2009 Vienna - European Society of Human Genetics

Cancer genetics
and MSH2 germline mutation were included in this study. All coding regions
and intron-exon boundaries of MSH6 gene were completely analysed
using direct sequence analysis. We detected 5 MSH6 mutation
(4 missense and 1 protein-truncating mutations). Although, missense
variants are labeled as doubtfully pathogenic, clinical data display a
great resemblance between missense-variant carriers and truncating
mutation carriers. We conclude that, in all patients suspected to have
HNPCC, MSH6 mutation analysis should be considered.
P06.147
Evaluation of mLH1 and msH2 gene mutations in a subset
of iranian families with hereditary nonpolyposis colorectal
colorectal cancer (HNPcc)
M. Salehi1 , S. Amani2 , S. Javan1 , M. Emami1 , M. Salamat1 , M. R. Noori Daloii3 ;
1 2 Isfahan Univ. of Medical Sciences, Isfahan, Islamic Republic of Iran, Iran Univ.
of Medical Sciences, Tehran, Islamic Republic of Iran, 3Tehran Univ. of Medical
Sciences, Tehran, Islamic Republic of Iran.
Hereditary nonpolyposis colorectal cancer is the most common form
of hereditary colorectal cancers accounting for 5 to 10% of all colon
carcinoma. It is inherited in an autosomal dominant mode and caused
by germline mutations in mismatch repair genes (MMR) chiefly MLH1
and MSH2.
The lifetime risk of colon cancer in affected persons is 80%. Screening,
prevention strategies and consequently treatment options will be
improved by understanding of the genetic basis of this disorder. The
aim of this study was to assess mutations in MLH1 and MSH2 genes
in a subset of Iranian HNPCC patients.
The families that fulfill Amsterdam criteria were selected as HNPCC
families. Genomic DNA was extracted from the peripheral blood of the
samples and germline mutations of MLH1 and MSH2 were detected by
PCR-single strand conformation polymorphism (PCR-SSCP) and DNA
sequencing techniques.
Germline mutations were found in 20 cases. Of these mutations, 14
were found in MLH1 and 6 in MSH2 genes thus MLH1 gene had higher
mutation rate than MSH2. Eighteen out of 20 detected mutations in our
population were previously reported and two were novel.
Our results demonstrated that mutation range as well as genes involved
in HNPCC is different from one region to other and characterizing
mutations could be very helpful in diagnosis of the at risk individuals.
P06.148
screening for germline mutations of mLH1, msH2, msH6 and
Pms2 genes in slovenian colorectal cancer
M. Ravnik-Glavac1 , G. Berginc1 , M. Bracko2 , D. Glavac1 ;
1 2 University of Ljubljana Faculty of Medicine, Ljubljana, Slovenia, Institute of
Oncology, Ljubljana, Slovenia.
Microsatellite instability (MSI) is present in more than 90% of hereditary
non-polyposis colorectal cancer (HNPCC) cases, and is therefore
a feasible marker for the disease. Mutations in MLH1, MSH2, MSH6
and PMS2, which are one of the main causes of deficient mismatch
repair and subsequent MSI, have been linked to the disease.
In order to establish the role of each of the 4 genes in Slovenian
HNPCC patients, we performed MSI analysis on 938 unselected CRC
patients and subsequently searched for the presence of point mutations,
larger genomic rearrangements and MLH1 promoter hypermethylation
in patients with MSI-high tumours.
We detected 68 (7.2%) patients with MSI-H tumours, of which 13 patients
(1.4%) harboured germline defects: 7 in MLH1, 5 in MSH2, 1 in
PMS2 and none in MSH6. Twenty-nine germline sequence variations
of unknown significance and 17 deleterious somatic mutations were
found. MLH1 promoter methylation was detected in 56% of patients
without detected germline defects and in 1 suspected HNPCC.
