Method for determining copy number variations

Abstract

The invention provides a method for determining copy number variations (CNV) of a sequence of interest in a test sample that comprises a mixture of nucleic acids that are known or are suspected to differ in the amount of one or more sequence of interest. The method comprises a statistical approach that accounts for accrued variability stemming from process-related, interchromosomal and inter-sequencing variability. The method is applicable to determining CNV of any fetal aneuploidy, and CNVs known or suspected to be associated with a variety of medical conditions.

1 . A method for identifying fetal trisomy 21, said method comprising the steps:
 (a) sequencing at least a portion of fetal and maternal nucleic acids of a maternal blood sample to obtain sequence information;   (b) using said sequence information to identify a number of mapped sequence tags for chromosome 21;   (c) using said sequence info illation to identify a number of mapped sequence tags for at least one normalizing chromosome;   (d) using said number of mapped sequence tags identified for chromosome 21 in step (b) and said number of mapped sequence tags identified for said at least one normalizing chromosome in step (c) to calculate a chromosome dose for chromosome 21; and   (e) comparing said chromosome dose to at least one threshold value, and thereby identifying the presence or absence of fetal trisomy 21,   wherein said normalizing chromosome is a chromosome or group of chromosomes that gives the smallest variability in chromosome dose across a plurality of qualified samples and/or gives the greatest differentiability in chromosome dose between an affected trisomy 21 sample from one or more unaffected samples.   
     
     
         2 . The method of  claim 1 , wherein step (d) comprises calculating a chromosome dose for chromosome 21 as a ratio of said number of mapped sequence tags identified for chromosome 21 and said number of sequence tags identified for said at least one normalizing chromosome. 
     
     
         3 . The method of  claim 1 , wherein step (d) comprises:
 (i) calculating a sequence tag density ratio for chromosome 21, by relating said number of mapped sequence tags identified for chromosome 21 in step (b) to the length of chromosome 21;   (ii) calculating a sequence tag density ratio for said at least one normalizing chromosome, by relating said number of mapped sequence tags identified for said at least one normalizing chromosome in step (c) to the length of said at least one normalizing chromosome; and   (iii) using the sequence tag density ratios calculated in steps (i) and (ii) to calculate a chromosome dose for chromosome 21, wherein said chromosome dose is calculated as a ratio of said sequence tag density ratio for chromosome 21 and said sequence tag density ratio for said at least one normalizing chromosome.   
     
     
         4 . The method of  claim 1 , wherein said fetal and maternal nucleic acid molecules are cell-free DNA molecules. 
     
     
         5 . The method of  claim 1 , wherein said sequencing is performed on an amplified library preparation. 
     
     
         6 . The method of  claim 1 , wherein said sequencing is next generation sequencing (NGS). 
     
     
         7 . The method of  claim 1 , wherein said sequencing is massively parallel sequencing-by-synthesis with reversible dye terminators. 
     
     
         8 . The method of  claim 1 , wherein said sequencing is sequencing-by-ligation. 
     
     
         9 . The method of  claim 1 , wherein said sequencing is single molecule sequencing. 
     
     
         10 . A method for identifying fetal trisomy 18, said method comprising the steps:
 (a) sequencing at least a portion of fetal and maternal nucleic acids of a maternal blood sample to obtain sequence information;   (b) using said sequence information to identify a number of mapped sequence tags for chromosome 18;   (c) using said sequence information to identify a number of mapped sequence tags for at least one normalizing chromosome;   (d) using said number of mapped sequence tags identified for chromosome 18 in step (b) and said number of mapped sequence tags identified for the at least one normalizing chromosome in step (c) to calculate a chromosome dose for chromosome 18; and   (e) comparing said chromosome dose to at least one threshold value, and thereby identifying the presence or absence of fetal trisomy 18,   wherein said normalizing chromosome is a chromosome or group of chromosomes that gives the smallest variability in chromosome dose across a plurality of qualified samples and/or gives the greatest differentiability in chromosome dose between an affected trisomy 18 sample from one or more unaffected samples.   
     
