Consensus Sequence of the Human BRCA1 Gene

This invention relates to a gene which has been associated with breast and ovarian cancer where the gene is found to be mutated. More specifically, this invention relates to the most likely sequence (i.e. "Consensus Normal DNA sequence") for the BRCA1 gene (BRCA1.sup.(omi) SEQ. ID. NO: 1) in normal individuals.

It has been estimated that about 5-10% of breast cancer is inherited Rowell, S., et al., American Journal of Human Genetics 55:861-865 (1994). Located on chromosome 17, BRCA1 is the first gene identified to be conferring increased risk for breast and ovarian cancer. Miki et al., Science 266:66-71 (1994). Mutations in this "tumor suppressor" gene are thought to account for roughly 45% of inherited breast cancer and 80-90% of families with increased risk of early onset breast and ovarian cancer. Easton et al., American Journal of Human Genetics 52:678-701 (1993).

Locating one or more mutations in the BRCA1 region of chromosome 17 provides a promising approach to reducing the high incidence and mortality associated with breast and ovarian cancer through the early detection of women at high risk. These women, once identified, can be targeted for more aggressive prevention programs. Screening is carried out by a variety of methods which include karyotyping, probe binding and DNA sequencing.

In DNA sequencing technology, genomic DNA is extracted from whole blood and the coding regions of the BRCA1 gene are amplified. Each of the coding regions is sequenced completely and the results are compared to the normal DNA sequence of the gene.

The BRCA1 gene is divided into 24 separate exons. Exons 1 and 4 are noncoding, in that they are not part of the final functional BRCA1 protein product. The BRCA1 coding region spans roughly 5600 base pairs (bp). Each exon consists of 200-400 bp, except for exon 11 which contains about 3600 bp. To sequence the coding region of the BRCA1 gene, each exon is amplified separately and the resulting PCR products are sequenced in the forward and reverse directions. Because exon 11 is so large, we have divided it into twelve overlapping PCR fragments of roughly 350 bp each (segments "A" through "L" of BRCA1 exon 11).

Many mutations and normal polymorphisms have already been reported in the BRCA1 gene. A world wide web site has been built to facilitate the detection and characterization of alterations in breast cancer susceptibility genes. Such mutations in BRCA1 can be accessed through the Breast Cancer Information Core at: http://www.nchgr.nih.gov/dir/lab.sub.-- transfer/bic. This data site became publicly available on Nov. 1, 1995. Friend, S. et al. Nature Genetics 11:238, (1995).

The genetics of Breast/Ovarian Cancer Syndrome is autosomal dominant with reduced penetrance. In simple terms, this means that the syndrome runs through families such that both sexes can be carriers (only women get the disease but men can pass it on), all generations will likely have breast/ovarian or both diseases and sometimes in the same individual, occasionally women carriers either die young before they have the time to manifest disease (and yet offspring get it) or they never develop breast or ovarian cancer and die of old age (the latter people are said to have "reduced penetrance" because they never develop cancer). Pedigree analysis and genetic counseling is absolutely essential to the proper workup of a family prior to any lab work.

Until now, only a single normal sequence for BRCA1 has been available for comparison. That sequence is available as GenBank Accession Number U15595. There is a need in the art, therefore, to have available a normal sequence which represents most likely BRCA1 sequence to be found in the majority of the normal population, the (i.e. "Consensus Normal DNA sequence"). A Consensus Normal DNA sequence will make it possible for true mutations to be easily identified or differentiated from polymorphisms. Identification of mutations of the BRCA1 gene and protein would allow more widespread diagnostic screening for hereditary breast and ovarian cancer than is currently possible.

A consensus normal gene sequence of the BRCA1 is provided which more accurately reflects the most likely sequence to be found in a subject. Use of the consensus normal gene sequence (BRCA1.sup.(omi) SEQ ID. NO: 1), rather than the previously published BRCA1 sequence, will reduce the likelihood of misinterpreting a "sequence variation" found in the normal population with a pathologic "mutation" (i.e. causes disease in the individual or puts the individual at a high risk of developing the disease). With large interest in breast cancer predisposition testing, misinterpretation is particularly worrisome. People who already have breast cancer are asking the clinical question: "is my disease caused by a heritable genetic mutation?" The relatives of the those with breast cancer are asking the question: "Am I also a carrier of the mutation my relative has? Thus, is my risk increased, and should I undergo a more aggressive surveillance program."

The present invention is based on the discovery of the most likely sequence to be found in normal human individuals for the BRCA1 gene.

It is an object of the invention to provide a consensus sequence for the normal BRCA1 gene, i.e. the consensus Sequence having the more commonly occurring nucleotides where normal polymorphisms occur.

It is another object of the invention to provide a consensus normal protein sequence of the BRCA1 protein

It is another object of the invention to provide a list of the codon pairs which occur at each of seven polymorphic points on the normal BRCA1 gene.

It is another object of the invention to provide the rates of occurrence for the codons.

It is another object of the invention to provide a method wherein BRCA1, or parts thereof, is amplified with one or more oligonucleotide primers.

It is another object of this invention to provide a method of avoiding misinterpretation of changes which a laboratory may find in the BRCA1 gene.

