Common Aneuploidies

Additional episodes that might be helpful for today:

• Soft Markers for Aneuploidy: https://creogsovercoffee.com/notes/2022/2/13/soft-markers-for-aneuploidy

• Updates in Prenatal Genetic Screening: https://creogsovercoffee.com/notes/2021/9/19/prenatal-genetic-screening-an-update

• Prenatal Genetic Screening and Testing: https://creogsovercoffee.com/notes/2018/11/2/prenatal-genetic-screening-and-testing 

What is aneuploidy?

• The occurrence of one or more extra or missing chromosomes leading to an unbalanced complement.

• Screening for aneuploidy occurs with either serum screening or cell free DNA.

• Diagnostic testing for aneuploidy is done with chorionic villus sampling or amniocentesis.

• As we discussed on the screening 2 episode; fluorescent in situ hybridization (FISH) can evaluate initially for common aneuploidies.

• Karyotypes are the confirmatory testing for common aneuploidy, as well as other ways to get aneuploidy we’ll review (triploidy, balanced translocations).

• Microarray can find other major aneuploidies, but can’t find triploidy or balanced translocations.

How does aneuploidy occur?

• Meiosis is the process of cell division that produces gametes – eggs and sperm. 

• Goal is to create daughter cells with a haploid chromosome number (in humans – 23).

• The two gametes generally fuse to create a diploid zygote with 46 chromosomes.

• If there’s an issue in the cell division process for a gamete, they may come into this fusion with an extra or missing chromosome.

• Remember in cell division, we have multiple phases: prophase, metaphase, anaphase, telophase.

• We’ll break it down simply into the stages you need to remember to get those bonus points!

• Meiosis is broken into two phases: meiosis I and meiosis II.

• In meiosis I, the starting cell is diploid – but after replication, ends up with 4n chromatids (held in 2n chromosome pairs, or sister chromatids). 

• In prophase I, each pair of chromosomes lines up and matches with a homologous partner. This allows for the phenomenon of crossing over, where homologous portions of the chromosomes can rearrange and exchange portions of their DNA.

• This is where things can get dicey for a particular type of uncommon aneuploidy, known as a translocation. 

• That is, rather than recombining with a portion of the homologous chromosome, it attaches to a different chromosome.

• These translocations can be:

• Balanced, where the genetic information is not gained or lost, but just rearranged differently. 

• So for example: A piece of chromosome 21 joins onto chromosome 14, and a piece of chromosome 14 joins onto the break at 21. 

• The cell at this point still technically is diploid – but there can be problems with this later on!

• Unbalanced, where the genetic information is split unequally.

• In the same example: a piece of chromosome 21 joins onto 14, but the piece from 14 is lost.

• A particular type of translocation is known as a Robertsonian translocation, which is where the full long arms of two acrocentric chromosomes are joined together.

• The acrocentric chromosomes are where the short arms are extremely short - these are 13, 14, 15, 21, and 22 in humans.

• One of the most discussed is a 14:21 translocation, which is responsible for some Down syndrome.

• These translocations typically result in familial cases of aneuploidy, as a parent may be a balanced carrier of an abnormal chromosome – issues don’t arise for aneuploidy until they start trying to have children, and the chromosome complement ends up unbalanced in offspring.

• In the female reproductive cycle, eggs arrest in the cell cycle at prophase I, and only complete the remainder of meiosis prior to that egg’s ovulation.

• So an egg can be arrested for 30-40 years! 

• Ultimately, with this extended pause, meiosis I in oocytes is where the majority of nondisjunction events occur.

• To complete meiosis I:

• Metaphase I: the homologous pair lines up across the metaphase plate (like a cell equator) to prepare for division

• Anaphase I: the homologues are separated to the opposite ends of the cell

• Or not, if they can’t be separated! – This is nondisjunction.

• Telophase I: the new cells are haploid in chromosome pairs.

• We then move to meiosis II, where the sister chromatids are split into haploid pairs:

• Metaphase II: the sister chromatids line up across the metaphase plate.

• Anaphase II: the sister chromatids are separated to the opposite ends of the cell.

• This is another point where nondisjunction can occur (less common than in meiosis I, though)!

• Telophase II: the new cells are haploid with 23 single chromosomes (no longer in pairs).

The robertsonian translocation and gamete production

Trisomy 21: Down Syndrome

• Syndrome resulting from the addition of an extra chromosome 21. 

• Most common aneuploidy: affects about 1 in 700 births in the USA.

