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Clinical characterization and the mutation spectrum in Swedish adenomatous polyposis families.

Kanter-Smoler G, Fritzell K, Rohlin A, Engwall Y, Hallberg B, Bergman A, Meuller J, Grönberg H, Karlsson P, Björk J, Nordling M - BMC Med (2008)

Bottom Line: Probands with a genotype (codon 1250-1464) predicting a severe phenotype had a median age at diagnosis of 21.8 (range, 11-49) years compared with 34.4 (range, 14-57) years among those with mutations outside this region (P < 0.017).Using a variety of mutation-detection techniques, we have achieved a 100% detection frequency in classical FAP.Probands with APC mutations outside codon 1250-1464, although exhibiting a less-severe phenotype, are at high risk of having a colorectal cancer at diagnosis indicating that age at diagnosis is as important as the severity of the disease for colorectal cancer morbidity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular and Clinical Genetics, Institute of Biomedicine, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden. gunilla.kantersmoler@astrazeneca.com

ABSTRACT

Background: The dominantly inherited condition familial adenomatous polyposis (FAP) is caused by germline mutations in the APC gene. Finding the causative mutations has great implications for the families. Correlating the genotypes to the phenotypes could help to improve the diagnosis and follow-up of patients.

Methods: Mutation screening of APC and the clinical characterization of 96 unrelated FAP patients from the Swedish Polyposis Registry was performed. In addition to generally used mutation screening methods, analyses of splicing-affecting mutations and investigations of the presence of low-frequency mutation alleles, indicating mosaics, have been performed, as well as quantitative real-time polymerase chain reaction to detect lowered expression of APC.

Results: Sixty-one different APC mutations in 81 of the 96 families were identified and 27 of those are novel. We have previously shown that 6 of the 96 patients carried biallelic MUTYH mutations. The 9 mutation-negative cases all display an attenuated or atypical phenotype. Probands with a genotype (codon 1250-1464) predicting a severe phenotype had a median age at diagnosis of 21.8 (range, 11-49) years compared with 34.4 (range, 14-57) years among those with mutations outside this region (P < 0.017). Dense polyposis (> 1000) occurred in 75% of the probands with a severe phenotype compared with 30% in those with mutations outside this region. The morbidity in colorectal cancer among probands was 25% at a mean age of 37.5 years and 29% at a mean age of 46.6 years.

Conclusion: Using a variety of mutation-detection techniques, we have achieved a 100% detection frequency in classical FAP. Probands with APC mutations outside codon 1250-1464, although exhibiting a less-severe phenotype, are at high risk of having a colorectal cancer at diagnosis indicating that age at diagnosis is as important as the severity of the disease for colorectal cancer morbidity.

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Detection of the mosaic c.2700_2701delTC mutation in patient C107. Nucleotide 2700 is indicated with an arrow. (A) The aberrant bands indicated by the bracket were excised from the SSCP/HD gel. The resulting DNA sequence is shown to the right. (B) DNA sequence from DNA extracted from tumor-derived cells from the patient. (C) The DNA sequence from DNA isolated from the patient's blood lymphocytes.
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Figure 2: Detection of the mosaic c.2700_2701delTC mutation in patient C107. Nucleotide 2700 is indicated with an arrow. (A) The aberrant bands indicated by the bracket were excised from the SSCP/HD gel. The resulting DNA sequence is shown to the right. (B) DNA sequence from DNA extracted from tumor-derived cells from the patient. (C) The DNA sequence from DNA isolated from the patient's blood lymphocytes.

Mentions: Three patients (C107, C257, and C505), negative for mutations in APC, were reported as de novo cases with no known family history of FAP. These patients where all screened for APC mutations present as low-frequency alleles using SSCP/HD. We did not detect any signs of low-frequency mutations in patients C257 and C505. However, in patient C107, aberrant bands, possibly originating from formation of heteroduplexes, was detected by SSCP/HD in a very low fraction of her blood lymphocytes. The c.2700_2701delTC mutation, which results in frame shift at codon 900, was found by sequencing of the aberrant bands excised from the SSCP/HD gel (Figure 2A). The mutation was detected in approximately one-third of the analyzed tumor-derived cells extracted from paraffin-embedded tissue by DNA sequencing (Figure 2B). The mutation was not detectable at all in the sequence determination of DNA extracted from blood lymphocytes from the patient (Figure 2C).


