2009 Vienna - European Society of Human Genetics

Cancer genetics
germline APC deletions in the French patients affected with classic
FAP, and to characterize the different breakpoints. All samples were
hybridized in a 244k oligonucleotide CGH-arrays. In parallel, we also
used a dedicated high-resolution oligonucleotide CGH array to exactly
size the deletions. We screened 126 patients with polyposis without
any point mutation in the APC gene by using Multiplex Ligation-dependent
Probe, and were able to detect 62 large rearrangements (8% of
all deleterious mutations). No rearrangement was recurrently found.
In the very large deletions with breakpoints outside the APC gene, the
size ranged from 50kb to 17Mb. We found 7 hot regions with more than
2 breakpoints within 30kb. Finally, we characterized a new large rearrangement
with an insertion-deletion. High-resolution oligonucleotide
array-CGH showed clearly its interest in the characterization of large
rearrangements of the APC gene. Screening for APC mutations in FAP
patients should benefit of this technique to identify precisely the origin
and better understand the underlying molecular mechanisms.
P06.160
A remarkable APC mosaicism with two mutant alleles
S. Baert-Desurmont 1 , N. Piton 1 , J. Bou 1 , J. Tinat 1 , R. Guimbaud 2 , J. Selves 3 ,
T. Frebourg 1 ;
1 Inserm U614, Faculty of Medicine University of Rouen, and Department of
Genetics, University Hospital, Institute for Medical Research, Rouen, France,
2 Department of Cancer Genetics, University Hospital and Claudius Regaud
Institute, Toulouse, France, 3 Department of Pathology, University Hospital,
Toulouse, France.
It has recently been estimated that APC mosaicism accounts for 11
% of the sporadic cases of Familial Adenomatous Polyposis (FAP).
We report a remarkable APC mosaicism characterized by the presence
of two mutant alleles. The index case presented a typical form of
FAP diagnosed at age 29. APC sequencing revealed a heterozygous
deleterious mutation within exon 15 (c.2099del, p.Asp700AlafsX18).
This mutation was inherited from his father who presented an attenuated
form of FAP diagnosed at age 54. Analysis of APC in an index
case’s brother detected, unexpectedly, another mutation of unknown
biological significance, affecting the same nucleotide (c.2099A>C,
p.Asp700Ala). Haplotype analysis showed that both mutations were
on the same paternal allele. In the index case’s father, specific analysis
of the c.2099 nucleotide by SNaPshot allowed us to detect the wild
type and both mutant alleles (c.2099del and c.2099A>C) in lymphocytes,
normal colorectal tissue, adenoma, adenocarcinoma, normal
liver tissue and liver metastasis, indicating therefore a remarkable
mosaicism affecting endoderm and mesoderm derivatives. The presence
of these two distinct alterations at the same position might be
explained by two hypotheses: The first one is an early post-zygotic
mutation (c.2099del or c.2099A>C) followed by an incorrect repair
(c.2099A>C or c.2099del, respectively); the second one is a de novo
pre-zygotic deleterious mutational event (c.2099del) in an index case’s
paternal grand-parent, followed by an incorrect post-zygotic reversion
(c.2099A>C) in the index case’s father. Since sequencing and SNaPshot
analyses showed that the c.2099del mutation is the predominant
mutation, this second hypothesis is the preferred one.
P06.161
APc gene mutation status in Polish FAP patients
A. Plawski1 , M. Podralska1 , R. Slomski1 , M. Skrzypczak1 , T. Banasiewicz2 , P.
Krokowicz2 ;
1 2 Institute of Human Genetics, Poznan, Poland, University of Medical Sciences,
Poznan, Poland.
Familial adenomatous polyposis (FAP) is hereditary predisposition to
occurrence numerous of polyps in the colon and rectum. There is a
high heterogeneity with regard to the number and time of the occurrence
of polyps. FAP is associated with mutations in the APC tumour
suppressor gene, which was described in 1991. Since then, many
studies have been done to analyse the distribution of mutations in individual
populations and to determine the function of the gene and a
diagnostic approach to FAP. Here the APC gene was studied with respect
to the occurrence of small mutations and large rearrangements
in 300 unrelated Polish FAP families. Ninety-seven mutations were
identified in 164 families. Out of these mutations, 80 were small mutations,
including 58 small mutations that were first identified in the Polish
population (42 novel and 16 described previously). An increased
frequency of mutation c.3927_3931delAAAGA was observed in 10%
of the Polish group. Seventeen large rearrangements were found in
29 families. Out of those rearrangements, 8 repeat rearrangements
occurred in 20 families. A problem in fast molecular diagnostics of FAP
is a high heterogeneity of mutations in the APC gene. It seems that a
multiplex ligation-dependent probe amplification test and searching for
small mutations by the use of screening methods at the 5’ end of exon
15 and exons 14, 9, 11, 13, 5, and 3, help to improve the molecular
diagnostics of FAP in Polish patients.