• Occurs via:

• Nondisjunction event: 95% of occurrences

• Robertsonian translocation: 5% of occurrences

• Mosaicism: infrequent (~1-2% max)

• This is where some cell lines have aneuploidy, and others do not. This occurs usually in early mitosis of the zygote, where the embryo during cell division recognizes the extra chromosome and tries to “kick it out” with aneuploidy rescue. We won’t spend too much time on that today! 

• Prenatal testing characteristics of trisomy 21:

• Cell free DNA: excellent test performance with 99% sensitivity and specificity.

• However, false positives still occur frequently, particularly in low-prevalence populations (i.e., around 50% false-positive risk in women aged 25).

• Serum screening: 

• Low msAFP

• Low estriol

• High HCG

• High inhibin A

• Ultrasound:

• 1st trimester: elevated NT (64-70%), absent/hypoplastic nasal bone.

• 2nd trimester:

• Various soft markers all have significance for T21: pyelectasis, echogenic bowel, echogenic cardiac focus, short femur.

• Most significant soft marker: thickened nuchal fold (LR 11-18 for T21)

• Practically pathognomonic findings:

• “Double bubble sign” – duodenal atresia - familiarize yourself with this ultrasound as it’s very commonly tested!

• Cardiac anomalies in ~50% – particularly significant / common are atrioventricular septal defects.

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DOUBLE BUBBLE - RADIOPAEDIA

Trisomy 18: Edward syndrome 

• Syndrome resulting from additional chromosome 18.

• Frequency: about 1 in 2k - 6k live births in USA.

• Occurs via:

• Nondisjunction event: over 95% of cases

• Mosaicism: around 4-5% of cases

• Translocations: rare, but has been reported.

• Prenatal testing characteristics:

• Cell free DNA: good, with over 96% sensitivity and over 99% specificity.

• However, given its infrequency, the positive-predictive value can still be low – 40% PPV in a woman at age 35. 

• Serum screening:

• All analytes decrease (though inhibin A can be normal).

• Ultrasound:

• 1st trimester: elevated NT, absent / hypoplastic nasal bone.

• 2nd trimester: multiple characteristic signs:

• Choroid plexus cysts are the most common soft-marker (though non-specific)

• “Strawberry skull” – flattened occiput, pointed frontal bones

• Clenched hands with overlapping fingers

• Rocker-bottom feet

• Cardiac anomalies

• Esophageal atresia, diaphragmatic hernias

• Growth restriction

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STRAWBERRY SKULL

Trisomy 13: Patau syndrome

• Syndrome resulting from additional chromosome 13

• Frequency: about 1 in 10k-16k live births in USA

• Occurs via:

• Nondisjunction event: most common

• Chromosome 13 is one of the acrocentric chromosomes so Robertsonian translocation can occur and familial forms have been reported.

• Mosaicism is also possible.

• Prenatal testing characteristics:

• Cell free DNA: similar story to trisomy 18. Sensitivity is around 91% and specificity over 99%.

• Given the low prevalence, positive-predictive values can still be low – around 20% for a woman at age 35. 

• Serum screening:

• No well-defined pattern, but elevated msAFP may be present given common CNS and other anomalies present in this syndrome.

• Ultrasound:

• 1st trimester: elevated NT, absent / hypoplastic nasal bone

• 2nd trimester: multiple characteristic signs, but remember: midline and CNS are classic:

• Holoprosencephaly: failure to divide brain into cerebral hemispheres (so no midline falx cerebri)

• Facial anomalies: cleft lip/palate, proboscis, micropthalmia/anopthalmia or cyclops eye

• Cardiac abnormalities - up to 80%

• Omphalocele

• Enlarged echogenic kidneys or horseshoe kidney

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ALOBAR HOLOPROSENCEPALY - RADIOPAEDIA

Monosomy X: Turner Syndrome

• Syndrome results from a missing sex chromosome - so 45, XO.

• 80% of the time this is paternally derived – one of the few circumstances this is the case!

• Frequency: 1 in 2k-5k live births

• Occurs via:

• Nondisjunction event: most common

• On the paternal side, given the mismatch of X and Y, the Y chromosome can be subject to “getting lost” in meiosis.

• Mosaicism can also occur with Turner syndrome in about 50% of individuals

• Cell lines are able to be mixed as 45, XO/46, XX, or 45, XO / 46, XY most commonly

• If Y chromosome is detected, gonadectomy is advised to reduce risk of gonadoblastoma in later life. 

• Prenatal testing characteristics:

• Cell free DNA: overall has about 90% sensitivity and over 99% specificity.