It is another object of this invention to provide a method of identifying individuals who carry no mutation(s) of the BRCA1 gene and are therefore at no increased risk or susceptibility to breast or ovarian cancer based on a finding that the individual does not carry an abnormal BRCA1 gene.

It is another object of this invention to provide a method of identifying a mutation leading to predisposition or higher susceptibility to breast or ovarian cancer.

It is another object of the invention to provide a method of classifying a tumor for diagnostic and prognostic purposes.

There is a need in the art for a consensus normal sequence of the BRCA1 gene and for the consensus normal protein sequence of BRCA1 as well as for an accurate list of codons which occur at polymorphic points on a normal sequence. A person skilled in the art of genetic susceptibility testing will find the present invention useful for:

a) identifying individuals having a normal BRCA1 gene, who are therefore not at risk or have no increased susceptibility to breast or ovarian cancer from a BRCA1 mutation;

b) avoiding misinterpretation of normal polymorphisms found in the normal BRCA1 gene;

c) determining the presence of a previously unknown mutation in the BRCA1 gene.

d) identifying a mutation which indicates a predisposition or higher susceptibility to breast or ovarian cancer; or for

e) classifying a tumor for diagnostic and prognostic purposes.

f) performing gene repair.

The following definitions are provided for the purpose of understanding this invention.

"Consensus Normal Sequence" refers to the nucleic acid or protein sequence, the nucleic or amino acids of which are known to occur with high frequency in a population of individuals who carry the gene which codes for a normally functioning protein, or which nucleic acid itself has normal function.

"Consensus normal DNA sequence" also called "consensus normal gene sequence" refers to a nucleic acid sequence, the nucleic acid of which are known to occur at their respective positions with high frequency in a population of individuals who carry the gene which codes for a normally functioning protein, or which itself has normal function.

"Consensus Normal Protein Sequence" refers to the protein sequence, the amino acids of which are known to occur with high frequency in a population of individuals who carry the gene which codes for a normally functioning protein. "BRCA1.sup.(omi) (SEQ ID NO: 1)" refers to a consensus sequence for the BRCA1 gene. The consensus sequence was found by end to end sequencing,of the BRCA1 gene from 5 individuals randomly drawn from the population and found to have no family history of breast or ovarian cancer. The sequenced gene was found not to contain any mutations. The consensus was determined by calculating the frequency with which nucleic acids occur and inserting the nucleic acid with highest frequency of occurrence at each polymorphic site. In some cases the insertion of a nucleic acid at a polymorphic site indicated a codon change and a change of amino acid from previously published information. In other cases the frequency of occurrence of a nucleic acid was found to differ from the published frequency.

The term "primer" as used herein refers to a sequence comprising about 20 or more nucleotides of the BRCA1 gene.

A "target polynucleotide" refers to the nucleic acid sequence of interest e.g., the BRCA1 encoding polynucleotide. Other primers which can be used for primer hybridization will be known or readily ascertainable to those of skill in the art.

The term "substantially complementary to" or "substantially the sequence" refers to primer sequences which hybridize to the sequences provided under stringent conditions and/or sequences having sufficient homology with BRCA1 sequences, such that the allele specific oligonucleotide primers hybridize to the BRCA1 sequences to which they are complimentary.

The term "isolated" as used herein includes oligonucleotides substantially free of other nucleic acids, proteins, lipids, carbohydrates or other materials with which they may be associated. Such association is typically either in cellular material or in a synthesis medium.

Any nucleic acid specimen, in purified or non-purified form, can be utilized as the starting nucleic acid or acids, providing it contains, or is suspected of containing, the specific nucleic acid sequence containing a polymorphic locus. Thus, the process may amplify, for example, DNA or RNA, including messenger RNA, wherein DNA or RNA may be single stranded or double stranded. In the event that RNA is to be used as a template, enzymes, and/or conditions optimal for reverse transcribing the template to DNA would be utilized. In addition, a DNA-RNA hybrid which contains one strand of each may be utilized. A mixture of nucleic acids may also be employed, or the nucleic acids produced in a previous amplification reaction herein, using the same or different primers may be so utilized. See TABLE II. The specific nucleic acid sequence to be amplified, i.e., the polymorphic locus, may be a fraction of a larger molecule or can be present initially as a discrete molecule, so that the specific sequence constitutes the entire nucleic acid. It is not necessary that the sequence to be amplified be present initially in a pure form; it may be a minor fraction of a complex mixture, such as contained in whole human DNA.

DNA utilized herein may be extracted from a body sample, such as blood, tissue material and the like by a variety of techniques such as that described by Maniatis, et. al. in Molecular Cloning:A Laboratory Manual, Cold Spring Harbor, N.Y., p 280-281, 1982). If the extracted sample is impure, it may be treated before amplification with an amount of a reagent effective to open the cells, or animal cell membranes of the sample, and to expose and/or separate the strand(s) of the nucleic acid(s). This lysing and nucleic acid denaturing step to expose and separate the strands will allow amplification to occur much more readily.

