guidelines<br />
published by the Clinical Molecular <strong>Genetics</strong> <strong>Society</strong>, UV1 corresponding to certainly<br />
non-pathogenic variants and UV4, considered as certainly pathogenic variants. This<br />
empirical method has already been applied to 115 missense variants identified in 6<br />
genes responsible for Usher syndrome or related non-syndromic affections, and will<br />
be extended to all identified missense variants in these genes. Moreover, this method<br />
could be applied to variants identified in genes involved in any recessively transmitted<br />
Mendelian disease.<br />
P12.163<br />
Vascular Ehlers-Danlos syndrome in Italy: identification <strong>of</strong> 15<br />
novel and 2 known COL A mutations<br />
B. Drera 1 , N. Zoppi 1 , M. Ritelli 1 , G. Tadini 2 , M. Venturini 3 , A. Wischmeijer 4 , M.<br />
Nicolazzi 5 , A. Musumeci 6 , M. Clementi 7 , P. Calzavara Pinton 3 , M. Valli 8 , S. Barlati<br />
1 , M. Colombi 1 ;<br />
1 University <strong>of</strong> Brescia, Dept. Biomedical Sciences and Biotechnology, Brescia,