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Title: Identification and characterization of NF1 mutations using single strand conformational polymorphism (SSCP) analysis

Abstract

Neurofibromatosis type 1 (NF1) is one of the most common human genetic disorders with a constellation of cutaneous and skeletal manifestations, intellectual impairment, and an increased risk for a variety of malignancies. The neurofibromin gene is also considered a tumor-suppressor gene since its loss of function is associated with a variety of sporadic cancers in the general population. The NF1 gene has a high spontaneous mutation rate, and while a number of laboratories are involved in a coordinated effort to identify NF1 mutations, only a small number of mutations have been characterized. Despite considerable efforts no high frequency or recurrent mutation has been found. We report the application of single strand conformational polymorphism (SSCP) and heteroduplex analysis on the Phastgel system to identify mutations in the neurofibromin gene. A DNA panel of patients representing 100 families from Ontario, Canada was used to screen fourteen NF1 exons encompassing 30% of the NF1 gene: the 5{prime} exons 1, 17, 24 and the 3{prime} exons 28-33, 39-42 and 49. SSCP and heteroduplex variants were identified in PCR products amplified from 8 exons and mutations were identified in 10% of patients. Three RFLPs also have been identified and three other SSCP variants are beingmore » characterized. While most small deletions and insertions form heteroduplexes readily detectable on native gels, our results suggest that the detection of heteroduplexes resulting from point mutations is best facilitated on native Phastgels at low temperature. Our results suggest that as point mutations comprise a significant proportion of NF1 mutations, optimization of the SSCP protocol is critical to ensure the detection of all sequence variants.« less

Authors:
; ;  [1]
  1. Children`s Hospital of Western Ontario (Canada) [and others
Publication Date:
OSTI Identifier:
134769
Report Number(s):
CONF-941009-
Journal ID: AJHGAG; ISSN 0002-9297; TRN: 95:005313-1508
Resource Type:
Journal Article
Resource Relation:
Journal Name: American Journal of Human Genetics; Journal Volume: 55; Journal Issue: Suppl.3; Conference: 44. annual meeting of the American Society of Human Genetics, Montreal (Canada), 18-22 Oct 1994; Other Information: PBD: Sep 1994
Country of Publication:
United States
Language:
English
Subject:
55 BIOLOGY AND MEDICINE, BASIC STUDIES; GENES; GENE MUTATIONS; SPONTANEOUS MUTATIONS; MUTATION FREQUENCY; DETECTION; SIZE; PATIENTS; MENTAL DISORDERS; SKIN DISEASES; NEOPLASMS; SKELETAL DISEASES; ONTARIO; EXONS; RFLPS; POLYMERASE CHAIN REACTION

