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9.3: Diagnosing Human Chromosome Abnormalities - Biology

9.3:  Diagnosing Human Chromosome Abnormalities - Biology


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Bright Field Microscopy

How can we confirm that a person has a specific chromosomal abnormality? The first method was simply to obtain a sample of their cells, stain the chromosomes with Giemsa dye, and examine the results with a light microscope (Figure (PageIndex{1})). Each chromosome can be recognized by its length, the location of its centromere, and the characteristic pattern of purple bands produced by the Giemsa. For example, if mitotic cells from a person consistently contained forty seven chromosomes in total with three chromosome 21s this would be indicative of Down syndrome. Bright field microscopy does has its limitations though - it only works with mitotic chromosomes and many chromosome rearrangements are either too subtle or too complex for even a skilled cytogeneticist to discern.

Fluorescence In Situ Hybridization

The solution to these problems was fluorescence in situ hybridization (FISH). The technique is similar to a Southern blot in that a single stranded DNA probe is allowed to hybridize to denatured target DNA (see Section 8.6). However, instead of the probe being radioactive it is fluorescent and instead of the target DNA being restriction fragments on a nylon membrane it is denatured chromosomes on a glass slide. Because there are several fluorescent colours available it is common to use more than one probe at the same time. Typically the chromosomes are also labeled with a fluorescent stain called DAPI which gives them a uniform blue colour. If the chromosomes have come from a mitotic cell it is possible to see all forty six of them spread out in a small area. Alternatively, if the chromosomes are within the nucleus of an interphase cell they appear together within a large blue circle.

Using FISH to Diagnose Down Syndrome

Most pregnancies result in healthy children. However in some cases there is an elevated chance that the fetus has trisomy-21. Older women are at a higher risk because the non-disjunction events that lead to trisomy become more frequent with age. The second consideration is what the fetus looks like during an ultrasound examination. Fetuses with trisomy-21 and some other chromosome abnormalities have a swelling in the back of the neck called a nuchal translucency. If either or both factors is present the woman may choose amniocentesis. In this test some amniotic fluid is withdrawn so that the fetal cells within it can be examined. Figure (PageIndex{2}) shows a positive result for trisomy-21. Based upon this image the fetus has two X chromosomes and three chromosome 21s and therefore has a karyotype of 47,XX,+21.

Using FISH to Diagnose Cri-du-Chat Syndrome

A physician may suspect that a patient has a specific genetic condition based upon the patient's physical appearance, mental abilities, health problems, and other factors. FISH can be used to confirm the diagnosis. For example, Figure (PageIndex{3}) shows a positive result for cri-du-chat syndrome. The probes are binding to two long arms of chromosome 5 but only one short arm. One of the chromosome 5s must therefore be missing part of its short arm.

Newer Techniques

FISH is an elegant technique that produces dramatic images of our chromosomes. Unfortunately, FISH is also expensive, time consuming, and requires a high degree of skill. For these reasons, FISH is slowly being replaced with PCR and DNA chip based methods. Versions of these techniques have been developed that can accurately quantify a person's DNA. For example a sample of DNA from a person with Down syndrome will contain 150% more DNA from chromosome 21 than the other chromosomes. Likewise DNA from a person with cri-du-chat syndrome will contain 50% less DNA from the end of chromosome 5. These techniques are very useful if the suspected abnormality is a deletion, a duplication, or a change in chromosome number. They are less useful for diagnosing chromosome inversions and translocations because these rearrangements often involve no net loss or gain of genes.

In the future all of these techniques will likely be replaced with DNA sequencing. Each new generation of genome sequencing machines can sequence more DNA in less time. Eventually it will be cheaper just to sequence a patient's entire genome than to use FISH or PCR to test for specific chromosome defects.


FAQs About Chromosome Disorders

What are chromosomes?
Chromosomes are organized packages of DNA found inside your body's cells.[1] Your DNA contains genes that tell your body how to develop and function. Humans have 23 pairs of chromosomes (46 in total). You inherit one of each chromosome pair from your mother and the other from your father. Chromosomes vary in size. Each chromosome has a centromere, which divides the chromosome into two uneven sections. The shorter section is called the p arm, and the longer section is called the q arm.[1][2] MedlinePlus Genetics has a helpful picture of a chromosome.


