Patent Publication Number: US-2012036116-A1

Title: Method and device for efficient searching of dna sequence based on energy bands of dna spectrogram

Description:
FIELD OF THE INVENTION 
     This invention pertains in general to the field of DNA sequences analysis. More particularly the invention relates to a method for DNA sequence analysis and a device for DNA sequence analysis. 
     BACKGROUND OF THE INVENTION 
     Bioinformatics seeks to organize tremendous volumes of biological data into comprehensible information, which can be used to derive useful knowledge. 
     One tool commonly used within the field of bioinformatics is the Basic Local Alignment Search Tool (BLAST). To run, BLAST requires a query sequence—also called the target sequence—to search for, and a sequence, or a sequence database containing multiple such sequences, to search against. Based on the query sequence, BLAST will find subsequences in the database which are similar to subsequences in the query. In typical usage, the query sequence is much smaller than the database, e.g., the query may be one thousand nucleotides while the database is several billion nucleotides. 
     A common problem for BLAST and other search tools known in the art is that the query sequence is limited. If the query sequence length is larger than around a few thousand nucleotides, the search tool will be unacceptably time consuming. Furthermore, with too large query sequences, the accuracy of the search tools diminishes. In order to make existing bioinformatics tools faster and more accurate, the query sequence is usually manually modified and only the data that is deemed to be most relevant is used for searching. This subjective approach is leading to unreliable results because of unacceptable approximations. 
     DNA spectral analysis offers an approach to systematically tackle the problem of deriving useful information from DNA sequence data. Generally, DNA spectral analysis involves an identification of the occurrences of each nucleotide base in a DNA sequence as an individual digital signal, and transforming each of the four different nucleotide signals into a frequency domain. The magnitude of a frequency component can then be used to reveal how strongly a nucleotide base pattern is repeated at that frequency. A larger magnitude/value usually indicates a stronger presence of the repetition. 
     Spectral analysis techniques, such as described in WO 2007/105,150, generally represent an improvement over manual DNA pattern analysis techniques, which aim at identifying DNA patterns serving as biological markers related to important biological processes. Traditionally, automatic analyses are performed directly on strings of DNA sequences composed of the four characters A, T, C and G, which represent the four nucleotide bases. However, due to the tremendous length of DNA sequences (e.g., the length of the shortest human chromosome is 46.9 Mb), the wide range of pattern spans associated with the limited character set, and the statistical nature of the problem, such an intuitive/manual approach is inefficient, if not impossible, for achieving the desired purpose. 
     Hence, an improved method for DNA sequence analysis would be advantageous and in particular a method allowing for increased flexibility, cost-effectiveness, or faster DNA sequence analysis would be advantageous. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention preferably seeks to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solves at least the above mentioned problems e.g. by providing a method for nucleotide sequence analysis based on nucleotide spectrogram database. Such database may e.g. be a DNA database or a RNA database, well known to a person skilled in the art. 
     In an aspect a method for DNA sequence analysis is provided. The method comprises building a DNA spectrogram database based on a DNA database comprising a number of sequences of nucleotides, by calculating an energy spectral density value for each group of nucleotides comprised in the DNA database. The method further comprises inputting a DNA query sequence. Moreover, the method comprises calculating an energy spectral density value for the DNA query sequence, resulting in an energy spectral density query. The method further comprises calculating a difference between the energy spectral density query value and an energy spectral density value comprised in the DNA spectrogram database. Furthermore, the method comprises selecting a calculated difference, pertaining to a first group of nucleotides, being within a predetermined threshold value range (±Φ Δ ). 
     In another aspect a use of the method in designing a test kit for diagnosing genetic diseases is provided. 
     In an aspect a device comprising a processor unit is provided. The processor unit is configured to build a DNA spectrogram database based on a DNA database comprising a number of sequences of nucleotides, by calculating an energy spectral density value for a group of nucleotides comprised in the DNA database. The processor unit is further configured to receive a DNA query sequence. Moreover, the processor unit is configured to calculate an energy spectral density value for the DNA query sequence, resulting in an energy spectral density query. Furthermore, the processor unit is configured to calculate a difference between the energy spectral density query value and an energy spectral density value comprised in the DNA spectrogram database. The processor unit is further configured to select a difference being lower than a predetermined threshold value. 