• Similarly: PPV is limited by prevalence

• cfDNA also has difficulty with mosaicism and delineating this specifically. 

• Ultrasound:

• The most commonly tested finding: cystic hygroma

• Present in 1st and/or 2nd trimester

• Can also present with more generalized edema

• Horseshoe kidney, cardiac abnormalities may also be present.

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CYSTIC HYGROMA - RADIOPAEDIA

Genetic Carrier Screening

Additional Reading
CO 690: Carrier Screening in the Age of Genomic Medicine
CO 691: Carrier Screening for Genetic Conditions
CO 816: Consumer Testing for Disease Risk

Previously on the podcast, we have talked through aneuploidy screening. But we’ve not talked in depth about carrier screening, so today’s podcast is dedicated to the other form of prenatal genetics we often consider! 

What is carrier screening?

• Aneuploidy screening: looking at some biochemical marker in an already pregnant individual to understand risk of trisomy (typically).

• Carrier screening: looking at genetics of parental contributions to assess potential risk in a current or hypothetical pregnancy. 

  • So this tells you - do you carry a condition that you are not affected by?

  • Only needs to be performed once in a lifetime - as opposed to aneuploidy screening, which needs to be re-performed with every pregnancy. 

• ACOG recommends that “information about carrier screening should be provided to every pregnant individual.” 

• Carrier screening most commonly looks for autosomal recessive conditions - that is, both parents need to be carriers in order for there to be a 25% risk of fetus being affected.

  • Certain X-linked conditions (i.e., hemophilia, Fragile X) can also be screened.

    • Information can be used in pregnancy planning, understanding risk of fetal condition that may impact life/lifespan of fetus, and choice for IVF with PGT or invasive testing in pregnancy.

  • Some other conditions may be discouraged from carrier screening (i.e., Huntington’s disease, BRCA genes) because of ethical concerns with doing carrier screening on fetuses, given these are adult-onset conditions. 

  • No “official threshold” for carrier screening generally, but most panels select conditions with a carrier frequency of ~1/100 or greater → generally a disease incidence of 1 in 40,000.

• There always remains some residual risk for carriage state/disease, even after carrier screening.

What strategies have been suggested for carrier screening?

• Historically, carrier screening was considered on an ethnicity basis (i.e., ethnic-based screening)

  • However, multiple limitations to this approach:

    • Challenging for individuals to define ancestry

    • Ancestral “mixing” between partners of different ethnicities causing different risks

    • The “pretest” probability of a positive is difficult to predict given these limitations

    • Couples with consanguinity may be at higher risk of recessive conditions being expressed in offspring, regardless of ethnic background.

• Current approaches favor panethnic or expanded carrier screening 

  • Panel of disorder screening is offered to all individuals regardless of ancestry.

  • The cost of screening has come down significantly, allowing for screening for hundreds of conditions at reasonable cost to patient.

• If family history of mutations/conditions are known, targeted screening can be considered to look for specific mutations.

What limitations are there in carrier screening? What does “residual risk” after carrier screening mean?

• These carrier screening panels look for known mutations in a population, based on a reference genome.

  • These reference genomes are overwhelmingly represented by White populations, so:

    • Carrier screening may not detect all mutant variants of an allele → residual risk

    • Carrier screening does not recognize new, potentially disease-causing variants.

      • Carrier testing is not sequencing! 

What conditions are recommended by ACOG to be screened for with carrier screening?

• Spinal muscular atrophy

  • Autosomal recessive disease with spinal cord motor neuron degeneration due to biparental inheritance of an SMN1 mutation/deletion.

  • Leading genetic cause of infant death.

  • Incidence of disease around 1 in 6-10k; carrier frequency in most populations around 1:40 to 1:60.

    • 2% of cases are the result of a new gene mutation. 

  • SMA has an interesting genetic profile:

    • There is generally one copy of SMN1 per chromosome, and a deletion/abnormality in each parental contribution leads to disease (again, autosomal recessive).

    • However, some of the population have two copies of SMN1 on a chromosome, and 0 copies on the other – so they are technically carriers (because of the chromosome with 0 copies).

    • Carrier screening tests for SMA generally look for the number of copies of SMN1 - so a patient with this particular variation (2+0) would be missed.

      • This 2+0 variation is much more common in African Americans - lowering the carrier detection rate of SMA from 95% in White patients to 71% in African Americans.

      • This leads to a higher residual risk from these tests as they may miss the 2+0 mutation.

