Prenatal Genetics Flashcards

Question

T/F: NIPT is not diagnostic

Answer 1

**TRUE** Recognized benefits to NIPT, but… - Currently not diagnostic: “Advanced screening test” - Confirmation with invasive testing is needed - Requires comprehensive genetic counseling **- Should only be used in validated populations (= high risk)** - Not recommended in low risk women (validation studies needed - For women at increased risk to have a child with a prenatally diagnosable disorder (i.e., Mendelian disorder, microdeletion syndrome), amnio or CVS still indicated

Answer 2

(If negative with normal US, no further assessment) - If positive with confirming US: offer invasive testing - If positive without confirming US: offer invasive testing - If negative results with abnormal US findings: offer invasive testing; consider microarray analysis

Answer 3

**- Confined placental mosaicism ~1%** * NIPT measures the genome of the entire cytotrophoblast - True fetal mosaicism - Maternal sex chromosome abnormality * May increase with age - Maternally inherited marker chromosome - Maternal deletion on chromosome 21 - Maternal tumor with high levels of cffDNA - Co-twin demise - Lab error

Answer 4

- Fetal fraction for each twin may be lower * May affect detection rate and ability to classify - Cannot differentiate between twins - Chorionicity does not appear to play a role - No good data on vanishing twin and NIPT - Not offered by all companies

Answer 5

**2**% of all screen positive are not T21, T13, or T18 - Nearly 1/3 of abnormalities found after 1st TM screening are different than expected: 10 yr experience from a single center

Answer 6

– Chorionic Villus Sampling (CVS) – Amniocentesis – Other options (less common) * Early amniocentesis * PUBS – Percutaneous Umbilical Cord Sampling (also called cordocentesis)

Answer 7

- Performed 10-14 weeks gestation - Ultrasound to locate premature placenta - Transcervical or transabdominal * 5-40 grams of chorionic villi - Placental cells obtained (fetal in origin) - Full bladder

Answer 8

- Speculum (or tenaculum) to open cervix - Antiseptic prep of external genitalia and cervix - Catheter inserted using US guidance - Aspiration of the villi

Answer 9

- Cervical stenosis - Vaginal infection - Active herpes - Low-lying myoma - Use of anticoagulants (must d/c prior)

Answer 10

- Double needle system - Single needle with syringe mounted on holder

Answer 11

- Unavoidable myomas - Posterior placenta - Unavoidable maternal intestines - Use of anticoagulants (must d/c prior)

Answer 12

- Allows for earlier information - Tissue taken allows for certain biochemical analysis not possible on amniocytes - Can be “like a pap smear - Operator experience and learning curve - Cannot test for NTDs: MSAFP at 16 weeks - Maternal cell contamination - Higher chance of mosaic result - Confined placental mosaicism

Answer 13

* Genetic studies: karyotype, FISH, CMA, mutational analysis, metabolic studies * AFAFP and acetylcholinesterase * Pulmonary maturity * Infections * Isoimmunization

Answer 14

• May be performed \>15 weeks * Majority 16-18 weeks * Skin cleansed with iodine-based solution * Few centers use local anesthetic * Ultrasound with continuous visualization (not always used)

Answer 15

**3-4%** of pregnancies miscarry in mid TM - Typically NOT attributable to procedure (1/1600 in FASTER, 1/770 in Odibo, 1/4000 in ACOG)

Answer 16

**\< 15 wks** - Remov 10-14 cc of amniotic fluid _Risks_ - **Tenting of membranes**: incomplete fusion of amnion and chorion - Risk of **SAb** may be higher (2-3%?) - Increased chance of **culture failure**? - Risk for **club foot** * 2ndary to decreased fetal mvt during a key phase in foot/ankle devo when fluid is removed that early on * This risk is highest if there is additional leakage of fluid

Answer 17

Percutaneous Umbilical Blood Sampling (PUBS) - Aka cordocentesis _Indications:_ - Mosaicism detected from amnio - Rapid karyotype * Late prenatal care * 2nd or 3rd trimester anomalies - Fetal infections - Hematologic * Hemoglobinopathies * Fetal blood type and Rh - Oligohydramnios/Anhydramnios