The deoxyribonucleotide triphosphates dATP, dCTP, dGTP, and dTTP are added to the synthesis mixture, either separately or together with the primers, in adequate amounts and the resulting solution is heated to about 90.degree.-100.degree. C. from about 1 to 10 minutes, preferably from 1 to 4 minutes. After this heating period, the solution is allowed to cool, which is preferable for the primer hybridization. To the cooled mixture is added an appropriate agent for effecting the primer extension reaction (called herein "agent for polymerization"), and the reaction is allowed to occur under conditions known in the art. The agent for polymerization may also be added together with the other reagents if it is heat stable. This synthesis (or amplification) reaction may occur at room temperature up to a temperature above which the agent for polymerization no longer functions. Thus, for example, if DNA polymerase is used as the agent, the temperature is generally no greater than about 40.degree. C. Most conveniently the reaction occurs at room temperature.

The allele specific oligonucleotide primers are useful in determining whether a subject is at risk of having breast or ovarian cancer, and also useful for characterizing a tumor. Primers direct amplification of a target polynucleotide prior to sequencing. These unique BRCA1 oligonucleotide primers of TABLE II were designed and produced specifically to optimize amplification of portions of BRCA1 which are to be sequenced.

The primers used to carry out this invention embrace oligonucleotides of sufficient length and appropriate sequence to provide initiation of polyrmerization. Environmental conditions conducive to synthesis include the presence of nucleoside triphosphates and an agent for polymerization, such as DNA polymerase, and a suitable temperature and pH. The primer is preferably single stranded for maximum efficiency in amplification, but may be double stranded. If double stranded, the primer is first treated to separate its strands before being used to prepare extension products. The primer must be sufficiently long to prime the synthesis of extension products in the presence of the inducing agent for polymerization. The exact length of primer will depend on many factors, including temperature, buffer, and nucleotide composition. The oligonucleotide primer typically contains 12-20 or more nucleotides, although it may contain fewer nucleotides.

Primers used to carry out this invention are designed to be substantially complementary to each strand of the genomic locus to be amplified. This means that the primers must be sufficiently complementary to hybridize with their respective strands under conditions which allow the agent for polymerization to perform. In other words, the primers should have sufficient complementarity with the 5' and 3' sequences flanking the mutation to hybridize therewith and permit amplification of the genomic locus.

Oligonucleotide primers of the invention are employed in the amplification process which is an enzymatic chain reaction that produces exponential quantities of polymorphic locus relative to the number of reaction steps involved. Typically, one primer is complementary to the negative (-) strand of the polymorphic locus and the other is complementary to the positive (+) strand. Annealing the primers to denatured nucleic acid followed by extension with an enzyme, such as the large fragment of DNA polymerase I (Klenow) and nucleotides, results in newly synthesized + and - strands containing the target polymorphic locus sequence. Because these newly synthesized sequences are also templates, repeated cycles of denaturing, primer annealing, and extension results in exponential production of the region (i.e., the target polymorphic locus sequence) defined by the primers. The product of the chain reaction is a discreet nucleic acid duplex with termini corresponding to the ends of the specific primers employed.

The oligonucleotide primers of the invention may be prepared using any suitable method, such as conventional phosphotriester and phosphodiester methods or automated embodiments thereof. In one such automated embodiment, diethylphosphoramidites are used as starting materials and may be synthesized as described by Beaucage, et al., Tetrahedron Letters, 22:1859-1862, 1981. One method for synthesizing oligonucleotides on a modified solid support is described in U.S. Pat. No. 4,458,066.

The agent for polymerization may be any compound or system which will function to accomplish the synthesis of primer extension products, including enzymes. Suitable enzymes for this purpose include, for example, E. coli DNA polymerase I, Klenow fragment of E. coli DNA polymerase, polymerase muteins, reverse transcriptase, other enzymes, including heat-stable enzymes (e.i., those enzymes which perform primer extension after being subjected to temperatures sufficiently elevated to cause denaturation), such as Taq polymerase. Suitable enzyme will facilitate combination of the nucleotides in the proper manner to form the primer extension products which are complementary to each polymorphic locus nucleic acid strand. Generally, the synthesis will be initiated at the 3' end of each primer and proceed in the 5' direction along the template strand, until synthesis terminates, producing molecules of different lengths.

The newly synthesized strand and its complementary nucleic acid strand will form a double-stranded molecule under hybridizing conditions described above and this hybrid is used in subsequent steps of the process. In the next step, the newly synthesized double-stranded molecule is subjected to denaturing conditions using any of the procedures described above to provide single-stranded molecules.

The steps of denaturing, annealing, and extension product synthesis can be repeated as often as needed to amplify the target polymorphic locus nucleic acid sequence to the extent necessary for detection. The amount of the specific nucleic acid sequence produced will accumulate in an exponential fashion.

Amplification is described in PCR. A Practical Approach, ILR Press, Eds. M. J. McPherson, P. Quirke, and G. R. Taylor, 1992.

The amplification products may be detected by Southern blots analysis, without using radioactive probes. In such a process, for example, a small sample of DNA containing a very low level of the nucleic acid sequence of the polymorphic locus is amplified, and analyzed via a Southern blotting technique or similarly, using dot blot analysis. The use of non-radioactive probes or labels is facilitated by the high level of the amplified signal. Alternatively, probes used to detect the amplified products can be directly or indirectly detectably labeled, for example, with a radioisotope, a fluorescent compound, a bioluminescent compound, a chemiluminescent compound, a metal chelator or an enzyme. Those of ordinary skill in the art will know of other suitable labels for binding to the probe, or will be able to ascertain such, using routine experimentation.