Due to the specific absence of germline defects in MSH6, we adapted
the HNPCC detection strategy for the Slovenian population of CRC
patients, whereby germline alterations should be first sought in MLH1
and MSH2 followed by a search for larger genomic rearrangements
and PMS2 mutations, and when no germline defects are found, mutation
analysis of the MSH6 gene should be performed. Our study demonstrates
that the incidence of MMR mutations in a population should
be known prior to the application of one of several suggested strategies
for detection of HNPCC.
P06.149
molecular characterization and screening of mismatch repair
genes mutations in 667 spanish patients with a familial form of
nonpolyposis colorectal cancer
E. Sánchez-Tomé 1 , B. Rivera 1 , P. Carbonell 2 , J. Perea 3 , F. Mercadillo 1 , J.
Benitez 1 , M. Urioste 1 ;
1 Centro Nacional de Investigaciones Oncológicas (CNIO), Madrid, Spain, 2 Unidad
de Genética del Hospital La Arrixaca., Murcia, Spain, 3 Servicio de Cirugía
B del Hospital 12 de Octubre, Madrid, Spain.
Introduction: Familial aggregation of colorectal cancer (CRC) is estimated
to be approximately 15-20% of all CRC. The autosomal dominant
Lynch syndrome (LS) is the most common hereditary CRC (2-7%
of all cases). Lynch tumours show microsatellite instability (MSI) due to
aberrant DNA mismatch repair (MMR). The genetic causes are mutations
in MLH1, MSH2, MSH6 and PMS2.
Aims: To characterize the molecular basis of CRC aggregation and determine
the minimal frequency of LS in a series of Spanish families.
Samples and methods: We studied 667 tumour samples belonging to
patients with a suspect of a familial form of CRC and collected clinical
and familial data of the index patients and pathological data of tumours.
MSI and/or immunohistochemical expression of MMR proteins
was assessed. In cases with MSI and/or lack of expression of at least
one MMR protein, we screened MLH1, MSH2 and MSH6 genes in peripheral
blood samples for both point mutations and great rearrangements.
Results: 182 cases (27.3%) showed MSI and/or lack of the expression
of MMR proteins. From these cases we have identified 66 families
(36.2%) with alteration in one MMR gene (Table 1).
MLH1 MSH2 MSH6
Deletereous point mutation 30 19 2
Great rearrangement 1 5
Unknown significant variant 5 3 1
Epimutation
Table 1. Distribution of MMR changes
1
Comments: Beside these cases, we identified 26 additional families that fulfilled the
clinical and molecular criteria of Familial CRC Type X.
Type of mutations and the correlation with clinical and familial data will be presented
in this series of families.
P06.150
Family history compared to age as indicator for msi testing
results in a comparable positive predictive value for Lynch
syndrome
N. Hoogerbrugge, P. Manders, C. Kets, A. van Remortele, K. Landsbergen, R.
Willems, D. Bodmer, K. Hebeda, J. van Krieken, M. J. L. Ligtenberg;
Radboud University Medical Center, Nijmegen, The Netherlands.
Introduction: Most colorectal tumours that are due to Lynch syndrome
show high microsatellite instability (MSI-high). Clinical geneticists use
MSI tests when a family history is suspected for Lynch syndrome. To
increase the detection of Lynch syndrome, also pathologists select patients
with colorectal or endometrial cancer for MSI testing in case they
are diagnosed younger than 50 years or have a second Lynch associated
cancer younger than 70 years (Gut 2005).
Methods: Index patients under suspicion for Lynch syndrome by a clinical
geneticist (n=885) or a pathologist (n=406) were tested for MSI.
When MSI-high, these patients could opt for germline mutation analysis
in MLH1, MSH2, MSH6 and/or PMS2.
Results: Comparison of the group of patients under suspicion for Lynch
syndrome by clinical geneticists or pathologists showed a comparable
mean age at diagnosis of 49 ± 12 versus 48 ± 13 years (p=0.7), the
percentage of MSI tests performed in a colorectal cancer (others mainly
endometrial cancer) was 77% versus 96% (p