Answer 18

Transabdominal needle introduction – Direct ultrasound guidance – Umbilical cord (vein) near placental insertion or fetal hepatic vein – MCV of sample to confirm fetal origin (higher) Performed **18-23 weeks** (depending upon operator)

Answer 19

**1-3% fetal loss rate** Rate is higher with a compromised fetus – Fetal growth restriction – Karyotypic abnormality

Answer 20

**Cytogenetics** - Analysis of banded metaphase chromosomes - Looks at all chromosomes at one time **Fluorescent in situ hybridization (FISH)** - Targets specific chromosomes or specific areas of a chromosome **Chromosome microarray/Comparative Genomic Hybridization** **Molecular testing** **WES** **NGS Panels** (not many in prenatal)

Answer 21

IDs all chromosomal aneuploidies and structural chromosomal abnormalities that are microscopically visible and at least 4-5MB in size _Limitations:_ –Low resolution –Does not detect point mutations –Need for cell culture à longer TAT (10-14 days) –Subjective interpretation –Requires a fresh sample containing live cells –Samples without live cells - cannot be used for chromosome analysis * Serum, mature red blood cells, biopsies which put into formalin or other preservatives * Some tissue samples from miscarriages may no longer be viable when fetal demise is discovered

Answer 22

**Chromosome specific probes** – Can be performed on non-dividing interphase cells without prior cell culture or on metaphase spreads from dividing cells – Interphase FISH * Quicker TAT (24-48 hours) * Typically used prenatally for rapid detection of common aneuploidies **Locus specific probes** – Regions known to be duplicated or deleted in specific syndromes – Used with proband at increased risk for a particular syndrome based on clinical findings or family setting * i.e., del22q probe

Answer 23

* Looks at entire genome for copy number variants (CNVs) * Different array types * Oligonucleotide * SNP * BAC * Combination platforms • Cell culture not always needed à faster TAT _CMA/aCGH detects CNVs_ * Aneuploidies * UNBALANCED chromosome rearrangements * Copy number changes from an entire chromosome down to a few kb in over 500 specific disease regions * Loss of heterozygosity (SNP platforms)

Answer 24

* **Pathogenic** variant – known to be disease causing * **Benign** variant – known to be a polymorphism * **Variant of uncertain clinical significance** * Likely benign * Likely pathogenic * Unknown

Answer 25

**1 – Easy: Gain or loss of no clinical consequence:** * Benign – reassuring: repeatedly observed in healthy individuals * Likely benign – reassuring but with some caution: in gene-devoid region, inherited, present in other healthy, not known to be associated with disease **2 – Harder: Established clinically significant gain or loss:** * Aneuploidy, loss or gain in known disease region – consistent phenotype * Uniparental (iso)disomy causing known disease * Unbalanced translocation **3 – Very challenging: Variant of uncertain clinical significance:** * Continuing = known phenotype but incompletely penetrant or variable * Temporary = del or dup in region not known to be associated with clinical disease – phenotype not yet well-described * –Dup of known deletion syndrome region – phenotype not yet well-described

Answer 26

– Cannot detect truly balanced chromosomal rearrangements (i.e. translocations, inversions, triploidy, polyploidy) – Does not detect all cases of mosaicism – Does not detect point mutations or intragenic mutations – CNV of uncertain significance (\<2%) _Limitations specific to prenatal CMA_ – Often no prenatal phenotype for known chromosomal abnormalities (dels/dups) or other genetic defects – Prenatal presentation and spectrum of anomalies associated with mutations in known disease genes is not always known – Penetrance of known genetic defects when detected prenatally in “asymptomatic fetus” is not always known

Answer 27

- **Amniocentesis or CVS with CMA** will detect a clinically significant abnormality if no other finding is present in **~1:60** of cases - Currently offered **Sequencing-based NIPT tests** on cell-free fetal DNA will detect a clinically significant abnormality in ~**1:500** cases