Are there different types of chromosomes?
Yes, there are two different types of chromosomes sex chromosomes and autosomal chromosomes. The sex chromosomes are the X and Y chromosomes. They determine your gender (male or female). Females have two X chromosomes, XX, one X from their father and one X from their mother. Males have one X chromosome from their mother and one Y chromosome, from their father, XY. Mothers always contribute an X chromosome (to either their son or daughter). Fathers can contribute either an X or a Y, which determines the gender of the child. The remaining chromosomes (pairs 1 through 22) are called autosomal chromosomes. They contain the rest of your genetic information.[1][2][3][4]


What are the different types of chromosome disorders?
Chromosome disorders can be classified into two main types numerical and structural. Numerical disorders occur when there is a change in the number of chromosomes (more or fewer than 46). Examples of numerical disorders include trisomy, monosomy and triploidy. Probably one of the most well-known numerical disorders is Down syndrome (trisomy 21).[1][2] Other common types of numerical disorders include trisomy 13, trisomy 18, Klinefelter syndrome and Turner syndrome.

Structural chromosome disorders result from breakages within a chromosome. In these types of disorders there may be more or less than two copies of any gene. This difference in number of copies of genes may lead to clinical differences in affected individuals. Types of structural disorders include the following: [1][2] (click on each type to view an illustration)

    , sometimes known as partial monosomies, occur when a piece or section of chromosomal material is missing. Deletions can occur in any part of any chromosome. When there is just one break in the chromosome, the deletion is called a terminal deletion because the end (or terminus) of the chromosome is missing. When there are two breaks in the chromosome, the deletion is called an interstitial deletion because a piece of chromosome material is lost from within the chromosome. Deletions that are too small to be detected under a microscope are called microdeletions.[1][2][5] A person with a deletion has only one copy of a particular chromosome segment instead of the usual two copies. Some examples of more common chromosome deletion syndromes include cri-du-chat syndrome and 22q11.2 deletion syndrome.
    , sometimes known as partial trisomies, occur when there is an extra copy of a segment of a chromosome. A person with a duplication has three copies of a particular chromosome segment instead of the usual two copies. Like deletions, duplications can happen anywhere along the chromosome.[1][2][5] Some examples of duplication syndromes include 22q11.2 duplication syndrome and MECP2 duplication syndrome.
    occur when a chromosome segment is moved from one chromosome to another. In balanced translocations, there is no detectable net gain or loss of DNA.[1][2][5]
    occur when a chromosome segment is moved from one chromosome another. In unbalanced translocations, the overall amount of DNA has been altered (some genetic material has been gained or lost).[1][2][5]
    occur when a chromosome breaks in two places and the resulting piece of DNA is reversed and re-inserted into the chromosome. Inversions that involve the centromere are called pericentric inversions inversions that do not involve the centromere are called paracentric inversions.[1][2][5]
    are abnormal chromosomes with identical arms - either two short (p) arms or two long (q) arms. Both arms are from the same side of the centromere, are of equal length, and possess identical genes. Pallister-Killian syndrome is an example of a condition resulting from the presence of an isochromosome.[2][5]
    result from the abnormal fusion of twp chromosome pieces, each of which includes a centromere.[5]
    form when the ends of both arms of the same chromosome are deleted, which causes the remaining broken ends of the chromosome to be "sticky". These sticky ends then join together to make a ring shape. The deletion at the end of both arms of the chromosome results in missing DNA, which may cause a chromosome disorder. MedlinePlus Genetics provides a diagram of the steps involved in the formation of a ring chromosome.[1][2][5] An example of a ring condition is ring chromosome 14 syndrome.