• Cystic fibrosis

  • Most common life-threatening AR condition in White population.

    • Incidence 1/2500 in White; considerably less common in other ethnic groups.

  • Two copies of CFTR mutations (chromosome 7) cause the disease.

  • Most carrier screening looks for one of the 23 most common mutations that exist – again, predominantly in White populations.

    • But there are over 1700 CFTR mutations identified that can lead to CF!

    • Performance ranges from 94% sensitivity in Ashkenazi Jewish populations to less than 50% in Asian populations. 

    • Because of the number of mutations, some have advocated for CFTR sequencing to supplant panel testing as a way to determine carrier status and reduce residual risk amongst all populations. 

• Hemoglobinopathies

  • We have talked about these on the show before - thalassemias and sickle cell disease.

  • CBC and RBC indices should be performed in all pregnant persons to assess for anemia and risk of hemoglobinopathy.

    • Hb electrophoresis can be considered in all patients with anemia, particularly if there is family history or ethnicity-based risk factor, to screen for hemoglobinopathy.

    • Alpha thalassemias, though, can only be detected with molecular genetic studies - so if the electrophoresis is not conclusive, DNA-based testing should be pursued to assess for alpha thal. 

• Fragile X Syndrome

  • Most common inherited form of intellectual disability; distinctive facial features in males, enlarged testicles, delay in fine and gross motor skills are some manifestations.

  • 1 in 3600 males; 1 in 4k-6k females. 

  • Carrier frequency in the US around 1 in 250 for no known risk factors, or 1 in 86 for those with a family history of intellectual disability.

  • X-linked disorder of mutation in FMR1 gene.

    • The mutation is characterized by expansion of a trinucleotide repeat sequence (CGG); the more repeats, the more significant the mutation:

      • Intermediate (45-54 repeats)

      • Premutation (55-200 repeats)

      • Full mutation (>200 repeats)

    • Females carrying a premutation or full-mutation X chromosome are also at risk for premature ovarian insufficiency. Females with full mutation may also have fragile X characteristics of disease like in males, though with variable expression. 

We hear a lot about “Ashkenazi Judaism” and carrier screening. What does that mean and what conditions should be screened?

• Ashkenazi Jewish is defined in the committee opinions as individuals of Eastern and Central European Jewish descent.

  • Not a super accurate or helpful designation, as most individuals with Jewish ancestry in the USA are descended from these areas.

• Recommendations for specific screening:

  • Tay Sachs Disease - severe, progressive neurodegenerative disease with functional deficiency in the gene encoding the hexosaminidase A enzyme. 

    • Carrier rate in Ashkenazi Jewish populations around 1 in 30.

  • Cystic fibrosis

  • Canavan disease - severe degenerative neurologic disease

  • Familial dysautonomia - severe disorder of sensory and autonomic nervous systems

  • Multiple others are also considered, including Gaucher disease, Joubert syndrome, maple syrup urine disease, Niemann-Pick disease, and a few others. 

    • The panels developed for this population are very ethnicity-specific - so while great for this population, residual risk discussion can be complicated in non-Jewish individuals (as the incidence of carriage is often very low).

What about the genetic screening tests advertised to patients online?

• There are a whole host of “carrier screens” that are direct-to-consumer, and even some of the more reputable companies in this space have direct-to-consumer options given the decreasing expense of this technology. 

• However, these companies have varying degrees of privacy protections for genetic data.

• They also may have implications on patient’s eligibility for disability and other types of insurance; long-term care considerations; and ownership of one’s own genetic data.

• Some direct-to-consumer testing uses different kinds of technology to develop a picture of risk for a patient, that may or may not be helpful in their context. Abnormal results of concern should always be reviewed with a genetic counselor.

  • If you have any concerns or need more time for your patients to discuss whether they want to have carrier screening, it’s worthwhile to send them to a GC! They can help patients navigate targeted vs expanded carrier screening and help make decisions that are right for each individual patient. 

Soft Markers for Aneuploidy

Here’s this week’s RoshReview Question of the Week!

A 38-year-old G1P0 woman at 20 weeks gestation presents to the clinic for her anatomy ultrasound examination. She underwent a first-trimester screen, which showed a borderline nuchal translucency of 3.1 mm. Which one of the following isolated ultrasound findings confers the greatest risk for trisomy 21?

• Atrial septal defect

• Echogenic bowel

• Echogenic intracardiac focus

• Thickened nuchal skin fold

Check out the links above to see if you answered correctly. Also, you can enter for a chance to win a Rosh Review Qualifying Exam (“written boards”) QBank!