The study was supported by the Polish Ministry of Science and Higher
Education project no. N401331936
P06.162
APc gene mutations in iranian patients with familial
adenomatous polyposi (FAP)
P. Rostami, B. Noorinayer, M. Chiani, M. Shahmoradgoli, M. Tashakori, F.
Ghaderi, S. Ebrahimkhani, M. Ghafar zadeh, M. Soltani, M. Zali;
Research Center for Gastroenterology and Liver Disease, shahid beheshti
university, tehran, Islamic Republic of Iran.
Background: Familial adenomatous polyposis (FAP) is an autosomal
dominant syndrome characterized by development of hundreds to
thousands of adenomatous polyps in the colon. In 80-90% of the cases
of classic FAP, mutations in the adenomatous polyposis coli (APC)
gene is the cause underlying the syndrome. The molecular epidemiology
of the APC gene mutations has not been investigated among
the Iranian patients. In this study we will report on the first systematic
investigation of the APC gene mutations.
Methods: Patients with FAP were enrolled into this study through referral
to our genetic counseling clinic. For genetic tests genomic DNA
was extracted from the 10ml of peripheral blood. Specific primers were
used to amplify coding regions of the APC gene. Amplicons was bidirectionally
sequenced.
Results: 25 probands was registered with the mean age of diagnosis
28.91and 64% male and 36% female. 52% had an autosomal dominant
pattern of inheritance and 48% had negative familial history. 3
nonsense, 3 missense and 2 sense mutations were found. The nonsense
mutations were Q264X, Q1303X, S1315X and Q264X. The missense
mutations were V1822D, E1317Q, N944I and sense mutations
were G1678G and T1493T.
Conclusion: APC mutations are found among the FAP families in Iran.
The complete mutational investigation of these families helps in preclinical
diagnosis of unaffected family members and may lead to potential
founder mutations underlying this disease in Iran.
P06.163
Molecular diagnostics in the Czech FAP families
M. Florianová 1 , L. Schwarzová 1 , J. Štekrová 1 , K. Hirschfeldová 1 , Z. Kleibl 2 , V.
Kebrdlová 1 , M. Kohoutová 1 ;
1 Institute of Biology and Medical Genetics of the First Faculty of Medicine and
General Teaching Hospital, Charles University, Prague, Czech Republic, 2 Institute
of Biochemistry and Experimental Oncology, the First Faculty of Medicine,
Charles University, Prague, Czech Republic.
Familial adenomatous polyposis (FAP) is autosomal dominant syndrome
associated with germline APC mutation with almost 100% risk
of colorectal cancer. The typical FAP is characterized by hundreds
to thousands of colorectal adenomatous polyps and by extracolonic
manifestations. An attenuated FAP (AFAP) is characterized by less
than 100 adenomas and later onset of the disease. The mutations in
MUTYH gene leads to MUTYH associated polyposis (MAP). MAP is
autosomal recessive form of polyposis with manifestation similar to
AFAP.
We analyzed the APC gene for germline mutations in 340 FAP/AFAP
patients. Mutation screening was performed using DGGE. DNA fragments
showing an aberrant electrophoretic banding pattern were
sequenced. In addition, all APC-mutation-negative probands were
screened for large deletions of the APC gene using multiplex ligation
dependent probe amplification (MLPA).
We identified 80 germline mutations among 126 unrelated probands
including large deletions. Nine germline APC mutations detected last
year have not been reported yet, which gives evidence of great variability
of mutations.
We examined the whole MUTYH gene in 120 APC-mutation-negative
probands, thereto we screened for mutations in the exon 7 and
13 of MUTYH gene in 72 APC-mutation-negative probands. Mutation
0