What causes chromosome disorders?
The exact cause is unknown, but we know that chromosome abnormalities usually occur when a cell divides in two (a normal process that a cell goes through). Sometimes chromosome abnormalities happen during the development of an egg or sperm cell (called germline), and other times they happen after conception (called somatic). In the process of cell division, the correct number of chromosomes is supposed to end up in the resulting cells. However, errors in cell division, called nondisjunction, can result in cells with too few or too many copies of a whole chromosome or a piece of a chromosome,[1][6] Some factors, such as when a mother is of advanced maternal age (older then 35 years), can increase the risk for chromosome abnormalities in a pregnancy.[1]


What is mosaicism?
Mosaicism is when a person has a chromosome abnormality in some, but not all, cells. It is often difficult to predict the effects of mosaicism because the signs and symptoms depend on which cells of the body have the chromosome abnormality.[2][7] MedlinePlus Genetics provides a diagram of mosaicism.


How are chromosome disorders diagnosed?
Chromosome disorders may be suspected in people who have developmental delays, intellectual disabilities and/or physical abnormalities. Several types of genetic tests can identify chromosome disorders:

What signs and symptoms are associated with rare chromosome disorders?
In general, the effects of rare chromosome disorders vary. With a loss or gain of chromosomal material, symptoms might include a combination of physical problems, health problems, learning difficulties and challenging behavior. The symptoms depend on which parts of which chromosomes are involved. The loss of a segment of a chromosome is usually more serious than having an extra copy of the same segment. This is because when you lose a segment of a chromosome, you may be losing one copy of an important gene that your body needs to function.[2]

There are general characteristics of rare chromosomal disorders that occur to varying degrees in most affected people. For instance, some degree of learning disability and/or developmental delay will occur in most people with any loss or gain of material from chromosomes 1 through 22. This is because there are many genes located across all of these chromosomes that provide instructions for normal development and function of the brain.[2] Health providers can examine the chromosome to see where there is a break (a breakpoint). Then they can look at what genes may be involved at the site of the break. Knowing the gene(s) involved can sometimes, but not always, help to predict signs and symptoms.


Can chromosome disorders be inherited?
Although it is possible to inherit some types of chromosomal disorders, many chromosomal disorders are not passed from one generation to the next. Chromosome disorders that are not inherited are called de novo , which means "new".[6] You will need to speak with a genetics professional about how (and if) a specific chromosome disorder might be inherited in your family.

How can I find individuals with the same chromosome disorder?
Chromosome Disorder Outreach (CDO) provides information on chromosomal conditions and family matching. Contact CDO for more information about how to connect with other families.

Chromosome Disorder Outreach
PO Box 724
Boca Raton, FL 33429
Family Helpline: 561-395-4252
E-mail: [email protected]
Web site: http://www.chromodisorder.org

Unique is a source of information and support for families and individuals affected by rare chromosome disorders. This organization is based in the United Kingdom, but welcomes members worldwide. Unique also has a list of Registered Chromosome Disorders.

Unique - Rare Chromosome Disorder Support Group
United Kingdom
Telephone: 440 1883 330766
E-mail: [email protected]
Web site: http://www.rarechromo.org


How can I find research studies for individuals with chromosome disorders?
The National Institute of General Medical Sciences (NIGMS) Human Genetic Cell Repository was established in 1972 to provide a readily accessible, centralized resource for genetic material from individuals with inherited defects in metabolism, chromosomal abnormalities, and other genetic disorders. This biobank creates cell lines, DNA and other materials from blood or tissue samples and makes these important resources available to scientists worldwide to facilitate research on the diagnosis, treatment and prevention of rare disorders. They are interested in collecting samples from individuals with chromosome disorders, including but not limited to: rare trisomies, ring chromosomes, micro deletion/duplication syndromes, and balanced and unbalanced translocations or inversions. Click on the link to learn more about this service.

The Developmental Genome Anatomy Project (DGAP) is a research effort to identify apparently chromosomal rearrangements in patients with multiple congenital anomalies and then to use these chromosomal rearrangements to map and identify genes that are disrupted or dysregulated in critical stages of human development. Click on the link to learn more about this study.