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Check out the SMFM Consult Series 57 for excellent companion reading!

What are the ultrasound soft markers, and why do we care? 

• In the era of cell-free DNA, you might ask: what is the utility of soft markers? Aren’t they poor predictors of aneuploidy?

  • Originally introduced to improve the detection of Down syndrome over that of just age-based or serum-based screening 

  • While it is true that each isolated soft marker may be poor predictors, if we see multiple soft markers, that does improve sensitivity  

  • There may also be some misunderstanding of soft markers seen on ultrasound, and so the purpose here is to review some of these soft markers in the setting of cfDNA and discuss next steps 

• Remember: patient’s baseline risk should not limit screening options, and cfDNA should be offered to all per ACOG and SMFM 

What are the first steps when you see a soft marker?

• Make sure that the soft marker is truly isolated - look for other soft markers, fetal growth restriction, or other anomalies 

  • If you feel that your office is not equipped to do this, can refer to MFM to have a level II ultrasound performed - this is of course a discussion with the patient, and not all patients will want further evaluation 

• Look at the patient’s history: 

  • What is their baseline risk? (age, family history, history of aneuploidy) 

  • What are their previous aneuploidy screening results? Did they have any? 

• Ok, so I see one of the soft markers, what do I do next?

  • First of all, have they had cfDNA?

    • Most of the time, there is not much to do after that (again: ISOLATED soft marker) 

    • This is because with cfDNA, the posttest probability of a common aneuploidy (ie. Trisomy 21) of negative cfDNA is very low - it is lowered by 300x for trisomy 21

      • Per the consult series, the residual risk of a 35-yo woman, whose age related risk of Down syndrome is 1/356 is reduced to <1/50,000 after a negative cfDNA result  

  • But what if they didn’t have cfDNA? 

    • If they have had negative serum screening, also ok, no need to do further testing at this time 

      • The detection rate of serum screening test for Down is still high, about 81%-99% depending on the test 

    • If no screening at all, counsel about noninvasive aneuploidy testing - not all patients will want screening 

  • Remember: there isn’t an established cut off residual risk when there is recommendation to do diagnostic testing 

    • Many labs will establish a cutoff of 1:250 or 1:300 

  • SMFM does not recommend diagnostic testing for aneuploidy only for evaluation of isolated soft marker following negative serum or cfDNA screening result 

The Soft Markers (all photo credit to Radiopedia)

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BRCA for the OB/GYN

Here’s the RoshReview Question of the Week:

A 37-year-old woman presents to your office for health care maintenance. She reports that her maternal cousin was diagnosed with advanced-stage breast cancer at the age of 35. Genetic testing was performed, and her relative tested positive for breast cancer susceptibility gene 1. Which of the following is associated with this condition?

• Microsatellite instability

• Mutation of tumor suppressor gene

• Oncogene

• PTEN mutation

Check your answer at the links above!

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Follow along with ACOG PB 182

What are we talking about, exactly?

• Certain germline mutations predispose patients to heritably higher risk of breast and ovarian cancer

• In particular, you have probably heard of BRCA1 and BRCA2

  • Others you may or may not have heard of include: 

    • Lynch syndrome genes (MSH2, MLH1, MSH6, PMS2), 

    • PTEN, 

    • TP53 (Li-Fraumeni syndrome), and 

    • STK11 (Peutz-Jehger Syndrome), just to name a few!

• However, we’ll spend today’s podcast focusing on BRCA specifically.

What exactly are the BRCA risks?

• Estimates of carrier frequency range from 1/300 to 1/800 for either genes.

• BRCA1 is found on Chr 17

• BRCA2 is found on Chr 13

• Both are tumor suppressor genes that function in DNA repair process.

  • The inherited mutation is non-functional or defective allele in some way, but patients usually have a second, functional copy.

  • If the second allele becomes nonfunctional due to somatic mutation, cancer can develop – 

    • Two-hit hypothesis of tumor suppressor genes.

• Risk of breast cancer in person without BRCA by age 70: ~12% (1/8)

  • Risk in patient by age 70 with BRCA1/2: 45-85%

    • Also more likely to be “triple negative” breast cancer for hormone and HER2 receptor

• Risk of ovarian / fallopian tube / primary peritoneal cancer:

  • BRCA1: 39-46% by age 70

  • BRCA2: 10-27% by age 70

  • Both associated with high grade, serous or endometrioid phenotype

• BRCA1/2 also associated with prostate, pancreatic, uterine cancers as well as melanoma

Who should I send for genetic counseling?