Citation Formats

Rodenhiser, D.I., Hovland, K., and Singh, S.M.. Identification and characterization of NF1 mutations using single strand conformational polymorphism (SSCP) analysis. United States: N. p., 1994. Web.
Rodenhiser, D.I., Hovland, K., & Singh, S.M.. Identification and characterization of NF1 mutations using single strand conformational polymorphism (SSCP) analysis. United States.
Rodenhiser, D.I., Hovland, K., and Singh, S.M.. 1994. "Identification and characterization of NF1 mutations using single strand conformational polymorphism (SSCP) analysis". United States. doi:.
@article{osti_134769,
title = {Identification and characterization of NF1 mutations using single strand conformational polymorphism (SSCP) analysis},
author = {Rodenhiser, D.I. and Hovland, K. and Singh, S.M.},
abstractNote = {Neurofibromatosis type 1 (NF1) is one of the most common human genetic disorders with a constellation of cutaneous and skeletal manifestations, intellectual impairment, and an increased risk for a variety of malignancies. The neurofibromin gene is also considered a tumor-suppressor gene since its loss of function is associated with a variety of sporadic cancers in the general population. The NF1 gene has a high spontaneous mutation rate, and while a number of laboratories are involved in a coordinated effort to identify NF1 mutations, only a small number of mutations have been characterized. Despite considerable efforts no high frequency or recurrent mutation has been found. We report the application of single strand conformational polymorphism (SSCP) and heteroduplex analysis on the Phastgel system to identify mutations in the neurofibromin gene. A DNA panel of patients representing 100 families from Ontario, Canada was used to screen fourteen NF1 exons encompassing 30% of the NF1 gene: the 5{prime} exons 1, 17, 24 and the 3{prime} exons 28-33, 39-42 and 49. SSCP and heteroduplex variants were identified in PCR products amplified from 8 exons and mutations were identified in 10% of patients. Three RFLPs also have been identified and three other SSCP variants are being characterized. While most small deletions and insertions form heteroduplexes readily detectable on native gels, our results suggest that the detection of heteroduplexes resulting from point mutations is best facilitated on native Phastgels at low temperature. Our results suggest that as point mutations comprise a significant proportion of NF1 mutations, optimization of the SSCP protocol is critical to ensure the detection of all sequence variants.},
doi = {},
journal = {American Journal of Human Genetics},
number = Suppl.3,
volume = 55,
place = {United States},
year = 1994,
month = 9
}
  • As genetic heterogeneity has proven to be the rule in genetic disease, a number of mutations scanning techniques have been described. To date, the most commonly used technique is SSCP. Unfortunately, there is no current bio-physical theory which can be used to predict the sensitivity of SSCP for the detection of mutations. Consequently, all such estimations have been made empirically. We created, by site directed mutagenesis, a DNA {open_quotes}toolbox{close_quotes} to more rigorously investigate the factors involved in the sensitivity of SSCP. The toolbox is a set of clones of various GC contents in which different clones have specific residues mutatedmore » to any base. Using PCR, fragments of varying GC content and length, containing any base at a specific location, can be prepared. We tested fragments of 40, 50, and 60% GC content (as well as a construct of 50% GC but purine rich) that were 100, 200, 300, or 400 bp in length. The bands were visualized by silver staining. We evaluated polyacrylamide (PA) (6%T,3.3%C and 10%T,2%C), Long Ranger (LR)(8%T), 0.5X MDE [ATB], and a novel vinyl-polymer matrix termed M13C5. Several distinct trends were noted. Sensitivity was highest for smaller fragments and higher GC contents on all matrices tested. The sensitivity order for the gel matrices was M13C5>0.5X MDE>10%PA>8%LR>6% PA. Where sensitivity was particularly poor (e.g. 40% GC), an improvement was seen with the addition of 10% glycerol.« less
  • Mutations in the p53 tumor-suppressor gene are commonly found in human cancers of diverse origin. Once of a number of methods developed to analyze large numbers of DNA samples for specific mutations is the single-strand conformation polymorphism (SSCP) analysis. This method is particularly well suited for analysis of tissues, such as brain tumors, with mixed cell populations. It takes advantage of the fact that, in a mixed cell population containing DNA with and without a mutation (e.g., the p53 gene mutation), both molecular species will be amplified by the PCR. A mutation within a PCR-amplified DNA fragment will alter themore » secondary structure of the amplified fragment and affect its electrophoretic mobility in a nondenaturing gel. The DNA fragments with the mutation are detected as an aberrantly migrating allele that can be seen concurrently with the wild-type allele. Although many studies have used this technique to screen for p53 mutations in tumors, with detection of a number of different mutations the limit of detection of point mutations in a background of wild-type DNA is not known. To test this, mixtures of mutant DNA from tumor D317 with a G-to-A point mutation in codon 272 of the p53 gene; or from tumor D263 (with a G-to-A point mutation in codon 175 of the p53 gene) and wild-type DNA from leukocytes, in ratios of 1:100, 5:95, 10:90, 15:85, 50:50, and 30:70, were prepared. The mixtures containing 100 ng of DNA were amplified using standard PCR technique. After the double-stranded DNAs were denatured, the DNA samples were loaded and electrophoresed on a nondenaturing acrylamide gel. The mutant allele was detectable even when the ratio of mutant to wild-type DNA was 5:95 in tumor D317. For tumor D263, the mutant allele was detectable when the ratio of mutant to wild-type DNA was 15:85, and it was not detectable at 10:90.« less