Chromosome Disorder Outreach provides information about latest research articles for chromosome disorders.


When might it be appropriate to speak with a genetics professional?
Individuals or families who are concerned about an inherited condition may benefit from a genetics consultation. The MedlinePlus Genetics Web site provides a list of reasons why a person or family might be referred to a genetics professional.

For more information on a specific chromosome abnormality, we encourage you to speak with a genetics professional. Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members.


Cause Cause

In most cases, chromosome 3p- syndrome occurs for the first time in the affected person ( de novo mutation ). However, the deletion is rarely inherited from a parent. In these cases, the deletion is passed down in an autosomal dominant manner. This means that a person with chromosome 3p- syndrome has a 50% chance with each pregnancy of passing the condition on to his or her child.

In theory, it is possible for a parent to not have the deletion in their chromosomes on a blood test, but have the deletion in some of their egg or sperm cells only. This phenomenon is called germline mosaicism . In these rare cases, it would be possible to have another child with the deletion. To our knowledge, this has not been reported with chromosome 3p- syndrome. [4]

People interested in learning more about genetic risks to themselves or family members should speak with a genetics professional.


Organizations Organizations

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.


When chromosomes do not segregate properly, cells can end up with missing or extra chromosomes. Chromosomal abnormalities characterized by an atypical number of chromosomes are called aneuploidy.

For instance, trisomy 21 (Down syndrome) is caused by an extra copy of chromosome 21 in the egg or sperm that results in the fertilized egg receiving three copies of chromosome 21. Mosaic trisomy 21 is a rare form of Down syndrome that happens after fertilization.

Trisomy 13 (Patau syndrome) causes severe intellectual and physical disabilities. Trisomy 18 (Edwards syndrome) is even more severe and can threaten children’s survival. Trisomy X is an extra copy of the X chromosome in female sex cells. Klinefelter syndrome happens when a male inherits an extra X chromosome from his mother the XXY condition is sometimes associated with advanced maternal age.

Monosomy occurs when one chromosome is partially or entirely missing. For example, females with Turner syndrome only have one X chromosome instead of two X chromosomes. Cri du chat syndrome results from a deletion of the short arm of chromosome 5.


Most cases of mosaic trisomy 9 occur due to a random event during the formation of the reproductive cells (egg and sperm) or after fertilization has taken place. An error in cell division (called nondisjunction ) may cause some eggs or sperm to have an abnormal number of chromosomes . If an egg or sperm with an extra chromosome 9 contributes to the genetic makeup of an embryo, the embryo will have an extra copy of chromosome 9 in each cell. As the embryo grows and divides, an attempt may be made to correct the mistake by eliminating one extra chromosome 9. In people with mosaic trisomy 9, this attempt may be partly successful, leaving some cells with an extra chromosome 9 and some cells with the extra chromosome deleted (the usual chromosome number). This correction process is called trisomy rescue. [1] [2]

In other cases, the egg and sperm may have a normal number of chromosomes, but an error of cell division (nondisjunction) occurs when the fertilized egg is growing and dividing. If an error occurs during one of the divisions, it can cause some cells to have an abnormal number of chromosomes. In people affected by mosaic trisomy 9, some of the body's cells have the usual two copies of chromosome 9, and other cells have three copies of this chromosome (trisomy). The percentage of cells with trisomy 9 and which parts of the body are affected vary from person to person. This leads to variability in the range and severity of symptoms. [1] [2]

In rare cases, mosaic trisomy 9 is inherited from a parent with a chromosomal rearrangement called a " pericentric inversion ." This occurs when a segment of chromosome 9 has broken off in two places, swiveled round 180 degrees and reinserted itself into the chromosome. If this rearrangement is considered "balanced," meaning the piece of chromosome is in a different order but no genetic material is gained or lost, it usually does not cause any symptoms or health problems. However, it can be associated with an increased risk of having children with an abnormal number or chromosomes. [1] [2]