• If your patient has a new cancer, genetics recommended:

  • New ovarian epithelial cancers (including fallopian tube or primary peritoneal)

  • Breast cancer at age 45 or less;

  • Breast cancer, and have a close relative with breast cancer at age 50 or less, or a relative with ovarian cancers at any age; or with limited/unknown family history

  • Breast cancer with two or more relatives affected by breast cancer at any age

  • Breast cancer and two or more close relatives with pancreatic cancer or aggressive prostate cancer

  • Two breast cancer primaries, with the first diagnosed under age 50

  • Triple negative breast cancer at under age 60

  • Breast cancer and Ashkenazi Jewish ancestry at any age

  • Pnacreatic cancer and have 2+ close relatives with breast, ovarian, pancreatic, or aggressive prostate cancer

• If your patient does not have a new cancer, genetics recommended based on the history of:

  • A first-degree or several close relatives that meet the above criteria

  • A close relative carrying a known BRCA1 or BRCA2 mutation

  • A close relative with male breast cancer

• If you’re not sure but the history seems high risk, a referral to cancer genetics to discuss is always worthwhile – the histories above should definitely prompt your referral though! 

• And as you’re taking family history - it bears special mention that both maternal and paternal histories are important!

  • Especially given association with male breast CA, prostate CA, melanoma – be sure to get both sides!

• Genetics may recommend performing BRCA mutation testing, which can have a variety of possible outcomes:

  • True positive: pathogenic BRCA variant identified

  • True negative: no pathogenic variant identified in someone who has known BRCA variant in family

  • Uninformative negative: no pathogenic variant identified, but uninformative because of:

    • a) other family members not tested

    • b) family carries a variant, but it was not detected because of test limitations

    • c) family carries a high risk mutation in another gene

    • d) there is no high risk mutation

  • Variant of uncertain significance (VUS): abnormality detected in BRCA gene, but unknown whether the variant is associated with increased cancer risk

• Patients should be informed about the possible outcomes before undergoing genetic testing so they are aware of potential limitations and importance of family testing.

  • Unintended consequences of testing can include anxiety/stress and family dynamic issues regarding need for disclosure.

• Multigene panel testing also exists to look for mutations beyond BRCA and can be suggested by genetic counselors if indicated. 

How do I counsel and care for the patient with BRCA1 or BRCA2 mutation?

Screening

• Breast:  broken out by age:

  • Age 25-29: clinical breast exam every 6-12 months and annual screen (preferably by MRI with contrast)

    • Avoid ionizing radiation at this younger age as this may increase risk of cancer

  • Age 30+: Annual breast mammography and MRI, generally alternating every 6 months, as well as continuing CBE q6-12 months

• Ovarian:

  • TVUS and CA-125 monitoring routinely is not recommended

    • However, could be considered for short term surveillance around age 30-35 until patient undergoes risk-reducing BSO.

Medical

• Breast:

  • Tamoxifen and raloxifene can be considered (SERMs)

    • Can be considered in patients age 35 or older and not planning on pregnancy, or on prophylactic mastectomy

    • Tamoxifen is used in pre-menopausal and post-menopausal women, and may reduce breast cancer risk by 62% in BRCA2 carriers, but has not been found to reduce risk of cancer in BRCA1 carriers (likely due to higher triple-negative rates in this pop)

    • Raloxifene has been found to be effective in reducing invasive breast cancer in postmenopausal women at increased risk, though not evaluated specifically in BRCA mutation carriers

      • Tamoxifen may have a more significant risk reduction based on one head-to-head trial

    • Recall side effects of SERMs: vasomotor symptoms, vaginal symptoms (dryness, itching, dyspareunia), and increased risk of VTE!

    • Tamoxifen: also associated with concern for endometrial hyperplasia. While generally preferred in pre-menopausal patients, consider this in patietns with risk factors for endometrial hyperplasia!

    • Raloxifene: other significant side effect is leg cramps! Does not act on endometrium so may be considered in patients with significant risk factors. 