Clinical characterization and the mutation spectrum in Swedish adenomatous polyposis families.

Kanter-Smoler G, Fritzell K, Rohlin A, Engwall Y, Hallberg B, Bergman A, Meuller J, Grönberg H, Karlsson P, Björk J, Nordling M - BMC Med (2008)

Detection of the mosaic c.2700_2701delTC mutation in patient C107. Nucleotide 2700 is indicated with an arrow. (A) The aberrant bands indicated by the bracket were excised from the SSCP/HD gel. The resulting DNA sequence is shown to the right. (B) DNA sequence from DNA extracted from tumor-derived cells from the patient. (C) The DNA sequence from DNA isolated from the patient's blood lymphocytes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2386495&req=5

Figure 2: Detection of the mosaic c.2700_2701delTC mutation in patient C107. Nucleotide 2700 is indicated with an arrow. (A) The aberrant bands indicated by the bracket were excised from the SSCP/HD gel. The resulting DNA sequence is shown to the right. (B) DNA sequence from DNA extracted from tumor-derived cells from the patient. (C) The DNA sequence from DNA isolated from the patient's blood lymphocytes.
Mentions: Three patients (C107, C257, and C505), negative for mutations in APC, were reported as de novo cases with no known family history of FAP. These patients where all screened for APC mutations present as low-frequency alleles using SSCP/HD. We did not detect any signs of low-frequency mutations in patients C257 and C505. However, in patient C107, aberrant bands, possibly originating from formation of heteroduplexes, was detected by SSCP/HD in a very low fraction of her blood lymphocytes. The c.2700_2701delTC mutation, which results in frame shift at codon 900, was found by sequencing of the aberrant bands excised from the SSCP/HD gel (Figure 2A). The mutation was detected in approximately one-third of the analyzed tumor-derived cells extracted from paraffin-embedded tissue by DNA sequencing (Figure 2B). The mutation was not detectable at all in the sequence determination of DNA extracted from blood lymphocytes from the patient (Figure 2C).

Bottom Line: Probands with a genotype (codon 1250-1464) predicting a severe phenotype had a median age at diagnosis of 21.8 (range, 11-49) years compared with 34.4 (range, 14-57) years among those with mutations outside this region (P < 0.017).Using a variety of mutation-detection techniques, we have achieved a 100% detection frequency in classical FAP.Probands with APC mutations outside codon 1250-1464, although exhibiting a less-severe phenotype, are at high risk of having a colorectal cancer at diagnosis indicating that age at diagnosis is as important as the severity of the disease for colorectal cancer morbidity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular and Clinical Genetics, Institute of Biomedicine, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden. gunilla.kantersmoler@astrazeneca.com

ABSTRACT

Background: The dominantly inherited condition familial adenomatous polyposis (FAP) is caused by germline mutations in the APC gene. Finding the causative mutations has great implications for the families. Correlating the genotypes to the phenotypes could help to improve the diagnosis and follow-up of patients.

Methods: Mutation screening of APC and the clinical characterization of 96 unrelated FAP patients from the Swedish Polyposis Registry was performed. In addition to generally used mutation screening methods, analyses of splicing-affecting mutations and investigations of the presence of low-frequency mutation alleles, indicating mosaics, have been performed, as well as quantitative real-time polymerase chain reaction to detect lowered expression of APC.

Results: Sixty-one different APC mutations in 81 of the 96 families were identified and 27 of those are novel. We have previously shown that 6 of the 96 patients carried biallelic MUTYH mutations. The 9 mutation-negative cases all display an attenuated or atypical phenotype. Probands with a genotype (codon 1250-1464) predicting a severe phenotype had a median age at diagnosis of 21.8 (range, 11-49) years compared with 34.4 (range, 14-57) years among those with mutations outside this region (P < 0.017). Dense polyposis (> 1000) occurred in 75% of the probands with a severe phenotype compared with 30% in those with mutations outside this region. The morbidity in colorectal cancer among probands was 25% at a mean age of 37.5 years and 29% at a mean age of 46.6 years.

Conclusion: Using a variety of mutation-detection techniques, we have achieved a 100% detection frequency in classical FAP. Probands with APC mutations outside codon 1250-1464, although exhibiting a less-severe phenotype, are at high risk of having a colorectal cancer at diagnosis indicating that age at diagnosis is as important as the severity of the disease for colorectal cancer morbidity.

Show MeSH
Related in: MedlinePlus