Fetal Loss

34.3.2 Pattern of Chromosome Abnormalities Seen in Aborted Pregnancies

The vast majority of chromosomal abnormalities observed in aborted fetuses evaluated by G-banding are numerical, including autosomal trisomies, polyploidy, sex chromosome monosomy and double trisomies (26) . A 2009 study, combining G-banding with MLPA and aCGH (27) on 115 first-trimester miscarriages, found 69 (60%) to be chromosomally abnormal. Of these, 69% had autosomal trisomy (including 2% with double trisomies), 12% were polyploid (primarily triploidy), and 10% had sex chromosome monosomy (45,X), with only 1% showing structural abnormalities and the rest showing errors not involving entire chromosomes, such as duplications or deletions. Similar results were reported by combining karyotype analysis with reflex FISH (28) , which observed 61% trisomy, 15% polyploidy (primarily triploidy), 14% sex chromosome monosomy and 7% structural abnormalities. It is not surprising that the most common abnormalities seen are autosomal trisomies, as it was recognized as early as 1984 by Hassold and Chiu (5) that the risk of both pregnancy loss and the incidence trisomy as the result of maternal nondisjunction increase with maternal age, and thus are likely to occur concurrently. Our own data (unpublished) shows the most frequent chromosome abnormalities in presumably sporadic fetal losses to be triploidy, sex chromosome monosomy, and trisomies (21, 22, 15, 18, 13 and 16 in descending order ( Figure 34-1 )). A slightly different pattern was observed among losses from women with a history of pregnancy loss, with the most prevalent abnormalities being triploidy, and trisomies 22, 16, 15 and 21. Interestingly, the pattern associated with sporadic loss is similar to that due to meiotic errors (9) , while the pattern seen in the women with recurrent loss has been associated with mitotic errors seen in mosaic IVF embryos. The relative paucity of sex chromosome monosomy among the recurrent losses might be related to the slightly advanced age (37.3 vs 36.2 years) in this group, as sex chromosome monosomy is most often due to nondisjunction in males, and thus would not necessarily be related to maternal age. Double trisomies, which, except in very rare instances involving the presence of an extra sex chromosome, are not viable, are not uncommon in abortus samples, representing about 1–2% of these cases (29) . They are almost always a result of maternal nondisjunction (30) and are also associated with older maternal age. It should be noted that while studies on preimplantation embryos (see earlier) often report autosomal monosomy, peaking at about the eight-cell stage, such karyotypes are inviable, and autosomal monosomy has not been reported in abortus specimens.

FIGURE 34-1 . Relative frequency of chromosome abnormalities observed in cytogenetically abnormal POCs from women with a reported history of recurrent pregnancy loss compared to those with reported sporadic pregnancy loss. Mean maternal age was 37.3 years in the recurrent group and 36.2 years in the sporadic group. Number of chromosomes involved presented across the X axis with 23 = double trisomy, 24 = monosomy X, 25 = triploidy, 26 = tetraploidy. The abnormalities that are considered viable (trisomy 13, 18 and 21 and monosomy X) are all more frequent in the group with sporadic losses, with trisomies 15, 16 and 22 being more prevalent among those with recurrent loss.


Where are chromosomes found in the body?

The body is made up of individual units called cells. Your body has many different kinds of cells, such as skin cells, liver cells and blood cells. In the center of most cells is a structure called the nucleus. This is where chromosomes are located.

The body is made up of individual units called cells. Your body has many different kinds of cells, such as skin cells, liver cells and blood cells. In the center of most cells is a structure called the nucleus. This is where chromosomes are located.


Karyotype, Karyotyping and Preparation of Idiogram

All species are characterized by a set of chromosomes to carry their genetic information. The chromosomal composition of each species has a number of characteristics. The Karyotype is a set of characteristics that identifies and describes a particular set of chromosome. These characteristics which are described by a karyotype are:-

(1). The chromosome number
(2). Relative size of different chromosomes
(3). Position of centromere and length of chromosomal arms
(4). Presence of secondary constrictions and satellites
(5). Banding pattern of the chromosome
(6). Features of sex chromosomes

What is Karyotyping? How to Prepare the Karyotype of Human?