Sequences amplified by the methods of the invention can be further evaluated, detected, cloned, sequenced, and the like, either in solution or after binding to a solid support, by any method usually applied to the detection of a specific DNA sequence such as PCR, oligomer restriction (Saiki, et. al., Bio/Technology,3:1008-1012, 1985), allele-specific oligonucleotide (ASO) probe analysis (Conner, et. al., Proc. Natl. Acad. Sci. U.S.A., 80:278, 1983), oligonucleotide ligation assays (OLAs) (Landgren, et. al., Science,241:1007, 1988), and the like. Molecular techniques for DNA analysis have been reviewed (Landgren, et. al., Science,242:229-237, 1988).

Preferably, the method of amplifying is by PCR, as described herein and as is commonly used by those of ordinary skill in the art. Alternative methods of amplification have been described and can also be employed as long as the BRCA1 locus amplified by PCR using primers of the invention is similarly amplified by the alternative means. Such alternative amplification systems include but are not limited to self-sustained sequence replication, which begins with a short sequence of RNA of interest and a T7 promoter. Reverse transcriptase copies the RNA into cDNA and degrades the RNA, followed by reverse transcriptase polymerizing a second strand of DNA. Another nucleic acid amplification technique is nucleic acid sequence-based amplification (NASBA) which uses reverse transcription and T7 RNA polymerase and incorporates two primers to target its cycling scheme. NASBA can begin with either DNA or RNA and finish with either, and amplifies to 10.sup.8 copies within 60 to 90 minutes. Alternatively, nucleic acid can be amplified by ligation activated transcription (LAT). LAT works from a single-stranded template with a single primer that is partially single-stranded and partially double-stranded. Amplification is initiated by ligating a cDNA to the promoter oligonucleotide and within a few hours, amplification is 10.sup.8 to 10.sup.9 fold. The QB replicase system can be utilized by attaching an RNA sequence called MDV-1 to RNA complementary to a DNA sequence of interest. Upon mixing with a sample, the hybrid RNA finds its complement among the specimen's mRNAs and binds, activating the replicase to copy the tag-along sequence of interest. Another nucleic acid amplification technique, ligase chain reaction (LCR), works by using two differently labeled halves of a sequence of interest which are covalently bonded by ligase in the presence of the contiguous sequence in a sample, forming a new target. The repair chain reaction (RCR) nucleic acid amplification technique uses two complementary and target-specific oligonucleotide probe pairs, thermostable polymerase and ligase, and DNA nucleotides to geometrically amplify targeted sequences. A 2-base gap separates the oligonucleotide probe pairs, and the RCR fills and joins the gap, mimicking normal DNA repair. Nucleic acid amplification by strand displacement activation (SDA) utilizes a short primer containing a recognition site for hincII with short overhang on the 5' end which binds to target DNA. A DNA polymerase fills in the part of the primer opposite the overhang with sulfur-containing adenine analogs. HincII is added but only cuts the unmodified DNA strand. A DNA polymerase that lacks 5' exonuclease activity enters at the cite of the nick and begins to polymerize, displacing the initial primer strand downstream and building a new one which serves as more primer. SDA produces greater than 10.sup.7 -fold amplification in 2 hours at 37.degree. C. Unlike PCR and LCR, SDA does not require instrumented Temperature cycling. Another amplification system useful in the method of the invention is the QB Replicase System. Although PCR is the preferred method of amplification if the invention, these other methods can also be used to amplify the BRCA1 locus as described in the method of the invention.

The BRCA1.sup.(omi) Consensus Normal DNA sequence was obtained by end to end sequencing of five normal subjects in the manner described above followed by analysis of the data obtained. The data obtained provided us with the opportunity to evaluate six previously published normal polymorphisms for correctness and frequency in the population, and to identify an additional polymorphism not previously found.

The consensus normal gene sequence can be used for gene therapy. A complete description of the method is provided in Anderson et al. U.S. Pat. No. 5,399,346, issued Mar. 21, 1995. The isolated consensus normal BRCA1 gene can be constructed from amplification products and inserted into a vector such as the LXSN vector. Fresh lymphocytes of a patient having a mutation in the BRCA1 gene, are cultured. The cells are transduced with the vector above, and culturing is continued. The cultured, transformed cells are infused into the patient.

The consensus normal BRCA1 amino acid sequence may be used to make diagnostic probes. Labeled diagnostic probes may be used by any hybridization method to determine the level of BRCA1 protein in serum or lysed cell suspension of a patient, or solid surface cell sample.

The consensus normal BRCA1 amino acid sequence may be used to provide a level of protection for patients against risk of breast or ovarian cancer. The isolated consensus normal BRCA1 gene can be constructed from amplification products and inserted into a vector such as the LXSN vector. Fresh lymphocytes of a patient having a mutation in the BRCA1 gene, are cultured. The cells are transduced with the vector above, and cultured. Extracted BRCA1 protein can be provided by injection or other known means to patients who are at risk.