  • Aromatase inhibitors

    • Two trials have shown reduction in breast cancer risk in at-risk postmenopausal individuals; could be considered as alternative if contraindication to SERM

    • Not used in premenopausal women because it would end up actually stimulating ovarian function (i.e., ovulation induction)

• Ovarian:

  • OCPs are reasonable to use for cancer prophylaxis until BSO:

    • Reduction of ovarian cancer risk estimated at 33-80% for BRCA1, 58-63% for BRCA2

    • No increased risk of breast cancer in those with BRCA mutations using OCPs

Surgical

• Breast: bilateral mastectomy

  • Can be offered to any patient with BRCA mutation; reduces risk by 85-100%, depending on procedure type

  • However, this is big surgery - should be referred to breast surgeon to discuss risks of surgery in short term (surgical issues like hematomas, flap issues, infection) and long-term (pain, numbness, swelling, breast hardnes)

    • 70+% of patients report satisfaction with choice to undergo mastectomy at a follow up of 14.5 years

• Ovarian: bilateral salpingoophorectomy

  • Most effective option for risk reduction; should be considered by age 35-40 for BRCA1 patients, 40-45 for BRCA2 patients

    • This can be individualized based on patient’s family history and plans for childbearing

    • Also worth discussion of fertility-preservation with oocyte or embryo cryoperservation

  • Salpingectomy alone is not recommended at this time; however, the PB notes that salpingectomy followed by future oophorectomy could be reasonable to consider for some patients desiring this.

  • How to perform a risk-reducing BSO:

    • Perform a survey on entry - visualize peritoneal surfaces for any obvious disease and perform pelvic washings

      • Inspect diaphragm, liver, omentum, bowel, paracolic gutters, appendix, ovaries, falliopian tubes, uterus, bladder serosa, and cul-de-sac; biopsy any abnormal areas

    • All tissue from ovaries and fallopian tubes need to be removed!

      • Ligate IP 2cm proximal to the end of identifiable ovarian tissue

        • Beware of your ureter!

      • If hysterectomy not performed, tubes should be divided at insertion to cornua, and ovary removed from utero-ovarian ligament as close to uterus as possible.

    • Frozen pathology not necessary, as most malignancies identified from this procedure are occult

      • Your pathologist needs to know that the patient is BRCA-carrier though! This will prompt them to perform complete, serial sectioning of the tissue with microscopic screening (rather than representative sections typically performed with other benign BSO)

  • Hysterectomy can be considered simultaneously:

    • Advantages: simplifies hormone therapy (estrogen alone, vs E-P if retained); removal of cornual aspect of fallopian tube; reduce endometrial cancer risk if genetically-predisposed or taking tamoxifen

    • Disadvantages: bigger surgery, longer recovery, higher risk of complications from surgery

  • After BSO:

    • Patients who are premenopausal will need HRT to mitigate effects of early menopause and help with cardiovascular health and bone protection

      • Recall that HRT in the WHI increased risk of breast cancer in the estrogen-progesterone arm, but not in the estrogen-alone arm.

      • Given the higher rates of triple-negative breast cancer in BRCA population – HRT would not alter that course. Data suggests that HRT does not seem to reduce the protective effects of risk-reducing surgery overall.

    • In post-menopausal patients, this is controversial – other options are generally preferred to HRT for VMS management.

    • Local estrogen therapy for vaginal symptoms (genitourinary syndrome of menopause) is safe and effective in BRCA population – please use it! 

    • Ongoing surveillance after BSO is not necessary - so no need to collect CA125 or perform surveillance imaging. Patients should report any concerning symptoms.

Prenatal Genetic Screening: An Update

One of our very first podcasts covered prenatal genetic screening and testing. Since then, ACOG has updated the former PB 163 to the new PB 226. For today, we’ll cover some changes/updates and get more into diagnostic testing, which we didn’t cover in depth on our previous episode. Diagnostic testing info remains well-covered by PB 162.

How do you provide genetic counseling to a patient? 

• Every pregnancy has a risk for genetic abnormality and review that this risk increases with increasing age

  • Average rate is 1/150 live births. There is also risk based on family history. 

    • Review family history of birth defects, genetic diagnoses in the family, etc. prior to discussion

  •  Risk of abnormalities based on age:

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• Review options for genetic screening for patients.

  • All types of genetic screening is limited, and all genetic screening tests detect fewer abnormalities than diagnostic tests with microarray. Diagnostic tests include CVS and amniocentesis.

• Screening and diagnostic testing should be discussed and offered to all patients early in pregnancy regardless of maternal age or baseline risk

What are the available tests?

• Preimplantation genetic testing/screening 

  • PGT-A (also called PGS previously) - preimplantation genetic testing for aneuploidies 

    • Biopsy of an embryo at the blastocyst stage, usually around day 5-6 of development 

    • Cells are taken from the outer layer of cells (trophectoderm) that will eventually become the placenta 

    • PGT-A just screens for aneuploidy, and the idea is to increase the chances of live birth by screening for embryos that have aneuploidy.