Ø The process of preparation of the karyotype of a species is called Karyotyping.

Ø Karyotyping is now most commonly used in clinical diagnosis and clinical genetics.

Ø Karyotype is prepared from the microphotographs of metaphase chromosomes.

Ø The metaphase chromosome is selected because at this stage the chromosome will have maximum condensation (maximum thickness).

Ø At metaphase stage, the chromosomes will be visible through an ordinary laboratory microscope.

Ø For the clinical karyotyping, the sample materials used may be cells from biopsies, bone marrow cells, blood cells or cells from amniotic fluid or chorionic villus.

Ø The sample cells were first cultured on artificial medium with suitable growth regulators.

Ø The then the cells are arrested at their mitotic metaphase phase by treating with Colchicine.

Ø Colchicine will arrest the cells at metaphase stage since it prevents the formation of spindle fibres.

Ø In the absence of spindle fibres, the metaphase stage cannot proceed to anaphase.

Ø Then the cells were fixed with suitable fixative and treated with specific stains to produce characteristic banding patterns in the chromosomes.

Ø Specific staining or banding techniques are used to identify the homologous pairs of chromosomes within the cells.

Ø Cells are then observed through the microscope and the photographs of the chromosomes were taken.

Ø The individual chromosomes are cut out from the microphotographs and then they are lined up by size with their respective partners to form the karyogram

Ø A uniformly accepted pattern is used for the arrangement of chromosomes in the preparation of karyogram.

Ø In a karyotype, the chromosomes of the organism are ordered in a series of its decreasing size (largest chromosome at first and smallest at last).

Ø In the case of human, the autosomes are numbered from 1 to 22 and arranged in the order of decreasing size.

Ø Sex chromosomes are arranged after the autosomes.

Ø Chromosomes in the karyogram are aligned along a horizontal axis shared by their centromeres.

Ø Individual chromosomes are always depicted with their short ‘p’ arms at the top, and their long ‘q’ arms at the bottom.

Ø The centromeric index is also noted in karyotype analysis.

Ø Centromeric index is the ratio of the length of long and short arms of the chromosome.

What is an Idiogram?

Ø The diagrammatic representation of a karyotype of a species is called Iiogram.

What are the Significance / Importance of Karyotype and Karyotyping?

Ø Karyotypes of different species can be easily compared.

Ø Similarities in the karyotypes represent the evolutionary relationship.

Ø Karyotypes can be used to solve taxonomic disputes.

Ø The karyotype can indicate primitive and advanced features of an organism.

Ø The karyotype of an organism may be symmetric or asymmetric.

Ø A symmetric karyotype possesses more or less similar sized and shaped chromosomes.

Ø An asymmetric karyotype will have huge differences in small and large chromosomes and contain less metacentric chromosomes.

Ø A symmetric karyotype is considered as primitive whereas, an asymmetric karyotype is considered as advanced.

Ø The zygomorphic flowers in plants are associated with asymmetric karyotype.

Ø Some species may have special characteristics in their karyotypes such as mouse has acrocentric chromosomes and many amphibians have only metacentric chromosomes.

Significance of Clinical Karyotype and Clinical Karyotyping of Human Chromosomes:

Ø Nowadays, the Karyotyping frequency used in clinical diagnosis.

Ø The karyotype provides the structural features of each chromosome in an individual.

Ø A clinical cytologist can analyze the karyotype an individual and can determine the gross genetic changes.

Ø Karyotype reveals the numerical anomalies of the chromosomes such as aneuploidy due to trisomy at 21st chromosome (Down syndrome) trisomy at sex chromosome- XXY (Klinefelters syndrome), monosomy at sex chromosome- XO (Turner syndrome) etc.

Ø Karyotypic analysis can also reveal the structural anomalies of the chromosome such as deletions, duplication, inversion and translocations.

Ø Thus karyotypic analysis can give important diagnostic information in sex determination, detection of birth defects, genetic disorders and detection of some cancers.