  • For single gene defects in which there are a variety of mutations with significant frequencies, it is a challenge to find an efficient and sensitive method for mutation detection. For example, although 70% to 75% of CF chromosomes in a North American Caucasian population have the mutation {delta}F508, more than 400 mutations (mostly single base pair substitutions) are represented on the remaining chromosomes. SSCP analysis is a relatively straightforward procedure and therefore suitable for routine use in a clinical laboratory. However, previous reports have demonstrated suboptimal sensitivity rates in screening for mutations. We have developed a novel set of conditionsmore » which greatly enhances sensitivity and efficiency of SSCP. Our protocol incorporates multiplex PCR, stepping of wattages during electrophoresis and increased salt concentration at the anode relative to the gel. To screen for mutations in the CFTR gene, three multiplex PCR reactions are performed using identical thermocycler parameters. Sizes of PCR products range from 441 bp to 196 bp: size differences of > 30 bp are necessary to ensure separation during electrophoresis. All PCR products are separated by electrophoresis at room temperature on a single gel containing 8% (37.5:1) polyacrylamide, 5% glycerol and 1x TBE. Using an anode buffer with increased salt (2x TBE) sharpens smaller sized bands, and stepping watts from 5W to 20W during electrophoresis enhances sensitivity. Positive controls were used to demonstrate that mutations could be detected. Other mutations or polymorphisms were verified by cycle sequencing of PCR products or by alternative PCR-based assays for the more common mutations. Thus, using 3 PCR reactions per patient and one gel condition, we are able to achieve a CF mutation detection rate of approximately 90% in a North American Caucasian population.« less
  • Detection of mutation, by SSCP or heteroduplex analysis, is important in medical genetics and oncology. Analysis of DNA binding proteins is a powerful tool in molecular biology research. Traditionally, these methods are performed using nondenaturing gel electrophoresis on poly-acrylamide or polyacrylamide-type matrices. Here we report the development of a new agarose gel matrix that can be used for all three methods. SSCP analyses were performed using the prototype agarose gel matrix for wild-type, polymorphic, and mutant samples from c-Kras exon 12, p53 exons 8 and 9, and HOX2B. We performed SSCP analyses using both isotopic and nonisotopic methods. We alsomore » analyzed the samples by deliberate HTX formation and subsequent gel analysis. Using the prototype agarose matrix, we detected single and multiple DNA sequence variants in 150-350 bp fragments with an efficiency comparable to polyacrylamide gels run under similar conditions. For SSCP and HTX assays, we achieved optimal resolution in gels run in vertical formats. However, some HTX samples could be resolved in horizontal gel systems. In addition, based on our studies, we have developed a useful battery of controls and standards for quality control of SSCP and HTX assays. We analyzed several different DNA/protein complexes (SP1, AP2, and octamer binding protein) using the prototype agarose matrix. We obtained good resolution in both vertical and horizontal gel formats. The horizontal gel system is generally superior for this application, due to its ease of use and slightly better resolution. This new prototype gel matrix offers an alternative for researchers performing analyses that previously could only be done on polyacrylamide-type gel matrices. For some applications, this new matrix offers the ease of horizontal gel casting. For all applications, this matrix offers the safety of a nontoxic system and the reproducibility of a thermally gelling system.« less
  • DNA single-strand conformational polymorphism (SSCP) analysis is widely used for detection of point mutations in clinical specimens. Performing SSCP analysis with cRNA instead of DNA has been shown to improve mutation detection frequency. RNA can exist in numerous metastable conformations, which appear as patterns of bands on nondenaturing electrophoresis gels. Single base mutations can cause not only mobility shifts of major bands, but also loss of some conformations and appearance of new conformations. Unique RNA SSCP patterns associated with specific base sequences in many cases allow visual identification of point mutations. However, in some cases, the RNA SSCP pattern ofmore » a single base change in a sequence is not sufficiently different for a positive identification of the mutation. Improvement in the detection capability of RNA SSCP was obtained by adding 3{prime}-deoxy-nucleotides to the transcription reaction. The presence of chain-terminating nucleotides in the transcription reaction formed numerous new RNA fragments, thereby generating complex band patterns ({open_quotes}bar codes{close_quotes}) unique to each RNA sequence. This method was applied to analyzing p53 mutations in patients with colon cancer. 8 refs., 3 figs.« less