     
         11 . The method of  claim 10 , wherein step (d) comprises calculating a chromosome dose for chromosome 18 as a ratio of said number of mapped sequence tags identified for chromosome 18 and said number of sequence tags identified for said at least one normalizing chromosome. 
     
     
         12 . The method of  claim 10 , wherein step (d) comprises:
 (i) calculating a sequence tag density ratio for chromosome 18, by relating said number of mapped sequence tags identified for chromosome 18 in step (b) to the length of chromosome 18;   (ii) calculating a sequence tag density ratio for said at least one normalizing chromosome, by relating said number of mapped sequence tags identified for said at least one normalizing chromosome in step (c) to the length of said at least one normalizing chromosome; and   (iii) using the sequence tag density ratios calculated in steps (i) and (ii) to calculate a chromosome dose for chromosome 18, wherein said chromosome dose is calculated as a ratio of said sequence tag density ratio for chromosome 18 and said sequence tag density ratio for said at least one normalizing chromosome.   
     
     
         13 . The method of  claim 10 , wherein said fetal and maternal nucleic acid molecules are cell-free DNA molecules. 
     
     
         14 . The method of  claim 10 , wherein said sequencing is performed on an amplified library preparation. 
     
     
         15 . The method of  claim 10 , wherein said sequencing is next generation sequencing (NGS). 
     
     
         16 . The method of  claim 10 , wherein said sequencing is massively parallel sequencing-by-synthesis with reversible dye terminators. 
     
     
         17 . The method of  claim 10 , wherein said sequencing is sequencing-by-ligation. 
     
     
         18 . The method of  claim 10 , wherein said sequencing is single molecule sequencing. 
     
     
         19 . A method for identifying fetal trisomy 13, said method comprising the steps:
 (a) sequencing at least a portion of fetal and maternal nucleic acids of a maternal blood sample to obtain sequence information;   (b) using the sequence information to identify a number of mapped sequence tags for chromosome 13;   (c) using the sequence information to identify a number of mapped sequence tags for at least one normalizing chromosome;   (d) using said number of mapped sequence tags identified for chromosome 13 in step (b) and said number of mapped sequence tags identified for the at least one normalizing chromosome in step (c) to calculate a chromosome dose for chromosome 13; and   (e) comparing said chromosome dose to at least one threshold value, and thereby identifying the presence or absence of fetal trisomy 13,   wherein said normalizing chromosome is a chromosome or group of chromosomes that gives the smallest variability in chromosome dose across a plurality of qualified samples and/or gives the greatest differentiability in chromosome dose between an affected trisomy 13 sample from one or more unaffected samples.   
     
     
         20 . The method of  claim 19 , wherein step (d) comprises calculating a chromosome dose for chromosome 13 as a ratio of said number of mapped sequence tags identified for chromosome 13 and said number of sequence tags identified for said at least one normalizing chromosome. 
     
     
         21 . The method of  claim 19 , wherein step (d) comprises:
 (i) calculating a sequence tag density ratio for chromosome 13, by relating said number of mapped sequence tags identified for chromosome 13 in step (b) to the length of chromosome 13;   (ii) calculating a sequence tag density ratio for said at least one normalizing chromosome, by relating said number of mapped sequence tags identified for said at least one normalizing chromosome in step (c) to the length of said at least one normalizing chromosome; and   (iii) using the sequence tag density ratios calculated in steps (i) and (ii) to calculate a chromosome dose for chromosome 13, wherein said chromosome dose is calculated as a ratio of said sequence tag density ratio for chromosome 13 and said sequence tag density ratio for said at least one normalizing chromosome.   
     
     
         22 . The method of  claim 19 , wherein said fetal and maternal nucleic acid molecules are cell-free DNA molecules. 
     
     
         23 . The method of  claim 19 , wherein said sequencing is performed on an amplified library preparation. 
     
     
         24 . The method of  claim 19 , wherein said sequencing is next generation sequencing (NGS). 
     
     
         25 . The method of  claim 19 , wherein said sequencing is massively parallel sequencing-by-synthesis with reversible dye terminators. 
     
     
         26 . The method of  claim 19 , wherein said sequencing is sequencing-by-ligation. 
     
     
         27 . The method of  claim 19 , wherein said sequencing is single molecule sequencing.