Answer 28

• Diagnostic procedure with karyotype and CMA: * Detects a clinically significant chromosomal abnormality in ~6-7% with single major anomaly and ~10% with multiple anomalies * This means that we do not have a genetic diagnosis in at least 90% of the cases * Many well-known syndromes caused by single-gene mutations, but not all aspects of these phenotypes are prenatally detectable * In pediatric patients the incremental benefit of whole-exome sequencing in unresolved cases is 25% * Many had more extensive work-up than CMA prior to WES • Supports that there will be benefit to single-gene mutation detection methods: WES or NGS panels

Answer 29

* Look for small DNA mutations * Indirect mutation analysis or linkage analysis * Used when the location of a gene is known, although the gene itself and its function are not, or when the gene is known but the mutations are too heterogeneous to make direct analysis practical * Often requires more than one affected individual in more than one generation. • Direct mutation analysis * Used when gene responsible for the condition has been ID AND specific mutations w/in the gene have been characterized

Answer 30

* Multi-gene, NGS panels to provide addtl diagnostic options for certain common and rare genetic disorders * Some disorders challenging to diagnosis due to overlapping, non0psecifi features that make targeting a specific gene difficult of impossible * Can be more cost-effective than single gene testing * Prenatal examples: Skeletal dysplasia panel (Greenwood), increased NT

Answer 31

* Not currently offered in prenatal * The EXOME is 1.5-2% of the whole GENOME, but makes up the part of the genome we best understand * Exons are short, functionally important sequences of DNA which represent the regions in genes that are translated into protein

Answer 32

* Test that “captures” or selects the coding regions or exons throughout the whole genome to then be sequenced nucleotide by nucleotide to a depth of coverage necessary to build a consensus sequence with high accuracy. * This consensus sequence is then compared to standards and references of what is normal in the population * Once identified through WES variations in an individual's DNA sequence can be related back to the individual's medical concerns in an effort to diagnose the cause of the medical disorder.

Answer 33

* Obtaining a diagnostic result * Improve preventive care through identification of medically actionable result * Probable cost-effectiveness

Answer 34

PROS: * WES is an efficient method of analyzing a patient's DNA to discover the genetic cause of diseases or disabilities because it analyzes the exons of tens of thousands of genes at the same time. * The exome is the part of the genome currently best understood * Ideal to help us understand highly penetrant allelic variation and relationship to a given phenotype * Less expensive and less data generated as compared to WGS and also takes less machine time CONS * Laboratory/Interpretation challenges: How to classify VUS, How to handle secondary findings? * Can be difficult to counsel * Identifying the genetic cause of the disease may not change medical management or help predict prognosis

Answer 35

* Due to technology limitations does not cover 100% of the exome. Coverage ranges from ~90%-95% depending on methodology. * Depth of coverage varies across exome * Not well detected: Triplet repeat expansions, large deletions & duplications * Detection of small indels may not be as accurate as detection of base substitutions * The mitochondrial genome is not sequenced by capture method * Genes that have closely related pseudogenes are not uniquely captured by this method

Answer 36

- Fetal age - Number of fetuses - Fetal viability - Structural abnormalities * Increased risk of fetal aneuploidy * Genetic syndromes - Fetal sex (Not all US are created equal!)

Answer 37

**Down syndrome** – Approximately 50% have a finding * Congenital defect (heart, duodenal atresia) * Soft markers (nuchal fold, pyelectasis) – 50% will not have a finding – Cannot see dysmorphic features on ultrasound **Trisomy 13 & 18** – Approximately 80-85% have a finding – Incidence of structural malformations higher **NTDs (Neural Tube Defects)** – 90-95% spina bifida seen by ultrasound * Splayed vertebrae * Abnormal shape of cerebellum (banana) and front of skull (lemon) – \>99% of anencephaly seen on ultrasound – As with all, position of fetus, size of defect, and maternal habitus play role

Answer 38

30% association with Down syndrome, but may also be seen with various other genetic, chromosomal, and sporadic syndromes

Answer 39

25% have aneuploidy, especially trisomy 13 or trisomy 18. Also think about Beckwith-Wiedemann (esp. if macrosomia, macroglossia, etc.)

