78 Z-Score With GC Correction Using an Internal

78 Z-Score With GC Correction Using an Internal selleck products Control A more recent strategy utilizes a specific internal reference chromosome for each chromosome being assessed. The optimal internal reference chromosome is one that has a similar GC content to the chromosome of clinical interest.83 This approach appears to be markedly more adept at detecting aneuploidies other than T21, and a recent proof of concept study using this approach demonstrated 100% accuracy for detection of T13, T18, T21, 45,X, and 47,XXY in a small sample of 32 aneuploid cases.83 Normalized Chromosome Value The normalized chromosome value (NCV) approach differs in the normalization process that compares the reads from the chromosome of interest with the number of counts from a reference set derived from an unaffected group of samples.

77,84 The NCV algorithm helps to minimize the intra- and inter-run sequencing variation.84 Parental Support? In contrast to the quantitative methods previously discussed in this review, Parental Support? (PS; Natera, San Carlos, CA) focuses on measuring single nucleotide polymorphisms (SNPs). By measuring polymorphic loci, this approach is able to extract multiple pieces of information (including the number and identity of each allele) from each sequence read. PS then incorporates allelic information from the mother (and from the father, if available) to model a set of hypotheses (viz, monosomy, disomy, or trisomy), corresponding to different genetic inheritance patterns and crossover locations for every possible copy number count.

Bayesian statistics then assign a probability to each hypothesis, and a maximum likelihood estimation analysis is performed to select the most likely hypothesis and calculate the probability of that hypothesis being correct.85 Commercial NIPT: Are We There Yet? A number of companies have been spearheading the effort to develop the next generation of NIPT tests, including Sequenom Center for Molecular Medicine (San Diego, CA), Verinata Health (Redwood City, CA), Ariosa Diagnostics (San Jose, CA), and Natera. These companies all use a sequencing-based approach for gathering the genetic information contained within the cfDNA. In some cases, MPSS is the sequencing methodology of choice, whereas targeted sequencing is utilized by others. Each entity utilizes a unique and proprietary algorithm for interpretation of the genetic data.

Although the exact technology may vary, the implications for clinical practice Drug_discovery are the same; namely, these are all screening tests performed by analyzing cfDNA in a sample of maternal blood, and all positive test results should be confirmed by amniocentesis or CVS before acting upon the information. Detection rates reported by the commercial entities differ, as does the scope of chromosomal aneuploidies assessed. These, together with the specific analysis technique offered, are described below and summarized in Table 2.

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