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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,

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