Answer 40

20-25% aneuploidy risk (esp. tri 18, 13, 21, and Turner). Also described with Fryns, Cornelia de Lange, and multiple other single gene disorders

Answer 41

* Multiple possible etiologies, usually multifactorial * Aneuploidy risk anywhere from 5-30%, depending on study * Some CHDs, such as AV canal defects, have stronger associations (40-70% Down syndrome risk) * May also be the result of a chromosome microdeletion or microduplication syndrome, such as 22q11 deletion (DiGeorge syndrome) * Environmental factors – teratogens (Lithium, alcohol, etc.) and maternal medical conditions (uncontrolled diabetes)

Answer 42

* Hypospadias, micropenis, clitoromegaly, cryptorchidism * Various causes * Chromosomal – 22q deletions and duplications, 9q subtelomere deletions * Microdeletions/microduplications * Single gene disorders – SLO, CAH, SRY deletions, partial androgen insensitivity syndromes, etc. • Only describes external genitalia, not always appropriate to describe the abnormality * Genital tubercle (not penis/clitoris) * Labioscrotal folds (not labia or scrotum) * Gonads (not testes or ovaries)

Answer 43

* Look for other anomalies, as some tend to go together (e.g. hydrocephalus and ONTDs) * Refer for genetic counseling * Full family history, discussion of possible etiologies, inheritance pattern(s), and recurrence risks if isolated • Refer for a level II ultrasound with an MFM * From there, may need MRI, fetal echo, pedi surgery, etc. • Offer invasive diagnostic testing

Answer 44

* Not considered malformations, but may indicate an increased risk for fetal trisomy * Characteristics * nonspecific * common in normal fetuses * often transient • Significance of isolated soft ultrasound findings is unclear

Answer 45

**• nuchal thickening** • choroid plexus cysts **• echogenic bowel** • shortened long bones **• echogenic intracardiac foci** **• fetal pyelectasis** * mild ventriculomegaly * single umbilical artery

Answer 46

* Nuchal fold measuring 5-6mm (or \>6mm) between 14-21 weeks gestation * Different than nuchal translucency (NT) in the first trimester

Answer 47

* Bowel with similar or greater echogenicity than surrounding bone * Diagnosed in 0.6 – 2.4% of second-trimester ultrasounds * Associations * normal variant * vaginal bleeding * cystic fibrosis * in utero infection * chromosome abnormalities

Answer 48

* Structures within the fetal heart which represent reflections from calcifications of the papillary muscle, with echogenicity similar to bone * Overall Incidence * 0.5% - 30.4% * Incidences may vary based on ethnicity * Asian = 30.4% * Caucasian = 10.5% * African American = 5.9%

Answer 49

* Dilation of the fetal renal pelvis of \>4mm in the transverse A-P diameter * Diagnosed in 0.7 – 2.9% of second-trimester ultrasounds

Answer 50

If isolated soft finding: – Assess other risk factors for aneuploidy – Address risk in terms of ultrasound findings, maternal age, and serum screen results – Discuss option of invasive and non-invasive testing including a comparison of risks for aneuploidy vs. risk for procedure-associated complications * In the absence of additional risk factors, offering invasive testing for an isolated finding is controversial and varies among different practices/clinics If non-isoalted: – In conjunction with other ultrasound findings or additional risk factors for aneuploidy, invasive testing should be offered.

Answer 51

• Ethnicity based carrier screening * ACOG and ACMG guidelines * Family history based carrier screening * Universal/expanded genetic screening

Answer 52

Highest prevalence in Caucasians - However, ACOG standards are to rpovide info about CF screening to ALL couples (since increasingly difficult to assign single ethnicity) - Carrier screening by panel of at least 25 of the most common DNA mutation analysis (not sequencing!)

