2008 Barcelona - European Society of Human Genetics

Cancer genetics
for endometrial carcinogenesis and invasion .
P04.016
Identification of four new patological mutations in HNPCC
patients of the Basque country
C. Martinez-Bouzas1 , E. Beristain1 , N. Puente-Unzueta1 , N. Viguera1 , E. Ojembarrena1
, J. Errasti2 , K. Mugica3 , M. I. Tejada1 ;
1 2 Hospital de Cruces, Barakaldo, Spain, Hospital de Txagorritxu, Vitoria-Gasteiz,
Spain, 3Instituto Oncologicao de Gipuzkoa, San Sebastian, Spain.
Hereditary non-polyposis colorectal cancer (HNPCC) is the most common
form of hereditary colorectal cancer (CRC), accounting for 1%-
5% of cases and is associated with germline mutations in the mismatch
repair genes (MMR) . We have studied families with HNPCC for
three years granted by the Public Health Department of the Basque
Country . The aim of this work is to establish whether the proportion
of mutation in our population is similar to others previously published .
Fifty-five index cases were analysed using heteroduplex, sequencing
and MLPA. Thirty patients fulfilled the Amsterdam criteria and twentyfive
fulfilled the Bethesda criteria. Ninety relatives were also tested.
We found in total twenty-three variatons (41 .8%): eight (14,5%) in
MLH1; nine (16,4%) in MSH2; and six (10,9%) in MSH6 . Of these
variations, eighteen were pathologic mutations, four of them being
novel . Furthermore, other three new variations were found, but without
aminoacid change . The 43 .3% of Amsterdam criteria patients had one
pathological mutation and so had 28% of the Bethesda criteria . Of the
thirty-nine relatives with mutation, six have only developed cancer . The
majority of pathological mutations in Amsterdam criteria were found in
the MLH1 and MSH2 genes . In the MSH6 the pathological mutations
were found in Bethesda criteria patients, that presented many different
types of cancer . In this study we haven’t found any rearrangements in
the MLH1 gene, as were described in other populations . In conclusion,
with this work we are contributing these new mutations to the wide
spectrum that alredy exits .
P04.017
Uncertain pathogenicity of msH2 variants N127s and G322D
challenges their classification
S. Ollila 1 , D. Dermadi Bebek 1 , M. Greenblatt 2 , M. Nyström 1 ;
1 Departmet of Biosciences, Division of Genetics, University of Helsinki, Helsinki,
Finland, 2 Vermont Cancer Center, University of Vermont, Burlington, VT,
United States.
Hereditary non-polyposis colorectal cancer (HNPCC) is associated
with germline mutations in mismatch repair (MMR) genes . Inherited
missense mutations, however, complicate the diagnostics since they
do not always cause unambiguous predisposition to cancer . This leads
to variable and contradictory interpretations of their pathogenicity .
Here, we establish evidence for the functionality of the two frequently
reported variations, MSH2 N127S and G322D, which have been described
both as pathogenic and non-pathogenic in literature and databases
. We report the results of three different functional analyses
characterizing the biochemical properties of these protein variants in
vitro . We applied an immunoprecipitation assay to assess the MSH2-
MSH6 interaction, a bandshift assay to study mismatch recognition
and binding, and a MMR assay for repair efficiency. None of the experiments
provided evidence on reduced functionality of these proteins
as compared to wild-type MSH2 . Our data demonstrate that MSH2
N127S and G322D per se are not sufficient to trigger MMR deficiency.
This together with variable clinical phenotypes in the mutation carriers
suggest no or only low cancer risk in vivo .
P04.018
Familial and clinicopathological differences in Amsterdamfamilies
according to their mismatch repair status
M. Pineda 1 , L. Benito 2 , C. Yagüe 2 , M. Salinas 2 , C. Lázaro 1 , S. González 1 , G.
Capellá 1 , I. Blanco 2 ;
1 Laboratori de Recerca Translacional, Institut Català d’Oncologia, Hospitalet de
Llobregat, Spain, 2 Unitat de Consell Genètic, Institut Català d’Oncologia, Hospitalet
de Llobregat, Spain.
The aim of this study was to establish the familial and clinicopathological
differences within Amsterdam-families according to their mismatch
repair (MMR) status .