Modern methods in the Preparation of Karyotype

@. Fluorescence in-situ Hybridization (FISH) is used in modern research for the preparation of Karyotypes.

@. FISH provide accurate details of the chromosome even at minute scale.

@. FISH preparations of chromosomes are visualized by Fluorescence Microscope


Discussion

TE cell samples derived from a total of 38 blastocysts were examined by MPS, and results were compared with those obtained with and SNP array. For the first time, we explored the use of MPS in chromosomal abnormality testing of human embryos, and demonstrated that low-coverage sequencing combined with WGA and bioinformatics analysis can effectively detect aneuploidies and unbalanced chromosomal rearrangements in TE cells.

A major advantage of this MPS-based approach to detection of chromosomal abnormality is the high accuracy of the approach, because it can correct the WGA bias during data analysis. The WGA bias cannot be avoided during SNP array analysis and may affect the reliability of the array results. Moreover, this new approach could provide relatively higher resolution for chromosomal abnormality detection. For each test sample, around 10 million reads were obtained as tags using the MPS-based approach, whereas the maximum density for SNP arrays is five million using Illumina. Moreover, extremely high genome coverage (more than 95%) and depth (over 16×) was also observed in mitochondrial DNA by MPS. Accordingly, the mitochondrial DNA can be evaluated in parallel, which may act as another marker for evaluation of embryo quality, with potential impact on developmental competence [ 21, 22].

Besides the accuracy, the costs of reagents, turnaround time, and throughput are also important factors when new technologies are suggested for application in clinical practice. In this study, the whole MPS-based procedure required 7–10 days in total and required cryopreservation of blastocysts to postpone transfer to the subsequent cycles. However, with the introduction of vitrification, pregnancy rates obtained with cryopreserved blastocysts after minimal or no stimulation may exceed those with fresh embryos [ 23, 24], and may also decrease the incidence of ectopic pregnancies [ 25]. Moreover, several studies indicated that the combined approach of biopsy at the blastocyst stage, comprehensive chromosome analysis, vitrification, and warming and transfer of a single normal embryo might dramatically improve the overall efficiency [ 9, 11, 26, 27]. On the other hand, the sustained technical improvement for the benchtop sequencing platforms, such as Ion Torrent and MiSeq, could generate modest sequencing data in just a few hours and may make fresh transfer possible in the near future.

Regarding the costs, it take only about $41 to generate 1 Gb sequencing data using Illumina HiSeq 2000 with paired-end 100-bp sequencing strategy [ 28], which makes the MPS-based test comparable with conventional approaches. In our study, we obtained around 10 million sequencing data reads for each test sample. However, the sensitivity/specificity evaluation by MPS simulation has demonstrated that a minimum 500 and 100 K effective data size is enough for detection of unbalanced rearrangements and aneuploidy, respectively, both with high sensitivity and specificity. Accordingly, the estimated reagent cost for chromosomal abnormality detection is less than $100. Further development of sequencing technology still has a huge potential to reduce the cost to or below that of conventional approaches. The high throughput is another notable advantage of this MPS-based approach. By using the Illumina HiSeq2000 platform, more than 160 embryos could be processed in parallel in a labor-saving manner.

This study demonstrated a promising application of MPS in PGD/PGS. Apart from the expected further improvement in efficiency and sensitivity of MPS, it can also be used for complex clinical abnormalities, such as mosaicism [ 29]. In the present study, TE biopsy was used to obtain samples for multiple cells [ 30] however, MPS may also be useful for analysis of biopsied blastomeres and polar bodies.

In summary, with the rapid development of sequencing technology and continuously decreasing cost and time of sequencing, it is foreseeable that MPS will play an increasingly significant role in clinical laboratories for human-assisted reproduction applications and studies. Our work was the first to demonstrate the possibilities of this application. Further studies with large sample sizes and in vivo outcomes are needed for comprehensive evaluation to outline the potential for routine clinical application.


Watch the video: sex chromosome aneuploidies T0-0174 (January 2023).