Answer 53

– Decreased carrier frequency and detection rate – Potential to detect an “affected” person through screening (i.e. person having two mutations and mild or no symptoms, like CBAVD) – Prenatal testing for women who are carriers when father of baby not available for carrier testing – Rare chance of uncovering non-paternity

Answer 54

_Highest carrier frequencies in:_ - **N European/Caucasian** (1/25 - 1/29) - **Ashkenazi Jewish** (1/25-1/29) - **S European Caucasian** (1/29) - Hispanic (1/46) - African American (1/65) - Asian (1/90) _Detection Rate highest in:_ **- Ashkenazi Jewish** (97%) **- N European Caucasian** (85-90%) - S European Caucasian (70-80%) - African American (72%) - Hispanic (57%) - Asian (30%) _Carrier risk after negative test highest in:_ - **Hispanic** (1/105) - **S European Caucasian** (1/97-1/140) - **African Americans** (1/210) - N European Caucasian (1/250) - Ashkenazi Jewish (1/800)

Answer 55

ACOG: Standard of care to offer to persons of AJ background or their partners prior to conception or during **1st trimester**: * **Cystic fibrosis** (1/25) * **Canavan Disease** (1/40) * **Familial Dysautonomia** (1/30) * **Tay Sachs Disease** (1/30) ACMG: recommend CF, Canavan, Familial dysautonomia, and Tay Sachs, PLUS: – **Bloom syndrome** (1/100) – **Gaucher Disease** (1/13) – **Nieman Pick Disease type A** (1/90) – **Fanconi Anemia, Type C** (1/89) – **Mucolipidosis, Type 4** (1/122) Additional disorders considered if AR, \>90% DR or allele frequency of \>1% in the AJ population

Answer 56

There is no standard protocol for carrier testing - CF carrier rate is 1/46 - CBC and/or hemoglobin electrophoresis * Risk varies greatly depending on country of origin

Answer 57

**Standard to review MCV** – If \< 80, screen for thalassemia w/quantitative Hb electrophoresis and ferritin: * **Alpha-thalassemia** carrier rates up to 1/20 * MCV \< 80, Hb electrophoresis nl, serum ferritin nl * DNA testing required for prenatal diagnosis * **Beta-thalassemia** carrier rates 1/30 (SE Asian) to 1/50 * MCV \< 80, Abnl peripheral blood smear with nucleated red blood cells, Normal iron studies, ↓ HbA2, ↑ HbF (after 12m) * DNA testing required for prenatal diagnosis **Cystic fibrosis** –carrier rate 1/90 or less – Detection rate is very low (~ 30%)

Answer 58

**Hemoglobin Electrophoresis** with quantitative A2 (regardless of MCV) * Will screen for: * **Sickle cell** (carrier freq 1/10-1/12) * Do NOT use sickle dex * **Beta-thalassemia** (1/75) * Other hemoglobinopathies **CF** carrier rate about 1/65

Answer 59

**Tay Sachs ENZYME testing\*** - Different mutations than in the AJ population **CF**

Answer 60

CBC and hemoglobin electrophoresis – **Beta-thalassemia** trait (1/20 – 1/30) – **Alpha thalassemia** trait (1/30 – 1/50) – **Sickle cell trait** (1/3 – 1/50) **CF**

Answer 61

CBC and hemoglobin electrophoresis – **Beta**-thalassemia trait (0.5 – 5.5%) – **Alpha** thalassemia trait (variable) – **Sickle cell trait** and other hemoglobin variants (variable) **CF**

Answer 62

- A new concept of carrier screening - Aka Expanded Multi-disease genetic carrier screening panel, aka Next generation carrier screening; all in one carrier screening - Allows to screen for hundred-ish conditions at once at reduced cost - Can be applied to all ethnicities

Answer 63

- Hemoglobinopathies/thalassemias à still need to following ethnicity/CBC guidelines - Tay Sachs enzyme testing BUT the platform is customizable - Can screen only for AJ diseases - Opt in/out of disease * If include opt in diseases, 40% of pts will screen (+) for at least 1 condition (frequency of MTHFR in general population) * If opt out of additional diseases, 20% of pts will screen (+) for at least 1 condition

Answer 64

Opt-in for common "milder" conditions and fragile X syndrome - Testing can be performed on blood or saliva sample

Answer 65

_Benefits_ – Finds most common mutations for conditions tested – Negative result lowers risk for affected child – \>75 condition typically included – Can have full reproductive testing options if tested preconceptionally – Cost is similar or less than most single gene tests _Limitations:_ – Does not test for all mutations – Does not cover some of the more common disorders (ex. CAH) – Some results are for mild conditions and can cause anxiety and confusion – Proprietary technology can prevent independent validation – Depending on lab can be expensive – For some condition there may be a more accurate less expensive screen