Seventy families fulfilling Amsterdam criteria II were included. MMR
status was determined by microsatellite analysis and/or immunohisto-
chemistry of MMR proteins . Families with microsatellite instability and/
or loss of expression of MMR proteins were considered MMR-deficient.
Families were classified in three groups: A: MMR mutation detected
(Lynch syndrome) (n=36); B: MMR-deficient families with no MMR mutation
detected (n=10); and C: MMR-proficient families (n=24).
Proband’s age of diagnosis was younger in Lynch syndrome families
(A, 40 y; B,50; C, 46 y; p=0 .028) . The presence of extracolonic tumors,
the absence of polyps and the number of first-degree relatives with
HNPCC-associated tumors were higher in Lynch syndrome families .
MMR-proficient families showed a predominance of left colon tumors
with no mucinous phenotype and a lower presence of metachronous
tumors .
These results confirm that the presence of a MMR mutation is associated
with an specific phenotype, while MMR-deficient families with no
detected mutation show a mixed phenotype likely reflecting misclassification.
P04.019
Pathogenicity analysis of six unclassified missense variations in
MMR genes identified in a selected population of Castilla-León
(spain)
L. Pérez-Cabornero 1 , E. Velasco 1 , M. Infante 1 , D. Sanz 1 , N. Martinez 1 , L.
Hernández 1 , N. Martínez 1 , E. Lastra 2 , C. Miner 1 , M. Durán 1 ;
1 IBGM, Valladolid, Spain, 2 Hospital General Yagüe, Burgos, Spain.
Lynch syndrome is the most common hereditary syndrome predisposing
to colorectal cancer . Mostly, it is caused by DNA variations in the
DNA mismatch repair (MMR) genes MLH1, MSH2 and MSH6 . Of considerable
relevance in the clinical management of colorectal cancer is
to know if the missense variants referred to as unclassified variants
(UVs) are or not cancer-causing . We report the mutational screening
of 100 index cases from the Counsil Genetics Unit of Castilla-León.
Of the 21 (21%) who carried germline mutation, 11 (52%) were categorized
as pathogenic (frameshift, large rearrangements, splicing
defects) and 10 (48%) as unclassified missense variants. The focus
of this report is the classification of six of these missense variants as
bening or pathogenic: MLH1 c .1852_1853AA>GC p.K618A; MLH1
c .2146G>A p.V716m; MSH6 c .2633 T>C p.V878A; MSH6 c .431 G>T
p.s144i and two novel variations MSH6 c .3425 C>T p.t1142m; MLH1
c .1574 G>A p.s505N. To test this, we have analyzed clinical and genetic
aspects including i) comparison between allelic frequency of the
variant in the cases and 700 unaffected controls from a National DNA
Register ii) a co-segregation study of the mutation with the disease
within pedigree iii) evolutionary conservation of the involved aminoacid
and type of aminoacid change iv) a prediction of the degree of
affectation at the protein function by two bioinformatics programs “Sort
intolerant from tolerant” (siFt; http://blocks .fhcrc .org/sift/SIFT .html)
and Polimorphism Phenotype (PolyPhen; www .bork .embl-heidelberg .
de/PolyPhen) . The combination of all these approaches helps us to
predict whether these contribute to the disease phenotype or merely
represent rare polymorphisms
P04.020
A Database to support the clinical interpretation of Human
mismatch Repair Gene Variants
R. H. Sijmons, R. M. W. Hofstra;
University Medical Center Groningen, Groningen, The Netherlands.
Germline mutations in the mismatch repair (MMR) genes MLH1, MSH2,
MSH6 and PMS2 can cause Lynch syndrome . Truncating MMR gene
mutations generally offer a clear handle for genetic counselling and
allows for pre-symptomatic testing . In contrast, the clinical implications
of most missense mutations and small in-frame deletions detected in
patients suspected of having Lynch syndrome are unclear . We have
constructed an online database dedicated to these unclassified variants
(UVs) of the MMR genes . It can be easily searched for information
on the results of functional assays and other findings, including tumour
characteristics, segregation within families and frequency in controls .
The clinical classification of MMR gene UVs will be a huge challenge.
Recently formed committees within the International Society for Gastrointestinal
Hereditary Tumours (InSiGHT) are working towards collecting
data and developing classification algorithms. Our MMR gene
missense database will be one of the tools to support that process . It
can be searched at www .MMRmissense .org