Materials and Methods

Approximately 150 volunteers were screened in order to identify individuals with no cancer history in their immediate family (i.e. first and second degree relatives). Each person was asked to fill out a hereditary cancer prescreening questionnaire See TABLE I below. Five of these were randomly chosen for end-to-end sequencing of their BRCA1 gene." A first degree relative is a parent, sibling, or off spring. A second degree relative is an aunt, uncle, grandparent, grandchild, niece, nephew, or half-sibling.

Genomic DNA was isolated from white blood cells of five normal subjects selected from analysis of their answers to the questions above. Dideoxy sequence analysis was performed following polymerase chain reaction amplification.

All exons of the BRCA1 gene were subjected to direct dideoxy sequence analysis by asymmetric amplification using the polymerase chain reaction (PCR) to generate a single stranded product amplified from this DNA sample. Shuldiner, et at., Handbook of Techniques in Endocrine Research, p. 457-486, DePablo, F., Scanes, C., eds., Academic Press, Inc., 1993. Fluorescent dye was attached for automated sequencing using the Taq Dye Terminator Kit (PERKIN-ELMER.RTM. cat# 401628). DNA sequencing was performed in both forward and reverse directions on an Applied Biosystems, Inc. (ABI) automated sequencer (Model 377). The software used for analysis of the resulting data was "Sequence Navigator" purchased through ABI.

1. Polymerase Chain Reaction (PCR) Amplification

Genomic DNA (100 nanograms) extracted from white blood cells of five normal subjects. Each of the five samples was sequenced end to end. Each sample was amplified in a final volume of 25 microliters containing 1 microliter (100 nanograms) genomic DNA, 2.5 microliters 10X PCR buffer (100 mM Tris, pH 8.3, 500 mM KCl, 1.2 mM MgCl.sub.2), 2.5 microliters 10X dNTP mix (2 mM each nucleotide), 2.5 microliters forward primer, 2.5 microliters reverse primer, and 1 microliter Taq polymerase (5 units), and 13 microliters of water.

The primers in Table II, below were used to carry out amplification of the various sections of the BRCA1 gene samples. The primers were synthesized on an DNA/RNA Synthesizer Model 394.RTM..

Thirty-five cycles were performed, each consisting of denaturing (95.degree. C.; 30 seconds), annealing (55.degree. C.; 1 minute), and extension (72.degree. C.; 90 seconds), except during the first cycle in which the denaturing time was increased to 5 minutes, and during the last cycle in which the extension time was increased to 5 minutes,

PCR products were purified using QIA-QUICK.RTM. PCR purification kits (QIAGEN, cat# 28104; Chatsworth, Calif.). Yield and purity of the PCR product determined spectrophotometrically at OD.sub.260 on a Beckman DU 650 spectrophotometer.

2. Dideoxy Sequence Analysis

Fluorescent dye was attached to PCR products for automated sequencing using the Taq Dye Terminator Kit (PERKIN-ELMER.RTM. cat#401628). DNA sequencing was performed in both forward and reverse directions on an Applied Biosystems, Inc. (ABI) Foster City, Calif., automated sequencer (Model 377). The software used for analysis of the resulting data was "SEQUENCE NAVIGATOR.RTM." purchased through ABI.

3. Results

Differences in the nucleic acids of the five normal individuals were found in seven locations on the gene. The changes and their positions are found on TABLE III, below.

A consensus normal sequence of the BRCA1 gene was determined by calculating the percentage of occurrence of each polymorphism and inserting the more frequently occurring polymorphism into the published BRCA1 (Genbank Accession Number U15595). The normal consensus BRCA1.sup.(omi) is shown as SEQ. ID NO. 1 at page 29.

The data show that for each of the samples. The BRCA1 gene is identical except in the region of seven polymorphisms. These polymorphic regions, together with their locations, the amino acid groups of each codon, the frequency of their occurence and the amino acid coded for by each codon are found in TABLE IV below.

A person skilled in the art of genetic susceptibility testing will find the present invention useful for:

a) identifying individuals having a normal BRCA1 gene, who are therefore not at risk or have no increased susceptibility to breast or ovarian cancer from a BRCA1 mutation;

b) avoiding misinterpretation of normal polymorphisms found in the normal BRCA1 gene;

Sequencing is carried out as in EXAMPLE 1 using a blood sample from the patient in question. However, the BRCA1.sup.(omi) sequence is used for reference and polymorphic sites are compared to the nucleic acid sequences listed above for normal codons at each polymophic site. A normal sample is one which compares to the BRCA1.sup.(omi) sequence and contains one of the normal base variations which occur at each of the polymorphic sites. The codons which occur at each of the polymorphic sites are paired below.

AGC and AGT at position 2201,

TTG and CTG at position 2430,

CCG and CTG at position 2731,

GAA and GGA at position 3232,

AAA and AGA at position 3667,

TCT and TCC at position 4427, and

AGT and GGT at position 4956.

The availability of these polymorphic pairs provides added assurance that one skilled in the art can correctly interpret the polymorphic variations without mistaking a normal variation for a mutation.