Answer 66

Most are **single gene disorders**; they account for - 10% of pediatric admissions (US) - 20% of infant mortality (US)

Answer 67

_Benefits_ – Negative screening provides much more significant risk reduction, particularly in ethnicities where genotyping panels have low detection rates – Good option for couples where one member has already been found to be a carrier for a condition _Limitations_ – Will not eliminate carrier risk – If lab reports all changes detected this may results in reporting of variants of uncertain significance – Will not pick up gene deletions or duplications – Still does not screen for all genetic conditions

Answer 68

* Ovulation problems (25%) * Tubal or peritoneal problems (35%) * **Age** * Cervical problems * Uterine problems * **Polycystic ovary syndrome (PCOS)** * **Congenital adrenal hyperplasia (CAH)** * Low ovarian reserve (high FSH or estradiol levels) * **Premature ovarian failure (POF)** * **Translocation carrier/other chromosome abnormality (~5%)** * Idiopathic

Answer 69

Cessation of menses for **\> 6 months before age 40** * Affects approximately **1% of women** * Increased incidence of **fragile X** syndrome premutations * 13-16% of familial cases * 1-3% of sporadic cases

Answer 70

_Classic CAH_ (**21-hydroxylase deficiency**) - **Virilized females** - **Salt wasting** - **Autosomal recessive** _Non-classic CAH_ - **Hirsuitism**, **amenorrhea**, **PCOS** - **Compound heterozygotes** (2/3 of affected females have "severe" CAH mutation)

Answer 71

- Semen abnormalities (volume, motility, morphology) - Varicocele or obstruction - **Translocation carrier/other chromosome abnormality** - **Y chromosome microdeletion** - **CBAVD**

Answer 72

* Volume – **2+ mL** * pH – **7.2 - 8** * Sperm concentration – 20 X 106 per mL * Motility – **≥50%** * Morphology - **≥30% normal** * WBC - ≤ 1 x 106 per mL

Answer 73

- **Oligospermia**: \< 20 million sperm - **Azoospermia**: NO sperm in semen analysis - **OAT** (Oligo-astheno-teratospermia): problems with count, motlity, and morphology

Answer 74

Chromosome abnormalities in men (including in those with 47,XXY and 46,XX cell lines) may result in oligospermia or azoospermia – 5-7% of men with oligospermia * usually structural rearrangement – 15-20% of men with azoospermia * usually sex chromosome abnormality The prevalence of karyotypic abnormalities in men with hypergonadotropic hypogonadism is approximately 15%, with 47,XXY being the most common and 46,XX the second most common abnormality Balanced translocations have been identified in 1% to 2% of men with severe oligospermia and azoospermia, whether or not hypogonadism is present.

Answer 75

Y chromosome microdeletions occur in **3-18%** of men with azoospermia or severe oligospermia - Most have deletions in **AZFc** - There is a correlation between specific deletion and presence of **spermatozoa in testes** * AZFc deletion: good prognosis * AZFb deletion: no spermatozoa

Answer 76

Congenital bilateral absence of vas deferens - 1-2% of men with infertility - Significant proportion of men with CBAVD have one or two mutations in the **CFTR gene** * Increased risk of having a child with **cystic fibrosis** * Sons may have similar fertility problem - 5T splice variant in intron 8 of the CFTR gene Men with CBAVD have **azoospermia** but they usually have **normal testicular sperm** - Epididymal or testicular aspiration may provide sperm for ICSI of oocytes at the time of IVF

Answer 77

- Infertility - Recurrent early pregnancy loss

Answer 78

**Parental karyotype** - Balanced translocations (reciprocal or Robertsonian) – seen in 2-5% of couples with RPL - Think of rare X-linked male-lethal disorders, e.g. incontinentia pigmenti, steroid sulfatase deficiency (miscarriage of male fetuses)

Answer 79

– Polar body biopsy – Cleavage stage (blastomere) biopsy – Blastocyst biopsy An option for women/couples to avoid the possibility of an affected pregnancy secondary to a genetic disorder by: – using IVF and genetic testing or screening – implanting only embryos that do not have the genetic abnormality (Prenatal diagnosis is still recommended)