     In yet another aspect a computer-readable medium having embodied thereon a computer program for processing by a processor is provided. The computer program comprises a first code segment for building a DNA spectrogram database based on a DNA database comprising a number of sequences of nucleotides, by calculating an energy spectral density value for a group of nucleotides comprised in the DNA database. The computer program further comprises a second code segment for inputting a DNA query sequence. Moreover, the computer program comprises a third code segment for calculating an energy spectral density value for the DNA query sequence, resulting in an energy spectral density query. Furthermore, the computer program comprises a fourth code segment for calculating a difference between the energy spectral density query value and an energy spectral density value comprised in the DNA spectrogram database. The computer program also comprises a fifth code segment for selecting a difference being lower than a predetermined threshold value. 
     The method may comprise the steps of building a DNA spectrogram database. The spectrogram database may be based on a DNA database comprising a number of sequences of nucleotides. This may be done by calculating an energy spectral density value for a group of nucleotides comprised in the DNA database. A DNA query sequence may be used as an input. The energy spectral density value for the DNA query sequence may be calculated, resulting in an energy spectral density query. Then, a difference between the energy spectral density query value and an energy spectral density value comprised in the DNA spectrogram database may be calculated. After this, a calculated difference, pertaining to a first group of nucleotides, being within a predetermined threshold value range (±Φ Δ ) may be selected. 
     The present invention according to some embodiments has the advantage over the prior art that it provides a possibility to compare sequences with large number of nucleotides. Moreover, the improved sequence comparison may also be performed faster than current solutions. 
     Other embodiments of the invention will be explained in further detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects, features and advantages of which the invention is capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which 
         FIG. 1  is a flowchart of a method according to an embodiment; 
         FIG. 2  is a flowchart of the building step of the method according to an embodiment; and 
         FIG. 3  is a block diagram of a device according to according to an embodiment. 
         FIG. 4  is a block diagram of a computer-readable medium according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Several embodiments of the present invention will be described in more detail below with reference to the accompanying drawings in order for those skilled in the art to be able to carry out the invention. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The embodiments do not limit the invention, but the invention is only limited by the appended patent claims. Furthermore, the terminology used in the detailed description of the particular embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. 
     The following description focuses on embodiments of the present invention applicable to efficient searching of DNA Sequence in a DNA sequence database based on energy bands of DNA Spectrogram. 
     In an embodiment, according to  FIG. 1 , a method  10  for DNA sequence analysis is disclosed. The method comprises building  110  a DNA spectrogram database based on a DNA database comprising a number of sequences of nucleotides, by calculating an energy spectral density value for a group of nucleotides comprised in the DNA database. The method may further comprise inputting  120  a DNA query sequence. Moreover, the method comprises calculating  130  an energy spectral density value for the DNA query sequence, resulting in an energy spectral density query. Furthermore, the method may comprise calculating a difference  140  between the energy spectral density query value and an energy spectral density value comprised in the DNA spectrogram database. The method may also comprise selecting  150  a difference being lower than a predetermined threshold value. 
     The group of nucleotides, corresponding to the selected difference, may then be further processed using sequence alignment e.g. a BLAST algorithm. Accordingly, the method may further comprise performing  160  sequence alignment the nucleotides comprised in a selected group. 
     According to one embodiment, the DNA spectrogram database is an energy spectral density (ESD) database. The DNA spectrogram database may be a genomic DNA spectral database. The ESD describes how the energy (or variance) of a signal or a time series is distributed with frequency. If f(t) is a finite-energy (square integrable) signal, the spectral density Φ(ω) of the signal is the square of the magnitude of the continuous Fourier transform of the signal. The energy is represented by the integral of the square of a signal. 
     As the signal is discrete with values f n , over an infinite number of elements, we still have an energy spectral density: 
     