  • PGT-M - preimplantation genetic testing for monogenetic/single gene mutations

    • Same as above in terms of how the cells are gotten, but in this case, tests are done for monogenic disease or single gene mutations 

    • Can be used to choose embryos that do not have a genetic disease, like screening for embryos that do not have Huntington’s or cystic fibrosis 

    • Disease and mutation must be known beforehand — this is a highly targeted screening.

  • PGT-SR - preimplantation genetic testing for structural rearrangements 

    • Useful when there are parental structural chromosomal abnormalities.

    • Detects things like translocation, inversion, deletions, insertions, etc.

  • With PGT, because the cells biopsied are destined to become placenta, other forms of pregnancy genetic screening should still be offered due to risk of mosiacism - that is, different genetic material in different cell lines.

• Screening and Testing During Pregnancy 

  • Discuss that many screening tests are sensitive for T21, but may have less sensitivity for other chromosomal disorders. 

  • Review these tests cannot detect other genetic abnormalities like point mutations, deletions, translocations, etc. 

  • Types of screening tests: 

    • NIPT (cell free DNA) – test any time around 9-10 weeks to term. 99% detection rate for trisomy 21. It has the highest DR of all tests and lowest false positive rate, but also may detect maternal aneuploidy or disease. Highest sensitivity and specificity. Does NOT test for open neural tube defects.

      • Someone with a screen positive serum analyte test may choose cfDNA for follow up if they want to avoid a diagnostic test, but they should be informed that it is still a screening test, meaning it can still fail to identify some chromosomal abnormalities and may delay definitive testing if positive.

    • Integrated screen – two tests. First is at 10w-13w6d. Then 15-22w. DR for T21 is 96%, but you need two samples and no first trimester results. Method: NT + PAPP-A in first trimester, then quad screen (hCG, AFP, uE3, inhibin A)

    • Sequential – 10w-13w6d, then 15-22 w. 95% DR for T21. Still need two samples, with first trimester NT + BHCG, PAPP-A and +/- AFP. Then quad screen.

    • Quad screen – 15w-22w. 81% DR for T21. It’s a one-time test, but also has lower DR than integrated

    • Other options with lower detection rates: first trimester screen (NT+PAPP-A, bHCG, AFP), Serum integrated (Integrated just without NT), NT alone

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ACOG PB 226

Diagnostic Testing

• The gold standard for detecting genetic abnormalities and should be offered after abnormal genetic screening tests.

• Chorionic villi sampling – done between 10-13 weeks. 

  • Get placental villi transabdominally or transcervically. 

  • Pregnancy loss rate 1/500. Limb reduction defect is super low, around 6/10,000. 

  • Can cause spotting/bleeding. Also the tissue is placental, so there is still possibility of mosaicism (ie. placenta doesn’t have abnormalities, but fetus does). 

    • Because of this, sometimes after CVS can still recommend amnio.

• Amniocentesis – done between 15-20 weeks usually, but can be done any time later too. 

  • Reason not to do too early: amnion and chorion not fused, increasing anomalies/loss rate.

  • Rate of loss is about 1:300 – 1:750 depending on studies. 

  • Other complications include spotting or loss of fluid. 

  • Cells are from sloughed off fetal skin cells, so can actually get fetal DNA.

• Type of tests that can be sent from diagnostic testing - a question you might get: what are you sending it for? 

  • Karyotype

    • Detects aneuploidies, like trisomies, 45X, 47 XXY.

    • Need culturable cells, so takes longer (7-10 days).

    • Cannot usually be done on dead tissue (ie. stillbirth), because the cells likely won’t grow 

  • Microarray

    • Can find major aneuploidies and submicroscopic changes that you can’t see just with karyotype.

    • Can’t detect balanced translocations and triploidy.

    • Can be done on cultured cells or uncultured tissue.

    • Can also be done on copy number variants If done on uncultured cells.

    • Can be fast turn-around (3-7 days).

  • FISH

    • Uses probes for specific chromosomes or chromosomal regions (ie, can detect T21 but also can detect 22q11.2 deletion).

    • Can be done on uncultured cells, so can get results in as few as 2 days.

    • Good to use if someone screens positive for T21 or other aneuploidy on serum analytes or cfDNA and you want a quick results before you get the full karyotype/microarray results

    • Often start with FISH, then reflex to microarray if normal, or karyotype if abnormal (to confirm).