Answer 80

* Pipette used to pierce zona pellucida of egg * Polar body removed by aspiration * Analysis of polar body performed * If testing indicates disease free, oocyte fertilized with sperm * Successful embryos available for transfer

Answer 81

_Pros:_ – Errors in both meiosis I and meiosis II recognized – Samples extra-embryonic material (non-invasive for embryo proper) _Cons:_ – Only detects maternally inherited mutations

Answer 82

* An opening is made in the outer covering of the embryo using a laser or acid solution * One or two blastomeres are removed by suction using a pipette

Answer 83

_Pros:_ – Can detect maternal and paternal abnormalities _Cons:_ – Limited amount of material available for analysis – Possible mosaicism

Answer 84

* Performed on day 5 or 6 after fertilization * An opening is made in the zona pellucida and multiple cells are removed from the early trophoblast

Answer 85

_Pros_: – Multiple cells removed allowing more material for analysis – Inner cell mass remains intact – Can detect material and paternal abnormalities _Cons:_ – Procedure more challenging, fewer centers currently perform – Fewer embryos reach the blastocyst stage * No blastocysts are available for biopsy in up to 40% of cycles – Allows for less time for genetic testing or requires freezing of the embryo – Mosaicisim may still be an issue due to possible differences between the trophectoderm and inner cell mass

Answer 86

– Applies when one or both parents **carry a gene mutation or balanced translocation** – Testing is performed to **determine** whether the specific mutation(s) or an unbalanced translocation has been **transmitted**

Answer 87

– Applies when the genetic parents are **known or presumed to be chromosomally normal** – Screening for **aneuploidy**

Answer 88

Metaphase (mCGH), array CGH (aCGH), and SNP array are being consdiered and examined for PGS

Answer 89

_mCGH_: - Can take **up to 72 hrs** with additional time required for the analysis of data so this method typically requires freezing embryos - Has been applied at the **polar body stage, cleavage stage, and blastocyst stage** _aCGH_: – can be performed **within 24 hours** – With **cleavage-stage**, biopsy embryo transfer can still be performed on **day 5** –With blastocyst biopsy and/or PGD requiring transport of cells for testing, freezing the embryos may still be preferred

Answer 90

_Advantages:_ - Allows all chromosomes to be analyze instead of a subset _Disadvantages:_ - Cannot detect polyploidies, such as triploidy - Cannot detect balanced translocations or inversions - Cannot detect changes in DNA sequence - Cannot detect gains or losses in regions of the genome not covered by the array

Answer 91

Additional options for testing that are not available with CGH-based analysis – Allows for simultaneous testing of specific diseases and aneuploidy in each embryo by using haplotyping of SNPs around and within the gene of interest – Haplotyping of various markers through the genome allows for analysis of live-born children to determine which embryo(s) implanted in any given cycle.

Answer 92

_Advantages:_ * Reduction in risk of genetic disease (for single gene disorders and translocations) * Reduction in aneuploidy rate? * Increased implantation rate? * Reduction in pregnancy loss rate? * Information with which to make decisions about future IVF cycles? _Disadvantages:_ * Risk of embryo biopsy * Risk for misdiagnosis * Mosaicism * Only specific disorders tested * Does not replace prenatal diagnosis * Need IVF (if not infertile already) * Less embryos available for transfer * Cost

Answer 93

– Before PGD is performed counseling must be provided to ensure patients fully understand the risks of having an affected child and limitations of PGD for the condition. – Prenatal diagnostic testing to confirm the results of PGD is strongly encouraged because of the limitations of PGD, including the possibility of a false negative result.

Answer 94

* Before PGS is performed counseling must be provided to ensure patients fully understand the limitations of PGS, the risk of error, and the lack of evidence that PGS improves live-birth rates. * Available evidence does not support the use of PGS as currently performed to improve live-birth rates in patients * of advanced maternal age * with previous IVF failure * with recurrent pregnancy loss

Answer 95

* Diagnostic accuracy * Use of IVF in fertile couples/increase in multiple births * Safety of biopsy * Access to services/high costs * Eugenic potential * Sex selection