       
         
           
             
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     where w is the angular frequency (2π times the cycle frequency) and F(ω) is the discrete-time Fourier transform of f n , and F*(ω) is its complex conjugate. The multiplicative factor of ½π is not absolute, but rather depends on the particular normalizing constants used in the definition of the various Fourier transforms. 
     According to one embodiment a set of color spectrums of the nucleotide segment, such as a DNA segment, is achieved in a way well known to a person skilled in the art. Next, the periodicity of different color spectrums is calculated by the formula: 
     
       
         
           
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     Here, STFT Window Size is the window size calculated by Short Time Fourier Transform (STFT), well known to a person skilled in the art, and Frequency is the frequency of which a certain color spectrum is occurring when the different color spectrums are aligned. For a particular STFT Window Size, Discrete Fourier Transforms (DFT) are combined in the color space, indicating a certain frequency. Then, the DFT values are squared and divided with the STFT Window Size to get the ESD. 
     In an embodiment according to  FIG. 2 , the building  110  of a DNA spectrogram database is shown. First DNA spectrograms are pre-computed  111  for a large number of genome sequences. A large number of ESD are computed according to above for various lengths of sequences, comprised in a DNA sequence database, and various overlapping starting points. Such pre-computed ESD values may be used as part of the header information of the query sequence similar to a FASTA header, known in the art. The ESD values may differ for a range of nucleotide lengths, e.g. Φ 1 , Φ 2 , . . . , Φ n  for nucleotide lengths 256, 1024 . . . , 8196 respectively. This may trigger the query and make another computation of ESD unnecessary. For example, in a certain color space, ESD computation may be derived by squaring DFT values and dividing them by the STFT Window Size. 
     The building  110  of the DNA spectrogram database may further comprise indexing  112  the pre-computed  111  DNA spectrograms in a structure based on phylogenetic distances. The building  110  of the DNA spectrogram database may further comprise assigning  113  a pointer to the spectrograms. Such pointer may be e.g. a reference to a local database, a URL to a web resource or a protected sequence. The spectrograms may then be stored  114 . 
     In an embodiment, an ESD database may be used in such a way as to provide a fast baseline of probable candidates of sequences from the DNA sequence database, wherein the candidates may be related to the query sequence based on the ESD. Accordingly, the candidates having a similar ESD value to the ESD value of the query sequence may rapidly be identified for further processing. This is due to the fact that the method identifies sequences having similar ESD values to the ESD value of the query sequence. Accordingly, sequences having ESD values within ±Φ Δ , may be selected for subsequent processing. 
     The ESD database also gives the possibility to identify mutations in the DNA sequence. If the specific DNA sequence location e.g. already is known, the energy spectral density (Φ Re f ) of the “healthy/valid” sequence is computed. In order to check for any mutation at that location in other DNA sequences, instead of comparing the sequence per nucleotide, in accordance with current solutions, the “energy spectral density” may be computed directly and changes in value of the “energy spectral density (Φ sam )” may be checked for. If Φ Re f ≠Φ sam , then there is a mutation, and whether it is fatal or not needs to be compared in depth using the existing search tools like BLAST. 
     In another embodiment the method comprises comparing “entire” chromosome or genomic sequence against the database of stored sequences without any huge penalty of comparing every nucleotide for producing search results, as the comparison is based on the “energy spectral density”. 
     According to one embodiment, the sequence alignment  160  is local alignment, such as alignment of short sequences or alignment of shot-gun sequencing results. 
     According to another embodiment, the sequence alignment  160  is global alignment, such as alignment of multiple sequences all at once or alignment of two or more genomes. 
     In an embodiment, according to  FIG. 3 , a device  30  is provided. The device comprises a processor unit configured to build  31  a DNA spectrogram database based on a DNA database comprising a number of sequences of nucleotides, by calculating an energy spectral density value for a group of nucleotides comprised in the DNA database. The processor unit is further configured to receive  32  a DNA query sequence. Moreover, the processor is configured to calculate  33  an energy spectral density value for the DNA query sequence, resulting in an energy spectral density query. Furthermore, the processor unit is configured to calculate  34  a difference  140  between the energy spectral density query value and an energy spectral density value comprised in the DNA spectrogram database. The processor unit is further configured to select  35  a difference being lower than a predetermined threshold value. 
     In an embodiment the processor unit is further configured to perform  36  sequence alignment the nucleotides comprised in a selected group. 
     In an embodiment the processor unit is configured to perform any one of the steps of the method according to some embodiments. 
     According to another embodiment, any of the abovementioned method may be used for designing test kits for diagnosing genetic diseases. 
     In one embodiment, a clinical genetics program is disclosed, the program comprising means to provide fast access to similar genomes of patients with similar disease conditions or provide fast access to similar patients with similar therapy response. The program may also comprise information from pharmacological databases for therapy response and associated genes with this therapy response as well as storage of genomic sequencing (like PACS for medical image). 
     According to one embodiment, genome-sequencing equipment is disclosed; the equipment needs to assemble full genomes. 
     Applications and use of the above-described method according to the invention are various and include exemplary fields such as clinical genetics or clinical genomics. 
     In an embodiment the device is comprised in a system adapted to operate and/or perform the method according to some embodiments. The system may be a medical workstation or medical system, such as a Computed Tomography (CT) system, Magnetic Resonance Imaging (MRI) System or Ultrasound Imaging (US) system. 
     In an embodiment, according to  FIG. 4 , a computer-readable medium is provided having embodied thereon a computer program for processing by a processor. The computer program comprises a first code segment  41  for building  110  a DNA spectrogram database based on a DNA database comprising a number of sequences of nucleotides, by calculating an energy spectral density value for a group of nucleotides comprised in the DNA database; a second code segment  42  for inputting  120  a DNA query sequence; a third code segment  43  for calculating  130  an energy spectral density value for the DNA query sequence, resulting in an energy spectral density query; a fourth code segment  44  for calculating a difference  140  between the energy spectral density query value and an energy spectral density value comprised in the DNA spectrogram database; and a fifth code segment  45  for selecting  150  a difference being lower than a predetermined threshold value. 
     In an embodiment the computer program further comprise a sixth code segment for performing  46  sequence alignment the nucleotides comprised in a selected group. 
     In an embodiment the computer program comprises code segments arranged, when run by an apparatus having computer-processing properties, for performing any one of the method steps defined in some embodiments. 
     The invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. However, preferably, the invention is implemented as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit, or may be physically and functionally distributed between different units and processors. 
     Although the present invention has been described above with reference to specific embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than the specific above are equally possible within the scope of these appended claims. 
     In the claims, the term “comprises/comprising” does not exclude the presence of other elements or steps. The terms DNA sequence and DNA spectrogram database, as represented in the claims, may be any nucleotide sequence, or nucleotide spectrogram database, which is easily understood by a person skilled in the art. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. The terms “a”, “an”, “first”, “second” etc do not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.