Exon 11 of the BRCA1 gene is subjected to direct dideoxy sequence analysis by asymmetric amplification using the polymerase chain reaction (PCR) to generate a single stranded product amplified from this DNA sample. Shuldiner, et al., Handbook of Techniques in Endocrine Research, p. 457-486, DePablo, F., Scanes, C., eds., Academic Press, Inc., 1993. Fluorescent dye is attached for automated sequencing using the Taq Dye Terminator Kit (PERKIN-ELMER.RTM. cat# 401628). DNA sequencing is performed in both forward and reverse directions on an Applied Biosystems, Inc. (ABI) automated Sequencer (Model 377). The software used for analysis of the resulting data is "SEQUENCE NAVIGATOR.RTM." purchased through ABI.

1. Polymer Chain Reaction (PCR) Amplification

Genomic DNA (100 nanograms) extracted from white blood cells of the subject is amplified in a final volume of 25 microliters containing 1 microliter (100 nanograms) genomic DNA, 2.5 microliters 10X PCR buffer (100 mM Tris, pH 8.3, 500 mM KCl, 1.2 mM MgCl.sub.2), 2.5 microliters 10X dNTP mix (2 mM each nucleotide), 2.5 microliters forward primer (BRCA1-11K-F, 10 micromolar solution), 2.5 microliters reverse primer (BRCA1-11K-R, 10 micromolar solution),and 1 microliter Taq polymerase (5 units), and 13 microliters of water. The PCR primers used to amplify a patient's sample BRCA1 gene are listed in Table II. The primers were synthesized on an DNA/RNA Synthesizer Model 394.RTM.. Thirty-five cycles are of amplification are performed, each consisting of denaturing (95.degree. C.; 30 seconds), annealing (55.degree. C.; 1 minute), and extension (72.degree. C.; 90 seconds), except during the first cycle in which the denaturing time is increased to 5 minutes, and during the last cycle in which the extension time is increased to 5 minutes.

PCR products are purified using QIA-QUICK.RTM. PCR purification kits (QIAGEN.RTM., cat# 28104; Chatsworth, Calif.). Yield and purity of the PCR product determined spectrophotometrically at OD.sub.260 on a Beckman DU 650 spectrophotometer.

2. Dideoxy Sequence Analysis

Fluorescent dye is attached to PCR products for automated sequencing using the Taq Dye Terminator Kit (PERKIN-ELMER.RTM. cat# 401628). DNA sequencing is performed in both forward and reverse directions on an Applied Biosystems, Inc. (ABI) Foster City, Calif., automated sequencer (Model 377). The software used for analysis of the resulting data is "SEQUENCE NAVIGATOR.RTM." purchased through ABI. The BRCA1.sup.(omi) sequence is entered into the Sequence Navigator software as the Standard for comparison. The Sequence Navigator software compares the sample sequence to the BRCA1.sup.(omi) standard, base by base. The Sequence Navigator highlights all differences between the BRCA1.sup.(omi) (SEQ ID. NO: 1) consensus normal DNA sequence and the patient's sample sequence.

A first technologist checks the computerized results by comparing visually the BRCA1.sup.(omi) standard against the patient's sample, and again highlights any differences between the standard and the sample. The first primary technologist then interprets the sequence variations at each position along the sequence. Chromatograms from each sequence variation are generated by the Sequence Navigator and printed on a color printer. The peaks are interpreted by the first primary technologist and a second primary technologist. A secondary technologist then reviews the chromatograms. The results are finally interpreted by a geneticist. In each instance, a variation is compared to known normal polymorphisms for position and base change. If the sample BRCA1 sequence matches the BRCA1.sup.(omi) standard, with only variations within the known list of polymorphisms, it is interpreted as a normal gene sequence.

A person skilled in the art of genetic susceptibility testing will find the present invention useful for determining the presence of a known or previously unknown mutation in the BRCA1 gene. A list of mutations of BRCA1 is publicly available in the Breast Cancer Information Core at: http://www.nchgr.nih.gov/dir/lab.sub.-- transfer/bic. This data site became publicly available on Nov. 1, 1995. Friend, S. et al. Nature Genetics 11:238, (1995). Sequencing is carried out as in EXAMPLE 1 using a blood sample from the patient in question. However, the BRCA .sup.(omi) (SEQ ID NO: 1) sequence is used for reference and polymorphic sites are compared to the nucleic acid sequences listed above for normal codons at each polymophic site. A normal sample is one which compares to the BRCA1.sup.(omi) sequence and contains one of the normal base variations which occur at each of the polymorphic sites. The codons which occur at each of the polymorphic sites are paired bellow.

AGC and AGT at position 2201,

TTG and CTG at position 2430,

CCG and CTG at position 2731,

GAA and GGA at position 3232,

AAA and AGA at position 3667,

TCT and TCC at position 4427, and

AGT and GGT at position 4956.

The availability of these polymorphic pairs provides added assurance that one skilled in the art can correctly interpret the polymorphic variations without mistaking a normal variation for a mutation.

As evident from the data in Table III and IV, the statistical analysis (on average) shows one or more normal codon pairs wherein the codons occur in the following frequencies in the normal population, respectively:

at position 2201, AGC and AGT occur at frequencies of about 40%, and from about 55-65%, respectively;

at position 2430, TTG and CTG occur at frequencies from about 35-45%, and from about 55-65%, respectively;

at position 2731, CCG and CTG occur at frequencies from about 25-35%, and from about 65-75%, respectively;

at position 3232, GAA and GGA occur at frequencies from about 35-45%, and from about 55-65%, respectively;

at position 3667, AAA and AGA occur at frequencies from about 35-45%, and from about 55-65%, respectively;

at position 4427, TCT and TCC occur at frequencies from about 45-55%, and from about 45-55%, respectively; and

at position 4956, AGT and GGT occur at frequencies from about 35-45%, and from about 55-65%, respectively.

Exon 11 of the BRCA1 gene is subjected to direct dideoxy sequence analysis by asymmetric amplification using the polymerase chain reaction (PCR) to generate a single stranded product amplified from this DNA sample. Shuldiner, et al., Handbook of Techniques in Endocrine Research, p. 457-486, DePablo, F., Scanes, C., eds., Academic Press, Inc., 1993. Fluorescent dye is attached for automated sequencing using the Taq Dye Terminator Kit (PERKIN-ELMER.RTM. cat# 401628). DNA sequencing is performed in both forward and reverse directions on an Applied Biosystems, Inc. (ABI) automated sequencer (Model 377) The software used for analysis of the resulting data is "SEQUENCE NAVIGATOR.RTM." purchased through ABI.

1. Polymerase Chain Reaction (PCR) Amplification

Genomic DNA (100 nanograms) extracted from white blood cells of the subject is amplified in a final volume of 25 microliters containing 1 microliter (100 nanograms) genomic DNA, 2.5 microliters 10X PCR buffer (100 mM Tris, pH 8.3, mM KCl, 1.2 mM MgCl.sub.2), 2.5 microliters 10X dNTP mix (2 mM each nucleotide), 2.5 microliters forward primer (BRCA1-11K-F, 10 micromolar solution), 2.5 microliters reverse primer (BRCA1-11K-R, 10 micromolar solution),and 1 microliter Taq polymerase (5 units), and 13 microliters of water. The PCR primers used to amplify a patient's sample BRCA1 gene are listed in Table II. The primers were synthesized on an DNA/RNA Synthesizer Model 394.RTM.. Thirty-five cycles are of amplification are performed, each consisting of denaturing (95.degree. C. 30 seconds), annealing (55.degree. C. 1 minute), and extension (72.degree. C.; 90 seconds), except during the first cycle in which the denaturing time is increased to 5 minutes, and during the last cycle in which the extension time is increased to 5 minutes.

PCR products are purified using QIA-QUICK.RTM. PCR purification kits (QIAGEN.RTM., cat# 28104; Chatsworth, Calif.). Yield and purity of the PCR product determined spectrophotometrically at OD.sub.260 on a Beckman DU 650 spectrophotometer.

2. Dideoxy Sequence Analysis

Fluorescent dye is attached to PCR products for automated sequencing using the Taq Dye Terminator Kit (PERKIN-ELMER.RTM. cat# 401628). DNA sequencing is performed in both forward and reverse directions on an Applied Biosystems, Inc. (ABI) Foster City, Calif., automated sequencer (Model 377). The software used for analysis of the resulting data is "SEQUENCE NAVIGATOR.RTM." purchased through ABI. The BRCA1.sup.(omi) sequence (SEQ ID. NO: 1) is entered into the Sequence Navigator software as the Standard for comparison. The Sequence Navigator software compares the sample sequence to the BRCA1.sup.(omi) standard (SEQ ID NO: 1), base by base. The Sequence Navigator highlights all differences between the BRCA1.sup.(omi) consensus normal DNA sequence and the patient's sample sequence.

A first technologist checks the computerized results by comparing visually the BRCA1.sup.(omi) standard (SEQ ID. NO: 1) against the patient's sample, and again highlights any differences between the standard and the sample. The first primary technologist then interprets the sequence variations at each position along the sequence. Chromatograms from each sequence variation are generated by the Sequence Navigator and printed on a color printer. The peaks are interpreted by the first primary technologist and also by a second primary technologist. A secondary technologist then reviews the chromatograms. The results are finally interpreted by a geneticist. In each instance, a variation is compared to known normal polymorphisms for position and base change. If the sample BRCA1 sequence matches the BRCA1.sup.(omi) standard, with only variations within the known list of polymorphisms, it is interpreted as a normal gene sequence. Mutations are noted by the length of non-matching variation. Such a lengthy mismatch pattern occurs with deletions and substitutions. An alteration such as a base substitution at a single position will be noted as a single mismatch between the standard and the patient's gene sample.

A person skilled in the art of genetic susceptibility testing will find the present invention useful for determining the presence of a known or previously unknown mutation in the BRCA1 gene. A list of mutations of BRCA1 is publicly available in the Breast Cancer Information Core at: http://www.nchgr.nih.gov/dir/lab.sub.-- transfer/bic. This data site became publicly available on Nov. 1, 1995. Friend, S. et al. Nature Genetics 11:238, (1995). In this example, a mutation in exon 11 is characterized by amplifying the region of the mutation with a primer which matches the region of the mutation. Exon 11 of the BRCA1 gene is subjected to direct dideoxy sequence analysis by asymmetric amplification using the polymerase chain reaction (PCR) to generate a single stranded product amplified from this DNA sample. Shuldiner, et al., Handbook of Techniques in Endocrine Research, p. 457-486, DePablo, F., Scanes, C., eds., Academic Press, Inc., 1993. Fluorescent dye is attached for automated sequencing using the Taq Dye Terminator Kit (Perkin-Elmer.RTM. cat# 401628). DNA sequencing is performed in both forward and reverse directions on an Applied Biosystems, Inc. (ABI) automated sequencer (Model 377). The software used for analysis of the resulting data is "Sequence Navigator" purchased through ABI. 1. Polymerase Chain Reaction (PCR) Amplification Genomic DNA (100 nanograms) extracted from white blood cells of the subject is amplified in a final volume of 25 microliters containing 1 microliter (100 nanograms) genomic DNA, 2.5 microliters 10X PCR buffer (100 mM Tris, pH 8.3, 500 mM KCl, 1.2 mM MgCl.sup.2), 2.5 microliters 10X dNTP mix (2 mM each nucleotide), 2.5 microliters forward primer (BRCA1-11K-F, 10 micromolar solution), 2.5 microliters reverse primer (BRCA1-11K-R, 10 micromolar solution), and 1 microliter Taq polymerase (5 units), and 13 microliters of water. The PCR primers used to amplify segment K of exon 11 (where the mutation is found) are as follows:

BRCA1-11K-F: 5'-GCA AAA GCG TCC AGA AAG GA-3' SEQ ID NO: 69

BRCA1-11K-R: 5'-AGT CTT CCA ATT CAC TGC AC-3' SEQ ID NO: 70

The primers are synthesized on an DNA/RNA Synthesizer Model 394.RTM.. Thirty-five cycles are performed, each consisting of denaturing (95.degree. C. 30 seconds), annealing (55.degree. C.; 1 minute), and extension (72.degree. C.; 90 seconds), except during the first cycle in which the denaturing time is increased to 5 minutes, and during the last cycle in which the extension time is increased to 5 minutes. PCR products are purified using QIA-QUICK.RTM. PCR purification kits (Qiagen.RTM., cat# 28104; Chatsworth, Calif.). Yield and purity of the PCR product determined spectrophotometrically at OD.sub.260 on a Beckman DU 650 spectrophotometer.

2. Dideoxy Sequence Analysis

Fluorescent dye is attached to PCR products for automated sequencing using the Taq Dye Terminator Kit (PERKIN-ELMER.RTM. Cat # 401628). DNA sequencing is performed in both forward and reverse directions on an Applied Biosystems, Inc. (ABI) Foster City, Calif., automated sequencer (Model 377). The software used for analysis of the resulting data is "SEQUENCE NAVIGATOR" purchased through ABI. The BRCA1.sup.(omi) sequence is entered into the SEQUENCE Navigator software as the Standard for comparison. The Sequence Navigator software compares the sample sequence to the BRCA1.sup.(omi) standard (SEQ ID. NO: 1), base by base. The Sequence Navigator highlights all differences between the BRCA1.sup.(omi) (SEQ ID. NO: 1) consensus normal DNA sequence and the patient's sample sequence.

A first technologist checks the computerized results by comparing visually the BRCA1.sup.(omi) standard against the patient's sample, and again highlights any differences between the standard and the sample. The first primary technologist then interprets the sequence variations at each position along the sequence. Chromatograms from each sequence variation are generated by the Sequence Navigator and printed on a color printer. The peaks are interpreted by the first primary technologist and a second primary technologist. A secondary technologist then reviews the chromatograms. The results are finally interpreted by a geneticist. In each instance, a variation is compared to known normal polymorphisms for position and base change. The seven known polymorphisms which occur in the Consensus Normal DNA sequence are:

AGC and AGT at position 2201,

TTG and CTG at position 2430,

CCG and CTG at position 2731,

GAA and GGA at position 3232,

AAA and AGA at position 3667,

TCT and TCC at position 4427, and

AGT and GGT at position 4956.

Mutations are noted by the length of non-matching variation. Such a lengthy mismatch pattern occurs with deletions and substitutions.

5. Result

Using the above PCR amplification and standard fluorescent sequencing technology, The 3888delGA mutation may be found. The 3888delGA mutation The BRCA1 gene lies in segment "K" of exon 11. The DNA sequence results demonstrate the presence of a two base pair deletion at nucleotides 3888 and 3889 of the published BRCA1.sup.(omi) sequence. This mutation interrupts the normal reading frame of the BRCA1 transcript, resulting in the appearance of an in-frame terminator (TAG) at codon position 1265. This mutation is, therefore, predicted to result in a truncated, and most likely, non-functional protein. The formal name of the mutation will be 3888delGA. This mutation is named in accordance with the suggested nomenclature for naming mutations, Baudet, A et al., Human Mutation 2:245-248, (1993).

Although the invention has been described with reference to the presently preferred embodiments, it should be understood that various modifications can be made without departing from the spirit of the invention. Accordingly, the invention is limited only by the following claims.